Posts by Jai Ganesh

Jai Ganesh · This is Cool

2506) Mountain Lion

Mountain Lion

Gist

Mountain lions are known by many names, including cougar, puma, catamount, painter, panther, and many more. They are the most wide-ranging cat species in the world and are found as far north as Canada and as far south as Chile.

The puma (Puma concolor) is a large cat belonging to the felidae family. It is similar in size to the jaguar, and is found is a wide variety of habitats throughout the Americas. It is also known as the cougar, mountain lion and a number of other names.

Summary

The cougar (Puma concolor), also called puma, mountain lion, catamount, and panther, is a large small cat native to the Americas. It inhabits North, Central and South America, making it the most widely distributed wild, terrestrial mammal in the Western Hemisphere, and one of the most widespread in the world. Its range spans Yukon, British Columbia and Alberta in Canada, the Rocky Mountains and areas in the western United States. Further south, its range extends through Mexico to the Amazon rainforest and the southern Andes Mountains in Patagonia. It is an adaptable generalist species, occurring in most American habitat types. It prefers habitats with dense underbrush and rocky areas for stalking but also lives in open areas.

The cougar is largely solitary. Its activity pattern varies from diurnality and cathemerality to crepuscularity and nocturnality between protected and non-protected areas, and is apparently correlated with the presence of other predators, prey species, livestock and humans. It is an ambush predator that pursues a wide variety of prey. Ungulates, particularly deer, are its primary prey, but it also hunts rodents. It is territorial and lives at low population densities. Individual home ranges depend on terrain, vegetation and abundance of prey. While large, it is not always the dominant apex predator in its range, yielding prey to other predators. It is reclusive and mostly avoids people. Fatal attacks on humans are rare but increased in North America as more people entered cougar habitat and built farms.

The cougar is listed as Least Concern on the IUCN Red List. Intensive hunting following European colonization of the Americas and ongoing human development into cougar habitat has caused populations to decline in most parts of its historical range. In particular, the eastern cougar population is considered to be mostly locally extinct in eastern North America since the early 20th century, with the exception of the isolated Florida panther subpopulation.

Details

The cougar is a cat of many names: Puma, mountain lion, and catamount, among others.

This adaptable predator has the widest range of any land mammal in the Western Hemisphere, and can be found in many habitats throughout the Americas, from Florida swamps to Canadian forests. In some areas, such as heavily urbanized southern California, cougars are increasingly sharing space with people.

Cougars are the world’s fourth largest wildcat after lions, tigers, and jaguars. They are stocky with large hind legs and a long tail—about a third of their length—which provides balance. Their strong back legs enable them to leap around 40 feet horizontally, or 18 feet vertically in a single jump.

Their scientific name—Puma concolor, which means “of one color” in Latin—refers to their evenly colored coat: usually a solid orange, yellow, tan, rusty brown, or gray with a white belly. In rare cases, cougars can be white, but no cases of black, or melanistic, cougars have ever been documented.

Hunting habits

Cougars hunt at dawn and dusk. They usually prey on deer, although these opportunistic predators also eat coyotes, moose, wild sheep, birds, and rodents. They even kill feral donkeys, an invasive species in California’s Death Valley National Park.

The cats silently stalk their prey, then pounce and kill them with a fatal bite to the back of the head or neck. When dealing with a large carcass, a cougar will eat as much as it can before hiding the rest to come back to later.

Harmful encounters with people are rare: Between 1924 and 2018, 74 cougar attacks—including 11 fatalities—were documented in 10 U.S. states.

Reproduction

Male cougars maintain large territories that overlap with several smaller territories of their mates. About three months after mating, a female gives birth to three or four kittens in a secluded den, where she stays for 10 days. Babies are born with camouflaged, spotted coats that fade into a solid color as they grow.

After six weeks, the family will leave the den, and kittens learn to hunt from their mother. Cougars are ready to set out on their own at around 18 months old. Males often strike out farther from their mother to avoid the threats of a rival male; one was recorded traveling 1,800 miles in search of a new home.

Hollywood cougar

Arguably the world’s most famous cougar was an animal called P-22, whose father was P-001—the first puma to be collared by the National Park Service. Born in the Santa Monica Mountains, P-22 left his birthplace to find his own territory and crossed some of the world’s busiest freeways to reach L.A.’s Griffith Park, part of the Hollywood Hills, where he lived for 10 years.

P-22 was compassionately euthanized in December 2022 when he was caught for an evaluation, which showed he was underweight, had organ failure, and was likely hit by a car.

Threats to survival

Cougars once roamed nearly all of the United States, but by the early 1900s, they were mostly hunted to extinction in the Midwest and eastern U.S. The Florida panther—a subspecies only found in Florida—survived, though today fewer than 200 individuals remain in the wild.

Overall, cougar populations are stable, and the International Union for the Conservation of Nature's Red List categorizes them as a species of least concern.

Yet throughout their wide range, the felines are threatened by poisonings from various substances, vehicle collisions, retaliatory killings, and hunting. (Learn more about cougars, also called ghost cats.)

Habitat fragmentation is also a pressing problem. Unlike P-22, most cougars can’t cross sprawling freeways, and this lack of connectivity causes low genetic diversity and inbreeding.

That’s why, in southern California, the Wallis Annenberg Wildlife Crossing will help various wildlife species safely cross U.S. Highway 101.

Additional Information

What's in a name? Mountain lion, puma, cougar, panther—these cats are known by more names than just about any other mammal! But no matter what you call them, they're still the same cat, Puma concolor, the largest of the "small cats." So why do we call them so many different names? Mostly because they have such a large range, and people from different countries have called them different things.

Early Spanish explorers of North and South America called them leon (lion) and gato monte (cat of the mountain), from which we get the name "mountain lion." “Puma” is the name the Incas gave these cats in their language. “Cougar” seems to have come from an old South American Indian word, cuguacuarana, which was shortened to "cuguar" and then spelled differently. And “panther” is a general term for cats that have solid-colored coats, so it was used for black pumas as well as black jaguars and black leopards. All of these names are considered correct, but in Southern California we most commonly call them mountain lions.

You may have heard of Florida panthers. They are a subspecies of mountain lion that used to be found from Texas throughout the southeast but now only live in southern Florida’s swamps. They are Endangered, with only about 200 cats left, and conservation efforts are underway to save them.

Mountain lions are generally a solid tawny color, with slightly darker hair on their back and a whitish underside. Those living in warm, humid areas tend to be a darker, reddish-brown color, and mountain lions found in colder climates have thicker, longer hair that is almost silver-gray in color. Adult males weigh 40 to 60 percent more than adult females. Scientists classify mountain lions as small cats, as they do not roar, but purr like smaller cats do. Their slender bodies and calm demeanor are more like that of a cheetah; both cats would rather flee than fight, and both rarely confront people.

Habitat and Diet

Besides people, mountain lions have the largest range of any terrestrial mammal in the Western hemisphere, from northern British Columbia to Argentina. They live in a variety of habitats, at home in forests, prairies, deserts, and swamps—they are very adaptable cats! Mountain lions are solitary, except during breeding or when a mother is caring for her cubs. But that doesn’t mean they don’t have any contact with one another.

Mountain lions live in home ranges that vary in size from 30 to 125 square miles (7,770 to 32,375 hectares). These ranges overlap, so cats share some parts. The home range of males tends to be largest and overlap the smaller ranges of several females. Mountain lions find shelter to rest or escape from bad weather in thick brush, rocky crevices, or caves, which might be anywhere in their home range.

Although cats may see each other occasionally, they mostly leave "messages," with feces, urine, scratched logs, or marks they scrape out in the dirt or snow. Mountain lions can also growl, hiss, mew, yowl, squeak, spit, and purr to get their message across to other cats, and they are known for a short, high-pitched scream and a whistle-like call.

Mountain lions are powerfully built, with large paws and sharp claws. Their hind legs are larger and more muscular than their front legs, which gives them great jumping power. They can run fast and have a flexible spine like a cheetah’s to help them maneuver around obstacles and change direction quickly.

Even so, mountain lions are mostly ambush hunters, launching at prey to knock it off balance. They have especially keen eyesight, and they usually find prey by seeing it move. These cats may be on the prowl during the day or at night, but they are most active at dusk and dawn.

Mountain lions hunt over a large area, and it can take a week for one to travel all the way around its home range. They eat a variety of prey depending on where they live, including deer, pigs, capybaras, raccoons, armadillos, hares, and squirrels. Some larger cats even bring down prey as big as an elk or a moose. But hunting large prey brings risk, and many mountain lions suffer life-threatening injuries received from a hunt, especially from a prey’s sharp horns, antlers, or hooves. Mountain lions often bury part of their kill to save for a later meal, hiding the food with leaves, grass, dirt, or even snow, depending on the habitat and time of year.

Family Life

A female ready to breed alerts any males in the area by calling and rubbing her scent on rocks and trees. A male may stay with a female for several days before looking for his next mate. An expectant mother sets up a den where she gives birth to one to six cubs. The newborns have spots, which may help them blend in with grass, brush, and dappled sunlight. Their mother nurses them for three months or so, but they can eat meat at about six weeks of age. At six months old, their spots begin to fade, and they learn to hunt. They continue to live with their mother until they're 12 to 18 months old.

Conservation

As more people have moved into mountain lion territory, the number of encounters with them has increased. This is often "big news" and frightens people. But overall, meeting a mountain lion is an unlikely event. Mountain lions don’t want to confront people, and they do their best to avoid us. You can avoid them, too, by not hiking alone, or at dusk and dawn when mountain lions are hunting. Make noise as you hike, and don’t leave food out around a cabin or campsite, especially at night. If you do happen across a mountain lion, never approach it—always keep a respectful distance.

When Europeans first settled in North America, mountain lions lived from coast to coast. But they soon came to be viewed as threats to livestock. By the 1940s, many states, including California, placed a bounty on mountain lions. Due in major part to the bounty system, mountain lions are now confined to the West, except for a small population in Florida. Some people continue to hunt them despite legal protections.

Mountain lions have an essential role to play in our ecosystem. They are one of the top predators, and without them, populations of deer and herbivores would become unhealthy and too large for the habitat. It’s true that mountain lions can be dangerous, and coexistence challenges should be reported to state or local wildlife organizations. But people like to live and play in or near natural habitats, so we need to understand and respect the wildlife that live there. If we take responsibility for our own actions, pets, livestock, and property, we can learn to peacefully coexist with mountain lions and appreciate their power and grace.

While globally mountain lion populations are stable, they still face threats like habitat loss and fragmentation, poaching of their prey, and retaliatory hunting. In California, mountain lions are classified as a specially protected mammal.

Jai Ganesh · Dark Discussions at Cafe Infinity

2443) Dickinson W. Richards

Gist:

Life

Dickinson Richards was born in New Jersey, the son of a lawyer. After liberal arts studies at Yale University, Richards studied medicine at Columbia University in New York, becoming a medical doctor in 1923. Following work at Presbyterian Hospital in New York and elsewhere, in 1931 he began a prolonged collaboration with André Cournand at Bellevue Hospital and Columbia University. Richards was married and had four children.

Work

Even though Werner Forssmann succeeded in inserting a catheter into his own heart in 1929, there was great hesitance about continuing this type of research. Nonetheless, beginning in 1941 Dickinson Richards and André Cournand published a series of studies that established use of cardiac catheterization, among other things, to introduce contrast fluid for X-ray images and to measure pressure and oxygen content. Because it was possible to reach the upper chambers of the heart, blood pressure and the blood’s oxygen content could be measured on the way from the heart to the lungs, which was impossible before.

Summary

Dickinson Woodruff Richards (born Oct. 30, 1895, Orange, N.J., U.S.—died Feb. 23, 1973, Lakeville, Conn.) was an American physiologist who shared the Nobel Prize for Physiology or Medicine in 1956 with Werner Forssmann and André F. Cournand. Cournand and Richards adapted Forssmann’s technique of using a flexible tube (catheter), conducted from an elbow vein to the heart, as a probe to investigate the heart.

Richards received an A.B. degree from Yale University in 1917 and later studied at Columbia University’s College of Physicians and Surgeons (M.A., 1922; M.D., 1923). After a hospital internship and a brief study in England, he returned to Columbia University in 1928 and taught there from 1947 to 1961. From 1945 to 1961 he worked at Bellevue Hospital, New York City, where he met Cournand. Their use and perfection of Forssmann’s method, known as cardiac catheterization, permitted them to measure blood pressure and other conditions inside the heart.

Details

Dickinson Woodruff Richards Jr. (October 30, 1895 – February 23, 1973) was an American physician and physiologist. He was a co-recipient of the Nobel Prize in Physiology or Medicine in 1956 with André Cournand and Werner Forssmann for the development of cardiac catheterization and the characterisation of a number of cardiac diseases.

Early life

Richards was born in Orange, New Jersey. He was educated at the Hotchkiss School in Connecticut, and entered Yale University in 1913. At Yale he studied English and Greek, graduating in 1917 as a member of the senior society Scroll and Key.

Career

He joined the United States Army in 1917, and became an artillery instructor. He served from 1918 to 1919 as an artillery officer in France.

When he returned to the United States, Richards attended Columbia University College of Physicians and Surgeons, graduating with an M.A. in 1922 and his M.D. degree in 1923. He was on the staff of the Presbyterian Hospital in New York until 1927, when he went to England to work at the National Institute for Medical Research in London, under Sir Henry Dale, on the control of circulation in the liver.

In 1928, Richards returned to the Presbyterian Hospital and began his research on pulmonary and circulatory physiology, working under Professor Lawrence Henderson of Harvard. He began collaborations with André Cournand at Bellevue Hospital, New York, working on pulmonary function. Initially their research focussed on methods to study pulmonary function in patients with pulmonary disease.

Their next area of research was the development of a technique for catheterization of the heart. Using this technique they were able to study and characterise traumatic shock, the physiology of heart failure. They measured the effects of cardiac drugs and described various forms of dysfunction in chronic cardiac diseases and pulmonary diseases and their treatment, and developed techniques for the diagnosis of congenital heart diseases. For this work, Richards, Cournand, and Werner Forssmann were awarded the Nobel Prize for Physiology or Medicine for 1956.

In 1945 Richards moved his lab to Bellevue Hospital, New York. In 1947 he was made the Lambert Professor of Medicine at Columbia University, where he had taught since 1925. During his career he also served as an advisor to Merck Sharp and Dohme Company, and edited the Merck Manual. Richards retired from his positions at Bellevue and Columbia in 1961.

Global policy

He was one of the signatories of the agreement to convene a convention for drafting a world constitution. As a result, for the first time in human history, a World Constituent Assembly convened to draft and adopt the Constitution for the Federation of Earth.

Honor

Richards received many other honors, including the John Phillips Memorial Award of the American College of Physicians in 1960, the Chevalier de la Legion d'Honneur in 1963, the Trudeau Medal in 1968, and the Kober Medal of the Association of American Physicians in 1970.

He died in Lakeville, Connecticut and his wife Constance in 1990.

Jai Ganesh · Dark Discussions at Cafe Infinity

Come Quotes - XV

1. Tell the truth, work hard, and come to dinner on time. - Gerald R. Ford

2. All the revision in the world will not save a bad first draft: for the architecture of the thing comes, or fails to come, in the first conception, and revision only affects the detail and ornament, alas! - T. E. Lawrence

3. 'Tis sweet to know there is an eye will mark our coming, and look brighter when we come. - Lord Byron

4. 'Obama and Biden want to raise taxes by a trillion dollars.' Guess what? Yes, we do in one regard: We want to let that trillion dollar tax cut expire so the middle class doesn't have to bear the burden of all that money going to the super-wealthy. That's not a tax raise. That's called fairness where I come from. - Joe Biden

5. And one who is just of his own free will shall not lack for happiness; and he will never come to utter ruin. - Aeschylus

6. Death means change our clothes. Clothes become old, then time to come change. So this body become old, and then time come, take young body. - Dalai Lama

7. Poetry is emotion put into measure. The emotion must come by nature, but the measure can be acquired by art. - Thomas Hardy

8. Basically it starts with four months of training, just basic stretching, kicking and punching. Then you come to the choreography and getting ready to put the dance together. - Keanu Reeves.

Jai Ganesh · Jokes

Q: What do you call a monkey that sells potato chips?
A: A chipmunk.
* * *
Q: What do you call a sleeping pizza?
A: A piZZZZZZa.
* * *
Q: Why did the boy put a candy bar under his pillow?
A: So he would have sweet dreams!
* * *
Q: If Jake has 30 chocolate bars, and eats 25, what does he have?
A: Diabetes..... Jake has diabetes...
* * *
Q: Why couldn't the teddy bear finish his dessert?
A: Because he was stuffed.
* * *

Jai Ganesh · This is Cool

Positron Emission Tomography

Gist

Positron emission tomography (PET) is a nuclear medicine imaging technique that uses radioactive tracers to visualize and measure metabolic activity and physiological functions in the body. By detecting gamma rays emitted from tracers (most commonly FDG), PET scans create 3D, high-resolution images to detect cancer, evaluate heart disease, and map brain disorders. (FDG: Fluorodeoxyglucose).

What is positron emission tomography used for?

Why is PET performed? In general, PET scans may be used to evaluate organs and/or tissues for the presence of disease or other conditions. PET may also be used to evaluate the function of organs, such as the heart or brain. The most common use of PET is in the detection of cancer and the evaluation of cancer treatment.

Summary

Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in metabolic processes, and in other physiological activities including blood flow, regional chemical composition, and absorption. In clinical practice it is used to diagnose and manage cancer treatment, in cardiology and cardiac surgery, and in neurology and psychiatry.

PET is a common imaging technique, a medical scintillography technique used in nuclear medicine. A radiopharmaceutical—a radioisotope attached to a drug—is injected into the body as a tracer. When the radiopharmaceutical undergoes beta plus decay, a positron is emitted, and when the positron interacts with an ordinary electron, the two particles annihilate and two gamma rays are emitted in opposite directions. These gamma rays are detected by two gamma cameras to form a three-dimensional image.

PET scanners can incorporate a computed tomography scanner (CT) and are known as PET–CT scanners. PET scan images can be reconstructed using a CT scan performed using one scanner during the same session.

One of the disadvantages of a PET scanner is its high initial cost and ongoing operating costs.

Details

Positron emission tomography (PET) is a type of nuclear medicine procedure that measures metabolic activity of the cells of body tissues. PET is actually a combination of nuclear medicine and biochemical analysis. Used mostly in patients with brain or heart conditions and cancer, PET helps to visualize the biochemical changes taking place in the body, such as the metabolism (the process by which cells change food into energy after food is digested and absorbed into the blood) of the heart muscle.

PET differs from other nuclear medicine examinations in that PET detects metabolism within body tissues, whereas other types of nuclear medicine examinations detect the amount of a radioactive substance collected in body tissue in a certain location to examine the tissue's function.

Since PET is a type of nuclear medicine procedure, this means that a tiny amount of a radioactive substance, called a radiopharmaceutical (radionuclide or radioactive tracer), is used during the procedure to assist in the examination of the tissue under study. Specifically, PET studies evaluate the metabolism of a particular organ or tissue, so that information about the physiology (functionality) and anatomy (structure) of the organ or tissue is evaluated, as well as its biochemical properties. Thus, PET may detect biochemical changes in an organ or tissue that can identify the onset of a disease process before anatomical changes related to the disease can be seen with other imaging processes such as computed tomography (CT) or magnetic resonance imaging (MRI).

PET is most often used by oncologists (doctors specializing in cancer treatment), neurologists and neurosurgeons (doctors specializing in treatment and surgery of the brain and nervous system), and cardiologists (doctors specializing in the treatment of the heart). However, as advances in PET technologies continue, this procedure is beginning to be used more widely in other areas.

PET may also be used in conjunction with other diagnostic tests, such as computed tomography (CT) or magnetic resonance imaging (MRI) to provide more definitive information about malignant (cancerous) tumors and other lesions. Newer technology combines PET and CT into one scanner, known as PET/CT. PET/CT shows particular promise in the diagnosis and treatment of lung cancer, evaluating epilepsy, Alzheimer's disease and coronary artery disease.

Originally, PET procedures were performed in dedicated PET centers, because the equipment to make the radiopharmaceuticals, including a cyclotron and a radiochemistry lab, had to be available, in addition to the PET scanner. Now, the radiopharmaceuticals are produced in many areas and are sent to PET centers, so that only the scanner is required to perform a PET scan.

Further increasing the availability of PET imaging is a technology called gamma camera systems (devices used to scan patients who have been injected with small amounts of radionuclides and currently in use with other nuclear medicine procedures). These systems have been adapted for use in PET scan procedures. The gamma camera system can complete a scan more quickly, and at less cost, than a traditional PET scan.

How does PET work?

PET works by using a scanning device (a machine with a large hole at its center) to detect photons (subatomic particles) emitted by a radionuclide in the organ or tissue being examined.

The radionuclides used in PET scans are made by attaching a radioactive atom to chemical substances that are used naturally by the particular organ or tissue during its metabolic process. For example, in PET scans of the brain, a radioactive atom is applied to glucose (blood sugar) to create a radionuclide called fluorodeoxyglucose (FDG), because the brain uses glucose for its metabolism. FDG is widely used in PET scanning.

Other substances may be used for PET scanning, depending on the purpose of the scan. If blood flow and perfusion of an organ or tissue is of interest, the radionuclide may be a type of radioactive oxygen, carbon, nitrogen, or gallium.

The radionuclide is administered into a vein through an intravenous (IV) line. Next, the PET scanner slowly moves over the part of the body being examined. Positrons are emitted by the breakdown of the radionuclide. Gamma rays called annihilation photons are created when positrons collide with electrons near the decay event. The scanner then detects the annihilation photons, which arrive at the detectors in coincidence at 180 degrees apart from one another. A computer analyzes those gamma rays and uses the information to create an image map of the organ or tissue being studied. The amount of the radionuclide collected in the tissue affects how brightly the tissue appears on the image, and indicates the level of organ or tissue function.

Why is PET performed?

In general, PET scans may be used to evaluate organs and/or tissues for the presence of disease or other conditions. PET may also be used to evaluate the function of organs, such as the heart or brain. The most common use of PET is in the detection of cancer and the evaluation of cancer treatment.

More specific reasons for PET scans include, but are not limited to, the following:

* To diagnose dementias (conditions that involve deterioration of mental function), such as Alzheimer's disease, as well as other neurological conditions such as:

** Parkinson's disease. A progressive disease of the nervous system in which a fine tremor, muscle weakness, and a peculiar type of gait are seen.
** Huntington's disease. A hereditary disease of the nervous system which causes increasing dementia, bizarre involuntary movements, and abnormal posture.
** Epilepsy. A brain disorder involving recurrent seizures.
** Cerebrovascular accident (stroke)

* To locate the specific surgical site prior to surgical procedures of the brain

* To evaluate the brain after trauma to detect hematoma (blood clot), bleeding, and/or perfusion (blood and oxygen flow) of the brain tissue

* To detect the spread of cancer to other parts of the body from the original cancer site

* To evaluate the effectiveness of cancer treatment

* To evaluate the perfusion (blood flow) to the myocardium (heart muscle) as an aid in determining the usefulness of a therapeutic procedure to improve blood flow to the myocardium

* To further identify lung lesions or masses detected on chest X-ray and/or chest CT

* To assist in the management and treatment of lung cancer by staging lesions and following the progress of lesions after treatment

* To detect recurrence of tumors earlier than with other diagnostic modalities

How is PET performed?

PET scans can be done on an outpatient basis. It is also possible that some hospital inpatients may undergo a PET examination for certain conditions.

Although each facility may have specific protocols in place, generally, a PET scan procedure follows this process:

1. The patient will be asked to remove any clothing, jewelry, or other objects that may interfere with the scan.

2. If asked to remove clothing, the patient will be given a gown to wear.

3. The patient will be asked to empty his or her bladder prior to the start of the procedure.

4. One or 2 IV lines will be started in the hand or arm for injection of the radionuclide.

5. Certain types of scans of the abdomen or pelvis may require that a urinary catheter be inserted into the bladder to drain urine during the procedure.

6. In some cases, an initial scan may be performed prior to the injection of the radionuclide, depending on the type of study being done. The patient will be positioned on a padded table inside the scanner.

7. The radionuclide will be injected into the IV. The radionuclide will be allowed to concentrate in the organ or tissue for about 30 to 60 minutes. The patient will remain in the facility during this time. The patient will not be hazardous to other people, as the radionuclide emits less radiation than a standard X-ray.

8. After the radionuclide has been absorbed for the appropriate length of time, the scan will begin. The scanner will move slowly over the body part being studied.

9. When the scan has been completed, the IV line will be removed. If a urinary catheter has been inserted, it will be removed.

Additional Information

Positron emission tomography, also called PET imaging or a PET scan, is a type of nuclear medicine imaging. A PET scan measures important body functions, such as blood flow, oxygen use, and sugar (glucose) metabolism, to help doctors evaluate how well organs and tissues are functioning.

PET is a powerful diagnostic test that is having a major impact on the diagnosis and treatment of disease. A PET scan (positron emission tomography scan) monitors the biochemical functioning of cells by detecting how they process certain compounds, such as glucose (sugar). PET can detect extremely small cancerous tumors, subtle changes of the brain and heart, and give doctors important early information about heart disease and many neurological disorders, like Alzheimer's.

Most common medical tests, like CT and MRI scans, only show details about the structure of your body. PET scans give doctors images of function throughout the entire body, uncovering abnormalities that might otherwise go undetected. This allows doctors to treat these diseases earlier and more accurately. A PET scan puts time on your side. The earlier the diagnosis, the better the chance for treatment.

For example, a PET scan is the most accurate, non-invasive way to tell whether or not a tumor is benign or malignant, sparing patients expensive, often painful diagnostic surgeries and suggesting treatment options earlier in the course of the disease. Although cancer spreads silently in the body, PET can inspect all organs of the body for cancer in a single examination.

Today, most PET scans are performed on instruments that are combined PET and CT scanners. The combined PET/CT scans provide images that pinpoint the location of abnormal metabolic activity within the body. The combined scans have been shown to provide more accurate diagnoses than the two scans performed separately.

About nuclear medicine

Nuclear medicine is a branch of medical imaging that uses small amounts of radioactive material to diagnose or treat a variety of diseases, including many types of cancers, heart disease, and certain other abnormalities within the body. Depending on the type of nuclear medicine exam you are undergoing, the radiotracer is either injected into a vein, swallowed or inhaled as a gas and eventually accumulates in the organ or area of your body being examined, where it gives off energy in the form of gamma rays. This energy is detected by a device called a gamma camera, a PET scanner and/or probe.

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Jai Ganesh · Science HQ

Latent Heat

Gist

Latent heat is the energy absorbed or released by a substance during a change in its physical state (solid, liquid, or gas) that occurs without changing its temperature. This "hidden" energy breaks or forms molecular bonds, with primary types being latent heat of fusion (melting/freezing) and vaporization (boiling/condensation).

Latent heat is the energy absorbed or released by a substance during a change of state (like melting, freezing, boiling, or condensing) without changing its temperature, acting as "hidden" energy to break or form molecular bonds. This energy is measured per unit mass (e.g., Joules/kg) and involves two main types: the latent heat of fusion (solid to liquid/liquid to solid) and the latent heat of vaporization (liquid to gas/gas to liquid).

Summary

Latent heat is energy absorbed or released by a substance during a change in its physical state (phase) that occurs without changing its temperature. The latent heat associated with melting a solid or freezing a liquid is called the heat of fusion; that associated with vaporizing a liquid or a solid or condensing a vapour is called the heat of vaporization. The latent heat is normally expressed as the amount of heat (in units of joules or calories) per mole or unit mass of the substance undergoing a change of state.

For example, when a pot of water is kept boiling, the temperature remains at 100 °C (212 °F) until the last drop evaporates, because all the heat being added to the liquid is absorbed as latent heat of vaporization and carried away by the escaping vapour molecules. Similarly, while ice melts, it remains at 0 °C (32 °F), and the liquid water that is formed with the latent heat of fusion is also at 0 °C. The heat of fusion for water at 0 °C is approximately 334 joules (79.7 calories) per gram, and the heat of vaporization at 100 °C is about 2,230 joules (533 calories) per gram. Because the heat of vaporization is so large, steam carries a great deal of thermal energy that is released when it condenses, making water an excellent working fluid for heat engines.

Latent heat arises from the work required to overcome the forces that hold together atoms or molecules in a material. The regular structure of a crystalline solid is maintained by forces of attraction among its individual atoms, which oscillate slightly about their average positions in the crystal lattice. As the temperature increases, these motions become increasingly violent until, at the melting point, the attractive forces are no longer sufficient to maintain the stability of the crystal lattice. However, additional heat (the latent heat of fusion) must be added (at constant temperature) in order to accomplish the transition to the even more-disordered liquid state, in which the individual particles are no longer held in fixed lattice positions but are free to move about through the liquid. A liquid differs from a gas in that the forces of attraction between the particles are still sufficient to maintain a long-range order that endows the liquid with a degree of cohesion. As the temperature further increases, a second transition point (the boiling point) is reached where the long-range order becomes unstable relative to the largely independent motions of the particles in the much larger volume occupied by a vapour or gas. Once again, additional heat (the latent heat of vaporization) must be added to break the long-range order of the liquid and accomplish the transition to the largely disordered gaseous state.

Latent heat is associated with processes other than changes among the solid, liquid, and vapour phases of a single substance. Many solids exist in different crystalline modifications, and the transitions between these generally involve absorption or evolution of latent heat. The process of dissolving one substance in another often involves heat; if the solution process is a strictly physical change, the heat is a latent heat. Sometimes, however, the process is accompanied by a chemical change, and part of the heat is that associated with the chemical reaction.

Details

Latent heat (also known as latent energy or heat of transformation) is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process—usually a first-order phase transition, like melting or condensation.

Latent heat can be understood as hidden energy which is supplied or extracted to change the state of a substance without changing its temperature or pressure. This includes the latent heat of fusion (solid to liquid), the latent heat of vaporization (liquid to gas) and the latent heat of sublimation (solid to gas).

The term was introduced around 1762 by Scottish chemist Joseph Black. Black used the term in the context of calorimetry where a heat transfer caused a volume change in a body while its temperature was constant.

In contrast to latent heat, sensible heat is energy transferred as heat, with a resultant temperature change in a body.

Usage

The terms sensible heat and latent heat refer to energy transferred between a body and its surroundings, defined by the occurrence or non-occurrence of temperature change; they depend on the properties of the body. Sensible heat is sensed or felt in a process as a change in the body's temperature. Latent heat is energy transferred in a process without change of the body's temperature, for example, in a phase change (solid/liquid/gas).

Both sensible and latent heats are observed in many processes of transfer of energy in nature. Latent heat is associated with the change of phase of atmospheric or ocean water, vaporization, condensation, freezing or melting, whereas sensible heat is energy transferred that is evident in change of the temperature of the atmosphere or ocean, or ice, without those phase changes, though it is associated with changes of pressure and volume.

The original usage of the term, as introduced by Black, was applied to systems that were intentionally held at constant temperature. Such usage referred to latent heat of expansion and several other related latent heats. These latent heats are defined independently of the conceptual framework of thermodynamics.

When a body is heated at constant temperature by thermal radiation in a microwave field for example, it may expand by an amount described by its latent heat with respect to volume or latent heat of expansion, or increase its pressure by an amount described by its latent heat with respect to pressure.

Latent heat is energy released or absorbed by a body or a thermodynamic system during a constant-temperature process. Two common forms of latent heat are latent heat of fusion (melting) and latent heat of vaporization (boiling). These names describe the direction of energy flow when changing from one phase to the next: from solid to liquid, and liquid to gas.

In both cases the change is endothermic, meaning that the system absorbs energy. For example, when water evaporates, an input of energy is required for the water molecules to overcome the forces of attraction between them and make the transition from water to vapor.

If the vapor then condenses to a liquid on a surface, then the vapor's latent energy absorbed during evaporation is released as the liquid's sensible heat onto the surface.

The large value of the enthalpy of condensation of water vapor is the reason that steam is a far more effective heating medium than boiling water, and is more hazardous.

Meteorology

In meteorology, latent heat flux is the flux of energy from the Earth's surface to the atmosphere that is associated with evaporation or transpiration of water at the surface and subsequent condensation of water vapor in the troposphere. It is an important component of Earth's surface energy budget. Latent heat flux has been commonly measured with the Bowen ratio technique, or more recently since the mid-1900s by the eddy covariance method.

Additional Information

Latent heat is defined as the heat or energy that is absorbed or released during a phase change of a substance. It could either be from a gas to a liquid or liquid to a solid and vice versa. Latent heat is related to a heat property called enthalpy.

However, an important point that we should consider regarding latent heat is that the temperature of the substance remains constant. As far as the mechanism is concerned, latent heat is the work that is needed to overcome the attractive forces that hold molecules and atoms together in a substance.

Let’s take an example. Suppose a solid substance is changing to a liquid; it needs to absorb energy to push the molecules into a wider, more fluid volume. Similarly, when a substance changes from a gas phase to a liquid, its density levels also need to go from a lower to a higher level, wherein the substance then needs to release or lose energy so that the molecules come closer together. In essence, this energy that is required by a substance to either freeze, melt or boil is said to be latent heat.

Early Developments of the Concept

The Scottish scientific expert, Joseph Black, presented the idea of latent heat somewhere close to the period 1750 and 1762. Scotch bourbon producers had employed Black to decide the best blend of fuel and water for refining and to examine changes in volume and weight at a steady temperature. Dark applied calorimetry for his investigation and recorded latent heat esteems.

British physicist James Prescott Joule portrayed latent heat as a type of potential vitality. Joule accepted that vitality relied upon the specific design of particles in a substance. Actually, it is the direction of particles inside an atom, their substance holding, and their extremity that influence latent heat.

Types of Latent Heat Transfer

Lets us discuss some of the different types of latent heat that can occur.

Latent Heat of Fusion

The latent heat of fusion is the heat consumed or discharged when matter melts, changing state from solid to fluid structure at a consistent temperature.

The ‘enthalpy’ of fusion is a latent heat, in light of the fact that during softening, the heat energy expected to change the substance from solid to fluid at air pressure is the latent heat of fusion, as the temperature stays steady during the procedure. The latent heat of fusion is the enthalpy change of any measure of substance when it dissolves.

At the point when the heat of fusion is referenced to a unit of mass, it is typically called the specific heat of fusion, while the molar heat of fusion alludes to the enthalpy change per measure of substance in moles.

The fluid state has higher inward energy than the solid state. This implies that energy must be provided to the solid so as to dissolve it, and energy is discharged from a fluid when it solidifies on the grounds that the particles in the fluid experience more fragile intermolecular force, and thus have higher potential energy (a sort of bond-separation energy for intermolecular powers).

At the point when fluid water is cooled, its temperature falls relentlessly until it drops just underneath the line of the point of solidification at 0 °C. The temperature at that point stays consistent at the point of solidification while the water takes shape. When the water is totally solidified, its temperature keeps on falling.

The enthalpy of fusion is quite often a positive amount; helium is the main known exception. Helium-3 has a negative enthalpy of fusion at temperatures beneath 0.3 K. Helium-4 additionally has a marginally negative enthalpy of fusion underneath 0.77 K (−272.380 °C). This implies that at suitable steady weights, these substances solidify with the expansion of heat. For the situation of 4He, this weight territory is somewhere in the range of 24.992 and 25.00 atm (2,533 kPa).

Latent Heat of Vaporization

Latent heat of vaporization is the heat consumed or discharged when matter disintegrates, changing state from fluid to gas state at a consistent temperature.

The heat of vaporization of water is the highest known. The heat of vaporization is characterised as the measure of heat expected to transform 1 g of a fluid into a fume without a change in the temperature of the fluid. This term isn’t in the rundown of definitions given by Weast (1964), so the definition originates from Webster’s New World Dictionary of the American Language (1959). The units are cal/gram. The heat of vaporization is latent heat. The word latent originates from the Latin word latere, which intends to lie covered up or hidden. Latent heat is the extra heat required to change the condition of a substance from solid to fluid at its softening point, or from fluid to gas at its breaking point after the temperature of the substance has come to both of these focuses.

Note that latent heat is related to no adjustment in temperature, yet a difference in the state. As a result of the high heat of vaporization, the vanishing of water has an articulated cooling impact, and buildup has a warming impact.

Similar to the case for ‘Heat of Fusion/Melting,’ the heat of vaporization/buildup additionally speaks to the measure of heat traded during a stage move. For vaporization, it is the amount of heat (540 cal g^{-1}) expected to change over 1 g of water to 1 g of water fume. A similar measure of heat is traded or discharged in the stage move during the buildup of 1 g water fume to 1 g of water.

Amphibian researchers might be normally intrigued with the enormous measure of heat traded (80 cal g−1) in the stage move from water to ice or from ice to water, yet the measure of heat traded (540 cal g^{-1}) in the stage move from water to water fume, or water fume to water is 6.75 times bigger (540/80 = 6.75). Despite the fact that the significance of this enormous measure of heat trade through vaporization or buildup might be undervalued by people, it is immense. On a little yet basic scale forever, water dissipating off sweating warm-blooded creatures, including people, keeps up internal heat levels inside thin survivable points of confinement. On a worldwide scale, the apparently perpetual stage moves between fluid water and water fume in the climate are the key determinants in the redistribution of water and heat inside the hydrological cycle far and wide.

The enthalpy of vaporization, ΔHv, is additionally named the “latent heat of vaporization.” And ΔHv is the distinction between the enthalpy of the soaked fume and that of the immersed fluid at a similar temperature. The enthalpy of vaporization information is utilised in process estimations, for example, the plan of alleviation frameworks, including unpredictable mixes. In refining, the heat of vaporization esteems are expected to discover the heat loads for the reboiler and condenser, and information on the enthalpy of vaporization is required in the structure of heat exchangers for disintegrating fluids.

Reasonable Heat

Although reasonable heat is frequently called latent heat, it is anything but a steady temperature circumstance or is a stage change included. Reasonable heat reflects heat move among an item and its environment. The heat can be “detected” as an adjustment in an item’s temperature.

Reasonable Heat and Meteorology

While latent heat of combination and vaporization are utilised in material science and science, meteorologists also consider reasonable heat. At the point when latent heat is ingested or discharged, it produces insecurity in the climate, conceivably delivering an extreme climate. The change in latent heat adjusts the temperature into contact with hotter or cooler air. Both latent and reasonable heat cause air to move, creating wind and vertical movement of air masses.

Instances of Latent and Sensible Heat

Everyday life is loaded up with instances of latent and reasonable heat:

Bubbling water on a stove happens when warm vitality from the heating component is moved to the pot, and thus to the water. At the point when enough vitality is provided, fluid water grows from the water fume and the water bubbles. A gigantic measure of vitality is discharged when water bubbles are formed. Since water has such a high heat of vaporization, it’s anything but difficult to get scorched by steam.

Correspondingly, significant energy must be assimilated to change over fluid water to ice in a cooler. The cooler expels heat energy to permit the stage progress to happen. Water has a high latent heat of combination, so transforming water into ice requires the expulsion of more energy than solidifying fluid oxygen into solid oxygen per unit gram.

Specific Latent Heat

Specific latent heat is characterised as the measure of heat energy (heat, Q) that is consumed or discharged when a body experiences a steady temperature process.

The formula for specific latent heat is:

L = Q/m

Where:

L is the specific latent heat

Q is the heat retained or discharged

m is the mass of a substance.

The most widely recognised kinds of consistent temperature forms are stage changes, for example, liquefying, solidifying, vaporization, or buildup. The energy is viewed as “latent” on the grounds that it is basically covered up inside the atoms until the stage change happens. The most well-known units of specific latent heat are joules per gram (J/g) and kilojoules per kilogram (kJ/kg).

Specific latent heat is an escalated property of the issue.

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2505) Atrophy

Gist

Atrophy is the wasting away, thinning, or decrease in size of cells, tissues, or organs, resulting in reduced function. It is caused by factors like disuse, poor circulation, nerve damage, malnutrition, or hormonal changes. Common forms include muscle, brain, or vaginal atrophy, often characterized by weakness and reduced size of the affected area.

Brain atrophy means the progressive loss of brain cells (neurons) and their connections, causing the brain to shrink in overall size or in specific regions, leading to impaired cognitive, motor, or functional abilities, and can be a normal part of aging or a symptom of diseases like Alzheimer's or MS (Multiple Sclerosis). It's diagnosed via brain scans like MRIs and CTs, which reveal the tissue loss, and treatment focuses on managing the underlying cause.

Summary

Muscle atrophy is the wasting or thinning of muscle mass. It can be caused by disuse of your muscles or neurogenic conditions. Symptoms include a decrease in muscle mass, one limb being smaller than the other, and numbness, weakness and tingling in your limbs. Disuse atrophy can be reversed with exercise and a healthy diet.

Muscle atrophy is the loss or thinning of your muscle tissue. If you have atrophied muscles, you’ll see a decrease in your muscle mass and strength. With muscle atrophy, your muscles look smaller than normal. Muscle atrophy can occur due to malnutrition, age, genetics, a lack of physical activity or certain medical conditions. Disuse (physiologic) atrophy occurs when you don’t use your muscles enough. Neurogenic atrophy occurs due to nerve problems or diseases.

What are the symptoms of muscle atrophy?

The symptoms of muscle atrophy differ depending on the cause of your condition. The most obvious sign of muscle atrophy is reduced muscle mass. Other signs of muscle atrophy may include:

* One arm or one leg is smaller than the other.
* Weakness in one arm and or one leg.
* Numbness or tingling in your arms and legs.
* Trouble walking or balancing.
* Difficulty swallowing or speaking.
* Facial weakness.
* Gradual memory loss.

Details

Atrophy is the partial or complete wasting away of a part of the body. Causes of atrophy include mutations (which can destroy the gene to build up the organ), poor nourishment, poor circulation, loss of hormonal support, loss of nerve supply to the target organ, excessive amount of apoptosis of cells, and disuse or lack of exercise or disease intrinsic to the tissue itself. In medical practice, hormonal and nerve inputs that maintain an organ or body part are said to have trophic effects. A diminished muscular trophic condition is designated as atrophy. Atrophy is reduction in size of cell, organ or tissue, after attaining its normal mature growth. In contrast, hypoplasia is the reduction in the cellular numbers of an organ, or tissue that has not attained normal maturity.

Atrophy is the general physiological process of reabsorption and breakdown of tissues, involving apoptosis. When it occurs as a result of disease or loss of trophic support because of other diseases, it is termed pathological atrophy, although it can be a part of normal body development and homeostasis as well.

Examples of atrophy as part of normal development include shrinking and the involution of the thymus in early childhood, and the tonsils in adolescence. In old age, effects include, but are not limited to, loss of teeth, hair, thinning of skin that creates wrinkles, weakening of muscles, loss of weight in organs and sluggish mental activity.

Muscle atrophies

Disuse atrophy of muscles and bones, with loss of mass and strength, can occur after prolonged immobility, such as extended bedrest, or having a body part in a cast (living in darkness for the eye, bedridden for the legs etc.). This type of atrophy can usually be reversed with exercise unless severe.

There are many diseases and conditions which cause atrophy of muscle mass. For example, diseases such as cancer and AIDS induce a body wasting syndrome called cachexia, which is notable for the severe muscle atrophy seen. Other syndromes or conditions which can induce skeletal muscle atrophy are congestive heart failure and liver disease.

During aging, there is a gradual decrease in the ability to maintain skeletal muscle function and mass. This condition is called sarcopenia, and may be distinct from atrophy in its pathophysiology. While the exact cause of sarcopenia is unknown, it may be induced by a combination of a gradual failure in the satellite cells which help to regenerate skeletal muscle fibers, and a decrease in sensitivity to or the availability of critical secreted growth factors which are necessary to maintain muscle mass and satellite cell survival.

Dystrophies, myositis, and motor neuron conditions

Pathologic atrophy of muscles can occur with diseases of the motor nerves or diseases of the muscle tissue itself. Examples of atrophying nerve diseases include Charcot-Marie-Tooth disease, poliomyelitis, amyotrophic lateral sclerosis (ALS or Lou Gehrig's disease), and Guillain–Barré syndrome. Examples of atrophying muscle diseases include muscular dystrophy, myotonia congenita, and myotonic dystrophy.

Changes in Na+ channel isoform expression and spontaneous activity in muscle called fibrillation can also result in muscle atrophy.

A flail limb is a medical term which refers to an extremity in which the primary nerve has been severed, resulting in complete lack of mobility and sensation. The muscles soon wither away from atrophy.

Gland atrophy

The adrenal glands atrophy during prolonged use of exogenous glucocorticoids like prednisone. Atrophy of the breasts can occur with prolonged estrogen reduction, as with anorexia nervosa or menopause. Testicular atrophy can occur with prolonged use of enough exogenous sex steroids (either androgen or estrogen) to reduce gonadotropin secretion.

Vaginal atrophy

In post-menopausal women, the walls of the math become thinner (atrophic vaginitis). The mechanism for the age-related condition is not yet clear, though there are theories that the effect is caused by decreases in estrogen levels. This atrophy, occurring concurrently with breast atrophy, is consistent with the homeostatic (normal development) role of atrophy in general, as after menopause the body has no further functional biological need to maintain the reproductive system which it has permanently shut down.

Research

One drug in test seemed to prevent the type of muscle loss that occurs in immobile, bedridden patients. Testing on mice showed that it blocked the activity of a protein present in the muscle that is involved in muscle atrophy. However, the drug's long-term effect on the heart precludes its routine use in humans, and other drugs are being sought.

Additional Information

Atrophy is a decrease in size of a body part, cell, organ, or other tissue. The term implies that the atrophied part was of a size normal for the individual, considering age and circumstance, prior to the diminution. In atrophy of an organ or body part, there may be a reduction in the number or in the size of the component cells, or in both.

Certain cells and organs normally undergo atrophy at certain ages or under certain physiologic circumstances. In the human embryo, for example, a number of structures are transient and at birth have already undergone atrophy. The adrenal glands become smaller shortly after birth because an inner layer of the cortex has shrunk. The thymus and other lymphoid tissues atrophy at adolescence. The pineal gland tends to atrophy about the time of puberty; usually calcium deposits, or concretions, form in the atrophic tissue. The widespread atrophy of many tissues that accompanies advanced age, although universal, is influenced by changes of nutrition and blood supply that occur during active mature life.

The normal cyclic changes of female reproductive organs are accompanied by physiologic atrophy of portions of these organs. During the menstrual cycle, the corpus luteum of the ovary atrophies if pregnancy has not occurred. The muscles of the uterus, which enlarge during pregnancy, rapidly atrophy after the delivery of the child, and after completion of lactation the milk-producing acinar structures of the breast diminish in size. After menopause the ovaries, uterus, and breasts normally undergo a degree of atrophic change.

Whole body atrophy

Atrophy in general is related to changes in nutrition and metabolic activity of cells and tissues. A widespread or generalized atrophy of body tissues occurs under conditions of starvation, whether because food is unavailable or because it cannot be taken and absorbed because of the presence of disease. The unavailability of certain essential protein components and vitamins disturbs the metabolic processes and leads to atrophy of cells and tissues. Under conditions of protein starvation, the body protein is broken down into constituent amino acids, which serve to provide energy and help maintain the structure and cells of the most essential organs. The brain, heart, adrenal glands, thyroid gland, pituitary gland, gonads, and kidneys show less atrophy, relatively, than the body as a whole, whereas the fatty stores of the body, liver, spleen, and lymphoid tissues diminish relatively more than the body as a whole. The brain, heart, and kidneys, organs with abundant blood supply, appear to be the least subject to the wasting effects of starvation.

Associated with the widespread atrophy due to lack of protein is the atrophy of certain tissues that is caused by deficiencies of specific vitamins. Atrophic changes of the skin increase because of the lack of vitamin A, and atrophy of muscle increases because of the unavailability of vitamin E.

After a growth period of human metabolism, there sets in a gradual decline: slow structural changes other than those due to preventable diseases or accidents occur. Aging eventually is characterized by marked atrophy of many tissues and organs, with both a decline in the number of cells and an alteration in their constitution. This is reflected eventually in the changed, diminished, or lost function characteristic of old age and eventuates in death. The changes in senescence are affected by both inherited constitution and environmental influences, including disease and accident.

Atrophic changes of aging affect almost all tissues and organs, but some changes are more obvious and important. Arteriosclerosis—the thickening and hardening of arterial walls—decreases the vascular supply and usually accentuates aging processes.

Atrophy in old age is especially noticeable in the skin, characteristically flat, glossy or satiny, and wrinkled. The atrophy is caused by aging changes in the fibres of the true skin, or dermis, and in the cells and sweat glands of the outer skin. Wasting of muscle accompanied by some loss of muscular strength and agility is common in the aged. In a somewhat irregular pattern, there is shrinkage of many individual muscle fibres as well as a decrease in their number. Other changes have been observed within the muscle cells.

Increase of the pigment lipofuscin is also characteristic in the muscle fibres of the heart in the aged in a condition known as brown atrophy of the heart. Wasting of the heart muscle in old age may be accompanied by increase of fibrous and fatty tissue in the walls of the right side of the heart and by increased replacement of elastic tissue with fibrous tissue in the lining and walls of coronary arteries within the heart muscle. Abnormal deposits of the protein substance amyloid also occur with greater frequency in the atrophic heart muscle in old age.

Atrophy of the liver in the aged is also accompanied by increased lipochrome pigment in the atrophied cells.

The bones become progressively lighter and more porous with aging, a process known as osteoporosis. The reduction of bone tissue is most marked in cancellous bone—the open-textured tissue in the ends of the long bones—and in the inner parts of the cortex of these bones. In addition to changes in and loss of osteocytes, or bone cells, there is decreasing mineralization, or calcium deposit, with enhanced fragility of the bones.

Atrophy of the brain in old age is shown by narrowing of the ridges, or gyri, on the surface of the brain and by increased fluid in the space beneath the arachnoid membrane, the middle layer of the brain covering. There is shrinkage of individual neurons, with an increase in their lipochrome pigment content, as well as a decrease in their number. Sometimes the nerve fibrils have degenerated, and deposits called senile plaques may be found between the neurons, particularly in the frontal cortex and hippocampus (a ridge in the wall of an extension, or horn, of the lateral ventricle, or cavity, of the brain). Similar atrophic changes are seen in the brain in Alzheimer disease, a condition of unknown cause most likely to occur in older patients. The mental deterioration (senile dementia) of the aged is the clinical manifestation of these changes. Senile atrophy may be increased and complicated by the presence of arteriosclerosis.

Simmonds disease is a chronic deficiency of function of the pituitary gland, a form of hypopituitarism, that leads to atrophy of many of the viscera, including the heart, liver, spleen, kidneys, thyroid, adrenals, and gonads. The disease results in emaciation and death if left untreated.

A destructive or atrophic lesion affecting the pituitary gland with loss of hormones leads to atrophy of the thyroid gland, adrenal glands, and gonads and in turn brings atrophic changes to their target organs and the viscera. The decrease in size of the endocrine glands may be extreme.

Atrophy of muscle or of muscle and bone

Local atrophy of muscle, bone, or other tissues results from disuse or diminished activity or function. Although the exact mechanisms are not completely understood, decreased blood supply and diminished nutrition occur in inactive tissues. Disuse of muscle resulting from loss of motor nerve supply to the muscle (e.g., as a result of polio) leads to extreme inactivity and corresponding atrophy. Muscles become limp and paralyzed if there is destruction of the nerve cells in the spinal cord that normally activate them. The shrinkage of the paralyzed muscle fibres becomes evident within a few weeks. After some months, fragmentation and disappearance of the muscle fibres occurs with some replacement by fat cells and a loose network of connective tissue. Some contracture may result.

The skeletal muscles forced to inactivity by paralysis (e.g., of a limb as a result of polio) also undergo disuse atrophy. If there is a tendency for bone to become lighter and more porous in some particular area, a condition known as local osteoporosis, this can be recognized by X-rays within a few weeks. The cortex of the long bones becomes considerably thinned or atrophic, with decreased mineral content. Disuse as a result of painfully diseased joints, as in rheumatoid arthritis, results in a similar but lesser degree of atrophy of muscles concerned with movement of the involved joint, and local atrophy may also occur in the bone in the neighbourhood of the joint. A local osteoporosis of bone known as Sudeck atrophy sometimes develops rapidly in the area of an injury to bone.

Severe or prolonged deficits of blood sugar deprive the nervous system of needed sources of energy and as a rare event result in degeneration of cells of the brain and peripheral nerves. The disuse atrophy of muscle or bone that may result is fundamentally similar to the other disuse atrophies of these tissues.

Persistent pressure will cause atrophy of a compressed cell, organ, or tissue, presumably because of interference with the nutrition and metabolic activity of the affected part. Cells in a local area (e.g., in the liver) atrophy from the pressure of materials such as amyloid deposited around them. The pressure of an expanding benign tumour causes atrophy of adjacent normal structures. The pressure of a localized dilatation of an artery (aneurysm) will cause atrophy of tissues, even bone, on which it impinges.

Bulging of an intervertebral disk or growth of a tumour sometimes brings pressure on nerves near their point of exit from the spinal cord; if the pressure is prolonged, the muscles normally controlled by these nerves may atrophy. Most often the calf muscles are affected. Pressure as a result of involvement of the vertebrae at the level of the neck, or from compression of the network of nerves called the brachial plexus by the scalenus anticus muscle, produces similar effects in the upper chest and arms.

Simple disuse of muscle or bone, as, for example, from the immobilization produced when a limb is put in a cast or sling, results in atrophy of these tissues. In the case of muscle, the degree of atrophy is generally less severe than that caused by injury to a nerve, although the nature of the change is similar.

Localized atrophies of leg and arm muscles may result from hereditary or familial diseases in which the nerves of the spinal cord that supply them are inactivated or destroyed. In Charcot-Marie-Tooth disease, the atrophy involves mainly the peroneal muscles, at the outer side of the lower legs, and sometimes the muscles of the hand as well. It commonly begins in childhood or adolescence. Peroneal muscle atrophy is also seen in the hereditary spinal cord degenerative disease known as Friedreich ataxia.

Atrophy of nerve tissue

Atrophy of brain or spinal cord tissue may be brought about by injuries that directly affect a localized area or that interfere with the blood supply to an area. When peripheral nerves are severed, degenerative and eventually atrophic changes ensue in the part beyond the injury. This type of atrophy is known as Wallerian degeneration. If conditions do not allow regeneration of nerve fibres from the proximal fragment of the cut nerve, atrophy is the eventual fate of the nerve tissue distal to the injury. Retrograde atrophy also occurs from disuse and affects the ganglion cells of the injured nerve.

Prolonged pressure brings about atrophy in the central nervous system as elsewhere. The pressure of an expanding tumour of the membranes covering the brain results in localized atrophy of the adjacent brain substance on which it impinges. In hydrocephalus more widespread atrophy of brain tissue results from the abnormal amounts of fluid confined within the rigid bony compartment of the skull. Increased pressure within the skull may force a portion of the brain through the foramen magnum, the bony opening at the base of the skull, and, if prolonged, results in a localized atrophy of cerebellar tissue pressed against the bony wall.

The late stages of chronic infections may be characterized by atrophy of the brain. A striking example of this is the variety of syphilitic infection of the nervous system known as general paresis in which the brain is shrunk and reduced in weight, the atrophy affecting mainly the cortex of the brain, particularly or most markedly in the frontal area. Occasionally the atrophy is local or affects only one side of the brain. The shrinkage of the brain tissue is mainly due to loss of many nerve cells of the cortex.

Atrophy of fatty tissue

Atrophy of adipose tissue of the body occurs as a part of the generalized atrophy of prolonged undernutrition. Localized atrophy of adipose tissue—lipodystrophy—may be the result of injury to the local area; e.g., repeated insulin injections cause atrophy of fatty tissue at the site of the injections. Progressive lipodystrophy is a disease of unknown cause in which the fatty tissue atrophies only in certain regions of the body. It occurs mainly in women and often begins in childhood. The progressive wasting of adipose tissue affects mainly the face, arms, and trunk. In the affected areas, the specialized fat-holding cells of adipose tissue disappear.

Atrophy of skin

A widespread atrophic change in the skin has been noted as a prominent part of the aging process. Similar atrophic changes in the skin appear to be brought about or enhanced by excessive exposure to sunlight. While a number of abnormal conditions of the skin may include localized atrophic changes in the epidermis or dermis as a part of their lesions, certain generalized diseases of the skin are particularly characterized by such changes. The hardening of the skin known as scleroderma may occur in a localized, or circumscribed, form called morphea or as a more diffuse and severe disease. Advanced stages of scleroderma are characterized by marked atrophy of the tissue and appendages of the true skin. Atrophic thinning of the overlying epidermis also may occur, and the underlying fatty tissue and muscle may atrophy as well. The chronic form of the disease discoid lupus erythematosus also is characterized by atrophy. In advanced stages atrophy occurs particularly in the epidermis in focal areas. The thinned layer of epidermis may be a prominent feature of the microscopic appearance of the skin.

Atrophy of glands

Endocrine glandular tissues may undergo atrophy when an excess of their hormonal product is present as a result of disease. An example is seen in connection with a hormone-producing tumour of the cortical tissue of one adrenal gland, which may be accompanied by marked atrophy of the cortical tissue of the opposite adrenal gland. This probably results from disturbance of the delicate mechanism of hormonal stimulation via the pituitary gland.

Various endocrine organs (thyroid gland, adrenal glands, gonads) depend for their activity on endocrine stimulation by hormones of the pituitary gland. A severe general failure of production of the pituitary hormones results in the widespread endocrine atrophy of Simmonds disease, as has been noted. Lesser degrees of pituitary functional disturbance may disturb a delicate balance, involving mainly one type of stimulating hormone of the pituitary, and may result in selective atrophy of the adrenal cortical tissue or of the gonads.

Glands that release their secretions through a duct (e.g., salivary glands, pancreas) may become atrophic as a result of obstruction of the duct. In the pancreas, a complete obstruction of its duct results in atrophy of the glandular tissue, except for the insulin-producing islets of Langerhans, the secretion of which is absorbed into the bloodstream. Factors of both disuse and increased pressure may be present in the atrophy resulting from obstruction of the outlet channel. Similarly, rapid and complete obstruction of a ureter is followed by atrophy of the corresponding kidney.

Chemical-induced atrophy

Cases of atrophy resulting from chemical injury are not common. In chronic math poisoning, however, degenerative changes occur in peripheral nerves, resulting in weakness and atrophy in the tissues (usually legs or arms) to which the nerves are distributed. Similar results may follow the peripheral neuropathy of chronic lead poisoning.

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Jai Ganesh · Dark Discussions at Cafe Infinity

2442) Werner Forssmann

Gist:

Life

Werner Forssmann was born in Berlin, where he also studied medicine. As a newly educated doctor, he served in Eberswalde and conducted his Nobel Prize-awarded experiment there in 1929. His experimentation met resistance, however, which impeded continued research in the field. After being chief surgeon in Dresden and Berlin, Forssmann served as a doctor in the army during World War II. After the war ended, he worked as a district medical officer, among other things. Forssmann and his wife, also a doctor, had six children.

Work

In 1929 the physician Werner Forssmann saw a picture in a book showing how a tube was inserted into the heart of a horse through a vein. A balloon at the other end of the tube showed changes in pressure. Forssmann was convinced that a similar experiment could be carried out on people. Despite the fact that his boss forbade him, Forssmann conducted the experiment on himself. From the crook of his arm he inserted a thin catheter through a vein into his heart and took an X-ray photo. The experiment paved the way for many types of heart studies.

Summary

Werner Forssmann (born Aug. 20, 1904, Berlin, Ger.—died June 1, 1979, Schopfheim, W. Ger.) was a German surgeon who shared with André F. Cournand and Dickinson W. Richards the Nobel Prize for Physiology or Medicine in 1956. A pioneer in heart research, Forssmann contributed to the development of cardiac catheterization, a procedure in which a tube is inserted into a vein at the elbow and passed through the vein into the heart. While a surgical resident in Berlin (1929), Forssmann used himself as the first human subject, watching the progress of the catheter in a mirror held in front of a fluoroscope screen. Forssmann’s daring experiment was condemned at the time as foolhardy and dangerous, and in the face of severe criticism he abandoned cardiology for urology.

Forssmann’s procedure, with slight modifications, was put into practice in 1941 by Richards and Cournand, and has since become an extremely valuable tool in diagnosis and research. It has made possible, among other things, precise measurement of intracardiac pressure and blood flow, injection into the heart of drugs and of opaque material visible on X-ray photographs, and insertion of electrodes for the regulation of the heartbeat.

Forssmann graduated in medicine from the University of Berlin (1928) and then did postgraduate study in urology at Berlin and Mainz. He served as chief of surgery at the city hospital in Dresden-Friedrichstadt and in 1958 was named chief of the surgical division of the Evangelical Hospital in Düsseldorf.

Details

Werner Theodor Otto Forßmann (29 August 1904 – 1 June 1979) was a German researcher and physician from Germany who shared the 1956 Nobel Prize in Medicine (with Andre Frederic Cournand and Dickinson W. Richards) for developing a procedure that allowed cardiac catheterization. In 1929, he put himself under local anesthesia and inserted a catheter into a vein of his arm. Not knowing if the catheter might pierce a vein, he put his life at risk. Forssmann was nevertheless successful; he safely passed the catheter into his heart.

Early life

Forssmann was born in Berlin on 29 August 1904. Upon graduating from Askanisches Gymnasium [de], he entered the University of Berlin to study medicine, passing the State Examination in 1929.

Career

He hypothesized that a catheter could be inserted directly into the heart, for such applications as directly delivering drugs, injecting radiopaque dyes, or measuring blood pressure. The fear at the time was that such an intrusion into the heart would be fatal. To prove his point, he decided to try the experiment on himself.

In 1929, while working in Eberswalde, he performed the first human cardiac catheterization. He ignored his department chief and persuaded the operating-room nurse in charge of the sterile supplies, Gerda Ditzen, to assist him. She agreed, but only on the promise that he would do it on her rather than on himself. However, Forssmann tricked her by restraining her to the operating table and pretending to locally anaesthetise and cut her arm whilst actually doing it on himself. He anesthetized his own lower arm in the cubital region and inserted a urinary catheter into his antecubital vein, threading it partly along before releasing Ditzen (who at this point realised the catheter was not in her arm) and telling her to call the X-ray department. They walked some distance to the X-ray department on the floor below where under the guidance of a fluoroscope he advanced the catheter the full 60 cm into his right ventricular cavity. This was then recorded on X-ray film showing the catheter lying in his right atrium.

The head clinician at Eberswalde, although initially very annoyed, recognized Werner's discovery when shown the X-rays; he allowed Forssmann to carry out another catheterization on a terminally ill woman whose condition improved after being given drugs in this way. An unpaid position was created for Forssmann at the Berliner Charité Hospital, working under Ferdinand Sauerbruch, although once Sauerbruch saw his paper, he was dismissed for continuing without his approval. Sauerbruch commented, "You certainly can't begin surgery in that manner". Facing such disciplinary action for self-experimentation, he was initially forced to leave the Charité, but was later reinstated until again being forced to leave in 1932 for not meeting scientific expectations. His surgical skills were noted, however, and he was recommended to another hospital where he worked for a while before leaving in 1933 after marrying Dr. Elsbet Engel, a specialist in urology there. Finding it difficult to get a job with his reputation, he quit cardiology and took up urology. He then went on to study urology under Karl Heusch at the Rudolf Virchow Hospital [de] in Berlin. Later, he was appointed chief of the surgical clinic at both the City Hospital at Dresden-Friedrichstadt and the Robert Koch Hospital [de] in Berlin.

From 1932 to 1945, he was a member of the Nazi Party. At the start of World War II, he became a medical officer. In the course of his service, he rose to the rank of major, until he was captured and put into a U.S. POW camp. Upon his release in 1945, he worked as a lumberjack and then as a country medic in the Black Forest with his wife. In 1950, he began practice as a urologist in Bad Kreuznach.

During the time of his imprisonment, his paper was read by André Frédéric Cournand and Dickinson W. Richards. They developed ways of applying his technique to heart disease diagnosis and research. In 1954, he was given the Leibniz Medal of the German Academy of Sciences. In 1956, the Nobel Prize in Physiology or Medicine was awarded to Cournand, Richards, and Forßmann.

After winning the Nobel Prize, he was given the position of honorary professor of surgery and urology at the University of Mainz. In 1961, he became an honorary professor at the National University of Córdoba. In 1962, he became a member of the executive board of the German Society of Surgery. He also became a member of the American College of Chest Physicians, honorary member of the Swedish Society of Cardiology, the German Society of Urology [de], and the German Child Welfare Association.

Personal life

He and Elsbet had six children: Klaus Forßmann in 1934, Knut Forßmann in 1936, Jörg Forßmann in 1938, Wolf Forßmann in 1939 (who was first to isolate the atrial natriuretic peptide), Bernd Forßmann in 1940 (who helped develop the first clinical lithotriptor), and Renate Forßmann in 1943.

He died in Schopfheim, Germany, of heart failure on 1 June 1979. His wife died in 1993.

Jai Ganesh · Jokes

Q: What does it do before it rains candy?
A: It sprinkles!
* * *
Q: When should you take a cookie to the doctor?
A: When it feels crummy.
* * *
Q: What does a gambling addict eat?
A: Poker chips and salsa.
* * *
Q: What is a monkey's favorite cookie?
A: Chocolate chimp!
* * *
Q: What does an excited fat kid do in the junk food isle?
A: The Moon-Pies Walk.
* * *

Jai Ganesh · Dark Discussions at Cafe Infinity

Come Quotes - XIV

1. It is important that those that do come to settle in the U.K. gain a sense of British identity and share British values. We have always attracted the best and brightest. - Rishi Sunak

2. The time has come for us to draw the line. The time has come for the responsible leaders of both political parties to take a stand against overgrown Government and for the American taxpayer. - Richard M. Nixon

3. Now, as a nation, we don't promise equal outcomes, but we were founded on the idea everybody should have an equal opportunity to succeed. No matter who you are, what you look like, where you come from, you can make it. That's an essential promise of America. Where you start should not determine where you end up. - Barack Obama

4. Every beauty which is seen here by persons of perception resembles more than anything else that celestial source from which we all are come. - Michelangelo

5. The tennis ball doesn't know how old I am. The ball doesn't know if I'm a man or a woman or if I come from a communist country or not. Sport has always broken down these barriers. - Martina Navratilova

6. The scientific man does not aim at an immediate result. He does not expect that his advanced ideas will be readily taken up. His work is like that of the planter - for the future. His duty is to lay the foundation for those who are to come, and point the way. - Nikola Tesla

7. Clouds come floating into my life, no longer to carry rain or usher storm, but to add color to my sunset sky. - Rabindranath Tagore

8. I have come to the conclusion that politics are too serious a matter to be left to the politicians. - Charles de Gaulle.

Jai Ganesh · This is Cool

Motor Neuron

Gist

Motor neurons (or motoneurons) are specialized efferent nerve cells originating in the brain or spinal cord that transmit impulses to effector muscles and glands, controlling voluntary and involuntary movements. They are classified into upper motor neurons (brain to spinal cord) and lower motor neurons (spinal cord to muscle).

Motor neurones are cells in the brain and spinal cord that allow us to move, speak, swallow and breathe by sending commands from the brain to the muscles that carry out these functions.

Summary

Motor neurons, also known as efferent neurons, are nerve cells responsible for carrying central nervous system signals towards muscles to cause voluntary or involuntary movement through the innervation of effector muscles and glands. Their nerve fibers are considered to be the longest in the human body. Motor neurons are the most common structure for neurons.

Motor neurons are divided into either upper or lower motor neurons. Each type of motor neuron utilizes different neurotransmitters to relay their signals.

* Upper motor neurons originate primarily in the cerebral cortex (primary motor cortex) and extend towards the brainstem or spinal cord, where they synapse. Upper motor neurons travel down specific pathways, including the pyramidal, extrapyramidal, rubrospinal, tectospinal and reticulospinal tracts. Glutamate is used as a neurotransmitter.
* Lower motor neurons originate in the brainstem (cranial nerve nuclei) and the spinal cord (anterior horn) and project to innervate muscles and glands throughout the body. Acetylcholine is used as a neurotransmitter.

The structure of a motor neuron is characterized by three components: the soma, the axon, and the dendrites. Motor neurons have a large cell body, or soma, and long projections used in transmitting information away from the soma. These projections are referred to as axons and dendrites. Axons send impulses away from the soma and dendrites carry incoming information. Motor neurons are typically considered multipolar in terms of their structure, which translates to having a single axon and multiple dendrites.

Myelin sheath surrounds the axon of the motor neuron. One of the key functions of myelin is to insulate the axon length ensuring that electrical impulses are transmitted quickly and efficiently to the target structure. Each motor neuron divides into many terminal branches which synapse with muscle fibers at neuromuscular junctions (NMJ), also known as myoneural junctions. Electrical impulses are transmitted from the motor neuron to the muscle fiber via axon terminals (also known as neuropodia or axon endfeet), to generate muscle contractions. Axon terminals function to release neurotransmitters which are received by specific parts of the muscle fiber membrane known as motor end plates, signalling muscle contraction.

A motor neuron and its associated muscle fibers make up a motor unit. Fine muscles (e.g. extraocular muscles) have small motor units and therefore can be controlled more precisely in comparison to larger muscles (e.g. biceps brachii).

Details

A motor neuron (or motoneuron), also known as efferent neuron is a neuron that allows for both voluntary and involuntary movements of the body through muscles and glands. Its cell body is located in the motor cortex, brainstem or the spinal cord, and whose axon (fiber) projects to the spinal cord or outside of the spinal cord to directly or indirectly control effector organs, mainly muscles and glands. There are two types of motor neuron – upper motor neurons and lower motor neurons. Axons from upper motor neurons synapse onto interneurons in the spinal cord and occasionally directly onto lower motor neurons. The axons from the lower motor neurons are efferent nerve fibers that carry signals from the spinal cord to the effectors. Types of lower motor neurons are alpha motor neurons, beta motor neurons, and gamma motor neurons.

A single motor neuron may innervate many muscle fibres and a muscle fibre can undergo many action potentials in the time taken for a single muscle twitch. Innervation takes place at a neuromuscular junction and twitches can become superimposed as a result of summation or a tetanic contraction. Individual twitches can become indistinguishable, and tension rises smoothly eventually reaching a plateau.

Although the word "motor neuron" suggests that there is a single kind of neuron that controls movement, this is not the case. Indeed, upper and lower motor neurons—which differ greatly in their origins, synapse locations, routes, neurotransmitters, and lesion characteristics—are included in the same classification as "motor neurons." Essentially, motor neurons, also known as motoneurons, are made up of a variety of intricate, finely tuned circuits found throughout the body that innervate effector muscles and glands to enable both voluntary and involuntary motions. Two motor neurons come together to form a two-neuron circuit. While lower motor neurons start in the spinal cord and go to innervate muscles and glands all throughout the body, upper motor neurons originate in the cerebral cortex and travel to the brain stem or spinal cord. It is essential to comprehend the distinctions between upper and lower motor neurons as well as the routes they follow in order to effectively detect these neuronal injuries and localise the lesions.

Disorders causing selective injury to motor neurons are classified as motor neuron diseases.

Additional Information

Motor neurons are nerve cells that carry messages from the brain and spinal cord to your muscles and glands. They control everything from blinking and walking to breathing and digestion.

By acting as messengers between the central nervous system (CNS) and the body, they make movement and essential bodily functions possible.

Motor neurons belong to a broader group called efferent neurons—cells that send signals outward from the CNS. These neurons are crucial for both voluntary actions, like typing, and involuntary ones, like maintaining your posture.

Key Takeaways

* Motor neurons carry messages from your brain and spinal cord to your muscles.
* They’re essential for movement, reflexes, and basic body functions.
* There are two main types: upper and lower motor neurons.
* Damage can cause serious issues, including paralysis and diseases like ALS.
* While some treatments exist, prevention and early detection are key.

(ALS: Amyotrophic lateral sclerosis)

How Do Motor Neurons Work?

Motor neurons act like messengers. They carry electrical signals from your brain or spinal cord to your muscles.

When the message reaches its destination, it triggers the release of a chemical called acetylcholine at a point where the nerve meets the muscle—this spot is called the neuromuscular junction.

Acetylcholine tells your muscle to contract, which produces movement.

Motor neurons have three main parts:

* Soma (cell body): The cell’s headquarters, where energy and proteins are produced.
* Dendrites: Short branches that receive messages from other neurons.
* Axon: A long fiber that carries the outgoing message to a muscle or gland.

Each part works together to ensure your body reacts smoothly and quickly.

What Are the Types of Motor Neurons?

Motor neurons are divided into two main groups, based on where they begin and what they control:

Upper Motor Neurons

These begin in the motor cortex of the brain or the brainstem. They send signals down to the spinal cord to help start and guide movement.

Key pathways include:

* Pyramidal tract: Controls deliberate, voluntary actions like lifting your arm.
* Extrapyramidal tracts: Manage automatic functions like balance and posture. This includes:
* Rubrospinal tract: Helps adjust body balance.
* Tectospinal tract: Affects neck muscle movement.
* Reticulospinal tract: Regulates automatic actions.

Lower Motor Neurons

These are the final link between your nervous system and your muscles. They carry messages directly to muscle fibers.

Lower motor neurons are categorized into:

* Somatic Motor Neurons:
** Alpha neurons: Connect to standard muscle fibers to produce forceful contractions.
** Beta neurons: Interact with both standard and sensory muscle fibers.
** Gamma neurons: Fine-tune muscle tone by connecting to stretch sensors.

* Special Visceral Efferent Neurons: Found in the brainstem, these are part of cranial nerves like the facial nerve and vagus nerve, which control facial expressions and digestion.

* General Visceral Motor Neurons: Part of the autonomic nervous system, they connect to organs like the heart and intestines.

What Do Motor Neurons Do?

Motor neurons allow your brain to control your body. Their responsibilities include:

* Voluntary movements: Walking, writing, smiling
* Involuntary reflexes: Pulling your hand away from something hot
* Autonomic functions: Breathing, heartbeat, digestion

They’re also essential for posture, balance, and muscle coordination—things we often take for granted.

Location

Motor neurons are located in the central nervous system (CNS), specifically in the motor cortex, brainstem, and spinal cord.

While the cell bodies (soma) of motor neurons remain within the CNS, their axons, called efferent fibers, project outward to reach muscles and other peripheral systems such as organs and glands.

These neurons are notable for having some of the longest axons in the body. In fact, the efferent fibers that extend from the base of the spinal cord to the toes represent one of the longest axon pathways in the human body.

With approximately 500,000 motor neurons in total, these cells form an extensive network carrying information from the CNS to peripheral organs, muscles, and glands.

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#10767. What does the term in Biology Guanine mean?

#10768. What does the term in Biology Habitat mean?

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#5963. What does the noun nectar mean?

#5964. What does the noun nectarine mean?

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#2578. What does the medical term Chlorambucil mean?

Jai Ganesh · Science HQ

Specific Heat

Gist

In thermodynamics, the specific heat capacity (symbol c) of a substance is the amount of heat that must be added to one unit of mass of the substance in order to cause an increase of one unit in temperature. It is also referred to as massic heat capacity or as the specific heat.

Specific heat (or specific heat capacity) is the amount of heat energy needed to raise the temperature of one unit of mass (like one gram or kilogram) of a substance by one degree Celsius (or Kelvin). It's a measure of how much heat a material can store, often called its thermal inertia, and substances with high specific heat, like water, resist temperature changes more than those with low specific heat, like gold. This property is crucial in understanding everything from cooking to climate science.

Summary

The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius. The relationship between heat and temperature change is usually expressed in the form shown below where c is the specific heat. The relationship does not apply if a phase change is encountered, because the heat added or removed during a phase change does not change the temperature.

The specific heat of water is 1 calorie/gram °C = 4.186 joule/gram °C which is higher than any other common substance. As a result, water plays a very important role in temperature regulation. The specific heat per gram for water is much higher than that for a metal, as described in the water-metal example. For most purposes, it is more meaningful to compare the molar specific heats of substances.

The molar specific heats of most solids at room temperature and above are nearly constant, in agreement with the Law of Dulong and Petit. At lower temperatures the specific heats drop as quantum processes become significant. The low temperature behavior is described by the Einstein-Debye model of specific heat.

The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius. The relationship between heat and temperature change is usually expressed in the form shown below where c is the specific heat. The relationship does not apply if a phase change is encountered, because the heat added or removed during a phase change does not change the temperature.

Details:

Understanding Specific Heat Capacity

This concept is fundamental to thermodynamics and heat transfer, since it expresses the amount of heat energy that must be supplied to a unit of mass of a substance to raise its temperature by one degree Celsius. This concept has several important applications in practice. Engineers and materials scientists use it to choose the right materials that will bring rapid temperature changes where needed and ensure thermal stability where necessary.

What is Specific Heat?

It is the amount of heat energy required to raise any substance’s temperature by one degree Celsius. This is an intrinsic property of the material and depends upon the nature of the substance. It is one of the most critical attributes for scientists and engineers because it touches areas from climate science to culinary arts. 1

Understanding this characteristic means that different materials, upon receiving the same amount of heat, change temperature by different amounts. This is due to the molecular structure and bonding nature of each substance. Imagine you are at the beach on a hot day. The sand feels extremely hot, while the water does not. It is because sand has a low specific heat, it warms relatively quickly. On the other hand, water’s high specific heat allows it to absorb more heat without raising its temperature as quickly.

What is Heat Capacity?

It is defined as the amount of heat energy required to increase the entire object’s temperature by one degree Celsius. Heat capacity does depend upon the mass of an object and its composition.

For example, while specific heat for both a large block of iron and a small iron nail is the same; heat capacity will be different as the large block of iron will need more heat to raise the temperature by one degree while the small iron nail would need relatively less heat to achieve the same temperature increase.

Some Examples of Specific Heat Capacity

Water (liquid) 4.18 J/kg/C: Water has great specific capacity, which is one of its best qualities since it helps it to conduct heat effectively. It can absorb and release massive amounts of energy without undergoing much variation in temperatures. For instance, car radiator systems and electricity generation amid other industries. 4

Steam 2.01 J/kg/C: The specific heat of steam is important in the design of steam engines and turbines. Since engineers must know how much energy is needed to make steam, and they also must know how much heat can be carried by the steam, they shall view power generation systems in relation to their efficiency.

Copper 0.385J/kg/C: The specific heat capacity of copper applies to both electrical engineers and plumbers because it can efficiently conduct heat. This property is very important when creating any electrical wiring or electronic circuit boards that involve heat exchange. This ensures the proper management of temperatures within an electronic device and system.

Iron 0.449J/kg/C: Iron’s specific heat capacity is an important factor not only in the manufacturing of cookware like pans and skillets but also in the construction industry. This property allows iron to effectively absorb and retain heat, making it valuable for creating materials that require durability and thermal stability.

Key Takeaways

For many scientific and engineering applications, it is important to understand specific heat capacity and its relationship with regards to heat capacity. The main messages that could be drawn from this discussion are below.

* Specific heat capacity: The amount of heat that needs to be supplied in order to raise the unit mass of substance by 1 degree Celsius.
* Heat Capacity vs Specific Heat Capacity: Heat capacity is dependent on the mass and composition of the object, but specific heat capacity is an intrinsic attribute of a material.
* In the case of gases, the specific heat capacity may be different while the process is occurring at constant pressure or at constant volume.
* In the case of solids and liquids, the difference between specific heat capacity at constant pressure and at constant volume may be considered negligible.

Therefore, it is a fundamental concept that connects theoretical understanding to practical applications. It plays a critical role in everything from industrial machinery to household appliances, enabling informed decisions about performance, safety, and energy efficiency. To ensure you’re making the best choices, it’s vital to have accurate instruments to measure thermal properties. Explore Thermtest’s product line to find the right tools for your needs.

Frequently Asked Questions:

What does the specific heat depend on?

Specific heat depends on the material’s molecular structure and bonding. Substances with stronger molecular bonds typically have higher specific heat because more energy is required to increase their temperature.

What is the specific heat of water?

The specific heat capacity of water at room temperature and pressure is approximately 4.18 J/g°C.

What material has the highest specific heat capacity?

Water has one of the highest specific heat capacities among common substances, at 4.18 J/g°C. This is because of the hydrogen bonding between water molecules, which requires significant energy to overcome. 5

How do you measure specific heat capacity?

It can be measured using a calorimeter, which quantifies the amount of heat transferred to or from a substance as its temperature changes.

What is the difference between heat capacity and specific heat?

Heat Capacity measures the heat required to raise the substance’s temperature by 1 degree. On the other hand, specific heat capacity is the amount of heat required to raise the temperature of 1 kg of a substance by 1 degree. While the former depends on the total mass or the amount of substance, the later does not. That is why the concept of heat capacity is used to understand how much an object can absorb or release heat during a given temperature change, and the concept of specific heat capacity is helpful in relating thermal properties of different materials.

What is the SI unit of specific heat capacity?

The SI unit is joules per kilogram per Kelvin (J/kg·K).

Additional Information

In thermodynamics, the specific heat capacity (symbol c) of a substance is the amount of heat that must be added to one unit of mass of the substance in order to cause an increase of one unit in temperature. It is also referred to as massic heat capacity or as the specific heat. More formally it is the heat capacity of a sample of the substance divided by the mass of the sample.

Specific heat capacity often varies with temperature, and is different for each state of matter.

While the substance is undergoing a phase transition, such as melting or boiling, its specific heat capacity is technically undefined, because the heat goes into changing its state rather than raising its temperature.

Specific heat is the quantity of heat required to raise the temperature of one gram of a substance by one Celsius degree. The units of specific heat are usually calories or joules per gram per Celsius degree. For example, the specific heat of water is 1 calorie (or 4.186 joules) per gram per Celsius degree. The Scottish scientist Joseph Black, in the 18th century, noticed that equal masses of different substances needed different amounts of heat to raise them through the same temperature interval, and, from this observation, he founded the concept of specific heat. In the early 19th century the French physicists Pierre-Louis Dulong and Alexis-Thérèse Petit demonstrated that measurements of specific heats of substances allow calculation of their atomic weights

specific-heat-1.jpg.webp

Jai Ganesh · Jai Ganesh's Puzzles

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#9864.

Jai Ganesh · Jai Ganesh's Puzzles

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#6358.

Jai Ganesh · Exercises

Hi,

2718.

Jai Ganesh · This is Cool

2504) Hydraulic Press

Gist

A hydraulic press works on the principle of Pascal's law, which states that when pressure is applied to a confined fluid, the pressure change occurs throughout the entire fluid.

In hydraulic presses, Pascal's law is applied: pressure in a confined fluid is transmitted equally in all directions. In mechanical presses, kinetic energy is stored in a flywheel and transmitted via clutch/crank mechanisms to the ram.

Summary

A hydraulic press uses a hydraulic cylinder to produce a compressive force. Within a hydraulic press, there is a plate where the sample is placed to be pressed for sample preparation.

How Does a Hydraulic Press Work?

A hydraulic press works on the principle of Pascal’s law, which states that when pressure is applied to a confined fluid, the pressure change occurs throughout the entire fluid. Within the hydraulic press, there is a piston that works as a pump, that provides a modest mechanical force to a small area of the sample. There is also a piston with a larger area, which produces a larger mechanical force.

Advantages

There are a variety of advantages to using hydraulic presses. This is evident in hand-fed hydraulic systems, where the ease and speed of sample switching is considerably improved.

These instruments are also extremely beneficial for high-volume sample preparation, also increasing the speed of sampling.

Details

A hydraulic press is a machine press using a hydraulic cylinder to generate a compressive force. It uses the hydraulic equivalent of a mechanical lever, and was also known as a Bramah press after the inventor, Joseph Bramah. He invented and was issued a patent on this press in 1795. As Bramah installed toilets and developed the modern flush toilet, he studied existing literature on the motion of fluids to develop the press.

Main principle

The hydraulic press depends on Pascal's principle. The pressure throughout a closed system is constant. One part of the system is a piston acting as a pump, with a modest mechanical force acting on a small cross-sectional area; the other part is a piston with a larger area which generates a correspondingly large mechanical force. Only small-diameter tubing (which more easily resists pressure) is needed if the pump is separated from the press cylinder.

Application

Hydraulic presses are commonly used for assembly and disassembly of tightly-fitting components. In manufacturing, they are used for forging, clinching, molding, blanking, punching, deep drawing, and metal forming operations. Hydraulic presses are also used for stretch forming, rubber pad forming, and powder compacting. The hydraulic press is advantageous in manufacturing, as it gives the ability to create more intricate shapes than other methods and can be economical with materials. A hydraulic press will take up less space compared to a mechanical press of the same capability. Hydraulic presses are also used for waste processing operations such as in garbage trucks and car crushers to reduce the size of waste material for easier more economic transportation.

In geology a tungsten carbide coated hydraulic press is used in the rock crushing stage of preparing samples for geochemical analyses in topics such as understanding the origins of volcanism.

In popular culture

The room featured in Fermat's Room has a design similar to that of a hydraulic press. Boris Artzybasheff also created a drawing of a hydraulic press, in which the press was created out of the shape of a robot.

In 2015, the Hydraulic Press Channel, a YouTube channel dedicated to crushing objects with a hydraulic press, was created by Lauri Vuohensilta, a factory owner from Tampere, Finland. The Hydraulic Press Channel has since grown to over 10 million subscribers on YouTube. There are numerous other YouTube channels that publish videos involving hydraulic presses that are tasked with crushing many different items, such as bowling balls, soda cans, plastic toys, and metal tools.

A hydraulic press is featured prominently in the Sherlock Holmes story "The Adventure of the Engineer's Thumb".

Additional Information

A hydraulic press, by definition, is a mechanical apparatus that leverages the static pressure of a liquid as explained by Pascal's principle. It's employed to form, reshape, and alter various materials including metals, plastics, rubber, and wood. The primary components of a hydraulic press comprise the mainframe, the power system, and the control mechanisms.

According to Pascal's principle, if pressure is exerted on a confined fluid, the pressure change spreads consistently throughout the liquid. In a hydraulic press, this applied pressure emanates from a piston, acting similarly to a pump to produce mechanical force.

The hydraulic press is a powerful machine widely used in industrial applications for metal forming, assembly, molding, and material compaction. The hydraulic press operates by forcing hydraulic fluid into a double-acting piston, relying on Pascal's Law to multiply force for heavy-duty tasks. The compressive force generated within the smaller hydraulic cylinder pushes the hydraulic oil (fluid) into a larger cylinder, where much greater force and pressure are applied. As the larger piston moves, it forces the fluid back into the smaller piston cylinder, maintaining a constant hydraulic pressure throughout the system.

This controlled fluid exchange between the two pistons increases mechanical pressure, creating the substantial force needed to drive the anvil of the hydraulic press downward onto a workpiece, shaping, compacting, or cutting the material into its desired form. Once the forming, punching, or pressing process is complete, the pressure is safely released, allowing the anvil and die to return to their original positions. Hydraulic presses are highly valued for their precision, repeatability, and ability to perform a variety of material processing operations, making them a cornerstone in manufacturing, automotive, aerospace, and fabrication industries.

How a Hydraulic Press Works

A typical hydraulic press consists of two cylinders, two pipes, and two pistons. One cylinder functions as the ram, while the other acts as the plunger; they are connected by a high-strength chamber filled with hydraulic fluid, often a specialized oil designed for high-pressure environments. The configuration of these components directly enables the powerful compression and shaping abilities for which hydraulic presses are known.

* Main Cylinder (Ram): Delivers force to the workpiece.
* Plunger: Initiates pressure transfer by pushing hydraulic fluid.
* Pipes and Hoses: Ensure secure fluid movement between components, preventing leaks and ensuring safety.
* Hydraulic Fluid Reservoir: Stores and supplies fluid to support continuous operation.
* Control Valves: Direct fluid flow, manage pressure, and ensure precise operation for various press functions such as forging, stamping, and embossing.

Ram

In advanced hydraulic systems, multiple rams are used, and the number depends on the required working load. Utilizing several smaller rams rather than a single larger one allows for finer control over the hydraulic thrust force, which is essential for delicate metal forming or precision stamping. Hydraulic fluid is routed to these rams by a hydraulic pump and an accumulator, which moderates pressure between the rams and pump, ensuring optimal performance for high-tonnage applications such as deep drawing, blanking, or coining.

Accumulator

The hydraulic accumulator is a critical component that stores pressurized hydraulic fluid, releasing it as needed to maintain system efficiency and responsiveness. It typically consists of a durable cylinder with a spring-loaded or pneumatic piston separator. The accumulator functions as an energy storage device, enabling the hydraulic press to quickly respond to sudden demands without requiring the hydraulic pump to operate continuously. The constant pressure provided by the accumulator is crucial for consistent operation in heavy manufacturing processes, energy efficiency, and reducing mechanical wear. Properly sized accumulators enhance the safety, speed, and reliability of industrial hydraulic press systems.

Pump

There are three main types of hydraulic pumps used in presses: vane, gear, and piston, with piston pumps prevailing in high-performance equipment due to their efficiency and durability under high loads. Hydraulic presses utilize positive displacement pumps, which deliver a precise, constant volume of hydraulic oil during each cycle, maintaining high forces required in automotive component manufacturing, metal stamping, and plastic molding applications. Positive displacement pumps can be either fixed or variable; fixed pumps operate at set speeds, while variable pumps allow for speed and direction changes, enabling customized pressure control based on specific pressing or forming requirements. Piston pumps—available as axial, bent axis, or radial designs—are especially suited for hydraulic press systems because they handle high pressure, provide superior volumetric efficiency, and minimize fluid leakage, ensuring long-term operational reliability in industrial and commercial environments.

Cylinders

The number and size of cylinders in a hydraulic press depend on the design and intended tonnage capacity. These cylinders generate the immense compressive force that drives the press ram and die to shape or cut metal, plastic, rubber, or composites. In a typical two-cylinder design, the cylinder paired with the ram has a larger diameter to produce maximum force, while the plunger cylinder is smaller and initiates fluid movement. Both are made from robust, pressure-rated steel, featuring input/output ports for controlled hydraulic fluid circulation to support heavy pressing operations.

Cylinders are interconnected via hydraulic pipes and hoses, which transmit high-pressure fluid. When the plunger's downward stroke applies pressure to the hydraulic oil, the resulting force is transferred to the main ram. This unidirectional force—delivered via a linear actuator—enables consistent, dynamic motion, critical for applications such as metalforming, compression molding, powder compacting, and precision stamping.

Hydraulic Press Process

The hydraulic press process is the foundation of modern metal forming, fabrication, and materials engineering. The animation below demonstrates how consistent hydraulic pressure from the system's cylinders powers the main ram, driving the press anvil downward onto the workpiece or slug positioned in the die cavity. The result is precise, repeatable compression, shaping, or assembly of materials into components for the automotive, aerospace, electronics, and appliance industries. Because hydraulic presses can deliver adjustable force, stroke length, and speed, they are ideal for a diverse range of processes, including forging, deep drawing, extrusion, lamination, and powder metallurgy. Their versatility and controllability ensure ideal results and cost-effective production in both high-volume and custom-manufacturing environments.

Choosing the Right Hydraulic Press for your production needs involves evaluating not only the type of hydraulic system, but also key factors such as required tonnage, workspace dimensions, safety features, energy consumption, and cycle speed. Leading hydraulic press manufacturers offer custom solutions designed for processes such as metal stamping, plastic injection, rubber molding, and powder compaction. When evaluating suppliers and comparing models, consider the quality of components (cylinders, pumps, seals, frames), after-sales technical support, and maintenance requirements to ensure long-term reliability and maximum return on investment.

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