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#1 Re: This is Cool » Miscellany » Today 15:25:39

1235) Spinal cord

Summary

Spinal cord is major nerve tract of vertebrates, extending from the base of the brain through the canal of the spinal column. It is composed of nerve fibres that mediate reflex actions and that transmit impulses to and from the brain.

Like the brain, the spinal cord is covered by three connective-tissue envelopes called the meninges. The space between the outer and middle envelopes is filled with cerebrospinal fluid, a clear, colourless fluid that cushions the spinal cord.

A cross section of the spinal cord reveals white matter arranged around a butterfly-shaped area of gray matter. The white matter consists of myelinated fibres, or axons, that form nerve tracts ascending to and descending from the brain. The white matter is grouped into discrete sectors called funiculi. The gray matter contains cell bodies, unmyelinated motor-neuron fibres, and interneurons connecting the two sides of the cord. Gray-matter cells form projections called horns. Fibres exiting the spinal cord from the dorsal and ventral horns join in paired tracts to form the spinal nerves. Information travels up the ascending tracts of neurons and is sorted by the brain. Responses are induced by nerve impulses traveling down the descending tracts that stimulate motor neurons or that initiate glandular secretion.

Details

The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column. It encloses the central canal of the spinal cord, which contains cerebrospinal fluid. The brain and spinal cord together make up the central nervous system (CNS). In humans, the spinal cord begins at the occipital bone, passing through the foramen magnum and entering the spinal canal at the beginning of the cervical vertebrae. The spinal cord extends down to between the first and second lumbar vertebrae, where it ends. The enclosing bony vertebral column protects the relatively shorter spinal cord. It is around 45 cm (18 in) long in adult men and around 43 cm (17 in) long in adult women. The diameter of the spinal cord ranges from 13 mm (1⁄2 in) in the cervical and lumbar regions to 6.4 mm (1⁄4 in) in the thoracic area.

The spinal cord functions primarily in the transmission of nerve signals from the motor cortex to the body, and from the afferent fibers of the sensory neurons to the sensory cortex. It is also a center for coordinating many reflexes and contains reflex arcs that can independently control reflexes. It is also the location of groups of spinal interneurons that make up the neural circuits known as central pattern generators. These circuits are responsible for controlling motor instructions for rhythmic movements such as walking.

Structure

The spinal cord is the main pathway for information connecting the brain and peripheral nervous system. Much shorter than its protecting spinal column, the human spinal cord originates in the brainstem, passes through the foramen magnum, and continues through to the conus medullaris near the second lumbar vertebra before terminating in a fibrous extension known as the filum terminale.

It is about 45 cm (18 in) long in men and about 43 cm (17 in) in women, ovoid-shaped, and is enlarged in the cervical and lumbar regions. The cervical enlargement, stretching from the C5 to T1 vertebrae, is where sensory input comes from and motor output goes to the arms and trunk. The lumbar enlargement, located between L1 and S3, handles sensory input and motor output coming from and going to the legs.

The spinal cord is continuous with the caudal portion of the medulla, running from the base of the skull to the body of the first lumbar vertebra. It does not run the full length of the vertebral column in adults. It is made of 31 segments from which branch one pair of sensory nerve roots and one pair of motor nerve roots. The nerve roots then merge into bilaterally symmetrical pairs of spinal nerves. The peripheral nervous system is made up of these spinal roots, nerves, and ganglia.

The dorsal roots are afferent fascicles, receiving sensory information from the skin, muscles, and visceral organs to be relayed to the brain. The roots terminate in dorsal root ganglia, which are composed of the cell bodies of the corresponding neurons. Ventral roots consist of efferent fibers that arise from motor neurons whose cell bodies are found in the ventral (or anterior) gray horns of the spinal cord.

The spinal cord (and brain) are protected by three layers of tissue or membranes called meninges, that surround the canal. The dura mater is the outermost layer, and it forms a tough protective coating. Between the dura mater and the surrounding bone of the vertebrae is a space called the epidural space. The epidural space is filled with adipose tissue, and it contains a network of blood vessels. The arachnoid mater, the middle protective layer, is named for its open, spiderweb-like appearance. The space between the arachnoid and the underlying pia mater is called the subarachnoid space. The subarachnoid space contains cerebrospinal fluid (CSF), which can be sampled with a lumbar puncture, or "spinal tap" procedure. The delicate pia mater, the innermost protective layer, is tightly associated with the surface of the spinal cord. The cord is stabilized within the dura mater by the connecting denticulate ligaments, which extend from the enveloping pia mater laterally between the dorsal and ventral roots. The dural sac ends at the vertebral level of the second sacral vertebra.

In cross-section, the peripheral region of the cord contains neuronal white matter tracts containing sensory and motor axons. Internal to this peripheral region is the grey matter, which contains the nerve cell bodies arranged in the three grey columns that give the region its butterfly-shape. This central region surrounds the central canal, which is an extension of the fourth ventricle and contains cerebrospinal fluid.

The spinal cord is elliptical in cross section, being compressed dorsolaterally. Two prominent grooves, or sulci, run along its length. The posterior median sulcus is the groove in the dorsal side, and the anterior median fissure is the groove in the ventral side.

Segments

The human spinal cord is divided into segments where pairs of spinal nerves (mixed; sensory and motor) form. Six to eight motor nerve rootlets branch out of right and left ventralateral sulci in a very orderly manner. Nerve rootlets combine to form nerve roots. Likewise, sensory nerve rootlets form off right and left dorsal lateral sulci and form sensory nerve roots. The ventral (motor) and dorsal (sensory) roots combine to form spinal nerves (mixed; motor and sensory), one on each side of the spinal cord. Spinal nerves, with the exception of C1 and C2, form inside the intervertebral foramen (IVF). These rootlets form the demarcation between the central and peripheral nervous systems.

The grey column, (as three regions of grey columns) in the center of the cord, is shaped like a butterfly and consists of cell bodies of interneurons, motor neurons, neuroglia cells and unmyelinated axons. The anterior and posterior grey column present as projections of the grey matter and are also known as the horns of the spinal cord. Together, the grey columns and the gray commissure form the "grey H."

The white matter is located outside of the grey matter and consists almost totally of myelinated motor and sensory axons. "Columns" of white matter carry information either up or down the spinal cord.

The spinal cord proper terminates in a region called the conus medullaris, while the pia mater continues as an extension called the filum terminale, which anchors the spinal cord to the coccyx. The cauda equina ("horse's tail") is a collection of nerves inferior to the conus medullaris that continue to travel through the vertebral column to the coccyx. The cauda equina forms because the spinal cord stops growing in length at about age four, even though the vertebral column continues to lengthen until adulthood. This results in sacral spinal nerves originating in the upper lumbar region. For that reason, the spinal cord occupies only two-thirds of the vertebral canal. The inferior part of the vertebral canal is filled with cerebrospinal fluid (CSF) and the space is called the lumbar cistern.

Within the Central Nervous System (CNS), nerve cell bodies are generally organized into functional clusters, called nuclei. Axons within the CNS are grouped into tracts.

There are 31 spinal cord nerve segments in a human spinal cord:

* 8 cervical segments forming 8 pairs of cervical nerves (C1 spinal nerves exit the spinal column between the foramen magnum and the C1 vertebra; C2 nerves exit between the posterior arch of the C1 vertebra and the lamina of C2; C3–C8 spinal nerves pass through the IVF above their corresponding cervical vertebrae, with the exception of the C8 pair which exit between the C7 and T1 vertebrae)
* 12 thoracic segments forming 12 pairs of thoracic nerves
* 5 lumbar segments forming 5 pairs of lumbar nerves
* 5 sacral segments forming 5 pairs of sacral nerves
* 1 coccygeal segment

In the fetus, vertebral segments correspond with spinal cord segments. However, because the vertebral column grows longer than the spinal cord, spinal cord segments do not correspond to vertebral segments in the adult, particularly in the lower spinal cord. For example, lumbar and sacral spinal cord segments are found between vertebral levels T9 and L2, and the spinal cord ends around the L1/L2 vertebral level, forming a structure known as the conus medullaris.

Although the spinal cord cell bodies end around the L1/L2 vertebral level, the spinal nerves for each segment exit at the level of the corresponding vertebra. For the nerves of the lower spinal cord, this means that they exit the vertebral column much lower (more caudally) than their roots. As these nerves travel from their respective roots to their point of exit from the vertebral column, the nerves of the lower spinal segments form a bundle called the cauda equina.

There are two regions where the spinal cord enlarges:

* Cervical enlargement – corresponds roughly to the brachial plexus nerves, which innervate the upper limb. It includes spinal cord segments from about C4 to T1. The vertebral levels of the enlargement are roughly the same (C4 to T1).
* Lumbar enlargement – corresponds to the lumbosacral plexus nerves, which innervate the lower limb. It comprises the spinal cord segments from L2 to S3 and is found about the vertebral levels of T9 to T12.

Development

The spinal cord is made from part of the neural tube during development. There are four stages of the spinal cord that arises from the neural tube: The neural plate, neural fold, neural tube, and the spinal cord. Neural differentiation occurs within the spinal cord portion of the tube.[8] As the neural tube begins to develop, the notochord begins to secrete a factor known as Sonic hedgehog or SHH. As a result, the floor plate then also begins to secrete SHH, and this will induce the basal plate to develop motor neurons. During the maturation of the neural tube, its lateral walls thicken and form a longitudinal groove called the sulcus limitans. This extends the length of the spinal cord into dorsal and ventral portions as well.[9] Meanwhile, the overlying ectoderm secretes bone morphogenetic protein (BMP). This induces the roof plate to begin to secrete BMP, which will induce the alar plate to develop sensory neurons. Opposing gradients of such morphogens as BMP and SHH form different domains of dividing cells along the dorsal ventral axis.[10] Dorsal root ganglion neurons differentiate from neural crest progenitors. As the dorsal and ventral column cells proliferate, the lumen of the neural tube narrows to form the small central canal of the spinal cord.[11] The alar plate and the basal plate are separated by the sulcus limitans. Additionally, the floor plate also secretes netrins. The netrins act as chemoattractants to decussation of pain and temperature sensory neurons in the alar plate across the anterior white commissure, where they then ascend towards the thalamus. Following the closure of the caudal neuropore and formation of the brain's ventricles that contain the choroid plexus tissue, the central canal of the caudal spinal cord is filled with cerebrospinal fluid.

Earlier findings by Viktor Hamburger and Rita Levi-Montalcini in the chick embryo have been confirmed by more recent studies which have demonstrated that the elimination of neuronal cells by programmed cell death (PCD) is necessary for the correct assembly of the nervous system.

Overall, spontaneous embryonic activity has been shown to play a role in neuron and muscle development but is probably not involved in the initial formation of connections between spinal neurons.

Blood supply

The spinal cord is supplied with blood by three arteries that run along its length starting in the brain, and many arteries that approach it through the sides of the spinal column. The three longitudinal arteries are the anterior spinal artery, and the right and left posterior spinal arteries. These travel in the subarachnoid space and send branches into the spinal cord. They form anastamoses (connections) via the anterior and posterior segmental medullary arteries, which enter the spinal cord at various points along its length. The actual blood flow caudally through these arteries, derived from the posterior cerebral circulation, is inadequate to maintain the spinal cord beyond the cervical segments.

The major contribution to the arterial blood supply of the spinal cord below the cervical region comes from the radially arranged posterior and anterior radicular arteries, which run into the spinal cord alongside the dorsal and ventral nerve roots, but with one exception do not connect directly with any of the three longitudinal arteries. These intercostal and lumbar radicular arteries arise from the aorta, provide major anastomoses and supplement the blood flow to the spinal cord. In humans the largest of the anterior radicular arteries is known as the artery of Adamkiewicz, or anterior radicularis magna (ARM) artery, which usually arises between L1 and L2, but can arise anywhere from T9 to L5. Impaired blood flow through these critical radicular arteries, especially during surgical procedures that involve abrupt disruption of blood flow through the aorta for example during aortic aneurysm repair, can result in spinal cord infarction and paraplegia.

Function:

Somatosensory organization

In the dorsal column-medial lemniscus tract, a primary neuron's axon enters the spinal cord and then enters the dorsal column. Here the dorsal column connects to the axon of the nerve cell. If the primary axon enters below spinal level T6, the axon travels in the gracile fasciculus, the medial part of the column. If the axon enters above level T6, then it travels in the cuneate fasciculus, which is lateral to the fasciculus gracilis. Either way, the primary axon ascends to the lower medulla, where it leaves its fasciculus and synapses with a secondary neuron in one of the dorsal column nuclei: either the nucleus gracilis or the nucleus cuneatus, depending on the pathway it took. At this point, the secondary axon leaves its nucleus and passes anteriorly and medially. The collection of secondary axons that do this are known as internal arcuate fibers. The internal arcuate fibers decussate and continue ascending as the contralateral medial lemniscus. Secondary axons from the medial lemniscus finally terminate in the ventral posterolateral nucleus (VPLN) of the thalamus, where they synapse with tertiary neurons. From there, tertiary neurons ascend via the posterior limb of the internal capsule and end in the primary sensory cortex.

The proprioception of the lower limbs differs from the upper limbs and upper trunk. There is a four-neuron pathway for lower limb proprioception. This pathway initially follows the dorsal spino-cerebellar pathway. It is arranged as follows: proprioceptive receptors of lower limb → peripheral process → dorsal root ganglion → central process → Clarke's column → 2nd order neuron → medulla oblongata (Caudate nucleus) → 3rd order neuron → VPLN of thalamus → 4th order neuron → posterior limb of internal capsule → corona radiata → sensory area of cerebrum.

The anterolateral system works somewhat differently. Its primary neurons axons enter the spinal cord and then ascend one to two levels before synapsing in the substantia gelatinosa. The tract that ascends before synapsing is known as Lissauer's tract. After synapsing, secondary axons decussate and ascend in the anterior lateral portion of the spinal cord as the spinothalamic tract. This tract ascends all the way to the VPLN, where it synapses on tertiary neurons. Tertiary neuronal axons then travel to the primary sensory cortex via the posterior limb of the internal capsule.

Some of the "pain fibers" in the ALS deviate from their pathway towards the VPLN. In one such deviation, axons travel towards the reticular formation in the midbrain. The reticular formation then projects to a number of places including the hippocampus (to create memories about the pain), the centromedian nucleus (to cause diffuse, non-specific pain) and various parts of the cortex. Additionally, some ALS axons project to the periaqueductal gray in the pons, and the axons forming the periaqueductal gray then project to the nucleus raphes magnus, which projects back down to where the pain signal is coming from and inhibits it. This helps control the sensation of pain to some degree.

Motor organization

The corticospinal tract serves as the motor pathway for upper motor neuronal signals coming from the cerebral cortex and from primitive brainstem motor nuclei.

Cortical upper motor neurons originate from Brodmann areas 1, 2, 3, 4, and 6 and then descend in the posterior limb of the internal capsule, through the crus cerebri, down through the pons, and to the medullary pyramids, where about 90% of the axons cross to the contralateral side at the decussation of the pyramids. They then descend as the lateral corticospinal tract. These axons synapse with lower motor neurons in the ventral horns of all levels of the spinal cord. The remaining 10% of axons descend on the ipsilateral side as the ventral corticospinal tract. These axons also synapse with lower motor neurons in the ventral horns. Most of them will cross to the contralateral side of the cord (via the anterior white commissure) right before synapsing.

The midbrain nuclei include four motor tracts that send upper motor neuronal axons down the spinal cord to lower motor neurons. These are the rubrospinal tract, the vestibulospinal tract, the tectospinal tract and the reticulospinal tract. The rubrospinal tract descends with the lateral corticospinal tract, and the remaining three descend with the anterior corticospinal tract.

The function of lower motor neurons can be divided into two different groups: the lateral corticospinal tract and the anterior cortical spinal tract. The lateral tract contains upper motor neuronal axons which synapse on dorsal lateral (DL) lower motor neurons. The DL neurons are involved in distal limb control. Therefore, these DL neurons are found specifically only in the cervical and lumbosacral enlargements within the spinal cord. There is no decussation in the lateral corticospinal tract after the decussation at the medullary pyramids.

The anterior corticospinal tract descends ipsilaterally in the anterior column, where the axons emerge and either synapse on lower ventromedial (VM) motor neurons in the ventral horn ipsilaterally or descussate at the anterior white commissure where they synapse on VM lower motor neurons contralaterally . The tectospinal, vestibulospinal and reticulospinal descend ipsilaterally in the anterior column but do not synapse across the anterior white commissure. Rather, they only synapse on VM lower motor neurons ipsilaterally. The VM lower motor neurons control the large, postural muscles of the axial skeleton. These lower motor neurons, unlike those of the DL, are located in the ventral horn all the way throughout the spinal cord.

Spinocerebellar tracts

Proprioceptive information in the body travels up the spinal cord via three tracks. Below L2, the proprioceptive information travels up the spinal cord in the ventral spinocerebellar tract. Also known as the anterior spinocerebellar tract, sensory receptors take in the information and travel into the spinal cord. The cell bodies of these primary neurons are located in the dorsal root ganglia. In the spinal cord, the axons synapse and the secondary neuronal axons decussates and then travel up to the superior cerebellar peduncle where they decussate again. From here, the information is brought to deep nuclei of the cerebellum including the fastigial and interposed nuclei.

From the levels of L2 to T1, proprioceptive information enters the spinal cord and ascends ipsilaterally, where it synapses in Clarke's nucleus. The secondary neuronal axons continue to ascend ipsilaterally and then pass into the cerebellum via the inferior cerebellar peduncle. This tract is known as the dorsal spinocerebellar tract.

From above T1, proprioceptive primary axons enter the spinal cord and ascend ipsilaterally until reaching the accessory cuneate nucleus, where they synapse. The secondary axons pass into the cerebellum via the inferior cerebellar peduncle where again, these axons synapse on cerebellar deep nuclei. This tract is known as the cuneocerebellar tract.

Motor information travels from the brain down the spinal cord via descending spinal cord tracts. Descending tracts involve two neurons: the upper motor neuron (UMN) and lower motor neuron (LMN). A nerve signal travels down the upper motor neuron until it synapses with the lower motor neuron in the spinal cord. Then, the lower motor neuron conducts the nerve signal to the spinal root where efferent nerve fibers carry the motor signal toward the target muscle. The descending tracts are composed of white matter. There are several descending tracts serving different functions. The corticospinal tracts (lateral and anterior) are responsible for coordinated limb movements.

Clinical significance

A congenital disorder is diastematomyelia in which part of the spinal cord is split usually at the level of the upper lumbar vertebrae. Sometimes the split can be along the length of the spinal cord.

Injury

Spinal cord injuries can be caused by trauma to the spinal column (stretching, bruising, applying pressure, severing, laceration, etc.). The vertebral bones or intervertebral disks can shatter, causing the spinal cord to be punctured by a sharp fragment of bone. Usually, victims of spinal cord injuries will suffer loss of feeling in certain parts of their body. In milder cases, a victim might only suffer loss of hand or foot function. More severe injuries may result in paraplegia, tetraplegia (also known as quadriplegia), or full body paralysis below the site of injury to the spinal cord.

Damage to upper motor neuron axons in the spinal cord results in a characteristic pattern of ipsilateral deficits. These include hyperreflexia, hypertonia and muscle weakness. Lower motor neuronal damage results in its own characteristic pattern of deficits. Rather than an entire side of deficits, there is a pattern relating to the myotome affected by the damage. Additionally, lower motor neurons are characterized by muscle weakness, hypotonia, hyporeflexia and muscle atrophy.

Spinal shock and neurogenic shock can occur from a spinal injury. Spinal shock is usually temporary, lasting only for 24–48 hours, and is a temporary absence of sensory and motor functions. Neurogenic shock lasts for weeks and can lead to a loss of muscle tone due to disuse of the muscles below the injured site.

The two areas of the spinal cord most commonly injured are the cervical spine (C1–C7) and the lumbar spine (L1–L5). (The notation C1, C7, L1, L5 refer to the location of a specific vertebra in either the cervical, thoracic, or lumbar region of the spine.) Spinal cord injury can also be non-traumatic and caused by disease (transverse myelitis, polio, spina bifida, Friedreich's ataxia, spinal cord tumor, spinal stenosis etc.)

In the U.S., 10,000–12,000 people become paralyzed annually as a result of various injuries to the spinal cord.

Treatment

Real or suspected spinal cord injuries need immediate immobilisation including that of the head. Scans will be needed to assess the injury. A steroid, methylprednisolone, can be of help as can physical therapy and possibly antioxidants. Treatments need to focus on limiting post-injury cell death, promoting cell regeneration, and replacing lost cells. Regeneration is facilitated by maintaining electric transmission in neural elements.

Lumbar puncture

The spinal cord ends at the level of vertebrae L1–L2, while the subarachnoid space —the compartment that contains cerebrospinal fluid— extends down to the lower border of S2. Lumbar punctures in adults are usually performed between L3–L5 (cauda equina level) in order to avoid damage to the spinal cord. In the fetus, the spinal cord extends the full length of the spine and regresses as the body grows.

Tumours

Spinal tumours can occur in the spinal cord and these can be either inside (intradural) or outside (extradural) the dura mater.

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#2 Re: Ganesh's Puzzles » English language puzzles » Today 13:30:18

Hi,

#4263. What does the noun rectitude mean?

#4264. What does the adjective recumbent mean?

#5 Jokes » Short Funny Jokes - 16 » Today 00:57:17

ganesh
Replies: 0

“Have you got anything to drink?”
“Water.”
“I meant something harder?”
“Ice.”
* * *
Some annoying cold caller was trying to sell me a luxury coffin.
I could only say, “Dude, that is the last thing I’ll need.”
* * *
My grandma gave me this great advice, “An apple a day keeps the doctor away.”
She was right!
You just have to really work on your aim.
* * *
Where do skeletons spend their vacation?
At the Dead Sea.
* * *
I ordered an extension course, “How to Deal With Life’s Disappointments”.
Yesterday, I got the first lesson by post.
It was an empty envelope.
* * *

#6 Re: Dark Discussions at Cafe Infinity » crème de la crème » Today 00:29:18

1006) Captain Tom Moore

Captain Sir Thomas Moore (30 April 1920 – 2 February 2021), more popularly known as Captain Tom, was a British Army officer and fundraiser who made international headlines in 2020 when he raised money for charity in the run-up to his 100th birthday during the COVID-19 pandemic. He served in India and the Burma campaign during the Second World War, and later became an instructor in armoured warfare. After the war, he worked as managing director of a concrete company and was an avid motorcycle racer.

On 6 April 2020, at the age of 99, Moore began to walk 100 lengths of his garden in aid of NHS Charities Together, with the goal of raising £1,000 by his 100th birthday on 30 April. In the 24-day course of his fundraising, he made many media appearances and became a popular household name in the UK, earning a number of accolades and attracting over 1.5 million individual donations. In recognition of his efforts, he received the BBC Sports Personality of the Year Helen Rollason Award at the 2020 ceremony. He performed in a cover version of the song "You'll Never Walk Alone" sung by Michael Ball, with proceeds going to the same charity. The single topped the UK music charts, making him the oldest person to achieve a UK number one.

On the morning of Moore's 100th birthday, the total raised by his walk passed £30 million, and by the time the campaign closed at the end of that day had increased to over £32.79 million (worth almost £39 million with expected tax rebates). His birthday was marked in a number of ways, including flypasts by the Royal Air Force and the British Army. He received over 150,000 cards, and was appointed as honorary colonel of the Army Foundation College. On 17 July 2020, he was personally knighted by the Queen at Windsor Castle. He died on 2 February 2021 at Bedford Hospital where he was taken after being treated for pneumonia and then testing positive for COVID-19.

(The Association of NHS Charities, operating as NHS Charities Together, is a federation of over 250 charitable organisations that supports all the devolved National Health Service (NHS), their staff, volunteers and patients, in the United Kingdom. The organisation acts as collective voice for NHS charities as well as coordinating national fundraising efforts.

The charity came to increased prominence during the COVID-19 pandemic, when 99-year old Captain Tom Moore raised over £30 million for them, by walking laps of his garden, and releasing a single with Michael Ball, which went to number 1 in the UK charts. In December 2020, the Duke and Duchess of Cambridge became joint patrons of the organisation.)

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#7 Re: Ganesh's Puzzles » Doc, Doc! » Today 00:06:40

Hi,

#1800. What does the medical term 'Asystole' mean?

#9 Re: Ganesh's Puzzles » General Quiz » Today 00:05:05

Hi,

#8151. Name the term in computer hardware : A microprocessor, ASIC, or expansion card designed to offload a specific task from the CPU, often containing fixed-function hardware. A common example is a graphics processing unit.

#8152. Name the term in computer hardware : A register in a CPU in which intermediate arithmetic and logic results are stored.

#10 Re: This is Cool » Miscellany » Yesterday 15:57:20

1234) Lantern

Summary

Lantern is a case, ordinarily metal, with transparent or translucent sides, used to contain and protect a lamp.

Lamp-containing lanterns have been found at Pompeii, Herculaneum, and other classical sites. They have been made of iron, silver, gold, and tin and their sides of horn, talc, leather, oiled paper, and glass. Designs have ranged from crude boxes pierced with nail holes to Oriental openwork bronze and exquisitely delicate examples of Renaissance and Baroque craftsmanship.

The bull’s-eye lantern, with one or more sides of bulging glass, was in popular use from the early 18th century, similar devices having been made at least as early as the 13th century. Dark until it was suddenly switched on by opening its door, it focused its light to some extent and served the purpose of the modern flashlight.

The hurricane lantern, or hurricane lamp, still in use as a warning flare, has a shield of glass and perforated metal surrounding its flame to protect it from strong winds.

Details

A lantern is an often portable source of lighting, typically featuring a protective enclosure for the light source - historically usually a candle or a wick in oil, and often a battery-powered light in modern times – to make it easier to carry and hang up, and make it more reliable outdoors or in drafty interiors. Lanterns may also be used for signaling, as torches, or as general light-sources outdoors.

Use

The lantern enclosure was primarily used to prevent a burning candle or wick being extinguished from wind, rain or other causes. Some antique lanterns have only a metal grid, indicating their function was to protect the candle or wick during transportation and avoid the excess heat from the top to avoid unexpected fires.

Another important function was to reduce the risk of fire should a spark leap from the flame or the light be dropped. This was especially important below deck on ships: a fire on a wooden ship was a major catastrophe. Use of unguarded lights was taken so seriously that obligatory use of lanterns, rather than unprotected flames, below decks was written into one of the few known remaining examples of a pirate code, on pain of severe punishment.

Lanterns may also be used for signaling. In naval operations, ships used lights to communicate at least as far back as the Middle Ages; the use of a lantern that blinks code to transmit a message dates to the mid-1800s. In railroad operations, lanterns have multiple uses. Permanent lanterns on poles are used to signal trains about the operational status of the track ahead, sometimes with color gels in front of the light to signify stop, etc. Historically, a flagman at a level crossing used a lantern to stop cars and other vehicular traffic before a train arrived. Lanterns also provided a means to signal from train-to-train or from station-to-train.

A "dark lantern" was a candle lantern with a sliding shutter so that a space could be conveniently made dark without extinguishing the candle. For example, in the Sherlock Holmes story "The Red-Headed League", the detective and police make their way down to a bank vault by lantern light but then put a 'screen over that dark lantern' in order to wait in the dark for thieves to finish tunneling. This type of lantern could also preserve the light source for sudden use when needed.

Lanterns may be used in religious observances. In the Eastern Orthodox Church, lanterns are used in religious processions and liturgical entrances, usually coming before the processional cross. Lanterns are also used to transport the Holy Fire from the Church of the Holy Sepulchre on Great Saturday during Holy Week.

Lanterns are used in many Asian festivals. During the Ghost Festival, lotus shaped lanterns are set afloat in rivers and seas to symbolically guide the lost souls of forgotten ancestors to the afterlife. During the Lantern Festival, the displaying of many lanterns is still a common sight on the 15th day of the first lunar month throughout China. During other Chinese festivities, kongming lanterns (sky lanterns) can be seen floating high into the air. Lanterns are the central theme of the Seoul Lantern Festival in South Korea. However, some jurisdictions and organizations ban the use of sky lanterns because of concerns about fire and safety.

The term "lantern" can be used more generically to mean a light source, or the enclosure for a light source, even if it is not portable. Decorative lanterns exist in a wide range of designs. Some hang from buildings, such as street lights enclosed in glass panes. Others are placed on or just above the ground; low-light varieties can function as decoration or landscape lighting, and can be a variety of colours and sizes. The housing for the top lamp and lens section of a lighthouse may be called a lantern.

Etymology

The word lantern comes via French from Latin lanterna meaning "lamp, torch," possibly itself derived from Greek.

An alternate historical spelling was "lanthorn", believed to derive from the early use of horn windows.

Construction

Lanterns were usually made from a metal frame with several sides (usually four, but up to eight) or round, commonly with a hook or a hoop of metal on top. Windows of some translucent material may be fitted in the sides; these are now usually glass or plastic but formerly were thin sheets of animal horn, or tinplate punched with holes or decorative patterns.

Paper lanterns are made in societies around the world.

A lantern generally contains a burning light source: a candle, liquid oil with a wick, or gas with a mantle.

Modern varieties often place an electric light in a decorative glass case.

History

Lanterns have been used functionally, for light rather than decoration, since antiquity. Some used a wick in oil, while others were essentially protected candle-holders. Before the development of glass sheets, animal horn scraped thin and flattened was used as the translucent window.

Beginning in the Middle Ages, European towns hired watchmen to patrol the streets at night, as a crime deterrent. Each watchman carried a lantern or oil lamp against the darkness. The practice continued up through at least the 18th century.

Public spaces became increasingly lit with lanterns in the 1500s, especially following the invention of lanterns with glass windows, which greatly improved the quantity of light. In 1588 the Parisian Parlement decreed that a torch be installed and lit at each intersection, and in 1594 the police changed this to lanterns. Beginning in 1667 during the reign of King Louis XIV, thousands of street lights were installed in Parisian streets and intersections. Under this system, streets were lit with lanterns suspended 20 yards (18 m) apart on a cord over the middle of the street at a height of 20 feet (6.1 m); as an English visitor enthused in 1698, 'The streets are lit all winter and even during the full moon!' In London, public street lighting was implemented around the end of the 17th century; a diarist wrote in 1712 that ‘All the way, quite through Hyde Park to the Queen's Palace at Kensington, lanterns were placed for illuminating the roads on dark nights.’

Modern lanterns:

Fueled lanterns

All fueled lanterns are somewhat hazardous owing to the danger of handling flammable and toxic fuel, danger of fire or burns from the high temperatures involved, and potential dangers from carbon monoxide poisoning if used in an enclosed environment.

Simple wick lanterns remain available. They are cheap and durable and usually can provide enough light for reading. They require periodic trimming of the wick and regular cleaning of soot from the inside of the glass chimney.

Mantle lanterns use a woven ceramic impregnated gas mantle to accept and re-radiate heat as visible light from a flame. The mantle does not burn (but the cloth matrix carrying the ceramic must be "burned out" with a match prior to its first use). When heated by the operating flame the mantle becomes incandescent and glows brightly. The heat may be provided by a gas, by kerosene, or by a pressurized liquid such as "white gas", which is essentially naphtha. For protection from the high temperatures produced and to stabilize the airflow, a cylindrical glass shield called the globe or chimney is placed around the mantle.

Manually pressurized lanterns using white gas (also marketed as Coleman fuel or "Camp Fuel") are manufactured by the Coleman Company in one and two-mantle models. Some models are dual fuel and can also use gasoline. These are being supplanted by a battery-powered fluorescent lamp and LED models, which are safer in the hands of young people and inside tents. Liquid fuel lanterns remain popular where the fuel is easily obtained and in common use.

Many portable mantle-type fuel lanterns now use fuel gases that become liquid when compressed, such as propane, either alone or combined with butane. Such lamps usually use a small disposable steel container to provide the fuel. The ability to refuel without liquid fuel handling increases safety. Additional fuel supplies for such lamps have an indefinite shelf life if the containers are protected from moisture (which can cause corrosion of the container) and excess heat.

Electric lanterns

Lanterns designed as permanently mounted electric lighting fixtures are used in interior, landscape, and civic lighting applications. Styles can evoke former eras, unify street furniture themes, or enhance aesthetic considerations. They are manufactured for use with various wired voltage supplies.

Various battery types are used in portable light sources. They are more convenient, safer, and produce less heat than combustion lights. Solar-powered lanterns have become popular in developing countries, where they provide a safer and cheaper alternative to kerosene lamps.

Lanterns utilizing LEDs are popular as they are more energy-efficient and rugged than other types, and prices of LEDs suitable for lighting have dropped.

Some rechargeable fluorescent lanterns may be plugged in at all times and may be set up to illuminate upon a power failure, a useful feature in some applications. During extensive power failures (or for remote use), supplemental recharging may be provided from an automobile's 12-volt electrical system or from a modest solar-powered charger.

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#11 Re: Ganesh's Puzzles » English language puzzles » Yesterday 13:33:16

Hi,

#4261.. What does the noun keepsake mean?

#4262. What does the noun keystone mean?

#15 Re: Ganesh's Puzzles » General Quiz » Yesterday 00:36:46

Hi,

#8149. With which field was/is Amelia Mary Earhart associated?

#8150. With which field was/is Sir Harold Matthew Evans associated?

#16 Re: Ganesh's Puzzles » General Quiz » Yesterday 00:36:20

Hi,

#8149. With which field was/is Amelia Mary Earhart associated?

#8150. With which field was/is Sir Harold Matthew Evans associated?

#17 Re: Ganesh's Puzzles » Doc, Doc! » Yesterday 00:06:15

Hi,

#1799. What does the medical term 'Convulsion' mean?

#18 Re: Ganesh's Puzzles » English language puzzles » Yesterday 00:05:34

Hi,

#4259. What does the adjective demure mean?

#4260. What does the noun denouement mean?

#19 Jokes » Short Funny Jokes - 15 » Yesterday 00:04:48

ganesh
Replies: 0

How do you know the ocean greets you? -  It waves.
* * *
A wife complains to her husband: “Just look at that couple down the road, how lovely they are.
He keeps holding her hand, holding the door for her, why can’t you do the same?”
The husband: “Are you mad? I barely know the woman!”
* * *
My wife divorced me recently because I’m a compulsive gambler.
All I can think about now is how to win her back.
* * *
I hate my mood swings.
They're great!
* * *
The boss said I should go home because I really don't look good.
I don't know if I should be happy to get the extra rest, or just offended.
* * *

#20 Dark Discussions at Cafe Infinity » Love Quotes » 2022-01-17 20:08:01

ganesh
Replies: 0

Love Quotes

1. 'Tis better to have loved and lost than never to have loved at all. - Alfred Lord Tennyson

2. Let us always meet each other with smile, for the smile is the beginning of love. - Mother Teresa

3. Life is the flower for which love is the honey. - Victor Hugo

4. Love has no age, no limit; and no death. - John Galsworthy

5. A flower cannot blossom without sunshine, and man cannot live without love. - Max Muller

6. For small creatures such as we the vastness is bearable only through love. - Carl Sagan

7. To love oneself is the beginning of a lifelong romance. - Oscar Wilde

8. Where there is love there is life. - Mahatma Gandhi

9. We are all born for love. It is the principle of existence, and its only end. - Benjamin Disraeli

10. Love and compassion are necessities, not luxuries. Without them humanity cannot survive. - Dalai Lama

11. I feel that there is nothing more truly artistic than to love people. - Vincent Van Gogh

12. Love is composed of a single soul inhabiting two bodies. - Aristotle

13. At the touch of love everyone becomes a poet. - Plato

14. Love is the wisdom of the fool and the folly of the wise. - Samuel Johnson

15. Life without love is like a tree without blossoms or fruit. - Khalil Gibran

16. Love is like a beautiful flower which I may not touch, but whose fragrance makes the garden a place of delight just the same. - Helen Keller

17. To fear love is to fear life, and those who fear life are already three parts dead. - Bertrand Russell

18. I have decided to stick with love. Hate is too great a burden to bear. - Martin Luther King, Jr.

19. Keep love in your heart. A life without it is like a sunless garden when the flowers are dead. - Oscar Wilde

20. To say 'I love you' one must first be able to say the 'I.' - Ayn Rand

21. One is loved because one is loved. No reason is needed for loving. - Paulo Coelho

22. You can't blame gravity for falling in love. - Albert Einstein

23. Love is a canvas furnished by nature and embroidered by imagination. - Voltaire

24. The best thing to hold onto in life is each other. - Audrey Hepburn

25. Love is an irresistible desire to be irresistibly desired. - Robert Frost

26. The way to love anything is to realize that it may be lost. - Gilbert K. Chesterton

27. Blessed is the influence of one true, loving human soul on another. - George Eliot

28. The moment you have in your heart this extraordinary thing called love and feel the depth, the delight, the ecstasy of it, you will discover that for you the world is transformed. - Jiddu Krishnamurti

29. Friendship is Love without his wings! - Lord Byron

30. Love is energy of life. - Robert Browning

31. Man must evolve for all human conflict a method which rejects revenge, aggression and retaliation. The foundation of such a method is love. - Martin Luther King, Jr.

32. If you would be loved, love, and be loveable. - Benjamin Franklin

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#22 Re: This is Cool » Miscellany » 2022-01-17 15:48:10

1233) Cheetah

Summary

The cheetah (Acinonyx jubatus) is a large cat native to Africa and central Iran. It is the fastest land animal, estimated to be capable of running at 80 to 128 km/h (50 to 80 mph) with the fastest reliably recorded speeds being 93 and 98 km/h (58 and 61 mph), and as such has several adaptations for speed, including a light build, long thin legs and a long tail. It typically reaches 67–94 cm (26–37 in) at the shoulder, and the head-and-body length is between 1.1 and 1.5 m (3 ft 7 in and 4 ft 11 in). Adults weigh between 21 and 72 kg (46 and 159 lb). Its head is small and rounded, and has a short snout and black tear-like facial streaks. The coat is typically tawny to creamy white or pale buff and is mostly covered with evenly spaced, solid black spots. Four subspecies are recognised.

The cheetah lives in three main social groups, females and their cubs, male "coalitions" and solitary males. While females lead a nomadic life searching for prey in large home ranges, males are more sedentary and may instead establish much smaller territories in areas with plentiful prey and access to females. The cheetah is active mainly during the day, with peaks during dawn and dusk. It feeds on small- to medium-sized prey, mostly weighing under 40 kg (88 lb), and prefers medium-sized ungulates such as impala, springbok and Thomson's gazelles. The cheetah typically stalks its prey to within 60–70 m (200–230 ft), charges towards it, trips it during the chase and bites its throat to suffocate it to death. It breeds throughout the year. After a gestation of nearly three months, a litter of typically three or four cubs is born. Cheetah cubs are highly vulnerable to predation by other large carnivores such as hyenas and lions. They are weaned at around four months and are independent by around 20 months of age.

The cheetah occurs in a variety of habitats such as savannahs in the Serengeti, arid mountain ranges in the Sahara and hilly desert terrain in Iran. The cheetah is threatened by several factors such as habitat loss, conflict with humans, poaching and high susceptibility to diseases. Historically ranging throughout most of Sub-Saharan Africa and extending eastward into the Middle East and to central India, the cheetah is now distributed mainly in small, fragmented populations in central Iran and southern, eastern and northwestern Africa. In 2016, the global cheetah population was estimated at around 7,100 individuals in the wild; it is listed as Vulnerable on the IUCN Red List. In the past, cheetahs were tamed and trained for hunting ungulates. They have been widely depicted in art, literature, advertising, and animation.

Details

Cheetah, (Acinonyx jubatus), is one of the world’s most-recognizable cats, known especially for its speed. Cheetahs’ sprints have been measured at a maximum of 114 km (71 miles) per hour, and they routinely reach velocities of 80–100 km per hour while pursuing prey. Nearly all the cheetahs remaining in the wild live in Africa.

Cheetahs are covered almost entirely with small black spots on a background of pale yellow and have a white underbelly. Their faces are distinguished by prominent black lines that curve from the inner corner of each eye to the outer corners of the mouth, like a well-worn trail of inky tears. Cheetahs have a long, slender body measuring 1.2 metres (4 feet), with a long tail (65–85 cm [2–3 feet]) that generally ends in a white tuft. They are about 75 cm tall at the shoulder. Weight ranges from 34 to 54 kg (75 to 119 pounds), males being slightly larger than females.

Natural history

Cheetahs have evolved many adaptations that enhance their ability to sprint. Their legs are proportionally longer than those of other big cats; an elongated spine increases stride length at high speeds; they have unretractable claws, special paw pads for extra traction, and a long tail for balance. Internally, the liver, adrenal glands, lungs, bronchi, nasal passages, and heart are all large to allow intense physiological activity. During a chase, cheetahs take about 3 1/2 strides per second and 60 to 150 breaths per minute. Chases are usually limited to sprints of less than 200–300 metres, however, because the increased physiological activity associated with running creates heat faster than it can be released through evaporative cooling (sweating through their paws and panting).

Unlike most carnivores, cheetahs are active mainly during the day, hunting in the early morning and late afternoon. A cheetah eats a variety of small animals, including game birds, rabbits, small antelopes (including the springbok, impala, and gazelle), young warthogs, and larger antelopes (such as the kudu, hartebeest, oryx, and roan). Prey is generally consumed quickly to avoid losing it to competitors such as lions, leopards, jackals, and hyenas.

Cheetahs inhabit a wide variety of habitats, including the dry, open country and grasslands where they are most often seen, as well as areas of denser vegetation and rocky upland terrain. Groups consist of a mother and her young or of coalitions made up of two or three males that are often brothers. Adult males and females rarely meet except to mate. Male coalitions live and hunt together for life and occupy an area that may overlap the range of several adult females. Female home ranges are generally much larger than those of male coalitions.

Following a gestation period of three months, the female gives birth to two to eight cubs, usually in an isolated spot hidden in the cover of tall grass or thicker vegetation. At birth, cubs weigh about 250 to 300 grams (slightly more than half a pound). Their fur is dark and includes a thick yellowish gray mane along the back, a trait that presumably offers better camouflage and increased protection from high temperatures during the day and low temperatures at night during the first few months of life. Mortality among young cubs can be as high as 90 percent in the wild, often because of other predators. The mother leaves her offspring when they are 16–24 months old. Young males are chased away by the resident male coalition, traveling several hundred kilometres before establishing residence and becoming sexually active at 2 1/2 to 3 years of age. Female offspring will generally inhabit the same vicinity as their mother. Life expectancy of cheetahs is about 7 years in the wild and generally from 8 to 12 years in captivity.

Status and taxonomy

The cheetah has lived in association with humans since at least 3000 BCE, when the Sumerians depicted a leashed cheetah with a hood on its head on an official seal. During this period in Egypt, the cheetah was revered as a symbol of royalty in the form of the cat goddess Mafdet. Cheetahs were kept as pets by many famous historical figures, such as Genghis Khan, Charlemagne, and Akbar the Great of India (who had more than 9,000 in his stable). These cats were also used for sport. Trained and tame, they were typically hooded and carried on horseback or in a cart, then dehooded and released near their quarry. In spite of the large numbers of cheetahs kept in captivity by royalty during the 14th–16th centuries, almost all were captured from the wild because there was essentially no captive breeding. Because of this continuous drain on wild Asiatic populations, cheetahs from Africa were being imported into India and Iran during the early 1900s.

In 1900 an estimated 100,000 cheetahs were found in habitats throughout continental Africa and from the Middle East and the Arabian Peninsula to India. Today cheetahs have been extirpated from a large portion of this area. In Asia they are nearly extinct, with the largest confirmed population (a few dozen) inhabiting northeastern Iran. In Africa there are an estimated 9,000 to 12,000 cheetahs, with the largest populations existing in Namibia, Botswana, and Zimbabwe in Southern Africa and Kenya and Tanzania in East Africa. Smaller, more isolated populations exist in other countries, including South Africa, Congo (Kinshasa), Zambia, Somalia, Ethiopia, Mali, Niger, Cameroon, Chad, and the Central African Republic. All populations are threatened, even within protected areas, because of increased competition from large predators such as lions and hyenas. Outside of reserves, humans pose a threat in several forms, including habitat loss, poaching, and indiscriminate trapping and shooting to protect livestock.

The cheetah was common throughout North America, Europe, and Asia until the end of the last ice age, about 11,700 years ago—a time coincident to when large numbers of mammals disappeared throughout the Northern Hemisphere. All North American and European cheetahs and most of those in Asia vanished. About this time the cheetah populations seem to have experienced what may have been the first and most severe of a series of size reductions (demographic bottlenecks). Modern cheetahs retain evidence of this historic event in their DNA. There is a very high level of genetic similarity in all but the most rapidly evolving parts of the cheetah’s genome, which makes all of today’s individuals appear highly inbred. This condition has been linked with increased susceptibility to infectious diseases (such as feline infectious peritonitis, or FIP), increased infant mortality, and high levels of abnormal sperm. No evidence, however, links low levels of genetic variation with reduced fitness in wild populations.

Early taxonomists interpreted the numerous specialized traits of cheetahs as evidence that they diverged from the other cat species early in the evolutionary history of the cat family (Felidae). The cheetah was therefore granted unique taxonomic status, and since the early 1900s it has been classified as the only species of genus Acinonyx. Cheetahs are often divided into five subspecies: A. jubatus jubatus in Southern Africa, A. jubatus fearsoni (including A. jubatus velox and A. jubatus raineyi) from eastern Africa, A. jubatus soemmeringii from Nigeria to Somalia, A. jubatus hecki from northwestern Africa, and A. jubatus venaticus from Arabia to central India. The king cheetah, once thought to be a distinct subspecies, is a Southern African form that has a “blotchy” coat pattern presumably from a rare recessive genetic mutation.

Numerous molecular genetic studies suggest that the cheetah shares a common ancestor with the puma and jaguarundi, from which it diverged six to eight million years ago, probably in North America. Fossils attributable to cheetahlike species dating from two to three million years ago have been found in North America in what is now Texas, Nevada, and Wyoming.

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