Math Is Fun Forum

Q: Why did the Oreo go to the dentist?
A: Because it lost its filling!
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Q: What does the ginger bread man put on his bed?
A: A cookie sheet.
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Q: What kind of keys do kids like to carry?
A: Cookies!
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Q: What is a monkey's favorite cookie?
A: Chocolate chimp!
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Q: What word backwards can predict the future?
A: Cookies (Seikooc as in psychic of you say it).
* * *

Intelligence Quotient

Gist

An Intelligence Quotient (IQ) is a standardized, numerical score derived from tests designed to measure human cognitive abilities—such as reasoning, logic, memory, and problem-solving—relative to a peer group. Modern IQ scores are calculated using a normal distribution (bell curve) with a mean of 100 and a standard deviation of 15, meaning ~68% of the population scores between 85 and 115.

IQ (Intelligence Quotient) is a score from standardized tests measuring cognitive abilities, originally calculated by dividing a person's mental age (MA) by their chronological age (CA) and multiplying by 100: IQ = (MA / CA) × 100, though modern tests use statistical norms with a mean of 100, says Wikipedia. It assesses logic, memory, problem-solving, and pattern recognition, with average scores around 100, while scores below 70 suggest extremely low intelligence and above 129 indicate giftedness.

Summary

IQ, (from “intelligence quotient”), is a number used to express the relative intelligence of a person. It is one of many intelligence tests.

IQ was originally computed by taking the ratio of mental age to chronological (physical) age and multiplying by 100. Thus, if a 10-year-old child had a mental age of 12 (that is, performed on the test at the level of an average 12-year-old), the child was assigned an IQ of 12/10 × 100, or 120. If the 10-year-old had a mental age of 8, the child’s IQ would be 8/10 × 100, or 80. Based on this calculation, a score of 100—where the mental age equals the chronological age—would be average. Few tests continue to involve the computation of mental ages.

Details

An intelligence quotient (IQ) is a total score derived from a set of standardized tests or subtests designed to assess human intelligence. Originally, IQ was a score obtained by dividing a person's estimated mental age, obtained by administering an intelligence test, by the person's chronological age. The resulting fraction (quotient) was multiplied by 100 to obtain the IQ score. For modern IQ tests, the raw score is transformed to a normal distribution with mean 100 and standard deviation 15. This results in approximately two-thirds of the population scoring between IQ 85 and IQ 115 and about 2 percent each above 130 and below 70.

Scores from intelligence tests are estimates of intelligence. Unlike quantities such as distance and mass, a concrete measure of intelligence cannot be achieved given the abstract nature of the concept of "intelligence". IQ scores have been shown to be associated with factors such as nutrition, parental socioeconomic status, morbidity and mortality, parental social status, and perinatal environment. While the heritability of IQ has been studied for nearly a century, there is still debate over the significance of heritability estimates and the mechanisms of inheritance. The best estimates for heritability range from 40 to 60% of the variance between individuals in IQ being explained by genetics.

IQ scores were used for educational placement, assessment of intellectual ability, and evaluating job applicants. In research contexts, they have been studied as predictors of job performance and income. They are also used to study distributions of psychometric intelligence in populations and the correlations between it and other variables. Raw scores on IQ tests for many populations have been rising at an average rate of three IQ points per decade since the early 20th century, a phenomenon called the Flynn effect. Investigation of different patterns of increases in subtest scores can also inform research on human intelligence.

Historically, many proponents of IQ testing have been eugenicists who used pseudoscience to push later debunked views of racial hierarchy in order to justify segregation and oppose immigration. Such views have been rejected by a strong consensus of mainstream science, though fringe figures continue to promote them in pseudo-scholarship and popular culture.

Additional Information

Earlier this year, 11-year-old Kashmea Wahi of London, England scored 162 on an IQ test. That’s a perfect score. The results were published by Mensa, a group for highly intelligent people. Wahi is the youngest person ever to get a perfect score on that particular test.           

Does her high score mean she will go on to do great things — like Stephen Hawking or Albert Einstein, two of the world’s greatest scientists? Maybe. But maybe not.

IQ, short for intelligence quotient, is a measure of a person’s reasoning ability. In short, it is supposed to gauge how well someone can use information and logic to answer questions or make predictions. IQ tests begin to assess this by measuring short- and long-term memory. They also measure how well people can solve puzzles and recall information they’ve heard — and how quickly.

Every student can learn, no matter how intelligent. But some students struggle in school because of a weakness in one specific area of intelligence. These students often benefit from special education programs. There, they get extra help in the areas where they’re struggling. IQ tests can help teachers figure out which students would benefit from such extra help.

IQ tests also can help identify students who would do well in fast-paced “gifted education” programs. Many colleges and universities also use exams similar to IQ tests to select students. And the U.S. government — including its military — uses IQ tests when choosing who to hire. These tests help predict which people would make good leaders, or be better at certain specific skills.

It’s tempting to read a lot into someone’s IQ score. Most non-experts think intelligence is the reason successful people do so well. Psychologists who study intelligence find this is only partly true. IQ tests can predict how well people will do in particular situations, such as thinking abstractly in science, engineering or art. Or leading teams of people. But there’s more to the story. Extraordinary achievement depends on many things. And those extra categories include ambition, persistence, opportunity, the ability to think clearly — even luck.

Intelligence matters. But not as much as you might think.

Measuring IQ

IQ tests have been around for more than a century. They were originally created in France to help identify students who needed extra help in school.

The U.S. government later used modified versions of these tests during World War I. Leaders in the armed forces knew that letting unqualified people into battle could be dangerous. So they used the tests to help find qualified candidates. The military continues to do that today. The Armed Forces Qualification Test is one of many different IQ tests in use.

IQ tests have many different purposes, notes Joel Schneider. He is a psychologist at Illinois State University in Normal. Some IQ tests have been designed to assess children at specific ages. Some are for adults. And some have been designed for people with particular disabilities.

But any of these tests will tend to work well only for people who share a similar cultural or social upbringing. “In the United States,” for instance, “a person who has no idea who George Washington was probably has lower-than-average intelligence,” Schneider says. “In Japan, not knowing who Washington was reveals very little about the person’s intelligence.”

Questions about important historical figures fall into the “knowledge” category of IQ tests. Knowledge-based questions test what a person knows about the world. For example, they might ask whether people know why it’s important to wash their hands before they eat.

IQ tests also ask harder questions to measure someone’s knowledge. What is abstract art? What does it mean to default on a loan? What is the difference between weather and climate? These types of questions test whether someone knows about things that are valued in their culture, Schneider explains.

Such knowledge-based questions measure what scientists call crystallized intelligence. But some categories of IQ tests don’t deal with knowledge at all.

Some deal with memory. Others measure what’s called fluid intelligence. That’s a person’s ability to use logic and reason to solve a problem. For example, test-takers might have to figure out what a shape would look like if it were rotated. Fluid intelligence is behind “aha” moments — times when you suddenly connect the dots to see the bigger picture.

Aki Nikolaidis is a neuroscientist, someone who studies structures in the brain. He works at the University of Illinois at Urbana-Champaign. And he wanted to know what parts of the brain are active during those “aha” episodes.

In a study published earlier this year, he and his team studied 71 adults. The researchers tested the volunteers’ fluid intelligence with a standard IQ test that had been designed for adults. At the same time, they mapped out which areas of test takers’ brains were working hardest. They did this using a brain scan called magnetic resonance spectroscopy, or MRS. It uses magnets to hunt for particular molecules of interest in the brain.

As brain cells work, they gobble up glucose, a simple sugar, and spit out the leftovers. MRS scans let researchers spy those leftovers. That told them which specific areas of people’s brains were working hard and breaking down more glucose.

People who scored higher on fluid intelligence tended to have more glucose leftovers in certain parts of their brains. These areas are on the left side of the brain and toward the front. They’re involved with planning movements, with spatial visualization and with reasoning. All are key aspects of problem solving.

“It’s important to understand how intelligence is related to brain structure and function,” says Nikolaidis. That, he adds, could help scientists develop better ways to boost fluid intelligence.

Personal intelligence

IQ tests “measure a set of skills that are important to society,” notes Scott Barry Kaufman. He’s a psychologist at the University of Pennsylvania in Philadelphia. But, he adds, such tests don’t tell the full story about someone’s potential. One reason: IQ tests favor people who can think on the spot. It’s a skill plenty of capable people lack.

It’s also something Kaufman appreciates as well as anyone.

As a boy, he needed extra time to process the words he heard. That slowed his learning. His school put him into special education classes, where he stayed until high school. Eventually, an observant teacher suggested he might do well in regular classes. He made the switch and, with hard work, indeed did well.

Kaufman now studies what he calls “personal intelligence.” It’s how people’s interests and natural abilities combine to help them work toward their goals. IQ is one such ability. Self-control is another. Both help people focus their attention when they need to, such as at school.

Psychologists lump together a person’s focused attention, self-control and problem-solving into a skill they call executive function. The brain cells behind executive function are known as the executive control network. This network turns on when someone is taking an IQ test. Many of the same brain areas are involved in fluid intelligence.

But personal intelligence is more than just executive function. It’s tied to personal goals. If people are working toward some goal, they’ll be interested and focused on what they are doing. They might daydream about a project even while not actively working on it. Although daydreaming may seem like a waste of time to outsiders, it can have major benefits for the person doing it.

When engaged in some task, such as learning, people want to keep at it, Kaufman explains. That means they will push forward, long after they might otherwise have been expected to give up. Engagement also lets a person switch between focused attention and mind wandering.

That daydreaming state can be an important part of intelligence. It is often while the mind is “wandering” that sudden insights or hunches emerge about how something works.

While daydreaming, a so-called default mode network within the brain kicks into action. Its nerve cells are active when the brain is at rest. For a long time, psychologists thought the default mode network was active only when the executive control network rested. In other words, you could not focus on an activity and daydream at the same time.

To see if that was really true, last year Kaufman teamed up with researchers at the University of North Carolina in Greensboro and at the University of Graz in Austria. They scanned the brains of volunteers using functional magnetic resonance imaging, or fMRI. This tool uses a strong magnetic field to record brain activity.

As they scanned the brains of 25 college students, the researchers asked the students to think of as many creative uses as they could for everyday objects. And as students were being as creative as possible, parts of both the default mode network and the executive control network lit up. The two systems weren’t at odds with each other. Rather, Kaufman suspects, the two networks work together to make creativity possible.

“Creativity seems to be a unique state of consciousness,” Kaufman now says. And he thinks it is essential for problem-solving.

Turning potential into achievement

Just being intelligent doesn’t mean someone will be successful. And just because someone is less intelligent doesn’t mean that person will fail. That’s one take-home message from the work of people like Angela Duckworth.

She works at the University of Pennsylvania in Philadelphia. Like many other psychologists, Duckworth wondered what makes one person more successful than another. In 2007, she interviewed people from all walks of life. She asked each what they thought made someone successful. Most people believed intelligence and talent were important. But smart people don’t always live up to their potential.

When Duckworth dug deeper, she found that the people who performed best — those who were promoted over and over, or made a lot of money — shared a trait independent of intelligence. They had what she now calls grit. Grit has two parts: passion and perseverance. Passion points to a lasting interest in something. People who persevere work through challenges to finish a project.

Duckworth developed a set of questions to assess passion and perseverance. She calls it her “grit scale.”

In one study of people 25 and older, she found that as people age, they become more likely to stick with a project. She also found that grit increases with education. People who had finished college scored higher on the grit scale than did people who quit before graduation. People who went to graduate school after college scored even higher.

She then did another study with college students. Duckworth wanted to see how intelligence and grit affected performance in school. So she compared scores on college-entrance exams (like the SAT), which estimate IQ, to school grades and someone’s score on the grit scale. Students with higher grades tended to have more grit. That’s not surprising. Getting good grades takes both smarts and hard work. But Duckworth also found that intelligence and grit don’t always go hand in hand. On average, students with higher exam scores tended to be less gritty than those who scored lower.

Students who perform best in the National Spelling Bee are those with grit. Their passion, drive, and persistance pay off and help them succeed against less “gritty” competitors.

But some people counter that this grit may not be all it’s cracked up to be. Among those people is Marcus Credé. He’s a psychologist at Iowa State University in Ames. He recently pooled the results of 88 studies on grit. Together, those studies involved nearly 67,000 people. And grit did not predict success, Credé found.

However, he thinks grit is very similar to conscientiousness. That someone’s ability to set goals, work toward them and think things through before acting. It’s a basic personality trait, Credé notes — not something that can be changed.

“Study habits and skills, test anxiety and class attendance are far more strongly related to performance than grit,” Credé concludes. “We can teach [students] how to study effectively. We can help them with their test anxiety,” he adds. “I’m not sure we can do that with grit.”

In the end, hard work can be just as important to success as IQ. “It’s okay to struggle and go through setbacks,” Kaufman says. It might not be easy. But over the long haul, toughing it out can lead to great accomplishments.

Combine Quotes - I

1. When you combine ignorance and leverage, you get some pretty interesting results. - Warren Buffett

2. I dream of the realization of the unity of Africa, whereby its leaders combine in their efforts to solve the problems of this continent. I dream of our vast deserts, of our forests, of all our great wildernesses. - Nelson Mandela

3. When bad men combine, the good must associate; else they will fall one by one, an unpitied sacrifice in a contemptible struggle. - Edmund Burke

4. I have done one thing that I think is a contribution: I helped Buddhist science and modern science combine. No other Buddhist has done that. Other lamas, I don't think they ever pay attention to modern science. Since my childhood, I have a keen interest. - Dalai Lama

5. I know of no single formula for success. But over the years I have observed that some attributes of leadership are universal and are often about finding ways of encouraging people to combine their efforts, their talents, their insights, their enthusiasm and their inspiration to work together. - Queen Elizabeth II

6. The attempt to combine wisdom and power has only rarely been successful and then only for a short while. - Albert Einstein

7. All the interests of my reason, speculative as well as practical, combine in the three following questions: 1. What can I know? 2. What ought I to do? 3. What may I hope? - Immanuel Kant

8. Invention is not enough. Tesla invented the electric power we use, but he struggled to get it out to people. You have to combine both things: invention and innovation focus, plus the company that can commercialize things and get them to people. - Larry Page.

Neuron

Gist

A neuron, or nerve cell, is the fundamental unit of the nervous system, specialized to transmit information via electrical and chemical signals, enabling functions from thinking and feeling to movement, and forms the basis of the brain and nerves throughout the body. Structurally, a neuron typically consists of a cell body (soma), dendrites that receive signals, and an axon that transmits signals to other cells.

The basic functions of neurons can be summarized into four main tasks: receiving signals, integrating these signals/generating signals and transmitting the signals to target cells and organs. These functions reflect in the microanatomy of the neuron.

Summary

A neuron (American English), neurone (British English), or nerve cell, is an excitable cell that fires electric signals called action potentials across a neural network in the nervous system, mainly in the central nervous system and help to receive and conduct impulses. Neurons communicate with other cells via synapses, which are specialized connections that commonly use minute amounts of chemical neurotransmitters to pass the electric signal from the presynaptic neuron to the target cell through the synaptic gap.

Neurons are the main components of nervous tissue in all animals except sponges and placozoans. Plants and fungi do not have nerve cells. Molecular evidence suggests that the ability to generate electric signals first appeared in evolution some 700 to 800 million years ago, during the Tonian period. Predecessors of neurons were the peptidergic secretory cells. They eventually gained new gene modules which enabled cells to create post-synaptic scaffolds and ion channels that generate fast electrical signals. The ability to generate electric signals was a key innovation in the evolution of the nervous system.

Neurons are typically classified into three types based on their function. Sensory neurons respond to stimuli such as touch, sound, or light that affect the cells of the sensory organs, and they send signals to the spinal cord and then to the sensorial area in the brain. Motor neurons receive signals from the brain and spinal cord to control everything from muscle contractions to glandular output. Interneurons connect neurons to other neurons within the same region of the brain or spinal cord. When multiple neurons are functionally connected together, they form what is called a neural circuit.

A neuron contains all the structures of other cells such as a nucleus, mitochondria, and Golgi bodies but has additional unique structures such as an axon, and dendrites. The soma or cell body, is a compact structure, and the axon and dendrites are filaments extruding from the soma. Dendrites typically branch profusely and extend a few hundred micrometers from the soma. The axon leaves the soma at a swelling called the axon hillock and travels for as far as 1 meter in humans or more in other species. It branches but usually maintains a constant diameter. At the farthest tip of the axon's branches are axon terminals, where the neuron can transmit a signal across the synapse to another cell. Neurons may lack dendrites or have no axons. The term neurite is used to describe either a dendrite or an axon, particularly when the cell is undifferentiated.

Most neurons receive signals via the dendrites and soma and send out signals down the axon. At the majority of synapses, signals cross from the axon of one neuron to the dendrite of another. However, synapses can connect an axon to another axon or a dendrite to another dendrite. The signaling process is partly electrical and partly chemical. Neurons are electrically excitable, due to the maintenance of voltage gradients across their membranes. If the voltage changes by a large enough amount over a short interval, the neuron generates an all-or-nothing electrochemical pulse called an action potential. This potential travels rapidly along the axon and activates synaptic connections as it reaches them. Synaptic signals may be excitatory or inhibitory, increasing or reducing the net voltage that reaches the soma.

In most cases, neurons are generated by neural stem cells during brain development and childhood. Neurogenesis largely ceases during adulthood in most areas of the brain.

Details

The nervous system consists of two main cell types, neurons and supporting glial cells. The neuron (or nerve cell) is the functional unit of both the central nervous system (CNS) and the peripheral nervous system (PNS). The basic functions of neurons can be summarized into four main tasks: receiving signals, integrating these signals/generating signals and transmitting the signals to target cells and organs. These functions reflect in the microanatomy of the neuron. As such, neurons typically consist of four main functional parts which include the:

* Receptive part (dendrites), which receive and conduct electrical signals toward the cell body
* Integrative part (usually equated with the cell body/soma), containing the nucleus and most of the cell's organelles, acting as the trophic center of the entire neuron. More importantly, it is here where inputs are processed and integrated to determine whether an electrical impulse (action potential) will be generated.
* Conductive part (axon), which conducts electrical impulses away from the cell body.
* Transmissive part (axon terminals), where axons communicate with other neurons or effectors (target structures which respond to nerve impulses)

Neurons are categorized into different types based on their unique morphologies and functions. This article will focus on the structure and physiology of a typical multipolar neuron, the primary neuronal type found in the CNS, and explore its parts and functions in greater detail.

Neurons: Structure and types:

Neuron structure

Description: Spherical or polygonal central component of a neuron
Function: Integration and signal processing, protein synthesis, metabolic activities
Components: Nucleus (DNA), cytoplasmic organelles (endoplasmic reticulum (smooth and rough), Golgi apparatus, microtubules, mitochondria, lysosomes), axon hillock

Axon hillock

Description: Specialized, cone-shaped region of the cell body which forms the initial segment of the axon
Function: Site for initiation of action potentials (with initial segment of axon)
Components:
- Devoid of large cytoplasmic organelles (Nissl bodies and Golgi apparatus),
- Contains high density of voltage-gated sodium channels

Dendrites

Description: Tree-like, short, tapering processes of varying shape
Function: Reception of synaptic signals and translation into electrical events
Components: Similar to the cell body, neurotransmitter receptors, dendritic shaft, dendritic spines

Axon (nerve fiber)

Description: Single long process arising from the axon hillock
Function: Conduction of electrical impulses away from the cell body
Components:
- Axolemma (cell membrane), axoplasm (cytoplasm), myelin sheath, myelin sheath gaps (nodes of Ranvier), terminal arborizations, terminal boutons, microtubules, intermediate filaments
- Devoid of endoplasmic reticulum and ribosomes

Cell body

The cell body of a neuron, also known as the soma, is typically located at the center of the dendritic tree in multipolar neurons. It is spherical or polygonal in shape and relatively small, making up one-tenth of the total cell volume.

The functionality of the neuron is highly dependent on its cell body as it houses the nucleus, which contains the genetic material (DNA) of the cell as well as various cytoplasmic organelles. These organelles include the endoplasmic reticulum (both smooth and rough), which clusters with free ribosomes to form what is known as chromatophilic substances ( Nissl bodies) and are involved in the protein synthesis of enzymes, receptors, ion channels and other structural components. Additionally, the cell body contains the Golgi apparatus and microtubules, involved in the packaging and transport of proteins; mitochondria, involved in energy production; and lysosomes involved in the waste management of the cell.

The axon hillock refers to an anatomically and functionally distinct area of the cell body which serves as the origin of the axon. It is cone-shaped and devoid of large cytoplasmic organelles such as chromatophilic substance (Nissl bodies) and Golgi apparatus. The axon hillock contains a high density of voltage-gated sodium channels, allowing it to serve as a critical site for determining whether or not the sum of all incoming signals warrants the propagation of an action potential. It also supports neuron polarity by separating the receptive/integrative parts from the conductive/transmissive parts, providing directionality in the flow of information from the dendrites to the cell body, axon and axon terminals.

The region of the axon laying between the axon hillock and the beginning of the myelin sheath is termed the initial segment. This is the actual site of action potential generation, although more recent research states that both the initial segment and axon hillock are capable of action potential generation.

Dendrites

Dendrites are tree-like processes extending from the cell body of the neuron and contain organelles similar to those in the cell body. The highly branched structure of dendrites provides an increased surface area for receiving information from other neurons at specialized areas of contact called synapses. Dendrites primarily consist of dendritic shafts, which serve as the main structural branches.

These are lined with numerous tiny protrusions called dendritic spines, which serve as sites for the initial processing of synaptic signals via membrane embedded neurotransmitter receptors; they translate the chemical messages received into electrical events, which travel down the dendrites. There are approximately ten trillion of these structures present across all dendrites of neurons in the human cerebral cortex (for 16-20 billion neurons), therefore they greatly increase the area available for synaptic events.

Axon

The axon of a neuron is also known as a nerve fiber. The membrane of an axon is known as the axolemma, while the cytoplasm is also referred to as axoplasm. Bundles of axons in the CNS form a tract, while in the PNS, they are referred to as fascicles (which, when bound together with connective tissue, form nerves). Axons originate from the axon hillock and conduct electrical impulses, in the form of action potentials, away from the cell body through a process of sequential depolarization and repolarization. Unlike dendrites that form a complex network with many tapering branches, the axon of a neuron is usually a single, long process that can extend for a considerable distance before it branches and terminates. The length of axons varies and can sometimes exceed a meter, such as in some peripheral nerves like the sciatic nerve, which extends from the spinal cord to the feet.

Axons typically terminate as fine branches called terminal arborizations; each of which is capped with a terminal bouton. These specialized structures contain synaptic vesicles that store neurotransmitters to be released into the synaptic cleft (a small gap at a synapse between neurons where nerve impulses are transmitted by a neurotransmitter) when an action potential reaches the axon terminal.

Axons can be enveloped in an insulating layer of lipids and proteins called the myelin sheath. This sheath protects the axon and prevents the loss of electrical charge (ions) during the transmission of action potentials along the neuron, increasing the speed of impulse transmission. The myelin sheath is formed by specific types of glial cells, namely oligodendrocytes in the CNS and Schwann cells (neurolemmocytes) in the PNS. The myelination of PNS axons involves many Schwann cells, each of which participates in the formation of the myelin sheath of a single axon, by wrapping around it multiple times. Not all axons are covered by myelin. In the PNS, multiple nonmyelinated axons can go through a single Schwann cell, without myelin sheath production. In contrast, an oligodendrocyte can myelinate multiple axons in the CNS, due to its arm-like processes twisting around them.

The outermost nucleated cytoplasmic layer of Schwann cells overlying the myelin sheath is called the neurolemma. This structural characteristic aids in the regeneration of damaged peripheral axons when the corresponding cell body remains intact. In contrast, CNS neurons, which lack a neurolemma, exhibit limited regenerative capacity.

Nerve fibers are classified into groups, based on their myelination; group A neurons are heavily myelinated, group B are moderately myelinated, and group C are nonmyelinated. Along myelinated axons, evenly distributed gaps known as myelin sheath gaps (commonly referred to as nodes of Ranvier) allow electrical impulses to jump from node to node. This propagation pattern is referred to as saltatory conduction. Myelin sheath gapsare more numerous in axons of the PNS compared to those of the CNS.

Since axons lack endoplasmic reticulum and ribosomes, proteins and organelles needed for its growth are synthesized in the cell body and then transported to the axon via axonal transport. This is facilitated by microtubules and intermediate filaments that provide cytoskeletal "tracks" for transportation. The microtubule arrangements overlap, providing routes for simultaneous transport of different materials to and from the cell body.

Additional Information

Neurons (also called neurones or nerve cells) are the fundamental units of the brain and nervous system, the cells responsible for receiving sensory input from the external world, for sending motor commands to our muscles, and for transforming and relaying the electrical signals at every step in between. More than that, their interactions define who we are as people. Having said that, our roughly 100 billion neurons do interact closely with other cell types, broadly classified as glia (these may actually outnumber neurons, although it’s not really known).

The creation of new neurons in the brain is called neurogenesis, and this can happen even in adults.

What does a neuron look like?

A useful analogy is to think of a neuron as a tree. A neuron has three main parts: dendrites, an axon, and a cell body or soma (see image below), which can be represented as the branches, roots and trunk of a tree, respectively. A dendrite (tree branch) is where a neuron receives input from other cells. Dendrites branch as they move towards their tips, just like tree branches do, and they even have leaf-like structures on them called spines.

The axon (tree roots) is the output structure of the neuron; when a neuron wants to talk to another neuron, it sends an electrical message called an action potential throughout the entire axon. The soma (tree trunk) is where the nucleus lies, where the neuron’s DNA is housed, and where proteins are made to be transported throughout the axon and dendrites.

There are different types of neurons, both in the brain and the spinal cord. They are generally divided according to where they orginate, where they project to and which neurotransmitters they use.

Concepts and definitions

Axon – The long, thin structure in which action potentials are generated; the transmitting part of the neuron. After initiation, action potentials travel down axons to cause release of neurotransmitter.

Dendrite – The receiving part of the neuron. Dendrites receive synaptic inputs from axons, with the sum total of dendritic inputs determining whether the neuron will fire an action potential.

Spine – The small protrusions found on dendrites that are, for many synapses, the postsynaptic contact site.

Action potential – Brief electrical event typically generated in the axon that signals the neuron as 'active'. An action potential travels the length of the axon and causes release of neurotransmitter into the synapse. The action potential and consequent transmitter release allow the neuron to communicate with other neurons.

Bowman's Capsule

Gist

The glomerular capsule, also known as Bowman's capsule, is the blind expanded end of a renal tubule. It is a double layered epithelial capsule surrounding the glomerulus. The glomerular capsule together with the glomerulus are termed the renal corpuscle, the site of blood filtration within the kidneys.

The fluid entering Bowman's capsule is called glomerular filtrate, which consists of plasma from blood minus large proteins and cells that cannot pass through the filtration barrier.

Bowman's capsule looks like a pouch, sac or cup. You can only see it under a microscope. Bowman's capsule contains fluid like blood plasma, but with no red or white blood cells or platelets.

Bowman's capsule surrounds the glomerular capillary loops and participates in the filtration of blood from the glomerular capillaries. Bowman's capsule also has a structural function and creates a urinary space through which filtrate can enter the nephron and pass to the proximal convoluted tubule.

Summary

Bowman's capsule (or the Bowman capsule, capsula glomeruli, or glomerular capsule) is a cup-like sac at the beginning of the tubular component of a nephron in the mammalian kidney that performs the first step in the filtration of blood to form urine. A glomerulus is enclosed in the sac. Fluids from blood in the glomerulus are collected in the Bowman's capsule.

Structure

Outside the capsule, there are two poles:

* The vascular pole is the side with the afferent arteriole and efferent arteriole.
* The tubular pole, is the side with the proximal convoluted tubule.

Inside the capsule, the layers are as follows, from outside to inside:

* Parietal layer—A single layer of simple squamous epithelium. Does not function in filtration.
* Bowman's space (or "urinary space", or "capsular space")—Between the visceral and parietal layers, into which the filtrate enters after passing through the filtration slits.
* Visceral layer—Lies just above the thickened glomerular basement membrane and is made of podocytes. Beneath the visceral layer lie the glomerular capillaries.
* Filtration barrier—The filtration barrier is composed of the fenestrated endothelium of the glomerular capillaries, the fused basal lamina of the endothelial cells and podocytes, and the filtration slits of the podocytes. The barrier permits the passage of water, ions, and small molecules from the bloodstream into the Bowman's space. The barrier prevents the passage of large and/or negatively charged proteins (such as albumin). The basal lamina of the filtration barrier is composed of three layers. The first layer is the lamina rara externa, adjacent to the podocyte processes. The second layer is the lamina rara interna, adjacent to the endothelial cells. The final layer is the lamina densa which is a darker central zone of the basal lamina. It consists of the meshwork of type IV collagen and laminin which act as a selective macromolecular filter.

Function

The process of filtration of the blood in the Bowman's capsule is ultrafiltration, and the normal rate of filtration is 125 ml/min, equivalent to 80 times the daily blood volume. It is a major site for blood filtration (including glomerulus).

Any proteins under roughly 30 kilodaltons can pass freely through the membrane, although there is some extra hindrance for negatively charged molecules due to the negative charge of the basement membrane and the podocytes.

Any small molecules such as water, glucose, salt (NaCl), amino acids, and urea pass freely into Bowman's space, but cells, platelets and large proteins do not.

As a result, the filtrate leaving the Bowman's capsule is very similar to blood plasma (filtrate or glomerular filtrate is composed of blood plasma minus plasma protein i.e. it contains all the components of blood plasma except the proteins) in composition as it passes into the proximal convoluted tubule.

Details

Bowman’s capsule is part of a nephron, a filter in your kidney. One million nephrons in each kidney clean your blood. A Bowman’s capsule in each nephron plays a part in the filtering process. After filtering, nutrients stay in your blood, and waste goes out through urine.

Overview

Bowman’s capsule surrounds blood vessels in each nephron that filters blood in your kidneys.

What is Bowman’s capsule?

Bowman’s capsule is a part of each filtering unit (nephron) in your kidney. You have about 1 million nephrons that filter blood in each of your two kidneys. Kidneys clean blood and return it to your body.

Every nephron has a glomerulus. A two-walled pouch, Bowman’s capsule covers the glomerulus. This group of tiny blood vessels is the starting point for filtering waste products out of your blood. Bowman’s capsule and the glomerulus make up the renal corpuscle.

You may hear other names for Bowman’s capsule, like:

* Glomerular capsule
* Malpighian capsule
* Renal corpuscular capsule

The space in between the walls (layers) of Bowman’s capsule is called Bowman’s space. You may hear healthcare providers refer to Bowman’s space as:

* Glomerular capsule space
* Filtration space
* Urinary space

Function:

What is the function of the Bowman’s capsule in the kidney?

The function of Bowman’s capsule is to help the glomerulus filter blood. Small molecules from your blood pass freely into Bowman’s space. Cells and large proteins stay in your blood.

The glomerular capsule also protects cells called podocytes by keeping white blood cells from getting in. White blood cells can’t pass through Bowman’s capsule. Podocytes in a kidney capsule have pedicels that manage what stays and what goes. Finger-like pedicels link together like they’re holding hands. The way they join creates slits that only let certain things go through. When you’re healthy, protein and cell content can’t get through.

The small molecules then pass through tubes in your kidney. Your kidney regulates which molecules your blood absorbs and which leave your body in pee (urine).

Waste materials go out of your body as urine through tubules (tiny tubes). The blood pressure in the glomerulus helps move the blood along. As the fluids leave, water and nutrients go back into your blood.

Two arterioles go into the Bowman’s capsule. One brings blood into the glomerulus. The other lets blood out.

Anatomy:

Where is Bowman’s capsule located?

Bowman’s capsule is in the renal cortex, part of your kidney. Your kidneys are in your back, below your rib cage. Usually, you have one kidney on either side of your spine. Your kidneys are between your intestines and diaphragm. Each kidney connects to your bladder by a tube called a ureter.

What does it look like?

Bowman’s capsule looks like a pouch, sac or cup. You can only see it under a microscope. Bowman’s capsule contains fluid like blood plasma, but with no red or white blood cells or platelets.

What are the parts of Bowman’s capsule?

The glomerular capsule has two layers. A type of body tissue, simple squamous epithelium, makes up the outer (parietal) layer. These parietal cells give structure to Bowman’s capsule. Cells called podocytes form the inner (visceral) layer.

Additional Information:

Introduction

Bowman’s capsule is a part of the nephron that forms a cup-like sack surrounding the glomerulus. Bowman’s capsule encloses a space called “Bowman’s space,” which represents the beginning of the urinary space and is contiguous with the proximal convoluted tubule of the nephron. Bowman’s capsule, Bowman’s space, and the glomerular capillary network and its supporting architecture can collectively be thought of as composing the glomerulus. There are an estimated 900000 glomeruli within the cortex of a mature human kidney.

Structure and Function

In the kidney, the glomerulus represents the initial location of the renal filtration of blood. Blood enters the glomerulus through the afferent arteriole at the vascular pole, undergoes filtration in the glomerular capillaries, and exits the glomerulus through the efferent arteriole at the vascular pole.

Bowman’s capsule surrounds the glomerular capillary loops and participates in the filtration of blood from the glomerular capillaries. Bowman’s capsule also has a structural function and creates a urinary space through which filtrate can enter the nephron and pass to the proximal convoluted tubule. Liquid and solutes of the blood must pass through multiple layers to move from the glomerular capillaries into Bowman’s space to ultimately become filtrate within the nephron’s lumen.

The first step of filtration occurs through the endothelial layer of the capillaries, which is composed of fenestrated endothelial cells. These fenestrations, or slits between endothelial cells, are approximately 60 to 80 nm wide and restrict the movement of matter above this size. In addition to filtering based on size, the fenestrated endothelium carries negative charges that preferentially restrict the movement of negatively charged substances into Bowman’s space.

Filtrate next moves through the glomerular basement membrane (GBM). From the direction of the capillaries and moving towards Bowman’s capsule, three layers compose the GBM – the lamina rara interna, the lamina densa, and the lamina rara externa. Mesangial cells within the glomerulus play a role in creating and maintaining the GBM, as well as holding capillary loops together.

Following the GBM, filtrate must pass through the epithelial layer of Bowman’s capsule, which is composed of podocytes. The podocytes feature finger-like projections of cytoplasm referred to as “foot processes” or “pedicels.” These foot processes interdigitate with one another and create a further barrier through which filtrate must pass. Structures called “slit diaphragms” bridge nearby foot processes and provide structural support. The podocytes are the primary cells of the epithelium adjacent to the capillaries (the visceral epithelium) and play a role in filtration. The parietal epithelium of Bowman’s capsule is the outer layer and is composed of simple squamous epithelial cells called “parietal cells.” The parietal layer is not directly involved with filtration from the capillaries. Parietal cells play a structural role in maintaining Bowman’s capsule and are also speculated to have the ability to differentiate into podocytes to replace damaged or old podocytes. Bowman’s space is the area between the visceral and parietal epithelium of Bowman’s capsule.

In summary, filtrate entering Bowman’s space traverses through glomerular capillaries, the GBM, and the interdigitated foot processes of the podocytes and is filtered based on size and electric charge. The filtrate entering Bowman’s space has a very similar composition to that of the blood in the glomerular capillaries except for the protein, and cell content as these are the components largely prevented from entering Bowman’s space when glomerular filtration is functioning properly.