# data[].attributes.attachment_link.readable_text
Information about the outside world as well as the inner workings of the human body speeds to and from the brain and spinal cord through nerves. Nerves are bundles of the long, tubelike extensions of nerve cells. Impulses fired through them uniquely convey information throughout the body.

The nervous system in humans has two main parts: the central nervous system and the peripheral nervous system. The central nervous system consists of the brain and spinal cord. The peripheral nervous system, which is the subject of this article, consists of the nerves, which relay impulses between the central nervous system and the rest of the body. They transmit information by electrochemical means.

Nerve impulses travel only in one direction. If information from the stomach, for example, is transmitted to the brain through one nerve, action orders from the brain cannot travel back to the stomach over the same nerve. Another must carry the return message.

Sensory nerves carry information from the sense organs and other body receptors to the central nervous system for processing. Then motor nerves carry the processed information from the central nervous system to the glands and muscles for appropriate action. The nervous system also includes mixed nerves, which have separate sensory nerve fibers and motor nerve fibers.

Nerves also can be classified as afferent and efferent. Afferent nerves feed input signals to the central nervous system for processing. Efferent nerves carry processed signals from the central nervous system to appropriate body areas for action.

Spinal Nerves
The peripheral nervous system includes spinal nerves, cranial nerves, and autonomic nerves. The spinal nerves are sensory and motor nerve bundles that emerge from the spinal cord. Humans have 31 pairs of these mixed nerves. Each pair connects the spinal cord with a specific region of the body. The sensory fibers in spinal nerves send sensory information from receptors in the skin, muscles, joints, tendons, and internal organs to the central nervous system. The motor fibers transmit messages to the muscles.

Cranial Nerves
The cranial nerves are a group of 12 pairs of nerves that connect the brain stem and other parts of the brain to the sense organs of the head as well as to muscles, internal organs, and glands in the head, neck, chest, and upper abdomen. They include sensory nerves, motor nerves, and mixed nerves. The cranial nerves connected to the sense organs relay information about smell, vision, hearing, and taste to the brain. Cranial nerves also control the muscles involved in making facial expressions, chewing, swallowing, and moving the eyes, head, shoulders, and neck, for instance.

Autonomic Nerves
The autonomic nervous system works to keep the body's internal environment in a state of balance called homeostasis-for example, by maintaining a normal body temperature and heart rate. This system normally regulates the workings of the internal organs without the person's conscious effort or even awareness.

The autonomic system regulates a great variety of bodily functions. For example, it includes motor nerves that innervate (supply with nerves) the smooth muscles of the blood vessels, the heart muscle, and the smooth muscles of the digestive system. Autonomic nerves also stimulate glands to release certain hormones related to the metabolism of energy and cardiovascular functions. The motor functions of the autonomic system have traditionally been emphasized, but nerves of the system also transmit sensory information about the state of the internal organs.

The autonomic nervous system has two major divisions: the sympathetic nervous system and the parasympathetic nervous system. Sympathetic nerves tend to prepare the body for emergencies such as temperature extremes, lack of water, or physical harm. On the other hand, parasympathetic nerves tend to keep the body running smoothly with a minimum outlay of energy. Ordinarily, the two kinds counteract each other. If a sympathetic nerve triggers muscle contraction, for instance, a parasympathetic nerve may order muscle relaxation.

The sympathetic nerves usually produce local adjustments, such as sweating when it gets hotter in the environment. Under conditions of stress, however, the entire sympathetic nervous system is activated. This prepares a person to respond to immediate danger through such actions as increasing the heart rate, increasing blood flow to the muscles, and decreasing blood flow to the skin. This is often called the "fight-or-flight" response, because it readies the body to either combat an enemy or quickly flee. The parasympathetic nerves are never activated all at once.

Sympathetic nerves emerge from about the last three quarters of the spinal cord. They connect with other sympathetic neurons in a chain of ganglia (clusters of nerve-cell bodies) running parallel with the spinal cord. Fibers from these ganglia join with spinal nerves and others to reach the limbs and organs they serve. Sympathetic ganglia are also located near the major organs in the abdomen.

Parasympathetic fibers are found in cranial nerves III, VII, IX, and X. Some also emerge from the tail end of the spinal cord. The most important nerve with parasympathetic functions is the vagus, or cranial nerve X, because it sends fibers to many parts of the body, including the heart, lungs, and stomach.

The autonomic nervous system also has a third division, the enteric nervous system. The nerves in this system control the movements and secretions of the gastrointestinal tract.

Nearly all neurons, or nerve cells, have the same general structure. They usually have a round or pyramid-shaped cell body, which contains the nucleus and other basic cell parts. "Trees" of branching fibers called dendrites sprout from the cell body. In general, the dendrites receive nerve impulses and conduct them toward the cell body. Also extending from the cell body is a long tubelike fiber called an axon. The axon generally transmits nerve impulses away from the cell body to other cells. In some neurons the axon is only thousandths of an inch long, while in others it reaches several yards. Near its end, the axon branches into many fingerlike extensions called axon terminals. In some neurons, particularly sensory ones, dendritelike parts link directly with the axon instead of the cell body, and the cell body is connected to a branch of the axon.

Neurons contain the molecular machinery common to all cells ( see biochemistry). When not too severely damaged, neurons in peripheral nerves can regrow. Nerve cells are so specialized, however, that they can no longer reproduce by cell division. And even regrowth is impossible in the central nervous system. This is why severe damage to the brain or spinal cord is permanent and can result in muscle or limb paralysis. Messages to activate those structures cannot be carried past the point of injury.

The brain also has a class of cells called glia. Glial cells are shaped to fit into the spaces between neurons. They stabilize the brain's neural circuits and also supplement the metabolic processes of neurons.

A neuron connects with others at junctions called synapses. A typical synapse is so small that many can be made between nerve cells. For example, any neuron may receive thousands of synaptic contacts from others and, in turn, may send out the same number of axon branches. Because the human nervous system contains billions of neurons (more than 10 billion are in the brain alone), scientists have a difficult job unraveling the "wiring" plan.

Typically, the axon of one neuron forms a synapse with the dendrite of another neuron. The axon terminal does not actually touch the dendrite of the other neuron, however; they communicate across a tiny gap. Each neuron is surrounded by a membrane. Thus, every synapse has the following components: the presynaptic membrane of the axon of one neuron; the postsynaptic membrane of the dendrite of the other neuron; and the tiny gap between them called the synaptic cleft.

Nerves, unlike telephone wires with which they are sometimes compared, generate their own self-amplified electrical signals-the nerve impulses. The electrical sign of a nerve impulse is an action potential, and it is generated when a neuron undergoes electrical change. Ions are atoms or groups of atoms that become electrically charged by losing or acquiring electrons. Ions occur in varying concentrations inside and outside a cell, causing a voltage difference on each side of the cell membrane. In a "resting" neuron the voltage difference is called the resting potential. The inside of a neuron at rest is electrically more negative than the outside, usually by between -50 and -100 millivolts (mV). In this condition the nerve membrane is polarized. A change that makes the inside of the neuron less negatively charged is called depolarization, while one that makes it even more negatively charged is called hyperpolarization.

When a voltage change brought on by a stimulus depolarizes the membrane, either of two things happens. If the stimulus is strong enough to breach a critical threshold level, an action potential is fired. If not, the voltage drops back to the resting potential.

If an action potential is fired, it moves along the axon. The voltage change and depolarization at one end of the axon "flows" to the next point, where the event is duplicated, and so on down the axon until the action potential reaches the axon terminals.

Scientists have a fairly clear idea of how action potentials form in a neuron. When a portion of the membrane is depolarized, special channels in it open and allow an inward rush of sodium ions, which are in higher concentration outside the cell. Then when the positively charged sodium ions flow into the negatively charged neuron interior, they cause further depolarization by making the interior electrically more positive. This, in turn, opens more channels, allowing more sodium ions to rush in. Once opened, however, the sodium channels slowly close in spite of the depolarization that originally made them open.

Channels for outgoing potassium ions are also in the neuron membrane. They, too, open during depolarization but more slowly than the sodium channels. When the potassium channels finally open, positively charged potassium ions flow to the outside of the cell, where they are in lower concentration. As they leave the cell, they hasten the return of the neuron's voltage to its resting level, and the interior again becomes electrically more negative than the exterior.

Action potentials travel faster in some neurons than in others. The transmission speeds range from about 3 to 330 feet (1 to 100 meters) per second-or about 2 to 225 miles (3 to 360 kilometers) per hour. The speed varies depending on the properties of the nerve fiber and its environment. In general, nerve impulses travel faster along thicker nerve fibers. The conduction velocity also increases at high temperatures and decreases at low temperatures. Moreover, many axons are covered with an insulating layer of a fatty substance called myelin. The myelin covers sections of the axon, which are separated by short segments of bare axon called nodes of Ranvier. In a myelinated axon the action potential jumps from one node to the next instead of traveling along the entire length of the axon, as it must in an unmyelinated axon. This speeds its transmission.

The chemicals that allow impulses to be transmitted from one neuron to another are called neurotransmitters. Many different chemicals, such as acetylcholine, norepinephrine (noradrenaline), dopamine, and serotonin, act as neurotransmitters. Some neurotransmitters activate neurons, while others inhibit them.

When a nerve impulse gets to the axon terminal, it triggers the release of a neurotransmitter from tiny sacs called synaptic vesicles into the synaptic cleft (the tiny gap). As "packets" of neurotransmitter spread throughout the synaptic cleft, some neurotransmitter molecules come into contact with receptor molecules in the postsynaptic membrane of the next neuron and merge into a transmitter-receptor complex. This complex then changes its shape and permits an inflow of sodium ions in some neurons and an outflow of potassium ions in others. More ions now flow through the postsynaptic membrane, causing a voltage change.

When sodium-ion permeability is increased, incoming positively charged sodium ions depolarize the neuron by raising its internal voltage. By contrast, when potassium-ion permeability is increased, outgoing potassium ions hyperpolarize the neuron by lowering its internal voltage. These chemically induced voltage changes are called postsynaptic potentials (PSPs). The depolarizing (positive-going) ones are excitatory postsynaptic potentials (EPSPs), and the hyperpolarizing (negative-going) ones are inhibitory postsynaptic potentials (IPSPs). EPSPs can produce action potentials. IPSPs oppose their production. Simple addition allows information to pass from one neuron to another. If an EPSP occurs just before a prior one dies away, it simply adds to the tail of the earlier one. By contrast, IPSPs subtract from the sum of EPSPs.

A typical neuron might receive both kinds of PSPs from a thousand other neurons, all of which are producing about ten action potentials a second. A neuron's voltage at any given moment, therefore, reflects all the summation activities of a thousand inputs. As the inputs arrive they are rapidly added to or subtracted from the total neuron voltage. If enough EPSPs overcome the IPSPs, the neuron fires an impulse. If IPSPs predominate, it does not.

What would normally happen if a depolarizing stimulus acted on a neuron continuously? After the first action potential was generated, a brief pause would ensue during the refractory period as the ion channels and other nerve-cell operations returned to normal. Then a second action potential would form, then another pause, then a third action potential, and so on, as long as the stimulus was there. A steady but spaced train of action potentials would run at a frequency of so many per second, speeding up or slowing down as the intensity of the above-threshold stimulus increased or decreased. This frequency constitutes the code by which commands are sent throughout the body.

Neurons are organized into pathways called circuits. The simplest neural circuits produce the reflexes, which are direct, immediate responses to stimuli without conscious thought-for instance, pulling one's hand away from a burning-hot surface or blinking when something touches one's eyeball. More complex circuits control various other functions, from coordinated movement of the muscles to thinking and remembering.

A circuit includes different types of cells that receive information, integrate it, and transmit it to the part of the body that will respond to the signal. First, a receptor cell receives a stimulus, from either the environment or within the body, and changes it into an electrical impulse. Sensory neurons transmit the impulse to the brain or spinal cord, in most cases to a neuron called an interneuron. The interneuron selects, interprets, or modifies the input and sends it to an efferent neuron, such as a motor neuron. Finally, the impulse is sent to an effector, such as a muscle or gland, which produces a response (such as contracting or secreting a hormone).

The receptor cells are clustered in sense organs, such as the eyes and ears, and scattered through the skin and elsewhere in the body, such as the muscles and internal organs. The receptors respond selectively to stimuli in the environment. Photoreceptors in the eyes, for example, respond to light but not to sound. Each receptor contains special sensory neurons with mechanisms capable of producing a generator potential, a depolarization (or sometimes a hyperpolarization) triggered by an outside stimulus. Like PSPs, generator potentials send a coded frequency of action potentials to the rest of the nervous system.

Ultimately, the action potentials reach an effector, such as a muscle cell. In turn, the depolarized muscle cell generates an action potential that causes it to contract. The strength of contraction depends on the number of nerve action potentials sent to the muscle per second. Thus, the nervous system's code is decoded by the action of individual muscle fibers. By controlling muscle contraction and body movements, the nervous system influences response to information from inside as well as outside the body.

Neurology is the study of the nervous system and the diseases that can affect it. Physicians who specialize in treating nervous disorders are called neurologists. Disorders of the human nervous system are characterized by an array of symptoms-from slight disturbances in personality to tragic crippling, blinding, or death. There are a variety of causes of nervous disorders, some hereditary and others infectious. The nervous system may, for example, be invaded by such disease-producing agents as bacteria and viruses. Disease symptoms are related to the infection site and the type of invading agent. There are two basic groups of infections- meningitis and encephalitis -depending on whether the coverings (the meninges) or the functioning elements, such as the neurons of the brain, are mainly affected.

Alzheimer's disease, almost unheard of until the 1980s, is now recognized as the major single cause of senility, or senile dementia. The symptoms of the disease almost always include short-term memory loss, disorientation, and difficulty with abstract thinking. Persons with Alzheimer's disease are unable to produce normal amounts of the chemical acetylcholine. They are, however, usually alert until the later stages of the disease.

Rabies, or hydrophobia, is usually transmitted to humans by a bite from an animal infected with the rabies virus. Humans vaccinated during the incubation period of the virus, 10 to 50 days, normally do not develop the disease.

Shingles, or herpes zoster, is caused by infection with the Varicella-zoster virus, which is also the chicken pox virus. It attacks the nerve endings and forms small blisters on the skin surface supplied by the affected nerves.

Tetanus, or lockjaw, is caused by infection with the bacterium Clostridium tetani found in soil and manure. It enters the nervous system through an open wound and thrives in an anaerobic environment. Incubation is from two days to several weeks, and the common early symptom is stiffness of the jaw muscles.

Syphilis is a contagious sexually transmitted disease caused by infection with the bacterial spirochete Treponema pallidum. The infection may occur years before the disease is diagnosed. In later stages, lesions form in the brain. Penicillin and other antibiotics are used as treatment.

Leprosy, or Hansen's disease, a chronic infectious neurological disease, is often curable when caught in the early stages. It is caused by the bacterium Mycobacterium leprae, which produces lesions in the skin, mucous membranes, and peripheral nerves.

Demyelinating diseases result in the loss of the nerves' myelin sheath. Nerve fibers cannot properly conduct impulses without this sheath, so function is altered. The most common demyelinating disease is multiple sclerosis, usually referred to as MS. The cause of multiple sclerosis is undetermined, and treatments vary. It is characterized by relapses and remissions.

Epilepsy is a nervous disorder of recurrent convulsive seizures in which consciousness is lost or impaired. Epilepsy can result from a wide variety of diseases and injuries.

Compression of the spinal cord, nerve roots, or peripheral nerves is often caused by neurological diseases. A slipped disk, certain cancers, tuberculosis of the spine, and arthritis can also cause this affliction.

Carpal tunnel syndrome is a condition in which the median nerve becomes compressed in the wrist, causing numbness, tingling, pain, and weakness in the hand and wrist. It is caused by repetitive finger or wrist movements over a long period of time, often from jobs on an assembly line or that require constant computer use.

Motor and neuromuscular disorders can disturb the movements of muscles under the direct control of motor neurons in the brainstem and spinal cord. During myotonia, muscles do not relax after contraction; the cause is unclear. Parkinson disease is characterized by rigidity of the muscles, a masklike face, speech difficulties, and tremors. Huntington's chorea, a hereditary disorder of nerve cell clusters in the brain, involves shrinkage of such brain parts as the cerebral cortex.

Amyotrophic lateral sclerosis (ALS) is a progressive disease that affects the motor neurons, causing muscle weakness, muscle wasting, and paralysis. It usually results in death from atrophy of the muscles that control breathing. Amyotrophic lateral sclerosis is also called Lou Gehrig disease, for the famous baseball player who died of it in 1941.

Poliomyelitis, or polio, is caused by a virus that attacks motor neurons, and it can result in permanent paralysis of parts of the body. It almost completely disappeared in industrialized countries after the introduction of the Salk and Sabin vaccines in the 1950s. In 1988 the World Health Organization and other groups established a program attempting to eliminate polio worldwide. It has been very successful, and the disease is now endemic to only a handful of countries.

All other vertebrates-the other mammals plus the birds, reptiles, amphibians, and fishes-have nervous systems that are similar to that of humans. In all vertebrates the nervous system is highly centralized, with a brain and spinal cord that play a dominant role in coordinating information and directing responses to that information. The peripheral nervous system relays messages between the brain and spinal cord and the rest of the body. Higher vertebrates- mammals, birds, and reptiles -have more complex nervous systems than lower vertebrates.

The nervous systems of invertebrates-the numerous kinds of animals that do not have backbones-are varied. Sponges lack a definite nervous system of any kind. Other lower invertebrates such as jellyfish, hydras, sea anemones, corals, and comb jellies have nervous systems, but they lack a brain or other centralized concentration of neurons. Instead, they have a nerve net, or a system of individual nerve cells and fibers dispersed through the body in a netlike pattern. Their bodies, and their nerve nets, are radially symmetrical, with similar parts arranged symmetrically around a hollow gut cavity in the center. The transmission of nerve impulses is slower in a nerve net than in other types of nervous system.

The most primitive invertebrates that can be said to have brains are the flatworms. They also have a kind of nerve net. A flatworm's brain consists of ganglia in the head that are connected to nerve cords running through the length of the body. Shorter nerves connect the nerve cords across the body, forming a ladderlike pattern.

Segmented worms, mollusks, and arthropods have more complex nervous systems, with a greater concentration of nervous functions in the brain. Like other invertebrates, they do not have myelinated axons. However, some have giant axons, which are comparatively much thicker than vertebrate axons and transmit nerve impulses quickly. The most highly developed nervous systems in invertebrates are found in octopuses, squids, cuttlefish, insects, and spiders.

Charles F. Stevens

Ed.

# data[].attributes.attachment_link.description
Information about the outside world as well as the inner workings of the human body speeds to and from the brain and spinal cord through nerves. Nerves are bundles of the long, tubelike extensions of nerve cells. Impulses fired through them uniquely convey information throughout the body.

# data[].attributes.headline
(Article) Kids Health--Brain and Nervous system (kids)

# data[].attributes.subject
(Article) Kids Health--Brain and Nervous system (kids)

# data[].attributes.attachment_link.readable_text
How do you remember the way to your friend's house? Why do your eyes blink without you ever thinking about it? Where do dreams come from? Your brain is in charge of these things and a lot more.

In fact, your brain is the boss of your body. It runs the show and controls just about everything you do, even when you're asleep. Not bad for something that looks like a big gray wrinkly sponge.

Your brain has many different parts that work together. We're going to talk about these five parts, which are key players on the brain team:

1. cerebrum (say: suh-REE-brum)

2. cerebellum (say: sair-uh-BELL-um)

3. brain stem

4. pituitary (say: puh-TOO-uh-ter-ee) gland

5. hypothalamus (say: hy-po-THAL-uh-mus)

The Biggest Part: the Cerebrum

The biggest part of the brain is the cerebrum. The cerebrum is the thinking part of the brain and it controls your voluntary muscles - the ones that move when you want them to. So you need your cerebrum to dance or kick a soccer ball.

You need your cerebrum to solve math problems, figure out a video game, and draw a picture. Your memory lives in the cerebrum - both short-term memory (what you ate for dinner last night) and long-term memory (the name of that roller-coaster you rode on two summers ago). The cerebrum also helps you reason, like when you figure out that you'd better do your homework now because your mom is taking you to a movie later.

The cerebrum has two halves, with one on either side of the head. Scientists think that the right half helps you think about abstract things like music, colors, and shapes. The left half is said to be more analytical, helping you with math, logic, and speech. Scientists do know for sure that the right half of the cerebrum controls the left side of your body, and the left half controls the right side.

The Cerebellum's Balancing Act

Next up is the cerebellum. The cerebellum is at the back of the brain, below the cerebrum. It's a lot smaller than the cerebrum. But it's a very important part of the brain. It controls balance, movement, and coordination (how your muscles work together).

Because of your cerebellum, you can stand upright, keep your balance, and move around. Think about a surfer riding the waves on his board. What does he need most to stay balanced? The best surfboard? The coolest wetsuit? Nope - he needs his cerebellum!

Brain Stem Keeps You Breathing - and More

Another brain part that's small but mighty is the brain stem. The brain stem sits beneath the cerebrum and in front of the cerebellum. It connects the rest of the brain to the spinal cord, which runs down your neck and back. The brain stem is in charge of all the functions your body needs to stay alive, like breathing air, digesting food, and circulating blood.

Part of the brain stem's job is to control your involuntary muscles - the ones that work automatically, without you even thinking about it. There are involuntary muscles in the heart and stomach, and it's the brain stem that tells your heart to pump more blood when you're biking or your stomach to start digesting your lunch. The brain stem also sorts through the millions of messages that the brain and the rest of the body send back and forth. Whew! It's a big job being the brain's secretary!

Pituitary Gland Controls Growth

The pituitary gland is very small - only about the size of a pea! Its job is to produce and release hormones into your body. If your clothes from last year are too small, it's because your pituitary gland released special hormones that made you grow. This gland is a big player in puberty too. This is the time when boys' and girls' bodies go through major changes as they slowly become men and women, all thanks to hormones released by the pituitary gland.

This little gland also plays a role with lots of other hormones, like ones that control the amount of sugars and water in your body.

Hypothalamus Controls Temperature

The hypothalamus is like your brain's inner thermostat (that little box on the wall that controls the heat in your house). The hypothalamus knows what temperature your body should be (about 98.6°F or 37°C). If your body is too hot, the hypothalamus tells it to sweat. If you're too cold, the hypothalamus gets you shivering. Both shivering and sweating are attempts to get your body's temperature back where it needs to be.

You Have Some Nerve!

So the brain is boss, but it can't do it alone. It needs some nerves - actually a lot of them. And it needs the spinal cord, which is a long bundle of nerves inside your spinal column, the vertebrae that protect it. It's the spinal cord and nerves - known as the nervous system - that let messages flow back and forth between the brain and body.

If a spiky cactus falls off a shelf headed right for your best friend, your nerves and brain communicate so that you jump up and yell for your friend to get out of the way. If you're really good, maybe you're able to catch the plant before it hits your friend!

The nervous system is made up of millions and millions of neurons (say: NUR-onz), which are microscopic cells. Each neuron has tiny branches coming off it that let it connect to many other neurons.

When you learn things, the messages travel from one neuron to another, over and over. Eventually, the brain starts to create connections (or pathways) between the neurons, so things become easier and you can do them better and better.

Think back to the first time you rode a bike. Your brain had to think about pedaling, staying balanced, steering with the handlebars, watching the road, and maybe even hitting the brakes - all at once. Hard work, right? But eventually, as you got more practice, the neurons sent messages back and forth until a pathway was created in your brain. Now you can ride your bike without thinking about it because the neurons have successfully created a "bike riding" pathway.

Emotion Location

With all the other things it does, is it any surprise that the brain runs your emotions? Maybe you had fun on your birthday and you were really happy. Or your friend is sick and you feel sad. Or your little brother messed up your room, so you're really angry! Where do those feelings come from? Your brain, of course.

Your brain has a little bunch of cells on each side called the amygdala (say: uh-MIG-duh-luh). The word amygdala is Latin for almond, and that's what this area looks like. Scientists believe that the amygdala is responsible for emotion. It's normal to feel all different kinds of emotions, good and bad. Sometimes you might feel a little sad, and other times you might feel scared, or silly, or glad.

Be Good to Your Brain

So what can you do for your brain? Plenty.

Eat healthy foods. They contain vitamins and minerals that are important for the nervous system.

Get a lot of playtime (exercise).

Wear a helmet when you ride your bike or play other sports that require head protection.

Don't drink alcohol, take drugs, or use tobacco.

Use your brain by doing challenging activities, such as puzzles, reading, playing music, making art, or anything else that gives your brain a workout!

# data[].attributes.attachment_link.description
How do you remember the way to your friend's house? Why do your eyes blink without you ever thinking about it? Where do dreams come from? Your brain is in charge of these things and a lot more. In fact, your brain is the boss of your body.

# data[].attributes.headline
(Article) Kids Health--Brain and Nervous system (teens)

# data[].attributes.subject
(Article) Kids Health--Brain and Nervous system (teens)

# data[].attributes.attachment_link.readable_text
What Does the Brain Do?

The brain controls what you think and feel, how you learn and remember, and the way you move and talk. But it also controls things you're less aware of - like the beating of your heart and the digestion of your food.

Think of the brain as a central computer that controls all the body's functions. The rest of the nervous system is like a network that relays messages back and forth from the brain to different parts of the body. It does this via the spinal cord, which runs from the brain down through the back. It contains threadlike nerves that branch out to every organ and body part.

When a message comes into the brain from anywhere in the body, the brain tells the body how to react. For example, if you touch a hot stove, the nerves in your skin shoot a message of pain to your brain. The brain then sends a message back telling the muscles in your hand to pull away. Luckily, this neurological relay race happens in an instant.

What Are the Parts of the Nervous System?

The nervous system is made up of the central nervous system and the peripheral nervous system:

The brain and the spinal cord are the central nervous system.

The nerves that go through the whole body make up the peripheral nervous system.

The human brain is incredibly compact, weighing just 3 pounds. It has many folds and grooves, though. These give it the added surface area needed for storing the body's important information.

The spinal cord is a long bundle of nerve tissue about 18 inches long and 1/2-inch thick. It extends from the lower part of the brain down through spine. Along the way, nerves branch out to the entire body.

The brain and the spinal cord are protected by bone: the brain by the bones of the skull, and the spinal cord by a set of ring-shaped bones called vertebrae. They're both cushioned by layers of membranes called meninges and a special fluid called cerebrospinal fluid. This fluid helps protect the nerve tissue, keep it healthy, and remove waste products.

What Are the Parts of the Brain?

The brain has three main sections: the forebrain, the midbrain, and the hindbrain.

The Forebrain

The forebrain is the largest and most complex part of the brain. It consists of the cerebrum - the area with all the folds and grooves typically seen in pictures of the brain - as well as other structures under it.

The cerebrum contains the information that essentially makes you who you are: your intelligence, memory, personality, emotion, speech, and ability to feel and move. Specific areas of the cerebrum are in charge of processing these different types of information. These are called lobes, and there are four of them: the frontal, parietal, temporal, and occipital lobes.

The cerebrum has right and left halves, called hemispheres. They're connected in the middle by a band of nerve fibers (the corpus callosum) that lets them communicate. These halves may look like mirror images of each other, but many scientists believe they have different functions:

The left side is considered the logical, analytical, objective side.

The right side is thought to be more intuitive, creative, and subjective.

So when you're balancing your checkbook, you're using the left side. When you're listening to music, you're using the right side. It's believed that some people are more "right-brained" or "left-brained" while others are more "whole-brained," meaning they use both halves of their brain to the same degree.

The outer layer of the cerebrum is called the cortex (also known as "gray matter"). Information collected by the five senses comes into the brain to the cortex. This information is then directed to other parts of the nervous system for further processing. For example, when you touch the hot stove, not only does a message go out to move your hand, but one also goes to another part of the brain to help you remember not to do that again.

In the inner part of the forebrain sits the thalamus, hypothalamus, and

pituitary gland :

The thalamus carries messages from the sensory organs like the eyes, ears, nose, and fingers to the cortex.

The hypothalamus controls your pulse, thirst, appetite, sleep patterns, and other processes in your body that happen automatically.

The hypothalamus also controls the pituitary gland, which makes the hormones that control growth, metabolism, water and mineral balance, sexual maturity, and response to stress.

The Midbrain

The midbrain, underneath the middle of the forebrain, acts as a master coordinator for all the messages going in and out of the brain to the spinal cord.

The Hindbrain

The hindbrain sits underneath the back end of the cerebrum. It consists of the cerebellum, pons, and medulla. The cerebellum - also called the "little brain" because it looks like a small version of the cerebrum - is responsible for balance, movement, and coordination.

The pons and the medulla, along with the midbrain, are often called the brainstem. The brainstem takes in, sends out, and coordinates the brain's messages. It also controls many of the body's automatic functions, like breathing, heart rate, blood pressure, swallowing, digestion, and blinking.

How Does the Nervous System Work?

The basic workings of the nervous system depend a lot on tiny cells called neurons. The brain has billions of them, and they have many specialized jobs. For example, sensory neurons send information from the eyes, ears, nose, tongue, and skin to the brain. Motor neurons carry messages away from the brain to the rest of the body.

All neurons relay information to each other through a complex electrochemical process, making connections that affect the way you think, learn, move, and behave.

Intelligence, learning, and memory. As you grow and learn, messages travel from one neuron to another over and over, creating connections, or pathways, in the brain. It's why driving takes so much concentration when someone first learns it, but later is second nature: The pathway became established.

In young children, the brain is highly adaptable. In fact, when one part of a young child's brain is injured, another part often can learn to take over some of the lost function. But as you age, the brain has to work harder to make new neural pathways, making it harder to master new tasks or change set behavior patterns. That's why many scientists believe it's important to keep challenging the brain to learn new things and make new connections - it helps keeps the brain active over the course of a lifetime.

Memory is another complex function of the brain. The things you've done, learned, and seen are first processed in the cortex. Then, if you sense that this information is important enough to remember permanently, it's passed inward to other regions of the brain (such as the hippocampus and amygdala) for long-term storage and retrieval. As these messages travel through the brain, they too create pathways that serve as the basis of memory.

Movement. Different parts of the cerebrum move different body parts. The left side of the brain controls the movements of the right side of the body, and the right side of the brain controls the movements of the left side of the body. When you press your car's accelerator with your right foot, for example, it's the left side of your brain that sends the message allowing you to do it.

Basic body functions. A part of the peripheral nervous system called the autonomic nervous system controls many of the body processes you almost never need to think about, like breathing, digestion, sweating, and shivering. The autonomic nervous system has two parts: the sympathetic nervous system and the parasympathetic nervous system.

The sympathetic nervous system prepares the body for sudden stress, like if you witness a robbery. When something frightening happens, the sympathetic nervous system makes the heart beat faster so that it sends blood quickly to the different body parts that might need it. It also causes the

adrenal glands at the top of the kidneys to release adrenaline, a hormone that helps give extra power to the muscles for a quick getaway. This process is known as the body's "fight or flight" response.

The parasympathetic nervous system does the opposite: It prepares the body for rest. It also helps the digestive tract move along so our bodies can efficiently take in nutrients from the food we eat.

The Senses

Sight. Sight probably tells us more about the world than any other sense. Light entering the eye forms an upside-down image on the retina. The retina transforms the light into nerve signals for the brain. The brain then turns the image right-side up and tells you what you're seeing.

Hearing. Every sound you hear is the result of sound waves entering your ears and making your eardrums vibrate. These vibrations then move along the tiny bones of the middle ear and turn into nerve signals. The cortex then processes these signals, telling you what you're hearing.

Taste. The tongue contains small groups of sensory cells called taste buds that react to chemicals in foods. Taste buds react to sweet, sour, salty, bitter, and savory. The taste buds send messages to the areas in the cortex responsible for processing taste.

Smell. Olfactory cells in the mucous membranes lining each nostril react to chemicals you breathe in and send messages along specific nerves to the brain.

Touch. The skin contains millions of sensory receptors that gather information related to touch, pressure, temperature, and pain and send it to the brain for processing and reaction.

# data[].attributes.attachment_link.description
If the brain is a central computer that controls all the functions of the body, then the nervous system is like a network that relays messages back and forth to different parts of the body. Find out how they work in this Body Basics article.

# data[].attributes.body
Sign in with your s###### and password to see the animation, description, image and video clip related to the nervous system

# data[].attributes.attachment_link.readable_text
JavaScript is required. This web browser does not support JavaScript or JavaScript in this web browser is not enabled.

To find out if your web browser supports JavaScript or to enable JavaScript, see web browser help.

Type your SPPS Active Diretory username and password

Login to your SPPS Discovery Education Account. District Staff: need additional help, please contact the Service Desk.

Students: need additional help, please contact your teacher.

# data[].attributes.body
Sign in to DE with your s###### and password, to explore which functions are controlled by certain parts of the brain.

# data[].attributes.attachment_link.readable_text
JavaScript is required. This web browser does not support JavaScript or JavaScript in this web browser is not enabled.

To find out if your web browser supports JavaScript or to enable JavaScript, see web browser help.

Type your SPPS Active Diretory username and password

Login to your SPPS Discovery Education Account. District Staff: need additional help, please contact the Service Desk.

Students: need additional help, please contact your teacher.

# data[].attributes.body
Log in to Brainpop using either of these usernames/passwords:
--mybarra, ybarra
--255q, brainpop

# data[].attributes.attachment_link.description
peripheral diagram human body parts organs spinal human anatomy cord central autonomic

# data[].attributes.headline
(Image Search) Google--Nervous System vector logo

# data[].attributes.subject
(Image Search) Google--Nervous System vector logo

# data[].attributes.attachment_link.title
nervous system vector logo - Google Search

# data[].attributes.attachment_link.description
png central nervous diagram cns cartoon parasympathetic brain human nervous peripheral nervous anatomy

# data[].attributes.headline
(DE Exploration) The Brain and Your Nervous system

# data[].attributes.subject
(DE Exploration) The Brain and Your Nervous system

# data[].attributes.body
sign in to DE using your s###### and password to do this exploration activity about the things your brain controls.

# data[].attributes.attachment_link.readable_text
JavaScript is required. This web browser does not support JavaScript or JavaScript in this web browser is not enabled.

To find out if your web browser supports JavaScript or to enable JavaScript, see web browser help.

Type your SPPS Active Diretory username and password

Login to your SPPS Discovery Education Account. District Staff: need additional help, please contact the Service Desk.

Students: need additional help, please contact your teacher.

# data[].attributes.body
Play along with these activities that reveal the inner workings of your brain...

# data[].attributes.attachment_link.description
Messages from your brain travel along your nerves at up to 200 miles an hour! Play along with these clips from Brain Games, the National Geographic Channel show that messes with your mind and reveals the inner-workings of your brain.