Glia: The Forgotten Brain Cell

The brain is made up of more than just nerve cells (neurons). Although there are about 100 billion neurons in the brain, there are about 10 to 50 times that many glial cells in the brain. But do you hear much about glia? NO! Because neurons get all the attention, you don't hear too much about glia. Although glia cells DO NOT carry nerve impulses (action potentials) they do have many important functions. In fact, without glia, the neurons would not work properly!

Types and Functions of Glia

• Astrocyte (Astroglia): Star-shaped cells that provide physical and nutritional support for neurons: 1) clean up brain "debris"; 2) transport nutrients to neurons; 3) hold neurons in place; 4) digest parts of dead neurons; 5) regulate content of extracellular space
• Microglia: Like astrocytes, microglia digest parts of dead neurons.
• Oligodendroglia: Provide the insulation (myelin) to neurons in the central nervous system.
• Satellite Cells: Physical support to neurons in the peripheral nervous system.
• Schwann Cells: Provide the insulation (myelin) to neurons in the peripheral nervous system.

There are a few ways in which glia cells are different from neurons:

1. Neurons have TWO "processes" called axons and dendrites....glial cells have only ONE.
2. Neurons CAN generate action potentials...glial cells CANNOT. However, glial cells do have a resting potential.
3. Neurons HAVE synapses that use neurotransmitters...glial cells do NOT have chemical synapses.
4. There are many MORE (10-50 times more) glial cells in the brain compared to the number of neurons.

Hear It!

"Astrocyte" | "Glia" | "Microglia" "Neuron" | "Oligodendroglia" | "Schwann cells"

More information about glia:

• Astrocytes and Neurogenesis - from Neuroscience for Kids
• Lowly glia strengthens brain cells
• Microglia Home Page
• New Knowledge of Neural Neighbors

Do We Use Only 10% of Our Brains?

Let me state this very clearly:

There is no scientific evidence to suggest that we use only 10% of our brains.

In other words, the statement, "We use only 10% of our brains" is false; it's a myth. We use all of our brain. Let's look at the possible origins of this myth and the evidence that we use all of our brain.

Where Did the 10% Myth Begin?

The 10% statement may have been started with a misquote of Albert Einstein or the misinterpretation of the work of Pierre Flourens in the 1800s. It may have been William James who wrote in 1908: "We are making use of only a small part of our possible mental and physical resources" (from The Energies of Men, p. 12).

Perhaps it was the work of Karl Lashley in the 1920s and 1930s that started it. Lashley removed large areas of the cerebral cortex in rats and found that these animals could still relearn specific tasks. We now know that destruction of even small areas of the human brain can have devastating effects on behavior. That is one reason why neurosurgeons must carefully map the brain before removing brain tissue during operations for epilepsy or brain tumors: they want to make sure that essential areas of the brain are not damaged.

Why Does the Myth Continue? Somehow, somewhere, someone started this myth and the popular media keep on repeating this false statement (see the figures). Soon, everyone believes the statement regardless of the evidence. I have not been able to track down the exact source of this myth, and I have never seen any scientific data to support it. According to the believers of this myth, if we used more of our brain, then we could perform super memory feats and have other fantastic mental abilities - maybe we could even move objects with a single thought. Again, I do not know of any data that would support any of this. What Does it Mean to Use Only 10% of Your Brain? What data were used to come up with the number - 10%? Does this mean that you would be just fine if 90% of your brain was removed? If the average human brain weighs 1,400 grams (about 3 lb) and 90% of it was removed, that would leave 140 grams (about 0.3 lb) of brain tissue. That's about the size of a sheep's brain. It is well known that damage to a relatively small area of the brain, such as that caused by a stroke, may cause devastating disabilities. Certain neurological disorders, such as Parkinson's Disease, also affect only specific areas of the brain. The damage caused by these conditions is far less than damage to 90% of the brain. Sheep Brain

The Evidence (or lack of it)

Perhaps when people use the 10% brain statement, they mean that only one out of every ten nerve cells is essential or used at any one time? How would such a measurement be made? Even if neurons are not firing action potentials, they may still be receiving signals from other neurons.

Furthermore, from an evolutionary point of view, it is unlikely that larger brains would have developed if there was not an advantage. Certainly there are several pathways that serve similar functions. For example, there are several central pathways that are used for vision. This concept is called "redundancy" and is found throughout the nervous system. Multiple pathways for the same function may be a type of safety mechanism should one of the pathways fail. Still, functional brain imaging studies show that all parts of the brain function. Even during sleep, the brain is active. The brain is still being "used," it is just in a different active state.

Finally, the saying "Use it or Lose It" seems to apply to the nervous system. During development many new synapses are formed. In fact, some synapses are eliminated later on in development. This period of synaptic development and elimination goes on to "fine tune" the wiring of the nervous system. Many studies have shown that if the input to a particular neural system is eliminated, then neurons in this system will not function properly. This has been shown quite dramatically in the visual system: complete loss of vision will occur if visual information is prevented from stimulating the eyes (and brain) early in development. It seems reasonable to suggest that if 90% of the brain was not used, then many neural pathways would degenerate. However, this does not seem to be the case. On the other hand, the brains of young children are quite adaptable. The function of a damaged brain area in a young brain can be taken over by remaining brain tissue. There are incredible examples of such recovery in young children who have had large portions of their brains removed to control seizures. Such miraculous recovery after extensive brain surgery is very unusual in adults.

So next time you hear someone say that they only use 10% of their brain, you can set them straight. Tell them:

"NOT TRUE; We use 100% of our brains."

If you find any news articles or advertisements using the 10% myth, please send them to me: Dr. Eric H. Chudler.

For a continuing discussion of this topic, please see:

1. Ten Percent and Counting - BrainConnection.com
2. The Ten-Percent Myth from the Skeptical Inquirer
3. The Ten-Percent Myth
4. Do People Use 10 Percent of Their Brains? - Scientific American
5. Humans use 100 percent of their brains--despite the popular myth - Ask a Scientist
6. Higbee, K.L. and Clay, S.L., College students' beliefs in the ten-percent myth, Journal of Psychology, 132:469-476, 1998.
7. B.L. Beyerstein, Whence Cometh the Myth that We Only Use 10% of Our Brains? in Mind Myths. Exploring Popular Assumptions about the Mind and Brain edited by S. Della Sala, Chichester: John Wiley and Sons, pages 3-24, 1999. This chapter is required reading for anyone who wants more information on the 10% myth.

Did you know?

Dr. James W. Kalat, author of the textbook Biological Psychology, has another idea for the origin of the 10% myth. Dr. Kalat points out that neuroscientists in the 1930s knew about the existence of the large number of "local" neurons in the brain, but the only thing they knew about these cells is that they were small. The misunderstanding of the function of local neurons may have led to the 10% myth. (Reference: Kalat, J.W., Biological Psychology, sixth edition, Pacific Grove: Brooks/Cole Publishing Co., 1998, p. 43.)

They said it!

"Myths which are believed in tend to become true..." --- George Orwell (in The Collected Essays, Journalism, and Letters of George Orwell, vol. 3, edited by Sonia Orwell and Ian Angus, New York: Harcourt Brace Jovanovich, 1968, page 6.) "In fact, most of us use only about 10 percent of our brains, if that." --- Uri Geller (in Uri Geller's Mindpower Kit, New York: Penguin Books, 1996.)

The Nervous System in Old Age

In the last 100 years, there has been a dramatic increase in the population of elderly (age 65 years and older) people. As shown in the graph, elderly people in the US made up only 4.1% of the population in 1900, but 8.1% in 1950 and 12.8% in 1995. By 2050, it is estimated that 20% of the population will be 65 years old or older. This increase in the elderly population and the high incidence of age-related neurological disorders make it important to understand how the human brain ages.

Data from Malmgren, R., in Textbook of Geriatric Neuropsychiatry, 2000.

To investigate the changes that the brain undergoes during aging, neuroscientists use brain imaging methods to observe the anatomy and physiology of the living brain. Scientists can also study autopsy specimens to investigate how the brain changes over time.

Brain Changes

• Enlargement of the ventricular system: as people get older, the volume of the ventricles (the spaces in the brain that contain cerebrospinal fluid) increases. It is thought that this enlargement occurs because cells surrounding the ventricles are lost.
• Widening of sulci (the grooves) on the surface of the brain.
• Reduced brain weight and brain volume: these changes are probably caused by the loss of neurons. Reductions in the size of many areas of the cerebral cortex have been reported.
• Neurological disorders: brain disorders such as Alzheimer's disease, Parkinson's disease and stroke are more common in the elderly.

Changes in the Senses

Vision

• Lens: proteins in the lens change with age and the elasticity of the lens is reduced. Therefore, many elderly individuals have trouble focusing their eyes. Exposure to ultraviolet light can also yellow the lens. Changes in the lens may affect color vision.
• Cornea: the cornea may become less transparent and more flat. This may cause images to appear distorted or blurred. There may also be a loss of color sensitivity to green, blue and violet shades.
• Pupil: changes in the autonomic nervous system alter the ability of older people to dilate the pupil. By age 70, the pupil may not dilate easily in low lighting conditions (Hampton, 1997).
• Cataracts: cloudy areas of the lens. Cataracts decrease the amount of light that passes through the lens and can bend light abnormally. The National Eye Institute estimates that more than 50% of Americans age 65 years and olderhave a cataract.
• Retina: the peripheral retina is thinner and contains fewer rods in older individuals.
• Other disorders of the eye common in the elderly: glaucoma, macular degeneration, presbyopia.

Olfaction

• Changes in the nasal mucosa, cribriform plate and air passages may contribute to impaired odor recognition.
• The amygdala and other brain areas involved with smell may be damaged in older individuals.

Taste

Impairment in the ability to taste may be caused by:

• Medications that the elderly need.
• Reductions in the number of taste buds.
• Dentures that cover taste buds on the soft palate.

Audition

Hearing loss in the elderly may result from:

• Ear wax build up.
• Stiffening of the tympanic membrane (eardrum).
• Atrophy of small ear muscles.
• Degeneration of hair cells and support cells in the cochlea.
• Stiffening of basilar membrane.
• Loss of nerve fibers leading from the cochlea to the brain.
• Loss of neurons in auditory areas of the brain.

Touch

Age-related changes in the ability to perceive tactile stimuli may be due to:

• Loss of various receptors (for example, Meissner's and Pacinian corpuscles) in the skin.
• Reductions in the number of sensory fibers innervating the skin.

For more information on the aging nervous system, see:

1. The American Psychiatric Press Textbook of Geriatric Neuropsychiatry, edited by C. E. Coffey, J. L. Cummings, Washington, DC: American Psychiatric Press, 2000.
2. Hampton, J.K., Craven, R.F., and Heitkemper, M.M. The Biology of Human Aging, Dubuque: Wm. C. Brown, 1997.
3. Hooper, C.R., Sensory and sensory integrative development, in Functional Performance in Older Adults, edited by B.R. Bonder and M.B. Wagner, Philadelphia: F.A. Davis Company, 2001, pp. 121-136.

Brain Development

The brain grows at an amazing rate during development. At times during brain development, 250,000 neurons are added every minute! At birth, almost all the neurons that the brain will ever have are present. However, the brain continues to grow for a few years after birth. By the age of 2 years old, the brain is about 80% of the adult size.

You may wonder, "How does the brain continue to grow, if the brain has most of the neurons it will get when you are born?". The answer is in glial cells. Glia continues to divide and multiply. Glia carries out many important functions for normal brain function including insulating nerve cells with myelin. The neurons in the brain also make many new connections after birth.

The Brain During Development

The nervous system develops from embryonic tissue called the ectoderm. The first sign of the developing nervous system is the neural plate that can be seen at about the 16th day of development. Over the next few days, a "trench" is formed in the neural plate - this creates a neural groove. By the 21st day of development, a neural tube is formed when the edges of the neural groove meet. The rostral (front) part of the neural tubes goes on to develop into the brain and the rest of the neural tube develops into the spinal cord. Neural crest cells become the peripheral nervous system.

At the front end of the neural tube, three major brain areas are formed: the prosencephalon (forebrain), mesencepalon (midbrain) and rhombencephalon (hindbrain). By the 7th week of development, these three areas divide again. This process is called encephalization.

Average brain weights (BW)

AGE          BW - Male (grams)   BW - Female (grams)
--------     -----------------   -----------------
Newborn           380                  360    
1 year            970                  940
2 years         1,120                1,040
3 years         1,270                1,090
10-12 years     1,440                1,260
19-21 years     1,450                1,310
56-60 years     1,370                1,250
81-85 years     1,310                1,170

(Data from Dekaban, A.S. and Sadowsky, D., Changes in brain weights during the span of human life: relation of brain weights to body heights and body weights, Ann. Neurology, 4:345-356, 1978)

Brain Weight

The top graph on the left shows the brain weights of males and females at different ages. The bottom graph shows the brain weight to total body weight ratio (expressed as a percentage). The adult brain makes up about 2% of the total body weight.
(Data from Dekaban, A.S. and Sadowsky, D., Changes in brain weights during the span of human life: relation of brain weights to body heights and body weights, Ann. Neurology, 4:345-356, 1978)

DID YOU KNOW? Touch is the first sense to develop. The developing fetus responds to touch of the lips and cheeks by 8 weeks and to other parts of its body at 14 week. The sense of taste may develop by 12 weeks and that of sound at 22-24 weeks. (Reference: Hepper, P., "Unraveling our beginnings", The Psychologist, 18:474-477, 2005.)

More about Brain Development

• The Teen Brain - Online Newshour (October 13, 2004)
• Embryological Development of the Human Brain
• Secret Life of the Brain - a PBS special exploring the brain from birth to old age
• Child Development Articles - from BrainConnection.com
• Development and Neurobiology Column
• The TEEN Brain - articles from US News and World Report (August 9, 1999).
• Inside the Teenage Brain - PBS
• Zero to Three - BrainWonders
• The brain during old age

A Computer in Your Head?

Eric H. Chudler, Ph.D.

Originally published in ODYSSEY magazine, 10:6-7, 2001 (March), Cobblestone Publishing Co.

What has billions of individual pieces, trillions of connections, weighs about 1.4 kilograms, and works on electrochemical energy? If you guessed a minicomputer, you're wrong. If you guessed the human brain, you're correct! The human brain: a mass of white-pink tissue that allows you to ride a bike, read a book, laugh at a joke, and remember your friend's phone number. And that's just for starters. Your brain controls your emotions, appetite, sleep, heart rate, and breathing. Your brain is who you are and everything you will be.

The amazing brain has been compared to many different objects and devices -- from a spider web to a clock to a telephone switchboard. Nowadays, people like to compare it to a computer. Is your brain really like the metal box that hums on your desk? Let's look at the similarities and differences between the two.

Going to the Source

Computers and brains both need energy. Plug your computer into the wall, push a button, and it will get the power it needs to run. Pull the plug and it will shut down. Your brain operates in a different way. It gets its energy in the form of glucose from the food you eat. Your diet also provides essential materials, such as vitamins and minerals, for proper brain function. Unlike a computer, your brain has no off switch. Even when you are asleep, your brain is active.

Although computers and brains are powered by different types of energy, they both use electrical signals to transmit information. Computers send electrical signals through wires to control devices. (Your brain also sends electrical signals, but it sends them through nerve cells, called neurons. Signals in neurons transfer information to other neurons and control glands, organs, or muscles.

There are fundamental differences in the way information is transferred through electrical circuits in a computer and through nerve cells in your brain. When a computer is turned on, electrical signals either reach parts of the machine or they do not. In other words, the computer uses switches that are either on or off. In the nervous system, neurons are more than just on or off. An individual neuron may receive information from thousands of other neurons. The region where information is transferred from one neuron to another is called the synapse. A small gap between neurons is located at the synapse. When information is transferred from one neuron to another, molecules of chemicals ("neurotransmitters") are released from the end of one neuron. The neurotransmitters travel across the gap to reach a receiving neuron where they attach to special structures called receptors. This results in a small electrical response within the receiving neuron. However, this small response does not mean that the message will continue. Remember, the receiving neuron may be getting thousands of small signals at many synapses. Only when the total signal from all of these synapses exceeds a certain level will a large signal (an "action potential") be generated and the message continue.

Form. . .and Function

Despite the differences in the way messages are sent through wires and neurons, computers and brains perform many similar functions. For example, both can store memories -- computers do it on chips, disks, and CD-ROMs, and brains use neuronal circuits throughout the brain. Both computers and brains can be modified to perform new tasks. New hardware and software can be installed in computers to add additional memory and programs. The brain undergoes continual modification and can learn new things. The brain can sometimes rewire itself when necessary! For example, after some kinds of brain injuries, undamaged brain tissue can take over functions previously performed by the injured area. I'd like to see a computer rewire itself after its hard drive failed!

Computers and brains both have the ability to monitor their surroundings and respond with behavior to manipulate their environment. Sensors attached to computers can sample temperature, humidity and light levels. Computers can be programmed to control heaters, lights, and other equipment in response to the information they receive. Your brain is also connected to sensors or receptors in your eyes, ears, nose, mouth, and skin. Your brain may respond to sensory information automatically (such as causing your body to shiver when it is very cold), or it may cause you to alter your behavior. For example, if a room is too cold, your brain might send signals to muscles to get you to move to a warmer place or to put on a sweater.

The delicate contents inside your computer are protected by a hard cover. Your skull provides a similar function for your brain. Nevertheless, the external and internal components of computers and brains are all susceptible to damage. If you drop your computer, infect it with a virus, or leave it on during a huge power surge, your precious machine will likely be on its way to the repair shop. When damaged parts are replaced or the virus-caused damage is removed, your computer should be as good as new. Unfortunately, brains are not as easy to repair. They are fragile and there are no replacement parts to fix damaged brain tissue. However, hope is on the horizon for people with brain damage and neurological disorders as scientists investigate ways to transplant nerve cells and repair injured brains.

The BIG Difference

No doubt the biggest difference between a computer and your brain is consciousness. Although it may be difficult for you to describe consciousness, you know you are here. Computers do not have such awareness. Although computers can perform extraordinary computational feats at astounding speeds, they do not experience the emotions, dreams, and thoughts that are an essential part of what makes us human. At least not yet! Current research in artificial intelligence is moving toward developing emotional capabilities in computers and robots. (See the January 2001 ODYSSEY issue for more on this.)

During the month of March, people around the world will be celebrating Brain Awareness Week (BAW). During BAW, students, teachers, and scientists around the country will be using their brains to share knowledge about the most wonderful, complicated, mysterious structure in the universe. So get your brain in gear and read this issue of ODYSSEY. It's a great way to begin.

Dr. Eric H. Chudler is consulting editor for this issue.

Brain’s ‘filing system’ may affect forgetfulness

Aging isn't necessarily to blame for memory lapses

Age is not entirely to blame for forgetfulness.

The reason that some people are absentminded and others have minds like a steel trap might have more to do with how the brain files memories and makes room for new ones, new research suggests.

The overstuffed file system that collects daily to-do’s while keeping track of childhood memories has remained an enigma, especially regarding the mechanism for such mega-bit storage amidst the deluge of incoming bytes.

Every minute, sensory data enters your brain in the form of electrical signals that jet from neuron to neuron via intersections called synapses. Scientists think memories form when this communication between brain cells increases.

Keep it quiet
In order to seal in a memory, chatter amongst bystander neurons needs to quiet down. Referred to as long-term depression (LTD), the process is akin to shushing cubicle mates so you can better hear a phone conversation.

"This is a normal process that helps with the sculpting of memory," said Thomas Foster of the McKnight Brain Institute of the University of Florida. "After all, we do not remember everything in perfect detail and we would not want to."

Foster and his colleagues trained aged and young rats to find a hidden platform and climb out of a pool of water, a task the rats learned quickly. They noted which rats showed superior memory and which had sluggish recall.

Then, the researchers anesthetized the rats and applied a weak electrical signal to their synapses to make them less sensitive and to depress cell-to-cell communication. Both old and young rats with the highest memory scores were more resistant to the electrical interference than the other rats.

The aged animals that showed impaired memories prior to analysis were much more susceptible to the electrical signals and had excessive long-term depression. In human terms, not only would your co-workers get quieter, the caller would too.

"When we see someone we know or perhaps even ourselves becoming more forgetful, we now know that this is not an inevitable process," Foster said.

In excess, the memory-boosting process can actually lead to forgetfulness as too many brain-cell links get weakened or quieted, as is seen during brain aging, the scientists suggest in their study report published this month’s online edition of the journal Neurobiology of Learning and Memory.

Further studies of how memory works could help scientists find ways to postpone or alleviate age-related forgetfulness, Foster said.

Brain Structures and their Functions

The nervous system is your body's decision and communication center. The central nervous system (CNS) is made of the brain and the spinal cord and the peripheral nervous system (PNS) is made of nerves. Together they control every part of your daily life, from breathing and blinking to helping you memorize facts for a test. Nerves reach from your brain to your face, ears, eyes, nose, and spinal cord... and from the spinal cord to the rest of your body. Sensory nerves gather information from the environment, send that info to the spinal cord, which then speed the message to the brain. The brain then makes sense of that message and fires off a response. Motor neurons deliver the instructions from the brain to the rest of your body. The spinal cord, made of a bundle of nerves running up and down the spine, is similar to a superhighway, speeding messages to and from the brain at every second.

The brain is made of three main parts: the forebrain, midbrain, and hindbrain. The forebrain consists of the cerebrum, thalamus, and hypothalamus (part of the limbic system). The midbrain consists of the tectum and tegmentum. The hindbrain is made of the cerebellum, pons and medulla. Often the midbrain, pons, and medulla are referred to together as the brainstem.

The Cerebrum:The cerebrum or cortex is the largest part of the human brain, associated with higher brain function such as thought and action. The cerebral cortex is divided into four sections, called "lobes": the frontal lobe, parietal lobe, occipital lobe, and temporal lobe. Here is a visual representation of the cortex:

What do each of these lobes do?

• Frontal Lobe- associated with reasoning, planning, parts of speech, movement, emotions, and problem solving
• Parietal Lobe- associated with movement, orientation, recognition, perception of stimuli
• Occipital Lobe- associated with visual processing
• Temporal Lobe- associated with perception and recognition of auditory stimuli, memory, and speech

Note that the cerebral cortex is highly wrinkled. Essentially this makes the brain more efficient, because it can increase the surface area of the brain and the amount of neurons within it. We will discuss the relevance of the degree of cortical folding (or gyrencephalization) later. (Go here for more information about cortical folding)

A deep furrow divides the cerebrum into two halves, known as the left and right hemispheres. The two hemispheres look mostly symmetrical yet it has been shown that each side functions slightly different than the other. Sometimes the right hemisphere is associated with creativity and the left hemispheres is associated with logic abilities. The corpus callosum is a bundle of axons which connects these two hemispheres.

Nerve cells make up the gray surface of the cerebrum which is a little thicker than your thumb. White nerve fibers underneath carry signals between the nerve cells and other parts of the brain and body.

The neocortex occupies the bulk of the cerebrum. This is a six-layered structure of the cerebral cortex which is only found in mammals. It is thought that the neocortex is a recently evolved structure, and is associated with "higher" information processing by more fully evolved animals (such as humans, primates, dolphins, etc). For more information about the neocortex, click here.

The Cerebellum: The cerebellum, or "little brain", is similar to the cerebrum in that it has two hemispheres and has a highly folded surface or cortex. This structure is associated with regulation and coordination of movement, posture, and balance.

The cerebellum is assumed to be much older than the cerebrum, evolutionarily. What do I mean by this? In other words, animals which scientists assume to have evolved prior to humans, for example reptiles, do have developed cerebellums. However, reptiles do not have neocortex. Go here for more discussion of the neocortex or go to the following web site for a more detailed look at evolution of brain structures and intelligence: "Ask the Experts": Evolution and Intelligence

Limbic System: The limbic system, often referred to as the "emotional brain", is found buried within the cerebrum. Like the cerebellum, evolutionarily the structure is rather old.

This system contains the thalamus, hypothalamus, amygdala, and hippocampus. Here is a visual representation of this system, from a midsagittal view of the human brain:

Click on the words to learn what these structures do:

• Thalamus
• Hypothalamus
• Amygdala
• Hippocampus

Brain Stem: Underneath the limbic system is the brain stem. This structure is responsible for basic vital life functions such as breathing, heartbeat, and blood pressure. Scientists say that this is the "simplest" part of human brains because animals' entire brains, such as reptiles (who appear early on the evolutionary scale) resemble our brain stem. Look at a good example of this here.

The brain stem is made of the midbrain, pons, and medulla. Click on the words to learn what these structures do:

• Midbrain
• Pons
• Medulla

Brain

You're in the middle of a meeting at work, but your mind keeps drifting to the parent-teacher conference you have tonight ... and the car you have to pick up at the shop on the way home ... and how you wish you hadn't skipped lunch because the rumbling in your stomach is driving you nuts. Then, suddenly, you're back in the moment, hoping nobody noticed your brief "departure."

It may seem as if your brain is always on the go. And it is. The brain not only controls what you think and feel, how you learn and remember, and the way you move and talk, but also many things you're less aware of — such as the beating of your heart, the digestion of your food, and yes, even the amount of stress you feel. Like you, your brain is quite the juggler.

Anatomy of the Nervous System

If you think of the brain as a central computer that controls all bodily functions, then 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 and 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 accidentally 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 takes a lot less time than it just took to read about it.

Considering everything it does, the human brain is incredibly compact, weighing just 3 pounds. Its many folds and grooves, though, provide it with the additional surface area necessary for storing all of the body's important information.

The spinal cord, on the other hand, is a long bundle of nerve tissue about 18 inches long and ¾ inch thick. It extends from the lower part of the brain down through spine. Along the way, various nerves branch out to the entire body. These are called the peripheral nervous system.

Both 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 as well as a special fluid called cerebrospinal fluid. This fluid helps protect the nerve tissue, keep it healthy, and remove waste products.

The arrival of mind reading.

Scientists in Germany used pattern recognition software to predict, from functional magnetic resonance imaging of people's brains, whether each person had secretly decided to add or subtract two numbers he was looking at. The computer correctly predicted the decision 71 percent of the time. The advertised application of this technology is computers that can discern and execute your will when you want them to—for example, if you're paralyzed or don't want to use a mouse. The feared application is mental surveillance.