Main->Readings->5th Grade Readings->Control Systems ->Part 1
Vocabulary |
A sponge does not have a brain. It has no nerves. It does not need them. A sponge sits stuck to a rock at the bottom of the ocean, and it does not have to move or think.
Like most vertebrate animals, however, a human being has a brain and many nerves. In fact, its brain is enormous for its body size. A human brain weighs around 3 pounds in an adult, has over 100 billion nerve cells in it, and is incredibly complicated. Why does a human being need a brain that big, when a sponge needs nothing at all?
People need brains, not just in order to think about things, but in order to see, feel, hear, taste, and smell. They need brains in order to sneeze and scratch. They need brains so they can walk, talk, eat, and sleep, and so they can balance, imagine, and remember. Humans also need nerves running through their bodies so they can send messages to and from their brains, and so they can adapt to the world outside.
There are many other jobs the human brain does, and neuroscientists are discovering new things all the time. A neuroscientist is a scientist who studies the brain and nerves.
The brain, spinal cord, and nerves are the organs of the nervous system. Like other organ systems, the nervous system organs are made of special tissues, and the tissues are made of special cells. One main type of cell in the nervous system is the neuron. The neuron is a cell that can receive and send messages, using very small amounts of chemicals and electricity. Neurons come in many different shapes and sizes, but they are alike in some important ways.
Like other cells, neurons have a cell body (with a nucleus and other normal parts of the cell). More importantly, they have branches coming out of them. Some of these branches are called dendrites. Dendrites get messages from other neurons. Other branches, long and thin, are called axons. Axons send messages to other neurons. Although neurons are tiny and axons are thin, one axon can be very long. For instance, an axon can reach from your spinal cord down to your toe. Most neurons are found in bundles, and a bundle of nerve cells is called a nerve.
The nervous system has two main parts. One is made of the nerves which extend throughout the body (it is called the peripheral (purr-IF-uhr-uhl) nervous system). The other main part is the brain and spinal cord (known as the central (SEN-truhl) nervous system).
The spinal cord goes down the back from the brain, passing through holes in the center of the vertebrae so it is protected from damage. It carries messages to and from the brain and the peripheral nervous system. Even though a message might have to travel from the brain to the tip of your finger and back again, it travels very fast. Nerves work very quickly, so quickly that you do not notice how long it takes.
The biggest part of the central nervous system is the brain, and it has three main parts. Each part has many jobs.
The brainstem is at the base of the brain, and it connects the brain to the spinal cord. It is the smallest part of the brain, but the jobs it does are very important. It automatically controls heartbeat, breathing, and digestion, so that a human being can stay alive while the other parts of the brain are working on other jobs. It also controls coughing, sneezing, vomiting, and swallowing, which are handy things to be able to do in an emergency.
The cerebellum, which is a larger part to the back of the brain stem, is also very important. It controls movement, balance, and coordination. When you learn to do something like walk, write with a pencil, or kick a ball, the cerebellum is what helps you learn.
The cerebrum is the biggest part of your brain. Without the cerebrum you wouldn't be able to talk, reason, feel, or move. Every part of the cerebrum has a special job, and neuroscientists keep finding more jobs, but all the parts of the brain work together.
For instance, seeing is a complicated thing. One part of the brain, when signals from the eyes reach it, "sees" horizontal lines, while another part sees vertical ones. Other parts see color, or size, or shape, or movement. The brain puts all this information together, and it does it so fast you think it happens right away.
One of the weirdest things about the brain is that it has a right half and a left half. If you look at a brain you can see a line going right down the center, dividing the two halves. The left and right sides of the brain are connected by a thick bundle of nerve fibers, called the corpus callosum, (COR-pus cal-LO-sum) but each side of the brain has its own special jobs.
The left side of the brain controls the right side of your body. If you raise your right hand, it's the left side of your brain sending the signal. To even things out, the right side of your brain controls the left side.
Another difference between the sides of the brain is that most of the time, the left side controls language, math, and logic, while the right side controls spatial abilities, face recognition, visual imagery, and parts of music. Sometimes we think of the left side as the logical, or thinking, side while the right side is the intuitive, or feeling side, but it is a lot more complicated than that.
The study of the nervous system is fascinating and strange, and the more you think about your own brain the stranger it seems.
Go on to Part 2: Acting and Reacting
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This page last updated on May 8, 2003