Overview of the Nervous System
The nervous system is your body's information processing and communication system. It receives messages, processes information, and then sends signals to the rest of your body telling it what to do.
The nervous system is made up of the:
The nervous system is involved in everything you think, say, and do.
Your brain is like the central processing unit (CPU) in a computer
The brain receives information from your eyes, ears, nose, and other sense organs. It processes information and generates thoughts and ideas. Then the brain sends messages to your body. For example, it tells your muscles how to move so you can walk, talk, and do the things you want your body to do. Your brain also controls a lot of what your body does without you thinking about it. For example, your brain automatically adjusts your breathing, heart rate, and blood pressure.
Your spinal cord is a long tube of nerves like a thick electrical cable.
The spinal cord runs from your brain down your back through the hollow center of your spine. Nerves in the brain send messages down your spinal cord. Other nerves in your spinal cord then relay those messages to your body. The spinal cord also carries messages from the body to your brain.
Your nerves are like signal wires.
Each nerve contains fibers from many nerve cells. The fibers are bundled together for strength and protection from injury.
The central nervous system is the brain and spinal cord. The nerves outside the brain and spinal cord are called the peripheral nervous system.
Your nervous system is made of:
There are billions and billions of nerve cells in your brain, your spinal cord, and in clumps just outside your spinal cord.
Each nerve cell has a microscopic body:
Each nerve cell has fibers going to and from it:
Sometimes nerve fibers are dozens of centimeters long. For example, a single nerve fiber may run from near your spinal cord all the way to your toe. Some nerve fibers that go to your skin or your organs have sensory receptors. For example, the receptors at the end of nerve fibers in your skin detect things that are sharp or hot.
Although nerve fibers and their signals act a lot like a wire carrying electrical signals, that's not exactly right. Nerve cells really send their signals using chemicals.
Chemical changes take place progressively along the length of a nerve fiber
When the chemical changes reach the end of the nerve fiber, they release other chemicals called neurotransmitters
The neurotransmitters drift across a microscopic gap where they hit the chemical receptors of another cell
The neurotransmitters trigger chemical changes in that other cell
If that cell is a nerve cell, then the progressive chemical changes continue down the fibers of that cell to pass the signal along
Other times the next cell is not a nerve cell—for example, if the next cell is a muscle cell, then the neurotransmitter causes chemical changes that make the muscle cell contract
One nerve cell sends just one kind of signal that can't carry a lot of information. However, when billions of nerve cells are interconnected like they are in your brain, they form a very powerful information processor.
Many problems can affect your nervous system, including:
Injuries that destroy nerve cells or cut nerves
Blockage or rupture of blood vessels that feed the nervous system, causing a stroke
Once nerve cells in your brain or spinal cord die, they can't grow back. However, nerve fibers sometimes can grow back if their cell body isn't hurt. It can take months for nerve fibers to grow back. Doctors sometimes can sew smaller nerves back together and get them to work again. Doctors can't repair the spinal cord or the brain.
As people get older, they have fewer nerve cells in their brain. It's harder for your body to make new nerve cells and fix damaged ones. Compared to younger people, older people are more likely to have:
The following may help keep your brain sharp longer: