Learn About The Nervous System

The nervous system is a very complex system in the body. It has many, many parts. The nervous system is divided into two main systems, the central nervous system (CNS) and the peripheral nervous system.

The spinal cord and the brain make up the CNS. Its main job is to get the information from the body and send out instructions. The peripheral nervous system is made up of all of the nerves and the wiring. This system sends the messages from the brain to the rest of the body.

Neurons
The cells that make up the nervous system are called neurons. Long, stringy neurons are perfect for carrying the electrical messages that are the "language" of the nervous system.
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Brain
The brain is the command center of your entire body. The brain is the body's main information center. It is made of billions of neurons. The brain helps the body respond to the information it receives from the senses. The brain also processes thoughts. When you think, neurons in your brain are working.
The brain has three main parts. The largest is the cerebrum, which controls vision, touch, and other senses. It also handles movements you have control over. Thinking takes place in the cerebrum. The cerebellum is another section of the brain. The cerebellum helps control balance and coordination. Another part of the brain is called the brain stem. The brain stem is the link to the spinal cord and it also controls digestion, breathing, and heartbeat.
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Spinal Cord
The spinal cord is a tube of neurons that runs up the spine and attaches to the brain stem. Information from nerves that branch out to the rest of the body goes to the spinal cord. Some messages are processed by the spinal cord but most information is sent on to the brain.
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A neuron is a nerve cell. The brain is made up of approximately 100 billion neurons.

Neurons are similar to other cells in the body in some ways such as:

* Neurons are surrounded by a membrane.
* Neurons have a nucleus that contains genes.
* Neurons contain cytoplasm, mitochondria and other "organelles".

However, neurons differ from other cells in the body in some ways such as:

* Neurons have specialized projections called dendrites and axons. Dendrites bring information to the cell body and axons take information away from thecell body.
* Neurons communicate with each other through an electrochemical process.
* Neurons form specialized connections called "synapses" and produce special chemicals called "neurotransmitters" that are released at the synapse.

There are approximately 1 quadrillion synapses in the human brain. That's 1,000,000,000,000,000 synapses! This is equal to about a half-billion synapses per cubic millimeter. (Statistic from Changeux, J-P. and Ricoeur, P., What Makes Us Think?, Princeton: Princeton University Press, 2000, p. 78)

The adult human brain weighs about 3 pounds (1,300-1,400 g).

The adult human brain is about 2% of the total body weight.

The elephant brain weighs about 6,000 g.

The cat brain weighs about 30 g.

The average human brain is 140 mm wide.

The average human brain is 167 mm long.

The average human brain is 93 mm high.

The human brain has about 100,000,000,000 (100 billion) neurons.

The octopus brain has about 300 million neurons.

The total surface area of the cerebral cortex is about 2500 sq. cm (~2.5 ft2)

The spinal cord is the main pathway for information connecting the brain and peripheral nervous system.

The human spinal cord is protected by the bony spinal column shown to the left. The spinal column is made up of bones called vertebrae. Although the spinal column is somewhat flexible, some of the vertebrae in the lower parts of the spinal column become fused.

The Brain: Our Nervous System [Paperback]