The Nervous System
Lesson 9, Page 2 of 19

The sympathetic division of the autonomic nervous system is called upon to stimulate and prepare the body for emergency action, such as in the "fight or flight" response.

The Nerve Cell

The basic unit of the nervous system is the nerve cell, or neuron. The basic function of the neuron is to transmit information. There are approximately 28 billion neurons in the human body penetrating every tissue in every part. Neurons vary greatly in size and shape, with the longest ones—those that extend down the leg as part of the sciatic nerve—measuring over one meter. All nerve cells have a similar structure.


A basic nerve cell consists of a cell body, an axon, and many dendrites. Dendrites are thread-like branches that increase the surface area of the cell making it possible for it to receive many connections with adjoining nerve cells. Signals picked up by the dendrites travel through the cell and continue along the axon where they are transmitted to the next cell. Synaptic bulbs on the ends of the axons make connections with other nerve cells, with tiny gaps or synapses between the cells.

The gap between nerve cells, through which the nerve cells communicate with each other, is referred to as the __________.

synaptic bulb

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