What is a nervous system?

Your nervous system is an interconected network of nerve cell,or neurons, that coordinates your actions.
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t senses the environment and helps you react to external stimuli by thinkng, moving, and speaking. Your nervous system also regulates your internal, involuntary function, such as breathing and heart rate.

All nerve pass information from one part of your body to another. To perform this function, some of the nerve cells are enlongate so that they can connet all parts of your body.
Simpler organisms have more elementary nervous system. A simple animal such as a jellyfish, with a limited range of actions, possesses a nervous system that operates almost entirely by means of simple reflex (see below).

Through such a system, the jellyfish is able to avoid danger, such as a poisonous subtance, or move toward desirable objects, such as food.

More advance animals developed the ability to learn from prvious experience. Because the simple reflexis too basic for this puspose, it must be augmented by an entire network of nerve cells that can analyze information from many sources, store the data, and coordinate the organism's responses.