In Short

The nervous system of multicelled, vertebrate animals is very sophisticated and is able to respond to many external and internal stimuli. The functional unit of the nervous system is the neuron, a cell with structures specialized in transmitting electrical impulses. A neuron must be able to receive information from internal or external sources, integrate the signal (especially if from multiple sources), send that signal to other parts of the body, and then deliver that message to another neuron, gland, or muscle. The electrical signal produced in the neuron, which travels down the axon, does not actually cross the tiny synaptic space between neurons (or their target organs). The nervous system relies upon chemical messengers called neurotransmitters to cross the gap. The vertebrate nervous system is divided into two major parts, the central nervous system and the peripheral nervous system.

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