The nervous system of higher vertebrates including humans is a widely distributed communication and processing network that serves controlling functions over other organ systems, possesses a key function in the orientation of the individual, controls its behaviour, motor function, sensory processing and contains mechanisms to store information.
The structural unit of nervous system are neurons. Neuron is a kind of cell that specialises in conducting electric signals between portions of the body. All neurons have a body called a Soma. The Soma contains the nucleus and all of the other organelles that are needed to keep the cell alive and functioning. Neurons also have directionality to them. On one side of the neuron are the dendrites. You can think of this side as being the 'input' side. The dendrites are branching structures which connect with the outputs of other neurons. They typically spread over a wide area in the immediate vicinity of the neuron. This allows the neuron to get inputs from a number of different synapses. The other end is the 'output'. It contains an axon and ends in a number of synapses which usually connect to the dendrites of other neurons or are connected directly to muscles. The axon is usually quite long compared to the rest of the neuron. In fact, you have some neurons with axons that extend the entire length of the body.
A classification of the nervous system can be performed under different aspects, of which the anatomical compartmentalization of its components defines the classical approach. Two major divisions of nervous can be described:
1. The central nervous system (CNS) 2. The peripheral nervous system (PNS).
Another approach is based on the functional compartmentalization between somatic and Autonomic autonomic parts of the nervous system. Both CNS and PNS comprise somatic and autonomic components. The autonomic nervous system consists of sympathetic and parasympathetic systems.
The neurons exist in all compartmentalization of the nervous system.
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