The structural and functional unit of nervous system is neuron. Neurons are long, thin delicate cells. A single neuron may extend from the spinal cord of man to the foot. Bundles of neuron fibres are called nerves. The portion of the neuron most resembling other cells is the cell body. The cell body contains a nucleus and cytoplasm. The long fibre of a neuron leading away from the cell body is the axon. An axon transmits impulses away from the cell body. The other end of the neuron is a highly branched structure called dendrites. Impulses move toward the cell body from the dendrites and from cell body to axon.
Long neuron fibres are covered by a fatty myelin sheath. Cells of myelin sheath are called Schwann cells. Small gaps between consecutive Schwann cells are called nodes of Ranvier. Both myelin sheath and the nodes of Ranvier are important in determining the speed with which impulses are conducted. Myelin sheath is an insulator so the membrane coated with this sheath does not conduct nerve impulse. In such a neuron, impulse jumps over the myelin going from node to node. These jumping or saltatory impulses increase the speed of nerve impulse.
5.3.1 Types of Neurons
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