Anatomy of a Nerve



More than ten thousand million nerve cells and their fibers, or axons, make up the nervous system. The axons are grouped together in nerve trunks containing sensory fibers, which conduct information from the sensory organs to the central nervous system, and motor fibers, which carry information to the central nervous system of the body. The nerve fibers which carry information quickly are enclosed in a thick sheath made of the fatty substance myelin. They are called myelinated nerve fibers. The myelinated sheath has regular indentations along its length called the nodes of Ranvier. The nonmyelinated nerve fibers, which carry information slowly, are grouped together and enclosed in a single sheath.

The anatomy of a nerve includes: the cell body, which is composed of cytoplasm and contains the cell nucleus; the nucleus, which contains the information needed to control the activity of the neuron; the dendrites, outgrowths of the cell body to which and from which they conduct impulses; the epineurium, a fibrous sheath that surrounds the whole nerve; the perineurium, the connective tissue sheath that surrounds bundles of nerve fibers; the endoneurium, the fine sheath of connective tissue around each nerve bundle; the axon, the extended fiber of the nerve cell which carries impulses to and from the cell body; the fatty myelin sheath, the insulating coat that separates the axon in a nerve bundle; the Schwann cell nucleus, the mechanism responsible for the production and maintenance of the myelin sheath and the Nodes of Ranvier, constrictions in the myelin sheath.