The Nervous System of man is divided into two main parts or divisions, the central nervous system consisting of the brain and spinal cord, and the peripheral nervous system consisting of the cranial and spinal nerves and their associated ganglia.

The central nervous system is composed of large numbers of nerve cells and their processes supported by specialized tissue called neuroglia. The neuron is the nerve cell and its processes. The long process of the nerve cell is called an axon or nerve fibers and the shorter ones are called the dendrites. The interior of the central nervous system is organized into gray and white matter. The gay matter consists of nerve cells and the proximal portions of their processes embedded in the neuroglia. The white matter consists of nerve fibers embedded in neuroglia.

There are twelve pairs of cranial nerves that leave the brain and pass through foramina in the skull. There are thirty one pairs of spinal nerves that leave the spinal cord and pass through the intervertebral foramina in the vertebral column. The spinal nerves are named according to the regions of the vertebral column with which they are associated: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal. Each spinal nerve is connected to the spinal cord by two roots, the anterior root and the posterior root. The anterior root consists of bundles of nerve fibers carrying nerve impulses away from the central nervous system. Such nerve fibers are called efferent fibers. Those efferent fibers that go to the skeletal muscles and cause them to contract are called motor fibers. Their cells of origin lie in the anterior gray horn of the spinal cord. The posterior root consists of bundles of nerve fibers that carry impulses towards the central nervous system and are called afferent fibers. Since these fibers are concerned with conveying information about sensations of touch, pain, temperature, and vibrations, they are called sensory fibers. The cell bodies of these nerve fibers are situated in a swelling on the posterior root called posterior root ganglion. At each intervertebral foramen the anterior and posterior roots unite to form a spinal nerve. Here the motor and sensory fibers become mixed together, so that a spinal nerve is made up of a mixture of motor and sensory fibers. On emerging from the foramen, the spinal nerves divide into a large anterior ramus and smaller posterior ramus.

The postrerior ramus passes posteriorly around the vertebral column to supply the muscles and skin of the back and the anterior ramus continues anteriorly to supply the muscles and skin over the anterolateral body wall and all the muscles and skin of the limbs. At the root of the limbs, the anterior rami join one another to form complicated nerve plexuses. At the root of the arms are the cervical and brachial plexuses, and at the root of the legs, the lumbar and sacral plexuses. The fine terminal branches of the sensory axon, called dendrites, leave the sensory organs of the skin and unite to form the axon of the sensory nerve. The axon passes up the leg in the sural nerve and then in the tibial and sciatic nerve s to the lumbosacral plexus. It then passes through the posterior root of the 1st sacral nerve to reach the cell body in the posterior root ganglion of the first sacral nerve. The central axon now enters the postrior white column of the spinal cord and passes to the nucleus gracilis in the medulla oblongata. This is a demonstration of how a touch on the little toe reaches the central nervous system.