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The human nervous system is a network of central and peripheral nerves, running from the base of the brain, through the spinal cord, and out to all parts of the body. A nerve is essentially a pathway for electrochemical impulses to travel, helping us to feel and move. Each anterior nerve gives these functions to forwardly located parts of our bodies, such as the chest and front of the leg.
The impulses or messages of sensation or movement are carried by individual neurons within the nerve. The impulse is passed along from one neuron to the next at exceptionally high speeds. The message is electrical within the nerve cell, then chemically transmitted to the next nerve cell, where the process begins again, allowing the impulse to travel from cell to cell.
Outside of the spinal cord and nerve roots, the term anterior nerve is used to classify the position of nerves within the body. Nerves can contain two kinds of nerve cells, named for their function instead of their position. Afferent or cutaneous nerves are those that supply sensations from the skin, the sense of touch. Efferent or interosseous nerves are those that carry the impulses that move our muscles. Some nerves serve both functions, providing both sensory and movement impulses.
Within the spinal cord, nerves are paired in bundles of fibers that exit the spinal cord in a rear, called posterior, or front, called anterior, position. These nerves are also called dorsal or ventral nerves, respectively. Where nerves meet with the spinal cord is called the nerve root. Each nerve root contains a posterior and anterior root within the nerve bundle. At this location, the anterior root transmits motor signals to the spinal cord and the posterior nerve root transmits sensory information.
The anterior nerve root is smaller than the posterior, as it carries fewer bundles of nerves, except for the first cervical nerve root, where the anterior nerve root is larger. The ratio of size between the anterior and posterior nerves depends on the location of the nerves. In the cervical spine, the posterior nerve roots are usually three times larger than the anterior nerve roots.
There are 31 pairs of nerves exiting the spinal cord at holes in the vertebrae known as foramina. The first eight nerves exit at the cervical spine, the neck, the next 12 exit from the thoracic spine. Another five exit at the lumbar spine, the lower back. There are five pairs of nerves exiting at the sacral spine and the final nerve exits in the topmost coccyx vertebra.