Nerves of the Chest and Upper Back

[Continued from above] . . . after time to form a network that extends throughout the body. In fact, thirty-one pairs of spinal nerves originate from the spinal cord. Most of these pairs exit the spinal column from within the chest. They are all mixed nerves, and they provide a two-way communication system between the spinal cord and parts of the arms, legs, neck, and trunk of the body. Although spinal nerves do not have individual names, they are grouped according to the level from which they stem, and each nerve is numbered in sequence. The thoracic nerves and lumbar nerves originate within the chest and exit the protection of the spinal column through nearly horizontal vertebral foramina.

The spinal cord serves as a sort of information highway within the chest. A cross section of the spinal cord reveals that it consists of two lanes: a core of grey matter (sensory) surrounded by a thicker section of white matter (motor). The pattern produced by the grey matter resembles a butterfly with outspread wings. At the level of the chest, the tracts that conduct impulses from the body to the brain carrying sensory information are called ascending tracts. Those that conduct motor impulses from the brain and through the spinal cord to muscles and glands are called descending tracts. This two-way road makes up and defines the nervous system within the chest.

It is also the section of the body and nervous system where largest numbers of the autonomous nerve functions are signaled, with unconscious nerve firings regulating the beating of the heart, along with the functioning of many of the body's other organs. The importance of the abdominal nervous system is such that injuries to the spinal cord below the neck may cause weakness or paralysis of the legs or in part of the trunk.