Peripheral Nervous System

The Peripheral Nervous System (PNS) includes all the nerves outside the central nervous system ~ the brain and spinal cord. The PNS encompasses the cranial nerves that connect the head, face, and eyes directly to the brain and all the nerves that connect the spinal cord to the rest of the body. There are 30 pairs of spinal nerves emerging from the spinal cord in constant communication with the brain. As the nerves exit the spinal cord, they interconnect through plexuses, or nerve bundles, in the neck, shoulder, and pelvis, then divide again before traveling outward to more distant parts of the body.

Peripheral nerves are actually bundles of nerve fibers that may contain only sensory fibers, motor fibers, or a mix of both. They range in size from a microscopic fraction of a hair width to quite large, the size of one’s thumb. Larger fibers convey messages that activate muscles and are responsible for non-painful sensations, whereas the smaller sensory nerve fibers transmit sensations of pain and control the automatic, non-voluntary functions of the body such as heart rate, blood pressure, and temperature control. These smaller “pain transmitting” fibers are, unfortunately, the most prone to damage due to their small size and peripheral, more physically exposed, location. Common diseases such as long-standing diabetes, nutritional problems, HIV disease, and toxic medications used for chemotherapy often result in a diffuse, small fiber “peripheral neuropathy”. This is the sensation of pain and/or numbness often confined to the extremities. It usually follows the distribution of someone wearing a stocking on the feet, or gloves on the hands, and is referred to in such terms. Peripheral neuropathies, for the most part, involve the extremities and rarely the torso.