Thirty-one pairs of nerves exit the spinal cord through openings in the vertebral column. These are spinal nerves. There are four main areas of the vertebral spine: the cervical spine, or neck; the thoracic spine, or chest; the lumbar spine, or lower back; and the sacrum, or tailbone. Below the sacrum, a small bone called the coccyx marks the end of the spinal column. The nerves that exit the spinal cord are named according to their corresponding region of the vertebral spine.
The posterior, or dorsal, roots of spinal nerves carry sensory information from the areas they serve back to the brain. Spine-Health explains that the area of skin from which a particular nerve receives sensory information is known as that nerve's "dermatome."
For example, the skin over the shoulders sends sensory information to the fourth and fifth cervical nerves, also known as C4 and C5. The C7 nerve detects sensation in the middle finger. The little toes send sensory information to the first sacral nerve. Pain or numbness specific to a dermatome could be a symptom of damage to its corresponding nerves.
The anterior, or ventral, roots of spinal nerves carry motor impulses from the brain to the muscles, instructing them to move. Damage to a nerve could cause weakness, or even paralysis, in the muscles that it serves.
The sciatic nerve is the largest nerve in the body. It exits the spinal column through an opening in the pelvis called the sciatic foramen. Sciatic nerve damage typically causes pain down the back of the legs, but orthopedic surgeon Stewart Edelson of SpineUniverse says that it can also cause weakness in the leg flexor muscles.
The thoracic nerves supply motor function to the muscles of the abdomen and chest, as well as the specific hand muscles that allow an individual to spread his fingers apart. The cervical nerves serve the muscles of the arm and hand.
The spinal nerves also regulate the proper functioning of internal organs. Dysfunction in the autonomic nervous system can lead to life-threatening conditions.
Apparelyzed Spinal Cord Injury Peer Support describes the symptoms of one such condition, autonomic dysreflexia, as "sweating, pounding headache, tingling sensation on the face and neck, blotchy skin around the neck and goose bumps." Autonomic dysreflexia can occur when there is an injury to the spinal cord above the mid-thoracic level. If left untreated, an individual with autonomic dysreflexia is vulnerable to the possibility of suffering a fatal stroke.