Our spinal nerves transmit information from our central nervous system to the peripheral nervous system, the two subdivisions of the nervous system. The central nervous system consists of the brain and the spinal cord. The peripheral nervous system consists of nerves that branch out of the brain and spinal cord which includes the spinal nerves.
The information that is transmitted is through motor signals, sensory signals or autonomic signals, which are signals for involuntary bodily functions. As spinal nerves contain multiple nerve fibres with different functions they are known as mixed nerves.
Regional Divisions of the Spinal Nerve
The spinal cord is made up of segments. There are 31 pairs of spinal nerves which include eight cervical pairs, twelve thoracic pairs, five lumbar pairs, five pairs and one coccygeal pair.
The cervical nerves mainly supply muscles and skin to the upper limbs and some areas in the head, neck and chest. The thoracic nerves supply the chest, ribcage, abdomen and lower back. The lumbar nerves mainly innervate the abdomen and pelvis. The sacral nerves supply the muscles and skin of the lower limb as well as some of the pelvis. The coccygeal nerve supplies the skin around the coccyx.
Spinal Nerve Branches
When the spinal nerve exits the spinal column it divides into branches. The dorsal ramus supplies the trunk. The ventral ramus supplies the trunk and the upper and lower limbs. The meningeal branches supply the structures within the spinal column. The rami commmunicantes supply our organs and contain autonomic nerves.
Spinal Nerve Fibres
Each nerve has four roots; two anteriorly (front) and two posteriorly (back). The anterior roots contain efferent nerve fibres and the posterior roots contain afferent nerve fibres. Afferent nerve fibres carry sensory information and efferent nerve fibres carry motor and autonomic information.
A dermatome is an area of the skin that is innervated by a single spinal nerve. These areas of skin are overlapped by the root nerve as well as the nerve which comes before and after. This means that if a single nerve loses signal through injury, you are still able to feel sensation from the other nerves which supply this area.
If the spinal cord is damaged it can cause a permanent or temporary change to what the person can feel. Often, there’s a loss of muscle function, sensation and/or a loss of the use of some limbs or body parts.