Overview of the Spinal Nerves
The spinal cord is an extension of the brainstem (the lowest part of the brain), extending from the base of the skull down to the low back. Along its length, it gives off 31 pairs of spinal nerves, which branch to form the peripheral nerves of the neck, trunk, and extremities. The origins of the nerves as they emerge from the spinal cord are called nerve roots.
They are bundles of nerve fibers connected to the spinal cord. Spinal nerves carry information to and away from the spinal cord. it supplies all the areas of the body except the head and neck region. Some structures in the head and neck region are also innervated or supplied by the nerves such as muscles of the neck.
When any area of the body escapes the control of the CNS, its functions are not regulated. As a result, that particular area of the body loses its functional ability and dies soon.
Spinal nerves distributions
The nerves are distributed in different regions of the body as follows:
Cervical nerves (C1 to C8) of spinal nerve
There are 8 pairs of spinal nerves in the cervical region. These nerves mainly supply the muscles, joints, and bones
, and skin of the upper limbs. The cervical nerves also supply some areas of the neck region, including some muscles of the neck. They also supply some patch of skin over the head and chest and some extrinsic muscles of the chest.
Thoracic nerves (T1 to T12)
There are 12 pairs of nerves that originate from the thoracic segments of the spinal cord. These spinal nerves mainly supply the skin over the chest and intrinsic muscles of the thoracolumbar region. The thoracic nerves also supply some of the areas of skin over the abdomen and axilla
Lumbar nerves (L1 to L5)
The lumbar segments of the spinal cord give rise to 5 pairs of the spinal cord. These nerves mainly supply the muscles of the abdomen and pelvis. Some muscles of the thigh are also supplied by the lumbar nerves. spinal nerves also supply the skin of the abdominal region, the skin of the back, skin of the anterior thigh, and skin of the inguinal region.
Sacral nerves (S1 to S5)
There are five pairs of spinal nerves that originate from the sacral segments of the spinal cord. The nerves provide innervation mainly to the lower limbs. The skin, muscles, and joints of the lower limb are supplied by the sacral nerves. However, these nerves also provide innervation to some muscles of the pelvic region.
Coccygeal nerve (Co1)
It is the last pair of spinal nerves that arises from the tapering part of the spinal cord, the conus medullaris. This nerve is distributed mainly to the skin over the coccyx. It has no other distribution in the body.
Formation of Spinal Nerve
The formation of the spinal nerve means the way the originates from the spinal cord. In this section, we will say how nerve fibers leave the spinal cord and join together to form the spinal nerve.
Each spinal nerve is made up of two roots.
- Anterior or Ventral root
- Posterior or Dorsal root
Both these roots emerge from the spinal cord and later join together to form a single spinal nerve.
In order to understand the formation of spinal nerves, let us understand how these roots originate and join together.
Anterior or Ventral Root of spinal nerve
The anterior root of the spinal nerve consists of the motor fibers. It contains the axons of the motor neurons located in the anterior gray horn of the spinal cord. These motor fibers represent the efferent fibers carrying information away from the spinal cord.