In order to categorize the spinal nerves, anatomists divide the vertebral column into four distinct areas, referred to as the cervical, thoracic, lumbar and sacral regions of the spine. Thirty-one pairs of nerves emerge from the spinal cord. Nerves that exit through openings between the vertebrae are called spinal nerves, while nerves that emerge through openings in the skull are known as cranial nerves.
Cervical Spinal Nerves
The cervical spine is named after the Latin word for neck, which is cervix. The cervical spine extends from the skull to the shoulders. This area of the spine is composed of seven bones called vertebrae. These bones are numbered from top to bottom and are referred to as C1 through C7.
The vertebrae are stacked on top of each other, separated by cartilaginous discs known as intervertebral discs. Openings between the vertebrae, called intervertebral foramina, allow the cervical nerves to emerge from the spinal cord and find their destination in the body.
There are eight cervical nerves. The cervical nerve roots emerge just above their corresponding vertebral segment. In other words, the C1 nerve exits the spine through a foramen above the C1 vertebrae. The C8 nerve emerges below the last cervical vertebra, C7, and above the first thoracic vertebra, T1.
Cervical nerves supply motor impulses to the arms, neck and upper torso, and conduct sensory impulses from these areas back to the brain.
Thoracic Spinal Nerves
The thoracic spine lies just below the cervical spine, and is the region that supports the trunk and ribcage of the body. There are 12 thoracic vertebrae, according to Cedars-Sinai, and 12 thoracic nerves. In contrast to cervical nerves, thoracic nerves exit the spinal column through foramen just below their corresponding thoracic vertebrae. The first thoracic nerve, T1, exits between the T1 and T2 vertebrae. The last thoracic nerve, T12, exits the spinal cord through the openings between the T12 vertebra and the first lumbar vertebrae, L1.
The thoracic nerves supply nerve impulses to the chest, upper back and abdomen.
Lumbar Spinal Nerves
The lumbar spine supports the lower back and is composed of five vertebrae. Five corresponding lumbar nerves emerge from the lumbar region of the spinal cord, which ends in the level of the first and second lumbar vertebrae. Spinal nerves below that level descend from the spinal cord within the vertebral column to find their respective exits to reach the peripheral nervous system. This region of the spinal nerves is known as the “cauda equina” due to its resemblance to a horse’s tail.
Lumbar nerves supply nerve impulses to the legs and internal organs involved in excretory and sexual functions.
Sacral Spinal Nerves
The sacrum is a solid, triangular-shaped bone that lies at the end of the spinal column. It is made up of vertebrae that have fused. At its tip lies the coccyx, another section of fused vertebrae commonly known as the tail bone. A total of five nerves emerge from holes in the sacrum. Though there is only one sacral segment of the spinal column, S1, there are five sacral nerves, S1 through S5.
These nerves supply impulses to the legs and lower abdominal organs.