Where is the spinal cord? Location, where it ends, 31 pairs of spinal nerves

Where is the spinal cord?

The spine is the column of bones; the spinal cord is the nerve tissue that runs inside it. Each vertebra has a large opening (the vertebral foramen), and stacked together these openings form a tunnel, the vertebral canal, that holds the cord.

At the top it is continuous with the medulla oblongata of the brainstem at the foramen magnum; brain and spinal cord together form the central nervous system. At the bottom it does not reach the end of the spine but tapers off at about the level of L1–L2. In adults it is about 40–45 cm long and about 1 cm thick. The level where it ends varies by about one vertebra between people.

31 pairs of spinal nerves

Paired spinal nerves leave the cord on each side, 31 pairs in all:

There are seven cervical vertebrae but eight cervical nerves, because the first cervical nerve leaves between the skull and the atlas. Cervical nerves exit above the vertebra of the same number; from the thoracic level down, each nerve exits below its vertebra.

The cord is slightly thicker at the neck and lower back. The cervical enlargement gives rise to the nerves of the brachial plexus for the arm, and the lumbar enlargement to the nerves for the leg.

The end of the cord and the cauda equina

If the cord ends in the upper lumbar region, how do the lower lumbar and sacral nerves reach their openings? Their roots run down inside the vertebral canal. Below the end of the cord, the roots of the lumbar, sacral and coccygeal nerves form a bundle called the cauda equina, Latin for horse's tail.

In the fetus the cord reaches the bottom of the spine, but the vertebral column grows longer than the cord, so in adults the cord ends higher up. As a result, spinal cord segments and vertebrae with the same number are not at the same level, and the gap grows further down.

Cross section: grey and white matter

A cross section shows an H-shaped, butterfly-like core of grey matter surrounded by white matter. Grey matter holds nerve cell bodies; white matter carries fibres running up and down between brain and body.

In the cerebrum the grey matter is outside (the cortex) and the white matter inside; in the spinal cord it is the other way round. Each posterior root has a swelling, the spinal ganglion, holding sensory cell bodies, and the anterior and posterior roots join near the intervertebral foramen to form a spinal nerve. The cord is wrapped in three membranes, the dura, arachnoid and pia mater, with cerebrospinal fluid between the arachnoid and pia.

Name and terms

Cord means a string and spinal means of the spine. The bones are the spine or vertebral column and each bone is a vertebra, so English also uses different words for the bone and the nerve. The Latin is medulla spinalis; cauda equina means horse's tail.

See it in the app

Because the cord lies inside bone, it is almost hidden in skeleton drawings. In the 3D anatomy app teamLabBody you can make the bones translucent and select the spinal cord. From the side you can see at a glance how it runs from below the skull to the upper lumbar spine; show the nerves and rotate to the back to follow the spinal nerves leaving on each side. Cross sections are available with the PREMIUM plan.

Related articles