Spinal cord

Abstract

The spinal cord and meninges lie in the vertebral canal. In the 3-month fetus, the spinal cord and vertebral canal are the same length but the vertebral canal grows more rapidly so that in the adult the cord extends from the foramen magnum to the level of the first or second lumbar vertebra. Thus, the adult spinal cord occupies only the upper two-thirds of the vertebral canal. It is roughly cylindrical in shape being slightly flattened antero-posteriorly and possesses cervical and lumbar enlargements from which originate the nerves supplying the upper limb (C4–T1) and the lower limb (L1–S3) plexuses. These enlargements lie opposite the lower cervical and lower thoracic vertebrae, respectively. 31 pairs of spinal nerves emerge from the cord and, since the adult spinal cord is shorter than the vertebral canal, these nerve roots descend in the canal, with increasing obliquity and length, to reach their appropriate intervertebral foramina, through which they exit the canal. The lumbar and coccygeal nerves are the longest and descend beyond the end of the spinal cord as the cauda equina (Figure 1). The inferior end of the spinal cord tapers (conus medullaris) and from its end a thin strand of pia mater, the filum terminale, descends through the cauda equina to be attached to the coccyx.