Human Anatomy - M.M. Kurepina, A.P. Ozhigova, A.A. Nikitina 2010

Nervous system
Spinal cord
External structure of the spinal cord

The Spinal Cord (Fig. 3.5) is a tube approximately 45 cm long in men and 42 cm in women. The cavity of the spinal cord—the central canal—is almost completely obliterated. It is enveloped by three Meninges: the dura mater, arachnoid mater, and pia mater.

The spinal cord extends from the Brain at the level of the foramen magnum and terminates at the level of the first or second lumbar vertebrae (I—II) in a tapered end, the conus medullaris. Extending downward from the conus is the filum terminale. It is composed of the arachnoid and pia mater, which anchor to the periosteum of the coccyx, helping to secure the spinal cord in place. The filum terminale is surrounded by the long roots of the lower spinal segments, which form the cauda equina.

The spinal cord consists of 31 segments (neuromeres): 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal.

The spinal cord features two enlargements: the cervical enlargement, which is most prominent at the level of the V—VI cervical neuromeres, and the lumbar enlargement, reaching its maximum width in the region of the III—IV lumbar segments. These enlargements are due to the concentration of A large number of Cell bodies and fibers in these regions that innervate the limbs.

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Fig. 3.5. Spinal cord (dura mater opened):

A — anterior view; B — posterior view; C (I—VIII) — cervical; Th (I—XII) — thoracic; L (I—V) — lumbar; S (I—V) — sacral Spinal Nerves; 1 — cervical enlargement; 2 — spinal ganglia; 3 — dura mater; 4 — lumbar enlargement; 5 — conus medullaris; 6 — cauda equina; 7 — filum terminale

On the anterolateral surface of the spinal cord, the ventral roots emerge from the anterolateral sulcus; on the posterolateral surface, the dorsal roots enter the posterolateral sulcus. The latter bear enlargements—the spinal ganglia—located within the intervertebral foramina (Atlas, Figs. 92, 96).

Along the midline of the anterior surface of the cord runs the anterior median fissure, into which a fold of the pia mater invaginates. This groove divides the cord into right and left halves but does not reach the Gray matter; between the gray matter and the floor of the fissure lies the white commissure, which connects the White matter OF both halves of the cord. On the posterior surface of the spinal cord, the posterior median sulcus is visible. Its walls are fused, and a glial septum extends from the surface through the entire thickness of the white matter.