Spinal Cord Anatomy

Anatomy of the Spinal Cord

Gross Anatomy and Relationship to Vertebral Levels

• The spinal cord attaches to the dura via dentate ligaments.
• It extends from the cranial border of the atlas, where it connects to the medulla oblongata, to the lower border of the first lumbar vertebra.
• Early in fetal development, the spinal cord reaches the lower end of the sacrum.
• At birth it extends to the upper border of the third lumbar vertebra.
• At 20 weeks' gestation, the conus medullaris is at the L4–L5 level.
• At 40 weeks' gestation, the conus medullaris is at the L3 level.
• By 2 months old, the conus reaches the adult L1–L2 level.
• Spinal cord is approximately 45 cm long in adult males, and 42 to 43 cm in adult females.
• The spinal column measures about 70 cm in length.
• The spinal cord, cylindrical and flattened dorsoventrally, occupies one-third to one-half of the vertebral canal.
• The cervical enlargement, from C5 to T1 spinal levels, innervates the upper extremities.
• The lumbar enlargement, from L3 to S2, innervates the lower extremities.
• The spinal cord narrows below the lumbar enlargement, forming the conus medullaris.
• The filum terminale, a pial thread, extends from the conus medullaris to the first coccygeal segment.
• The spinal cord has 31 segments corresponding to 31 pairs of spinal nerves, including 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal.
• Lumbar and sacral nerve roots travel a considerable distance in the subarachnoid space to reach their intervertebral foramina.
• The cauda equina is formed by the lower nerve roots around the filum terminale within the spinal theca
• The cervical spinal cord corresponds roughly to the spine.
• The thoracic spinal cord lies within the spinal canal formed by the T1–T8 vertebrae.
• The lumbar spinal cord is located in the canal between the T9–T11 vertebrae.
• The sacral spinal cord is situated in the canal between the T12 and L2 vertebrae.
• In the cervical region, the spinous process of a vertebra aligns with the corresponding spinal cord segment.
• In the upper thoracic region, there is a two-segment discrepancy (e.g., the fourth thoracic spinal segment overlies the sixth).
• A three-segment discrepancy is present in the lower thoracic region.
• The T11 spinous process overlies the third lumbar cord segment, and T12 overlies the first sacral cord segment.
• The spinal cord's external surface features a ventral median fissure and a dorsal median sulcus, dividing it into symmetric halves.
• The dorsolateral sulcus marks the entry of dorsal nerve roots.
• The ventrolateral sulcus is less defined, with ventral nerve roots emerging as separate twigs.

Cross-Sectional Anatomy of the Spinal Cord

• Gray matter is centrally located in the spinal cord, shaped like a butterfly or modified H, surrounded by white matter.
• Lateral columns of gray matter are connected by a transverse commissure.
• Each lateral column contains a dorsal (posterior) horn and a ventral (anterior) horn.
• The central canal of the spinal cord, linked to the fourth ventricle, sits in the center of the gray commissure.
• Gray matter is more prominent in the cervical and lumbosacral regions, which innervate the upper and lower limbs.
• The intermediolateral gray column, present from segments T1 through L2, gives rise to preganglionic sympathetic autonomic fibers.
• An intermediolateral zone of gray matter at the second, third, and fourth sacral segments serves as the origin of the sacral parasympathetic outflow.