GLOSSARY

Spinal cord segments are functional divisions of the spinal cord, each giving rise to one pair of spinal nerves (one on each side); the cord has 31 segments.

Divisions

• Cervical: 8 segments (C1–C8), although there are only 7 cervical vertebrae.
• Thoracic: 12 segments (T1–T12).
• Lumbar: 5 segments (L1–L5).
• Sacral: 5 segments (S1–S5).
• Coccygeal: 1 segment.

Mismatch Between Segments and Vertebrae

Because the cord ends at about L1–L2, the segments lie higher than the vertebrae of the same name; for example, the lumbar and sacral segments lie at the level of the T10–L1 vertebrae, and the lower roots run downward to reach their foramina, forming the cauda equina.

Importance