The Human Spinal Cord

The spinal cord is located in the vertebral foramen and is made up of 31 segments: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal. A pair of spinal nerves exits from each segment of the spinal cord. The spinal cord is about 45 cm long in men and 43 cm long in women. The length of the spinal cord is much shorter than the length of the bony spinal column. In fact, the spinal cord extends down to only the last of the thoracic vertebrae. Therefore, nerves that branch from the spinal cord from the lumbar and sacral levels must run in the vertebral canal for a distance before they exit the vertebral column. This collection of nerves in the vertebral canal is called the cauda equina (which means "horse tail"). Receptors in the skin send information to the spinal cord through the spinal nerves. The cell bodies for these nerve fibers are located in the dorsal root ganglion. The nerve fibers enter the spinal cord through the dorsal root. Some fibers make synapses with other neurons in the dorsal horn, while others continue up to the brain. Many cell bodies in the ventral horn of the spinal cord send axons through the ventral root to muscles to control movement.