Spinal Cord

The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain. The brain and spinal cord together make up the central nervous system. Enclosed within, and protected by, the bony vertebral column, the spinal cord functions primarily in the transmission of neural signals between the brain and the rest of the body, but also contains neural circuits that can independently control numerous reflexes and central pattern generators.

Structure

The spinal cord is the main pathway for information connecting the brain and peripheral nervous system. The length of the spinal cord is much shorter than the length of the bony spinal column. The human spinal cord extends from the medulla oblongata and continues through the conus medullaris near the first or second lumbar vertebrae, terminating in a fibrous extension known as the filum terminale.

It is about 45 cm long in men and 43 cm long in women, ovoid-shaped, and is enlarged in the cervical and lumbar regions. In cross-section, the peripheral region of the cord contains neuronal white matter tracts containing sensory and motor neurons. Internal to this peripheral region is the gray, butterfly shaped central region made up of nerve cell bodies. This central region surrounds the central canal, which is an anatomic extension of the spaces in the brain known as the ventricles and, like the ventricles, contains cerebrospinal fluid.

The three meninges that cover the spinal cord—the outer dura mater, the arachnoid mater, and the innermost pia mater are continuous with that in the brainstem and cerebral hemispheres. Similarly, cerebrospinal fluid is found in the subarachnoid space. The cord is stabilized within the dura mater by the connecting denticulate ligaments which extend from the enveloping pia mater laterally between the dorsal and ventral roots. The dural sac ends at the vertebral level of the second sacral vertebra.