The spinal cord is protected within the spinal canal of the vertebral column.  The adult spinal cord averages 42-45 cm in length extending from the brainstem down to the approximate level of the first lumbar vertebrae (L1).  The adult spinal cord weighs approximately 30-35 grams and is on the average 2.5-cm wide.  Regions of spinal cord enlargement occur in the neck (cervical) and low back (lumbar) areas of the spinal cord.

These areas are larger than the other areas because there are a greater number of nerve cell bodies, neurons, and interneurons needed to provide innervation to the arms and legs. The spinal cord terminates in a conical tapering fashion, called the conus medullaris.  Lumbar and sacral spinal nerve roots originate in the conus and descend to form the cauda equina (horses tail appearance). 

A thick membranous rope-like structure extends from the conus or tip of the spinal cord to the end of the spinal canal at the tailbone. It is called the filum terminale.

With the central portion of the spinal cord, there is a specialized group of nerve cell bodies referred to as the gray matter.  There arrangement resembles an “Hâ€? configuration on cross section of the cord. Surrounding the “Hâ€? configuration of nerve cell bodies there are columns of myelinated nerves.  Within each column, there are specialized nerve tracts, which carry information to and from the brain to the body. Each tract has specific functions.