The spinal cord originates in the brain, exiting through a hole at the skull base called the foramen magnum and coursing through the spinal canal of the cervical, thoracic and upper lumbar spine before ending most commonly between the first and second lumbar vertebrae.
Nerve roots exiting from the lower end of the spinal cord continue as a structure called the cauda equina, or horse's tail, to provide nerves to the lower trunk, legs, bowels, bladder and sexual organs.
Several protective membranes cover the spinal cord. The outermost layer (dura mater) forms a tough tube that encases the two inner membranes (arachnoid and pia mater) and contains spinal fluid, commonly called cerebrospinal fluid (CSF). This fluid cushions, protects and nourishes the spinal cord and nerve roots. Enough cerebrospinal fluid to fill a soft drink can (about 350 cubic centimeters) is reabsorbed and replenished daily.
The spinal cord itself is a large, nearly circular mass of nerve tissue. It carries messages from the brain to the rest of the body. It also carries messages or sensations from the rest of the body to the brain. The spinal cord gives off branches or paired nerve roots at each level of the spine, except the top cervical vertebrae. These roots leave the spine on both sides through spaces (neural foramina) between each vertebra.
Damage to the nerves can cause pain, tingling, numbness or weakness in the area where the nerve travels. Damage to the spinal cord at any level can cause many symptoms, from paralysis to numbness.