In Depth: Spine
The spinal cord begins at the base of the brain and extends into the pelvis. Many of the nerves of the peripheral nervous system, or PNS, branch out from the spinal cord and travel to various parts of the body.
Information from the senses travels through the nerves of the PNS to the spinal cord and then to the brain for processing, and commands from the brain travel down the spinal cord and then to the appropriate part of the PNS, where nerves transport the instructions to the appropriate body part where action is needed.
To facilitate this process, the spinal cord is divided into two kinds of pathways called tracts. Ascending tracts carry sensory input from the body to the brain, and descending tracts carry commands from the brain down to specific tissues and organs.
The spinal cord is also essential for reflex function. Reflexes are the body’s way of coping with stimuli that require an immediate response. For example, jerking away from something hot or sharp is a reflex action. It happens immediately because instructions come from the spine (rather than the brain) to avoid injury.
The spinal cord, like the brain, has two major layers of protection. First are the vertebrae of the spine, and underneath those are three layers of tough membrane called the meninges.
The meninges surround both brain and spinal cord and are filled with a liquid called cerebrospinal fluid. The fluid has several functions, and one of them is shock absorption.
The spinal cord can suffer physical damage that can hamper or even halt communication between brain and body. If the spinal cord is severed, the part of the body below the damage is cut off from the commands of the brain, which causes paralysis.
The spinal cord can also be afflicted by disease or disorder. Among these is the birth defect spina bifida, which is the incomplete development of the central nervous system, including the spine. This can affect movement of the legs, incomplete sensation, or loss of bladder control.
The spinal cord can also be damaged by tumors. Whether cancerous or benign, they can put pressure on the cord and impair sensory or motor function.