The spinal cord is the main pathway of communication between the brain and the rest of the body. The spine (spinal column) is divided into four areas: cervical (neck), thoracic (chest), It is a long, fragile, tubelike structure that extends downward from the base of the brain. The cord is protected by the back bones (vertebrae) of the spine (spinal column), which are separated and cushioned by disks made of cartilage.

The spinal cord is the major bundle of nerves that carry nerve impulses to and from the brain to the rest of the body. The brain and the spinal cord constitute the Central Nervous System. Motor and sensory nerves outside the central nervous system constitute the Peripheral Nervous System, and another diffuse system of nerves that control involuntary functions such as blood pressure and temperature regulation are the Sympathetic and Parasympathetic Nervous Systems.

The spinal cord is surrounded by rings of bone called vertebra. These bones constitute the spinal column (back bones). In general, the higher in the spinal column the injury occurs, the more dysfunction a person will experience. The vertebra are named according to their location. The eight vertebra in the neck are called the Cervical Vertebra. The top vertebra is called C-1, the next is C-2, etc. Cervical SCIs usually cause loss of function in the arms and legs, resulting in quadriplegia. The twelve vertebra in the chest are called the Thoracic Vertebra. The first thoracic vertebra, T-1, is the vertebra where the top rib attaches. Injuries in the thoracic region usually affect the chest and the legs and result in paraplegia.

The vertebra in the lower back - between the thoracic vertebra, where the ribs attach, and the pelvis (hip bone), are the Lumbar Vertebra. The sacral vertebra run from the pelvis to the end of the spinal column. Injuries to the five Lumbar vertebra (L-1 thru L-5) and similarly to the five Sacral Vertebra (S-1 thru S-5) generally result in some loss of functioning in the hips and legs.