The Spinal Cord

The spinal cord is a long, cylindrical part of the central nervous system enclosed within the vertebral column, running as a direct downward continuation of the medulla oblongata from the base of the skull to about the level of the first or second lumbar vertebra. Along its length, thirty-one pairs of spinal nerves emerge at regular intervals through gaps between successive vertebrae, connecting the spinal cord to the trunk and limbs.

The spinal cord performs two broad kinds of function. First, it acts as the main conduction pathway between the brain and the rest of the body below the neck: bundles of nerve fibres running the length of the cord — ascending tracts — carry sensory information (touch, pain, temperature, position sense and so on) up towards the brain, while descending tracts carry motor commands from the brain down to the muscles and glands of the trunk and limbs. Second, and just as importantly, the spinal cord itself acts as an independent reflex centre: its grey matter contains the sensory-relay and motor neurons, and often interneurons, needed to complete many reflex arcs entirely at the level of the cord, without requiring the impulse to travel all the way up to the brain and a response to travel all the way back down. This is what allows spinal reflexes — described in detail in the section on ref …