The Spinal Cord: Where Mind and Body Meet

In tending to the spine, your practitioner is fine-tuning one of the most vital parts of the body. Follow Groupon’s journey along the spinal cord to learn just what’s going on inside it.

Your feet may carry you for miles and your skin may be your largest organ, but the spine is arguably your hardest-working body part. It doesn’t just tie your limbs together and keep you standing upright—it also contains the body’s information highway, the spinal cord. Within a bundle roughly as thick as your finger, that highway contains millions of “lanes”, nerve fibers along which electrical signals travel. Most of them carry traffic in one direction only: ascending toward the brain and carrying sense data, or descending from the brain and carrying instructions for motion.

Insulating this bundle from the bony vertebrae is the sheath known as the dura mater, filled with protective fluid. Seen from the outside, the whole package resembles a tall pine trunk with regularly spaced branches and, hopefully, no leaves. These branches are the nerve roots, and they pass electrical signals between the brain and muscles in an orderly fashion: those branching from the topmost vertebrae control the arms and chest muscles, the next set run to the rest of the torso, and so on. The spinal nerves have very precise functions—for instance, the nerve anatomists call C7 is reserved for sensations in the middle finger. They all come together in a central mass of white matter surrounding a core of gray matter. The white matter is made primarily of axons designed to transmit electrochemical signals from the gray matter’s motor and sensory neurons.

Gray matter also contains interneurons, which form local circuits with other neurons rather than serving as part of the great brain-body highway. This means that not all information processed in the spinal cord passes through the brain. When a spinal reflex occurs, sense signals provoke motor signals with no need for the brain to get involved. For example, when you touch something hot, pull away, and shift your balance to avoid falling over, this entire sequence of action may be processed entirely within the spinal cord thanks to the interneurons. Meanwhile, of course, the sensory information itself is passed up the spinal cord to the brain, meaning that you’re not doomed to keep trying to smooch the same fire demon forever.