The information highway between brain and body — and a processor in its own right, handling reflexes and rhythmic patterns like walking. Its structure, its nerves and what happens when it is injured.
Spinal Cord & Body Wiring
Beginner
The Spinal Cord
The Editors
November 17, 2025
2 min read
In plain English
The spinal cord is a long bundle of nerve tissue running down inside your spine. It carries messages between your brain and body, and it can handle some actions — like reflexes — all on its own. Injury to it can cause paralysis below the damaged level.
Beginner level: No background needed. Everyday language, everyday examples — the place to start.
Concepts to know first
The spinal cord is a cylinder of nervous tissue about 45 centimetres long in adults, roughly the width of a finger, running from the base of the brainstem down through the vertebral canal. Surprisingly, it stops short of the bottom of the spine — usually around the first or second lumbar vertebra. Below that, a bundle of nerve roots continues downward, called the cauda equina ("horse's tail"), which is why a lumbar puncture needle can be inserted there safely.
Grey butterfly, white wiring
In cross-section, the cord has a butterfly- or H-shaped core of grey matter (cell bodies) surrounded by white matter (myelinated axons carrying signals up and down). The back (dorsal) horns of the grey matter receive sensory input; the front (ventral) horns contain the motor neurons that drive muscles.
31 pairs of nerves
Thirty-one pairs of spinal nerves leave the cord: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal. Each attaches by a dorsal root, carrying sensory fibres in, and a ventral root, carrying motor fibres out — the Bell–Magendie law, worked out in the early 19th century. Each spinal nerve serves a strip of skin called a dermatome; shingles typically produces a rash along one of them.
A processor, not just a cable
The cord organises reflexes — the knee jerk, withdrawal from pain — without the brain. It also contains central pattern generators: networks that produce rhythmic patterns for walking. Cats with the cord disconnected from the brain can, with treadmill support, still produce stepping movements.
Spinal cord injury
Injury damages the pathways at and below the injured level. Injury in the neck can cause tetraplegia (quadriplegia), affecting all four limbs; lower injuries can cause paraplegia. The central nervous system regenerates poorly. Recent advances — epidural electrical stimulation combined with rehabilitation, and brain-spine interfaces that bridge the injury — have helped some people with chronic paralysis stand and take steps.
Everyday examples & things to try
Try it
Find a dermatome
Lightly run a fingertip down the outside of your forearm to your little finger. That strip of skin is served largely by a single spinal nerve root (C8) in your lower neck. Doctors test strips like this to locate spinal injuries.
Key takeaways
- The spinal cord runs from the brainstem to about the L1–L2 vertebra, with 31 pairs of spinal nerves.
- Dorsal roots carry sensation in; ventral roots carry motor commands out.
- It handles reflexes and walking rhythms itself; injury causes paralysis below the level of damage.
Explore further
Search YouTube for…
Tap a phrase to copy it, then paste it into YouTube's search box. This site doesn't link to other websites — pick channels from universities, hospitals and established science educators.
Tagswiringspinal cordreflexesinjury
Keep reading
Spinal Cord & Body Wiring
Intermediate
Cerebrospinal Fluid and the Ventricles
The clear fluid that cushions the brain and spinal cord: where it's made, how it circulates through four ventricles, what a lumbar puncture tells doctors, and what happens when it backs up.
May 28, 2026 · 3 min read
Spinal Cord & Body Wiring
Intermediate
The Brain's Blood Supply
Four arteries, a safety ring called the circle of Willis, and an organ that can't store fuel: how the brain is fed, why blood flow follows activity, and what goes wrong in a stroke.
April 9, 2026 · 2 min read
Spinal Cord & Body Wiring
Beginner
The Autonomic Nervous System
Fight or flight versus rest and digest: the sympathetic and parasympathetic systems that run your heart, lungs, gut, pupils and sweat glands without asking — and the vagus nerve at its heart.
November 8, 2025 · 2 min read