spinal cord
Meaning of spinal cord: A cable of nervous tissue about as thick as a finger, and considerably shorter than the bony canal that houses it.
Definition of spinal cord
The spinal cord is the thick bundle of nerve tissue running from the base of the brain down inside the backbone, wrapped in three membranes and cushioned by fluid. It carries signals between the brain and the rest of the body and generates reflexes of its own. Together with the brain it forms the central nervous system, and it ends well above the base of the spine.
Where does it actually end?
Higher up than most people expect. It tapers to a point at about the level of the lowest ribs, near the top of the lumbar vertebrae, while the bony canal carries on down to the tailbone. The space below is filled by a spray of nerve roots travelling to their own exits, named the cauda equina for its likeness to a horse's tail. The cord grows more slowly than the spinal column during childhood, which is why it appears to have ridden upward. That anatomy is exactly why a spinal tap is performed low in the back, where a needle meets loose floating roots rather than the cord itself.
How is it arranged inside?
Cut across, it shows a butterfly of gray matter surrounded by white matter, the reverse of the arrangement in the brain. The gray wings hold nerve cell bodies: those toward the back receive incoming sensation, those toward the front send commands out to muscle. The white matter around them is built of insulated fibers running up and down in defined tracts, each carrying one kind of traffic, so a particular pattern of lost sensation or weakness points to a particular part of the cross section. Pairs of nerve roots leave at every level and merge into the nerves of the limbs and trunk.
What happens when it is damaged?
| Level of damage | Usual consequence |
|---|---|
| Neck | Weakness of arms and legs, and breathing may be affected |
| Chest | Weakness of the legs, with the trunk involved |
| Lowest part of the cord | Leg weakness with loss of bladder and bowel control |
| Nerve roots below the cord | Patchy leg weakness and numbness across the saddle area |
Everything below a damaged level is cut off from the brain, so the height of an injury sets the extent of loss far more than its size does. Fibers within the cord do not regrow across a gap, so the damage tends to be permanent, and pressure from a tumor, an abscess or a collapsed vertebra produces spinal cord compression, where the speed of relief governs how much function returns.
Also known as
Used in a sentence
Imaging showed compression of the spinal cord at the mid thoracic level.
Good to know
The cord ends near the top of the lumbar vertebrae rather than running the whole length of the backbone, so a needle placed below that point meets loose nerve roots, and the level of an injury rather than its size determines how much function is lost.
Word origin
Where “spinal cord” comes from
Spinal comes from the Latin spina, meaning thorn and then backbone; cord from the Greek chorde, a string.