About 45 cm long, running from the foramen magnum to the level of the first or second lumbar vertebra
Spinal cord — it ends well above the bottom of the vertebral column.
Anatomy · Brain & nerves
Spinal cord
About 45 cm long
Central nervous system · vertebral canal
The long, thin, cylindrical bundle of nerve tissue that runs from the base of the brain down through the vertebral canal, about 45 cm long in men and 43 cm in women, ending near the level of the first or second lumbar vertebra. It carries messages between the brain and the body, and coordinates simple reflexes without involving the brain. Thirty-one pairs of spinal nerves branch from it.
How to spot them
- ▸A pale cord about as thick as a finger, running inside the vertebral canal, wrapped in three membranes
- ▸In cross-section, a central grey butterfly or H shape surrounded by white matter — the reverse of the brain
- ▸Two bulges, cervical and lumbar, where the nerves for the limbs join
- ▸Tapers into a cone (conus medullaris) around the level of the first or second lumbar vertebra, below which hangs a bundle of nerve roots like a horse's tail
What to know
Thirty-one pairs of nerves branch from it: eight cervical, twelve thoracic, five lumbar, five sacral and one coccygeal
Spinal cord — 31 pairs of spinal nerves.
In cross-section it shows a central H- or butterfly-shaped area of grey matter, surrounded by white
Spinal cord — grey matter inside, white matter outside.
Below its tapered end, a bundle of nerve roots resembling a horse's tail fills the lower canal
Spinal cord — the cauda equina, below the conus medullaris.
A needle can be safely inserted below its end, at the L3–L4 or L4–L5 level, to sample cerebrospinal fluid
Spinal cord — lumbar puncture.
Sensory fibres enter by its dorsal roots, and motor fibres leave by its ventral roots — the Bell–Magendie law
Spinal cord — dorsal sensory, ventral motor.
An injury at the very top of it in 1995 left the actor Christopher Reeve dependent on a ventilator
Spinal cord — a cervical-level injury (C1–C2).
The knee-jerk is coordinated here, without the brain being involved
Spinal cord — the reflex arc.
Key ideas
- Grey matter holds cell bodies, white matter the ascending and descending tracts; the reverse of the arrangement in the cerebrum.
- Because the cord stops at about L1–L2 while the column continues to the sacrum, spinal nerve roots run down a long way before they exit — the cauda equina.
Quick-fire facts
- •About 45 cm long in men and 43 cm in women, and roughly 1 cm thick
- •It ends at the conus medullaris, at about the L1–L2 level in adults; in newborns it extends lower, to about L3
- •There are 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal
- •It has two enlargements: cervical (for the arms) and lumbar (for the legs)
- •The filum terminale, a thin strand of pia mater, anchors it to the coccyx
- •Wrapped in the same three meninges as the brain, with cerebrospinal fluid in the subarachnoid space
- •The central canal runs through it, continuous with the ventricles of the brain
- •Christopher Reeve, the Superman actor, was paralysed by a cervical cord injury in 1995
- •Lumbar punctures are performed below its end, usually at L3–L4 or L4–L5
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Sources
- Cleveland Clinic — Spinal cord
- OpenStax — 13.2 The Central Nervous System — Anatomy and Physiology 2e