Structures · Cord and roots
Cauda equina
The bundle of lumbar and sacral nerve roots that runs down the canal below the end of the cord, before each root leaves at its own level.
What the sources say
“As the vertebral column grows, these nerves grow with it and result in a long bundle of nerves that resembles a horse’s tail and is named the cauda equina .” Betts et al. 2022, §13.2
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- Conus medullaris and cauda equina
Where the spinal cord ends and what fills the canal below it. Why the cord stops near L1, how much that varies, and how the lower nerve roots travel down as the cauda equina.
- Spinal nerves and roots
The 31 pairs of mixed nerves that connect the cord to the body. How each forms from a sensory and a motor root, where it leaves the column, and how the nerves regroup into plexuses.
- The L4–L5 motion segment
Two lumbar vertebrae, the disc between them, the joints and ligaments that tie them, and the nerves that pass by. One of the two most common places for a disc to herniate, and a good place to see how bone, disc and nerve fit together.
- The spinal cord
The part of the central nervous system inside the vertebral column. How it is built from grey horns and white columns, why it is shorter than the column, and how its regions are named.
- Vertebral and spinal cord levels
Why "L1" can mean two different places. The vertebrae and the spinal cord segments have their own numbering, and below the neck they drift apart, because the column grows longer than the cord.
For learning only. Levels and sizes vary between people; nothing here describes a particular person or gives medical advice. Sources: Betts et al. 2022, §13.2.