Spinal Cord Anatomy and Development

Study Notes

The spinal cord is a major component of the central nervous system
It extends from the medulla oblongata at the foramen magnum to the lower limit of the first lumbar vertebra (L1).
It is approximately 45 cm in length in males and 42 cm in females.
It occupies the upper 2/3 of the vertebral column.

During the 3rd month of intrauterine (IU) life, the spinal cord extends the entire length of the vertebral column.
At birth, it ends at the level of the L3 vertebra.
In adults, it ends at the disc between the L1 and L2 vertebrae.

The spinal cord has a cylindrical shape with two enlargements:
- Cervical enlargement: C5-T1 segments (for nerves to upper limbs)
- Lumbar enlargement: L1-S3 segments (for nerves to lower limbs)

The spinal cord consists of an "H"-shaped gray matter surrounded by white matter.

Six longitudinal grooves or sulci are present on the external surface of the spinal cord:
- Anterior median fissure: The deepest groove.
- Posterior median sulcus:
- Two anterolateral sulci: Where the ventral (motor) root exits.
- Two posterolateral sulci: Where the dorsal (sensory) root enters.

Spinal nerves emerge from the spinal cord through openings in the vertebral column.
Each spinal nerve consists of a dorsal (sensory) root and a ventral (motor) root.

The cauda equina is a collection of long lumbar and sacral nerve roots that descend within the vertebral canal below the end of the spinal cord (below L1).
These roots form a "horse's tail" shape, floating in the cerebrospinal fluid (CSF) of the subarachnoid space.
The length of these nerve roots increases as you go down the vertebral canal because the spinal cord ends higher than the vertebral column.
This arrangement allows for lumbar punctures to be safely performed below L2 without risking injury to the spinal cord.