The spinal cord is part of the central nervous system. It serves as the connection between the brain and the spinal nerves that emerge from the spinal cord.
Emerging from the brain, the spinal cord emerges from the brain as the medulla oblongata at the foramen magnum, and from there continues on as the medulla spinalis that is about 45 cm long and has a round-oval cross-section. The spinal cord lies in the spinal canal where it is protected by the vertebral bodies and arches. It grows narrower as it descends and in adults ends in the pointed medullary cone (conus medullaris) at the level of the 2nd lumbar vertebra.
Below the tip of the medullary cone at the level of the 2nd lumbar vertebra, the cord continues downward for about 25 cm in a much reduced form called the filum terminale to the 2nd coccygeal vertebra. The nerve fibers emerging from the lower spinal cord continue down the spinal canal below the 2nd lumbar vertebra. These tightly bundled nerve fibers look like a horse’s tail, which is why this segment is known as the cauda equina.
The spinal cord, like the brain, is surrounded by cerebrospinal fluid (liquor cerebrospinalis) and three protective sheaths (meninges):
- The ”hard” spinal meninx (dura mater spinalis) is the outer sheath that extends from the occipital foramen to the sacral canal
- The middle meninx is formed by connective tissue called the arachnoid membrane (arachnoidea spinalis) with its many blood vessels
- The inner sheath is the ”soft” meninx (pia mater spinalis) in direct contact with the spinal cord.
The cross-section of the spinal cord reveals its typical structure. The grey matter (substantia grisea) at the center is butterfly-shaped in cross-section. It is formed by many nerve cells and runs the entire length of the spinal cord.
The grey matter is enclosed by the white matter (substantia alba) that consists mainly of long nerve fibers.
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