canal extends to the first few coccygeal vertebrae. This inequality is due to differential growth rates of the cord and vertebrae and the relative shift in position carries the spinal cord segments cranially from their original position within the vertebrae of the same numerical designation. This shift is most pronounced in the caudal segments. We see this shift as progressively longer courses of the spinal nerves within the vertebral canal to reach their respective foramen; this arrangement is known as cauda equina.
External Topography
The spinal cord is essentially a cylindrical structure, slightly flattened dorso-ventrally, surrounded by the spinal meninges. The caudal termination of the cord presents 4 important features:
1. The spinal cord itself ends as a blunt, tapering process known as the Conus medullaris.
2. The spinal pia mater is continued caudally beyond the spinal cord as a fine strand of tissue called the filum terminale, which attaches to the end of the vertebral canal and acts as a caudal anchor. 3. The spinal dura mater also continues caudally beyond the conus medullaris for a short distance before abruptly joining with the pia mater; this arrangement forms a blind sac, lumbar cistern, which is continuous with the subarachnoid space. 4. The cauda equina is contained within the lumbar cistern before the nerves pass through the dura mater.
Internal Arrangement
When viewed in cross section 2 zones of colouration and texture may be distinguished. There is a centrally place blue-grey zone shaped like the letter ‘H’; this is known as the central grey matter.
The dorsal and ventral horns of grey matter meet in the middle at the grey commissure.
In the center is a small roundish opening, the central canal of the spinal cord, which is lined by ependymal cells and contains CSF. The central canal communicates with the 4 th ventricle and the lumbar cistern.
Surrounding the grey matter is the white matter of the spinal cord. These areas are known as dorsal, lateral and ventral funiculi or columns.
A distinguishing feature of the thoracic and upper lumbar spinal cord should be noted: the sympathetic component of the ANS arises from the thoracic and upper lumbar levels, specifically; the nerve cell bodies of preganglionic axons are located in the intermediolateral grey column.
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