Parts of the spinal cord with its spinal roots, cauda equina and filum terminale
This is a specimen showing the lowermost region of the spinal cord, i.e. the sacral region. The tapered end of the spinal cord is called the conus medullaris, and this lower portion of the cord corresponds approximately to the sacral segments. The collection of dorsal and ventral nerve roots, below the level of the termination of the cord, is collectively called the cauda equina. These roots, which belong to the lumbar and sacral segments of the spinal cord, occupy the expanded subarachnoid space in this region, known as the lumbar cistern. The nerve roots are traveling from various levels of the spinal cord to exit at their corresponding intervertebral level. The pia mater covering the spinal cord gathers at the tip of the conus medullaris to form a ligament-like structure called the filum terminale.
The spinal cord is the lower elongated part of the central nervous system. It extends as a downward continuation of the medulla oblongata in the vertebral column. It measures about 45 cm long and contains ascending and descending tracts that serve as conduits for nervous information. It is composed of outer white matter and inner grey matter. The inner grey matter encloses the central canal which contains cerebrospinal fluid. It also provides attachment to 31 pairs of spinal nerves.
The main functions of the spinal cord are:
- Execution of simple reflexes
- Transmission of impulses to and from the brain
The conus medullaris is a lower tapering extremity of the spinal cord. It typically occurs at the level of L1 vertebra in adults.
The cauda equina (Latin: horse's tail) is a bundle of spinal nerves and spinal nerve rootlets, consisting of the paired L2-L5, S1-S5 spinal nerves, and the coccygeal nerve. These nerves arise from the lumbar enlargement and the conus medullaris of the spinal cord.
The lumbar cistern is an enlargement of the subarachnoid space in lower lumbar part of the spinal canal. It lies distal to the conus medullaris. It contains cerebrospinal fluid and the nerve roots of the cauda equina. The cistern extends from the L2 down to S2 vertebral levels. The lumbar puncture is done at this site (the interspinous space between L3 and L4 is the most preferred site) to withdraw the CSF.
The filum terminale is a delicate, glistening white thread-like structure extending from the tip of conus medullaris to the first coccygeal vertebra. The filum terminale is an extension of the spinal cord and is about 20 cm long. It is mainly composed of non-nervous fibrous tissue (pia mater) and a few nerve fibers (rudiments of 2nd, 3rd, and 4th coccygeal nerves).