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The Spinal Cord and Spinal Nerves
1. Structure of the spinal cord The spinal cord (medulla spinalis) is an elongated structure that is more or less cylindrical. It is part of the CNS. It is slightly flattened dorsoventrally, and has some regional variations in form and dimensions. The most important of these are the swellings (intumescentiae) that give rise to the nerves supplying the limbs, and the final caudal tapering of the cord (conus medullaris). The spinal cord can be divided into cervical (C1-C6), cervicothoracic (C7-T2), thoracolumbar (T3-L3), lumbosacral (L3-S2) and sacral (S3 onwards). The spinal cord consists of a central mass (mantle) of grey matter surrounding the central spinal canal. The grey matter is roughly H shaped, and is described as having ventral and dorsal horns or columns. The dorsal horn corresponds to the alar plate. It contains somatic afferent neurons dorsomedially and visceral afferent neurons dorsolaterally. The ventral horn corresponds to the basal plate. It contains somatic efferent neurons ventrally, and visceral efferent neurons, which form an additional lateral horn in the thoracolumbar and sacral regions of the spinal cord only. The grey matter is enveloped by white matter (marginal layer). It is divided into three funiculi on each side. The dorsal funiculus is contained between the dorsal sulcus, the dorsal median septum and the dorsal roots of the spinal nerves. The lateral funiculus is contained between the dorsal and ventral roots. The ventral funiculus is contained between the roots of the ventral spinal nerves and ventral fissure that is filled with pia mater. The funiculi contain ascending and descending nerve fibres. The spinal cord is contained within protective meninges - the outer dura mater, the middle arachnoid mater and the inner pia mater. The dura mater is a fibrous, tough layer, and is separated from the periosteum by the epidural space, which is filled with fat. The pia mater is a thin layer which is adherent to the underlying spinal cord. It is filled with capillaries, and it blends with the fibres of the arachnoid mater. Denticulate ligaments provide an attachment between the pia-arachnoid and dura mater. The meninges extend along dorsal and ventral nerve roots into the intervertebral foraminae.
2. Vasculature The spinal cord is supplies by three arteries that run its length. The largest, the ventral spinal artery, follows the ventral fissure of the cord. Paired dorsolateral spinal arteries run close to the furrow from wghich the dorsal roots of the spinal nerves arise. All three of these arteries are periodically reinforced by regional arteries. The ventral spinal artery supplies the cord of the cord, the grey matter and adjacent layer of white matter. The majority of the white matter is supplied by the dorsolateral spinal arteries. The spinal cord is drained by the vertebral venous plexus.
3. Spinal nerves
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