CLINICAL ANATOMY OF THE SPINAL CORD1
The spinal cord contains lower motor neurons, first-order sensory neurons, second-order spinothalamic neurons, interneurons, as well as the ascending and descending tracts that connect these cells with the brain. The spinal cord is surrounded by the vertebral column, which consists of a number of discrete bones called the vertebrae. Each vertebra consists of a cylindrical bone anteriorly called the body, two lateral processes called transverse processes, and a dorsal process called the spinal process. The transverse processes are connected to the vertebral body by the pedicles and to the spinous process by the laminae. The hollow in the ring is formed by the posterior vertebral body, pedicles, laminae, medial transverse process and anterior spinous process forms part of the spinal canal. The successive vertebrae articulate with one another intervened by discs and facet joints (Figure 38-1).
The vertebral column and its tranverse and longitudinal structures.
The spinal cord is segmentally organized. These segments correspond embryologically to the nerve supply of somites, which give rise to the musculature. There are 31 spinal cord segments: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal. Each segment corresponds to a spinal nerve. These nerves are named after the segment from which they originate. C1–7 exist in the spinal canal above their corresponding vertebrae and the rest exist below their vertebrae. The spinal cord ends at the level L1, so that with more caudal segments the distance between the spinal segment and the point of exit of the spinal nerve from the vertebral column increases. In the lumbar vertebral column, the spinal roots have to travel a distance to reach their point of exit. The mass of stringy roots travelling in the lower vertebral column resemble a horse’s tail or cauda equina.
The spinal cord is supplied by one anterior and two posterior spinal arteries. The anterior spinal artery is formed from branches of the vertebral artery and runs caudally along the anterior fissure of the spinal cord, while two paired posterior spinal arteries travel in the dorsolateral sulci. Segmental arteries supply and supplement the blood in the spinal arteries. The most significant of these radicular arteries is the artery of Adamkiewicz.
The cross section of the spinal cord is characterized by a central area of an “H”-shaped gray matter surrounded by white matter. The gray matter has two dorsal horns that serve predominantly a sensory role, two anterior horns that contain motor neurons and interneurons, and an intermediate gray that intervenes between the two on the lateral side and contain autonomic cells. The area around the central canal (which is continuous with the ventricular system) is called central gray. The gray matter divides the white matter into anterior, lateral, and posterior segments. The posterior “column” contains the spino-lemniscal pathway, ...