lec12-03 - SPINAL CORD{3rd1 Edition pages 293 right and 294...

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Unformatted text preview: SPINAL CORD: {3rd1 Edition: pages 293 right and 294 top; Fig. 9-7}. The spinal cord is divided into five major regions: cervical, thoracic, lumbar, sacral and coccygeal. The top cervical region has 8 segments, thoracic has 12 segments, lumbar has 5 segments, sacral has 5 and coccygeal 1. At each level or segment, two nerve bundles (one on right and one on left) carry sensory information from the body to the CNS. These are called dorsal roots. The cell bodies of the sensory nerves lie outside the spinal cord in a dorsal root ganglion (the swellings in B part of Figure 4-B). Also, two nerve bundles (one on right and one on left) carry information from the spinal cord to the muscles. These bundles are called ventral roots. At each level and on each side, the ventral root and the dorsal root join to form the spinal nerve of that segment {3rd Ed: Fig. 9-7a}. Thus there are two spinal nerves at each segment of the spinal cord. If you cut the spinal cord in a plane parallel to the ground when you are standing, you will see a cross section of the spinal cord. This cross section shows that the spinal cord consists of gray matter and white matter. The gray matter consists mainly of neuronal cell bodies while the white matter consists of axons carrying messages to and from the higher centres. Note: there are no cell bodies in the white matter. Gray matter is divided into three parts: dorsal horn, ventral horn and intermediate zone. The lateral part of the intermediate region is called the lateral horn where cell bodies of autonomic efferents are located (to be done later). Cell bodies of neurons that carry messages to the muscles lie in the ventral horn. These cells are called motoneurons. The rest of the gray matter contains cell bodies of various interneurons, and cell bodies of neurons which carry messages to the higher centres. O Descending tracts O Ascending tracts Figure 4-C ...
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