THE SOMATOTOPY OF THE SPINAL CORD: A COMPREHENSIVE DESCRIPTION

For the benefit of medical students, in this paper we examine the somatotopic organization of the spinal cord, which shows a similar organization in mammalians. The dorsal horn is comprised of sensory nuclei with deutoneurons; the lateral horn contains preganglionic visceral motoneurons; the ventral horn is subdivided into a medial column innervating the paravertebral muscles, a central column, C3-C6, innervating the diaphragm, and a lateral column innervating the limb muscles. In the lateral column of the ventral horn, the dorsal motoneuron groups innervate the intrinsc arm muscles; the dorsal posterior motoneuron groups innervate hand muscles; the lateroventral motoneuron groups innervate the shoulder. Furthermore, the rostral and caudal motoneuron groups innervate the proximal and the distal muscles, respectively. In cat spinal cord, the medial columns 1-2 innervate the paravertebral muscles, and columns 3 -6 are divisible into groups, each innervating specific muscle groups. In human spinal cord, 11 motor columns have been identified: column 1 is located in the medial part and columns 2-11 in the lateral part of the ventral horn. Columns 1-2 extend to S3, while columns 3-8 are confined to the cervical and T1 segments, and columns 9-11 are situated in the lumbosacral segments.