What is the anatomy of the spinal cord relative to dermatomes?

Updated: Oct 13, 2017
  • Author: Stephen Kishner, MD, MHA; Chief Editor: Thomas R Gest, PhD  more...
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The spinal cord has 31 segments, each with a pair (right and left) of ventral (anterior) and dorsal (posterior) nerve roots that innervate motor and sensory function, respectively. The anterior and posterior nerve roots combine on each side to form the spinal nerves as they exit the vertebral canal through the intervertebral foramina or neuroforamina.

The 31 spine segments on each side give rise to 31 spinal nerves, which are composed of 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal spinal nerve. Dermatomes exist for each of these spinal nerves, except the first cervical spinal nerve. Sensory information from a specific dermatome is transmitted by the sensory nerve fibers to the spinal nerve of a specific segment of the spinal cord.

The C1-C7 nerve roots emerge above their respective vertebrae; the C8 nerve root emerges between the C7 and T1 vertebrae. The remaining nerve roots emerge below their respective vertebrae.

Along the thorax and abdomen, the dermatomes are evenly spaced segments stacked up on top of each other, and each is supplied by a different spinal nerve. The dermatomes along the arms and legs differ from the pattern of the trunk dermatomes, because they run longitudinally along the limbs. The general pattern is similar in all people, but significant variations exist in dermatome maps from person to person. [1]

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