MORE ON SENSORY PHYSIOLOGY

Dermatomes and Spinal Segments:  The spinal cord can be recognized as having 31 fairly distinct segments.  Each spinal segment receives information from the region of the surface of the body innervated by the spinal nerve emanating from the segment of the spine.  Each area on the surface of the body sending information to the brain through each spinal nerve is called a dermatome.  Thus, there are 31 dermatomes.  Loss of sensory information from specific dermatomes can be used as evidence of damage to specific spinal nerve pathways.  We can further see how sensory information is "mapped" onto the sensory cortex of the brain by looking at a "sensory homunculus."  The sensory homunculus show the proportion of the sensory cortex dedicated to interpreting sensory information from various areas of the body.  The sensory homunculus is shown to the right of left of the diagram and the "motor homunculus" to the right.  In regions of the body where there are several dermatomes present, for example the hands, sensory perception is very good.