Final answer:
A dermatome is the area of skin supplied by a single spinal nerve, essential for testing somatosensation and determining the integrity of sensory perception in various skin regions.
Step-by-step explanation:
The area of skin mainly supplied by a single spinal nerve is called a dermatome. Dermatomes are topographic regions on the surface of the skin that are associated with the sensory endings based on the spinal nerve containing those fibers. For instance, the sensory fibers of the eighth cervical nerve innervate the medial surface of the forearm and extend out to the fingers. The sensory exam may involve a simple stimulus, like the light touch of a cotton-tipped applicator, to test somatosensation within these regions. This testing helps determine whether sensory perception is normal across different areas of the skin corresponding to specific spinal nerves.