Final answer:
The dermatomes that are blocked are the sensory regions of the skin that are innervated by the spinal nerves containing the blocked fibers. These dermatomes can be identified by the location where sensory endings are found in the skin.
Step-by-step explanation:
The dermatomes that are blocked are the sensory regions of the skin that are innervated by the spinal nerves containing the blocked fibers. These dermatomes are organized in a topographical manner and can be identified by the location where sensory endings are found in the skin. For example, the eighth cervical nerve innervates the medial surface of the forearm and extends out to the fingers.
To test sensory perception within a dermatome, the patient is asked if they can perceive touch at different positions on the skin within that dermatome. This is done by applying a light touch with a soft cotton-tipped applicator at various locations on the skin.