Final answer:
To test the C3 dermatome, one would apply light touch with a cotton-tipped applicator to the neck and back of the head, which corresponds to the sensory innervation of the C3 spinal nerve.
Step-by-step explanation:
To test for the C3 dermatome, which is the skin region innervated by the third cervical spinal nerve, one would apply a simple stimulus such as the light touch of the soft end of a cotton-tipped applicator to the areas of the skin associated with the C3 spinal nerve. The C3 dermatome includes parts of the neck and back of the head. Testing involves applying the stimulus from distal to proximal locations on the skin in this region to assess whether the sensation of light touch is perceived accurately. In a clinical setting, this might be one of the tests used to determine the integrity of sensory nerve pathways following an injury or in the diagnosis of neurological conditions.