Final answer:
To test the T3 dermatome, apply a light touch using a cotton-tipped applicator to the skin at the level of the third rib, corresponding to the T3 spinal nerve, and ask the patient about their sensation.
Step-by-step explanation:
To test for the T3 dermatome, which corresponds to the third thoracic spinal nerve, apply a light touch stimulus such as the soft end of a cotton-tipped applicator to the skin. The T3 dermatome encompasses the skin that covers the chest around the level of the third rib. This area corresponds to the sensation received by the T3 spinal nerve, which originates from the spinal cord at the level of the third thoracic vertebra. Testing this dermatome involves touching the area with a cotton applicator and asking the patient if they perceive it, and to describe any differences in sensation. Besides level T3, you would also assess other dermatomes to compare sensation and ensure spatial specificity of perception. Proprioception, or the sense of position and motion, is tested in a similar manner by moving the fingers or toes and asking the patient about their sensation of the movement.