For a special Thanksgiving Day edition, here’s a quick way to remember a handful of deep tendon reflexes, muscle innervations, and dermatomes for your neurological exam. Remembering DTRs and the dermatomes of the arm are as easy as counting 1,2,3, 4. For DTRs, start at the Achilles’ tendon, now go to the patellar, followed by the biceps, and finally the triceps. Now count, 1/2, 3/4, 5/6, and 7/8. The Achilles’ DTR is sacral 1 and 2, the patellar DTR is lumbar 3 and 4, the bicep DTR is cervical 5 and 6, and the tricep DTR is cervical 7 and 8. Similarly, efferent muscle innervations for muscle strength testing follow a similar format.
The dermatomes of the arm follow a similar 5, 6, 7, 8, 1, 2 pattern. However, it’s important to remember that this is all in anatomical position, which is the arm down by the side, palm forward. The lateral side of the upper arm is C 5, the lateral side of the lower arm and hand is C 6, the middle finger is C 7, the inside of part of the hand is C 8, the inside part of the lower arm is T 1, and the inside part of the upper arm and the top of the axilla is T 2. One thing to note with dermatomes is that there is some variations between references and individuals, but this does represent a quick a dirty way of remembering what spinal level innervates what part of the arm.