Dermatomes and Myotomes

A dermatome is an area of skin supplied by a single spinal nerve root. A myotome is the group of muscles supplied by a single spinal nerve root. Understanding these patterns is essential for localizing spinal nerve and spinal cord lesions.

Key dermatome landmarks: C5 (lateral arm), C6 (thumb), C7 (middle finger), C8 (little finger), T4 (nipple line), T10 (umbilicus), L1 (inguinal region), L4 (medial leg), L5 (dorsum of foot), S1 (lateral foot).

Key myotome actions: C5 (shoulder abduction), C6 (elbow flexion, wrist extension), C7 (elbow extension, wrist flexion), C8/T1 (finger flexion), L2 (hip flexion), L3 (knee extension), L4 (ankle dorsiflexion), L5 (great toe extension), S1 (ankle plantarflexion).

Spinal cord injury at a specific level causes sensory and motor loss below that level, identifiable by dermatome and myotome testing.