Dermatomes and Myotomes
A dermatome is the area of skin supplied by a single spinal nerve. A myotome is the group of muscles that a single spinal nerve innervates. Understanding these is essential for localizing spinal cord lesions.
Key Clinical Landmarks
| Level | Dermatome Landmark | Myotome Action |
|---|---|---|
| C6 | Thumb | Wrist extension |
| C7 | Middle finger | Elbow extension |
| C8 | Little finger | Finger flexion |
| T4 | Nipple line | N/A |
| T10 | Umbilicus | N/A |
| L4 | Medial malleolus | Ankle dorsiflexion |
| S1 | Lateral malleolus/heel | Ankle plantarflexion |
High-Yield Exam Pearl:
“C6-C7-C8” matches the fingers: C6 for the thumb (1st digit), C7 for the middle finger (3rd digit), and C8 for the little finger (5th digit). For lower limbs, remember L4-L5-S1 as the order for the foot: L4 is medial, L5 is the dorsum, and S1 is the lateral side/heel.