Which law explains yoked muscles?

• A. Donder's Law
• B. Sherrington's Law
• C. Troxler Effect
• D. Hering's Law of Equal Innervation

Answer: (D)

Yoked muscles are the corresponding muscles in each eye that move together to produce the same direction of gaze. The principle that explains their coordinated action is Hering's Law of Equal Innervation: for any eye movement, the same amount and pattern of neural input is sent to the yoked muscle pair in both eyes. This ensures conjugate movements, so when you look in a direction, both eyes receive equal innervation to their respective muscles, keeping them aligned.

If the equal innervation to yoked muscles were not maintained, the eyes wouldn’t move together smoothly, leading to misalignment or diplopia. Other options describe different ideas—Donder's Law relates innervation to final eye position rather than inter-eye equality, Sherrington's Law concerns reciprocal innervation within an eye, and the Troxler Effect is a perceptual phenomenon unrelated to eye muscle innervation.