Excessive muscle contraction will activate (A) muscle spindles. (B) Golgi tendon organs. (C) Merkel disks. (D) Meissner corpuscles.

Excessive muscle contraction primarily activates **Golgi tendon organs**. Here's a breakdown of each option: - **(A) Muscle spindles**: These receptors detect changes in muscle length and the rate of that change, playing a key role in the stretch reflex but are not directly activated by excessive contraction. - **(B) Golgi tendon organs**: Located at the junction between muscles and tendons, these organs sense changes in muscle tension. When muscle contraction is excessive, Golgi tendon organs are activated to inhibit further contraction and prevent potential damage, acting as a protective mechanism. - **(C) Merkel disks**: These are mechanoreceptors in the skin responsible for detecting light touch and pressure, not related to muscle contraction. - **(D) Meissner corpuscles**: Also mechanoreceptors in the skin, primarily sensitive to light touch and vibration, and not involved in sensing muscle contraction. **Answer:** **(B) Golgi tendon organs.**