During maximal voluntary contraction, tension in the quadriceps rises sharply. A reflex then limits further force generation by inhibiting the same muscle's alpha motor neurons. The receptor and afferent fiber responsible are:

• A Muscle spindle primary ending, Ia fiber
• B Golgi tendon organ, Ib fiber ✓
• C Free nerve ending, group III fiber
• D Pacinian corpuscle, A-beta fiber

Explanation

The Golgi tendon organ lies in series with muscle fibers at the musculotendinous junction and senses tension rather than length. Its Ib afferents excite an inhibitory interneuron in the spinal cord, which suppresses homonymous alpha motor neurons; this is autogenic or inverse myotatic inhibition. It protects against forces that could tear tendon or bone and may serve to equalize load distribution among motor units. The muscle spindle, in parallel, senses length and mediates the opposite, excitatory stretch reflex.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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