Forceful passive stretching of a contracted quadriceps triggers reflex relaxation of that same muscle. The afferent limb of this response originates from which receptor?

• A Primary endings of the muscle spindle
• B Ib afferents of the Golgi tendon organ ✓
• C Secondary endings of the muscle spindle
• D Free nerve endings in the joint capsule

Explanation

The Golgi tendon organ sits in series with muscle fibres at the musculotendinous junction and senses tension rather than length. When tension rises sharply, Ib afferents activate an inhibitory interneuron that suppresses the alpha motor neurons of the same muscle, producing autogenic inhibition. Spindle primary and secondary endings sense length and would produce excitation, the opposite sign of reflex effect, which is what makes them the tempting distractors here.

Reference: Ganong's Review of Medical Physiology, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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