In the stretch reflex (myotatic reflex), Ib afferents from Golgi tendon organs produce which effect when the muscle is overloaded?

• A Monosynaptic excitation of homonymous alpha motor neurons, increasing muscle tension
• B Disynaptic inhibition of the homonymous muscle and excitation of the antagonist (inverse stretch reflex) ✓
• C Polysynaptic facilitation of gamma motor neurons to increase spindle sensitivity
• D Direct excitation of Renshaw cells producing recurrent inhibition

Explanation

Golgi tendon organs (GTOs) are tension sensors in musculotendinous junctions activated by active contraction (more so than passive stretch). Ib afferents from GTOs synapse on inhibitory interneurons (Ib interneurons) in the spinal cord that inhibit alpha motor neurons of the homonymous and synergist muscles, simultaneously exciting antagonist motor neurons — the inverse myotatic (autogenic inhibition) reflex. This protective reflex prevents muscle damage from excessive tension. Ia afferents from muscle spindles mediate the monosynaptic stretch reflex (tapping a tendon); this is the Ia circuit, not the Ib circuit.

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

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