The stretch reflex (myotatic reflex) is mediated by which receptor and pathway?

• A Golgi tendon organ → Ib afferent → inhibitory interneuron → muscle relaxation
• B Free nerve endings → C fibers → polysynaptic pathway → flexion reflex
• C Muscle spindle → Ia afferent → direct monosynaptic excitation of alpha motor neuron ✓
• D Muscle spindle → Ib afferent → excitatory interneuron → contraction

Explanation

The stretch reflex is a monosynaptic reflex mediated by Ia afferents from the nuclear bag and nuclear chain fibers of the muscle spindle. When a muscle is stretched, the Ia afferent directly synapses on and excites the alpha motor neuron supplying the same muscle, causing contraction that resists the stretch. The Golgi tendon organ (Ib afferent) mediates the inverse myotatic reflex causing inhibition of the same muscle.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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