Ia afferents from muscle spindles terminate monosynaptically on alpha motor neurons to produce the stretch reflex. Which inhibitory interneuron ensures that the antagonist muscle relaxes during this reflex?
- A Renshaw cell
- B Golgi tendon organ Ib interneuron
- C Ia inhibitory interneuron (reciprocal inhibition via glycine release) ✓
- D Purkinje cell of the cerebellum
Correct answer: C. Ia inhibitory interneuron (reciprocal inhibition via glycine release)
Explanation
The stretch reflex arc involves: Ia afferent → monosynaptic excitation of agonist alpha-MN (muscle contracts) AND simultaneous activation of Ia inhibitory interneurons, which release glycine onto antagonist alpha-MNs, inhibiting them (reciprocal inhibition). This disynaptic pathway ensures coordinated, smooth movement. Renshaw cells provide recurrent inhibition of the same alpha-MN pool (collateral feedback). Ib interneurons mediate the inverse myotatic reflex (autogenic inhibition) activated by Golgi tendon organs during excessive force.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.