When a stretch reflex occurs the muscles that antagonize the action of the muscle involved relaxes. This phenomenon is known as:

Reciprocal innervation is a phenomenon in which, when a stretch reflex occurs the muscles that anotogonize the action of the muscle involved relaxes. The pathway mediating this effect is bisynaptic. Golgi bottle neurons (inhibitory interneurons) are involved in this phenomenon. Ref:Ganong's Review of Medical Physiology, 21st Edition, Page 133