When a stretch reflex occurs, the muscles that antagonize the action of the muscle must relax. This is ini-tiated by a simultaneous inhibition of the nerve to the antagonistic muscle. A branch of the sensory nerve synapses with an interneuron that secretes an in-hibitory neurotransmitter. This way, every time an impulse travels up the sensory nerve, the motor nerve to the antagonistic muscle is inhibited (see Figure 5.32). This is known as reciprocal innervation.