Illustration showing the parts of the body involved in a patellar reflex. The afferent impulse (blue) goes from the muscle to the bone marrow through the sensory neuron which responds to the stimulation of a reflex hammer on the patellar ligament. This activates the efferent impulse (red) which leads to the muscle contracting and the instant extension of the leg. The efferent impulse (purple) which leads to the antagonist muscle contracting is inhibited.