Stock Photo - Illustration of the patellar reflex. On the left, an illustration of the nerve signal with, in blue, the journey of the afferent impulse from the muscle spindle in the muscle near the bone marrow, counterbalanced by the efferent impulse response (red) which triggers muscle contraction, resisting and opposing stretching, and the efferent impulse (purple) which prevents the antagonistic muscle contracting. The leg remains static. On the right, an illustration of the actors in the patellar reflex. The afferent impulse (blue) goes from the muscle to the bone marrow through the sensory nerve which responds to stimulation sent via the contact of the hammer on the patellar ligament. It sets off the efferent impulse (red) which results in the muscle contracting and the instantaneous extension of the leg. The efferent impulse (purple) which makes the antagonstic muscle contract is suppressed.