The withdrawal reflex. When a painful stimulus activates a receptor in the paw,action potentials are generated in the corresponding afferent pathway,which propagates the electrical signals to the CNS. Once the afferent neuron enters the spinal coed,it diverges and terminates on three different types of interneurons (only one of each type is depicted): (1) excitatory interneurons, which in turn stimulate the efferent motor neurons to the biceps,causing the leg to flex and pull the foot away from the painful stimulus; (2)inhibitory interneurons, which inhibit the efferent motor neurons to the triceps, thus preventing counterproductive contraction of this antagonistic muscle; and (3) interneurons that carry the signal up the apinal cord via an ascending pathway to the brain for awareness of pain,memory storage, and so on.