A reflex is a quick and automatic response to a stimulus, like pulling your hand away from heat or lifting your foot off a sharp object. A reflex arc is the pathway that nerve impulses follow to produce a reflex action. It is made up of five main components. The first component is a sensory receptor that generates a nerve impulse when stimulated. The second component is a sensory neuron that carries the impulses from the receptor to the central nervous system or the CNS. The third component is an integration center located in the CNS, which processes the information provided by the sensory neurons. Integration centers can be a single synapse between a sensory and motor neuron or multiple synapses with chains of interneurons in between. The fourth component is a motor neuron, which carries motor instructions from the integration center to an effector muscle or a gland. The fifth and final component is an effector muscle or a gland, which contracts or secretes a hormone to produce the reflex action.