Effector organs are smooth muscle, cardiac muscle and glands that respond to nerve impulses from the central nervous system without conscious thought. They are part of the automatic, or involuntary, nervous system, along with receptors, afferent nerves and efferent nerves.
The digestive system, the heart, the lungs and the diaphragm are examples of effector organs. A living being does not have to use conscious thought to breathe, to digest food or to make its heart beat. Reflex arcs also make use of effectors. A reflex arc is the rapid and involuntary response to specific stimuli, such as the contraction of skeletal muscle to remove a hand from a hot surface.
The activation of effector organs is a relatively complex process. Sensory receptors react to a stimulus, or a change in the internal or external environment, and transform the stimulus into an electronic signal. This signal passes to a sensory neuron, which acts as an intermediary, bridging the gap between the sensory receptors, which are part of the peripheral nervous system, to the central nervous system. The sensory neuron transmits the signal to the central nervous system, where it undergoes processing. The central nervous system then sends a message, as a nerve impulse, to the corresponding motor neurons, which carry the impulse to the effector organ, which finally translates the nerve impulse into a response or movement.