A reflex action is an involuntary response in the body to a stimulus. Many such actions in the body, from breathing to moving away from a hot object, are done without requiring thought. A group of neurons called a neuron arc cause the reflex action to occur; the neuron arc consists of the receptor, the sensory neuron, the interneuron, the motor neuron and the effector.
The receptor is the involved sense organ, and the effector is the structure by which the body responds. The other parts are all carriers to, within and from the central nervous system. The reflex actions are done without the control of the person or animal in which they occur. When a doctor wants to check a patient's reflexes, he taps the patient's knee with a small mallet, and the knee jerks upward. Reflexes help protect the body from falling or being harmed in some other way. Babies are born with several reflex actions that disappear over time but serve a vital function early in life. The rooting reflex causes a baby to open his mouth when his cheek is touched. This reflex encourages the baby to take to the breast for nourishment. The sucking reflex is also present from birth to help the baby understand how to eat. Other such reflexes involve grasping, startling and stepping.