A reflex action is an automatic nervous action in which a stimulus causes a rapid response. For example, if a person accidentally touches a hot stove, he would immediately jerk away his hand before he has time to think about it. In this case, the hot stove is a stimulus, and the jerk is the response.
Reflexes, such as the ‘pupil reflex’ are quite common. When a bright beam of light hits a person’s eye, his pupil automatically becomes smaller. And if the light is taken away and his eyes are shaded, the pupil returns to its normal size. Here the light acts as the stimulus and the reaction of the pupil is the eye’s response.
Reflex actions are of two types: unconditioned and conditioned. Unconditioned reflex actions are exemplified by the reflex tests of the physician. When a doctor tests a person’s reflexes, he makes sure that the different parts of his nervous system are functioning properly. One reflex action frequently tested is the knee-jerk action. In this the doctor lightly strikes an area just below the knee cap with a rubber hammer. This causes the lower part of the leg to jerk upward suddenly. This is because the nerve impulses move via the spinal cord directly to the leg muscle and are not controlled by the brain. Such reflex actions are called ‘unconditioned reflex actions’. These take place without any special learning or experience.
The conditioned reflex actions are a result of particular internal or external stimuli. Such conditioning process was popularized by the Russian physiologist I.P. Pavlov and his associates. Pavlov believed that whenever there was a response to a particular stimulus, a kind of reflex was established in the brain. However, most psychologists today believe that the mechanism of learning is much more complicated than explained by him.
Now the question arises what causes a reflex action? To explain in simple terms, four basic processes are involved in a reflex action. These are: reception, conduction, transmission and response. The stimulus is received by receptors (nerve endings). Energy from the stimulus is changed into nerve impulses and carried from the receptor to the central nervous system. The nerve impulses are then sent to the motor nerves. The motor nerves control muscle action, causing the muscles and glands to respond (act). Most reflex actions, however, are much more complicated and also involve other parts of the nervous system like brain.
More than 90% of all the actions are performed by man’s nervous system and reflex actions.