Reflex action: Encyclopedia II - Reflex action - Explanation

Reflex action - Explanation

A reflex action or reflex is a biological control system linking stimulus to response and mediated by a reflex arc. Reflexes can be built-in or learned. It occurs very quickly before thinking. Before the message is sent to the brain the spine picks it up and sends it back to the muscle causing spasm.

Reflex action - Simple reflex

A simple reflex is entirely automatic and involves no learning. Examples of such reflexes include the sudden withdrawal of a hand in response to a pain stimulus, or the jerking of a leg when the kneecap is tapped. Sensory cells (receptors) in the stimulated body part send signals to the spinal cord along a sensory nerve cell. Within the spine a reflex arc switches the signals straight back to the muscles of the body (in this case the arm or the leg) (effectors) via an intermediate nerve cell and then a motor nerve cell; contraction of the leg occurs, and the muscle contracts (the arm or leg jerks upwards). Only three nerve cells are involved, and the brain is only aware of the response after it has taken place. Such reflex arcs are particularly common in animals, and have a high survival value, enabling organisms to take rapid action to avoid potential danger.

Reflex action - Conditioned reflex

A conditioned reflex involves the modification of a reflex action in response to experience (learning). A stimulus that produces a simple reflex response becomes linked with another, possibly unrelated, stimulus. For example, a dog may salivate (a reflex action) when it sees its owner remove a tin-opener from a drawer because it has learned to associate that stimulus with the stimulus of being fed.

Reflex action - Reaction time

For a reflex, reaction time or latency is the time from the onset of a stimulus until the organism responds.

Adapted from the Wikipedia article "Explanation", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki