The word Reflex is used to convey sudden and immediate action in response to something. There are certain actions in the body that are spontaneous and do not need any processing by the brain. Such actions or responses are called reflex actions.
Reflex actions are involuntary actions that occur without conscious thought processes. For example:
When some particles fall into your eye, there is immediate flushing of tears to wash them out (glandular secretion).
When your hand accidentally touches a hot pan, you withdraw it instantaneously (muscular movement).
You shiver when it is very cold (muscular contractions) or sweat when it is too hot (glandular secretion).
A reflex action may be defined as a spontaneous, autonomic and mechanical response to a stimulus controlled by the spinal cord and without the involvement of the brain. All involuntary actions or reflexes are initiated by some kind of sensory stimulations resulting in either a muscular action or a glandular secretion.
Stimulus → receptor in the sense organ → afferent (sensory) nerve fibre → CNS → efferent (motor) nerve fibre → muscle (to contract) or gland (to secrete)
Reflexes are of two types:
1. Natural (inborn) reflex
Activities in which no previous experience or learning is required are termed as natural reflexes. These reflexes are inborn, i.e. inherited at the time of birth. Examples are: swallowing, coughing and blinking of eyelids.
2. Conditioned (acquired) reflex
Actions which develop during the lifetime due to experience or learning are termed as conditioned reflex. For example, salivation occurs at the smell of the food as the brain is able to remember the taste of the food and works in an unconscious way. Such reflexes are not inborn and hence conditioned reflexes are acquired.
In order to preserve the conditioned reflex, it is necessary to reinforce it periodically. For example, once the reflex is formed, the mere smell of the food initiates salivation. However, if repeatedly the smell of the favourite food item is not followed by the food itself, you will stop reacting to the smell with salivation after a certain time.