A reflex action is defined as a spontaneous, automatic and mechanical response to a stimulus without the will of an individual. In such actions there is no involvement of the brain. All reflex actions are conveyed through the spinal cord by a path called reflex arc. The reflex action travels in the following sequence:
The reflex arc constitutes the following components:
(i) A receptor to perceive the stimulus.
(ii) A sensory or afferent nerve which carries the message from the receptor to the spinal cord.
(iii) The neurons of spinal cord transmit the impulse from afferent neurons to efferent neurons.
(iv) The motor or efferent nerve carries messages from the spinal cord to the muscles (effectors) that show the response.
Some examples of reflex actions are:
(i) Blinking of eyes when a foreign particle gets in them.
(ii) Sneezing if an unwanted particle enters the nose.
(iii) Watering of mouth at the sight or smell of good food.
(iv) Withdrawal of foot while walking if a nail comes in the way and pricks the foot.
(v) Immediate withdrawal of hand of a person if some hot thing touches it.
