What is reflex action ? Explain the mechanism of reflex action with a suitable example.

Reflex action is a form of animal behaviour in which the stimulation of a sensory organ (receptors) results in the activity of some organ without the intervention of will. Actually it is a spontaneous automatic mechanical response to a stimulus without the will of the animal.

MECHANISMS OF REFLEX ACTION: If the reflex action is controlled by the spinal cord it is called spinal reflex action and if it is controlled by the brain ,it is known as cerebral reflex action. For a reflex action five things are normally essential: i) receptor, ii) sensory nerve fibres, iii) a part of the central nervous system, iv) motor nerve fibres and v) effector organ such as muscles and glands. The sensory nerve fibres bring sensory impulses from the receptor organ to the central nervous system. The motor nerve fibres relay the motor impulses from the central nervous system to the effector organs. Thus, an impulse travels a path during reflex action which is called reflex arc.

Examples of reflex action are,

i) Closing of eyes when strong light is flashed across them.

ii) Withdrawal of limbs when they are touched by hot things.

iii) Watering of mouth on seeing favourite food.

iv) Withdrawal of limbs in a decapitated frog when dipped in warm water or touched with an acid.