Write a short note on Reflex action and Reflex arc.

Explanation

Reflex action is a fast, involuntary unplanned sequence of actions that occurs in response to a particular stimulus. e.g., closing the eyelids when dust falls in the eyes, withdrawing hand on touching a hot pan. It is brought about by the spinal cord. The nervous elements involved in carrying out the reflex actions constitute a reflex arc.
Reflex arc has
Sensory receptors: It is a sensory structure that responds to a specific stimulus.
Sensory neuron: This neuron takes sensory impulse to the grey matter of the spinal cord through the dorsal root of the spinal cord.
Interneurons: one or two interneurons serve to transmit impulses from the sensory neuron to the motor neuron.
Motor neuron: It transmits impulse from the central nervous system to the effector organ.
Effector organs: It may be a muscle or gland which responds to the impulse received.