Reflex Action

A reflex action is a quick involuntary action in response to an external or internal stimulus, generally without the involvement of the brain.

E.g. A tap on the knee results in a spontaneous withdrawal i.e. a knee-jerk. Similarly, when we touch a hot object, we spontaneously withdraw our hand.

Reflex action is of two types:

(1) Unconditioned reflex - Inborn and inherited. E.g. sneezing and coughing.

(2) Conditioned reflex - Learned reflexes. E.g. cycling and salivation on smelling one's favourite food.

1.0Significance of Reflex Action

Act as an alarm which indicates about some unnatural incidents that are going to happen.

Quick and sudden reflexes protect us from the dangers and injuries.

Reflex Arc: A reflex arc is the shortest route that can be taken by an impulse from receptor to an effector.

The basic components of reflex arc are a receptor, a sensory neuron, a centre, a motor neuron and an effector.

2.0Components of reflex arc are

(1) Receptor: The dendrite of sensory neuron receives stimulus and initiates a nerve impulse.

(2) Sensory neuron: The nerve impulse passes from the dendrites to the axon terminal branches of the sensory neuron in the spinal cord.

(3) Centre: It is the region in the spinal cord or brain where the incoming sensory impulse generates an outgoing motor impulse. Relay neurons are found in the brain and spinal cord and allow sensory and motor neurons to communicate.

(4) Motor neuron: It transmits the impulse generated by the sensory neuron in the centre to the effector organ of the body that will respond, such as a muscle or gland.

(5) Effector: It is the organ of the body that responds to motor nerve impulse.