Reflex action is an automatic response produced by effectors.
In other words, Reflex actions are spontaneous, automatic and mechanical responses without involving the will.
Spinal cord controls reflex action.
In animals, most of the activities and responses to stimuli are involuntary and not under conscious control of the brain.
Reflex actions occur rapidly without involving the brain.
Examples of reflex actions are,
i) If you accidentally step on some sharp objects such as a pin or nail, you withdraw your leg quickly from the source of irritation without thinking what to do.
ii) In humans, useful responses such as breathing, sneezing, yawning, coughing, enlargement or contraction of the pupil of the eye with the change of light intensity are some examples of reflex action.
iii) Shivering when there is cold, watering of the mouth after smelling food, blinking of the eyes to avoid danger are some examples of reflex action.
Reflex action must be very rapid to avoid harm to the body.
Reflex arc is the route taken by nerve impulses from the receptors to the effectors during involuntary actions.
It consists of 5 parts. They are
1) Receptor organ/skin:
It receives the stimulus and initiates a sensory nerve impulse e.g. skin and other sense organs.
2) Sensory or afferent nerve:
It conducts impulses from the receptor to the spinal cord.
It acts as modulator and changes the sensory impulse into the motor impulse.
4) Motor or efferent nerve:
It conducts impulses from the interneuron (spinal cord) to the effector organs (muscle or gland).
5) Effector or organ/muscles:
It responds to the impulses received by muscles and glands.
Significance/Importance of reflex action
1. It enables the body to give quick response to harmful stimuli because to protect our body from damages.
2. It prevents overloading of the brain.
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