Question

Explain reflex-action in short.

Answer 1

Hint: It is necessary to understand the meaning of stimulus and response to explain reflex action. Stimulus is nothing but the change in an environment which causes the organism to react to it. The reaction of the organism is the response.

Complete answer:
Reflex action can be defined as the involuntary or automatic response to stimulus. The simple examples of reflex action are blinking of eyes or withdrawal of a hand when you touch a hot object. It mainly happens due to the body remembering the past experiences mainly bad experiences happened in the past. Reflex action plays a vital role in evolution of an organism and also the survival of an organism.
The different events that happen in the reflex action can be summed up as follows. The process of reflex action contains different neurons such as sensory neuron, motor neuron and relay neuron.
The first step is the receptor detecting the stimulus or the change in the environment. Stimulus is usually from a sensory organ such as the skin. The stimulus is then passed on to the relay neuron and the next neuron that comes into picture is the motor neuron. Motor neurons further send the signal to the effector. Effector produces the response; for example, the moving away of the hand while touching a hot object. Here touching the hot object can be said as the stimulus and moving away of the hand is the response. We can summarize the above steps as the efferent neuron receives a signal from the sensory organ and then it transmits the impulse into the central nervous system. The efferent neuron then carries the signal from the central nervous system and shows the response through the effector.

Note:
It can be noted that the signals are not sent to the brain instead it is sent to the synapse in the spinal cord hence the reaction is much faster and instantaneous. The whole pathway that controls a reflex action is defined as the reflex arc.