Reaction vs Reflex
Human beings have got various sense organs through which they feel and respond to different kinds of stimuli. For example, we respond in a voluntary manner to cold and heat and respond according to the messages sent by sensory nerves through the brain. If we are bitten by a mosquito, we feel irritation in the body part where it has bitten and try to rub the part to lessen the irritation. This is an involuntary response to the stimulus. On the other hand, there are certain responses that our body is capable of, and are involuntary and we react almost instantaneously in response to stimuli. For example, if a fast moving ball comes near our face, our eyes automatically close to protect them from the impact of the ball. Similarly if something hits our knee cap in a hard manner, we stretch our knees in defense in a fast, instantaneous manner which is a reflex and not a reaction. If our hand touches a very hot object, hand withdraws in a very quick manner which is different from the normal reaction which is late and takes time. Let us know a bit more about reaction and reflex.
In a normal reaction, sensory nerves carry the information to the brain which perceives and then sends message to the motor nerves to respond to the stimulus in a particular manner. In the case of a reflex, though sensory nerves are still involved, they carry the message only up to the central nervous system (CNS), and then quickly back to the motor nerves. Thus brain is bypassed and you do not need to think about the stimuli and proceed accordingly. Thus you pull off your leg when you feel a nail beneath, you feel the pain an instant later. It is through a reflex action that you pull your leg, and you have already pulled your leg away in the time your brain send the message of pain to the motor nerves. Had there been no reflex action, the nail would have hurt much more because the time taken by the brain to send the message to the motor nerves is much more than the time taken by CNS to send the message to the motor nerves.
Reflex vs Reaction
• Reaction is voluntary while reflex is involuntary
• Reaction takes place through sensory nerves that bring back message from the brain to the motor nerve whereas sensory nerves bypass brain and go up to CNS only in the case of reflex.
• This is why reflex is faster than reaction.