Every time you accidentally touch a hot surface, your hand withdraws itself immediately. It is like an automated action that happens without you having to think about it. In scientific terms, this action is called reflex action. Such Actions occur because of numerous neural pathways that are known as reflex arcs that act on an impulse before it reaches the brain. These actions can be inherited from parents or are learned throughout their lifetime. Read the article to explore more about the physiology and significance of reflex action.

What is Reflex Action?

Reflex action refers to the simplest form of response in the nervous system, which may be defined as the spontaneous, automatic and mechanical response to a stimulus acting on a specific receptor without conscious effort or thought and requires the involvement of a part of the central nervous system.

Physiology of Reflex Action

i. Reflex action is a rapid, simple, automatic response to a stimulus that is not under the voluntary control of the brain.
ii. It is an involuntary action.
iii. It takes very less time, about a few milliseconds, to show response during reflex action.
iv. Reflex action generally involves the spinal cord for quick response to a specific stimulus. Such reflexes are termed spinal reflexes. Then information input goes on to the brain, where the thinking process occurs later.
v. Reflexes maintain balance & posture. E.g. Spinal reflexes – control trunk and limb muscles.
vi. Reflex actions that involve smooth muscles are called visceral reflexes (e.g. beating of the heart), while reflex actions that involve skeletal muscles are called somatic reflexes (e.g. Knee-jerk).
vii. Some reflexes, though performed without our will but, are in our knowledge, like watering of the mouth, blinking of eyes, etc.
viii. But some reflexes are there which are performed without our knowledge, like the flow of bile from the gallbladder.

Types of Reflex Action

1. Natural reflex– It refers to the reflexes in which no previous learning is required, i.e., are inherited from parents or inborn or unconditioned reflexes, like salivation, swallowing, peristalsis, blinking of eyes, etc.
2. Conditioned reflex– It refers to the reflexes that are acquired or learned during its lifetime. It is developed by experience and is not transmitted through heredity—E.g. Salivation in a hungry dog in response to a dinner bell.

Reflex Action Examples

Examples of Natural Reflexes:
1. Withdrawal of hand suddenly from a hot object or if it gets pricked.
2. Coughing
3. Sneezing
4. Closing of eyelids when some particles enter the eye.
5. Shivering when it is too cold.
6. Knee-jerk reflex- This can be experienced when the area below the kneecap is tapped.
a. Message received by the receptors sent to the muscles of the thigh. Then, muscles in the front of our thigh contract and the muscles in its back relax. Resulting in foot jerking.

Fig: Knee-Jerk reflex

Examples of Conditioned or acquired Reflexes
1. Playing of musical instrument
2. Tying shoelace
3. Applying brakes when someone suddenly comes in front.
4. Typing on the computer.

Reflex Arc

Reflexes are motor responses to specific sensory stimuli, and this process takes place in so less time that it can hardly be estimated when the stimulus was generated and when the action took place. These reflex actions are mediated via the reflex arc.

Fig: Reflex Arc

The reflex arc is the  neural pathway that begins with a sensory neuron at a receptor (e.g., a pain receptor in the fingertip) and ends with a motor neuron at an effector (e.g., a skeletal muscle), and as mentioned above, it has following parts:
1. A receptor, which receives stimulus from the surroundings.
2. Afferent or sensory nerve, which takes a sensory impulse to the spinal cord or brain.
3. The central nervous system (brain or spinal cord) interprets the impulse and sets a motor impulse accordingly.
4. Efferent or Motor nerve, which carries motor impulse to the specific effector organs.
5. Effector organ, which acts according to the information received from the motor neuron.
6. Interneurons may be present between sensory and motor neurons.

Fig: Pathway of Impulse in the Reflex Arc

Importance of Reflex Action

1. As it is a fast action, it enables the animal to respond immediately to the harmful stimuli so that no harm is caused to it.
2. It relieves the brain of too much work, thus preventing it from being exhausted.

Summary

From the above discussion, we can conclude that there are some actions that can be controlled by the spinal cord itself. These types of actions are involuntary, i.e., not in our control. For example, if we touch a hot object, we immediately remove our hands from it. Had this been taken care of by the brain, then some severe damage would have been caused to the hand.

So, we can say that these types of actions need immediate reaction to prevent damage to the organs of the body. Such types of actions are reflex actions. It can be either natural or conditioned. Natural reflex actions are inherited from parents, while conditioned reflexes are learned throughout their lifetime.

Frequently Asked Questions (FAQs) on Reflex Action

Q.1. What is reflex action with an example?
Ans: Reflex action refers to the simplest form of response in the nervous system, which may be defined as the spontaneous, automatic and mechanical response to a stimulus acting on a specific receptor without the will of an animal. E.g., Flushing of tears from our eyes when some particle enters the eye.

Q.2. What are the steps of a reflex action?
Ans: 1. A specific receptor, which receives stimulus from the surroundings.
2. Afferent or sensory nerve, which takes a sensory impulse to the spinal cord or brain.
3. Central nervous system (brain or spinal cord) interprets the impulse and sets a motor impulse accordingly.
4. Efferent or Motor nerve, which carries the motor impulse to the specific effector organs.
5. Effector organ, which acts according to the information received from the motor neuron.

Q.3. What are the types of reflex action?
Ans: Types of reflex action are-
I. Natural reflexes
II. Conditioned reflexes

Q.4. Who controls the reflex action?
Ans: Spinal cord controls reflex.

Q.5. Is blinking of eyes a reflex action?
Ans: Yes, blinking of eyes is a reflex action.

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