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Reflex Action

Last Updated : 30 Nov, 2023
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Reflex action is an involuntary and automatic response to a specific stimulus. Reflex action is a type of behavior that is not consciously controlled by the brain, but rather, it is mediated by the spinal cord and peripheral nerves. Reflex action is an essential survival mechanism that allows an organism to respond quickly to potentially harmful stimuli.

Understanding reflex actions is essential for healthcare professionals, as reflex testing can provide valuable information about the function of the nervous system. In this article, we will study the Reflex action, Reflex arc, and Diagram of reflex action.

What is Reflex Action?

The word ‘reflex’ means any sudden action. Reflex action is an automatic, rapid, spontaneous, protective quick response or reaction to a stimulus without being under control. E.g. Blinking of eyes, Touching a flame, and then withdrawing hand. In general, reflex action provides a protective pathway to prevent any injury, which helps avoid pain.

When you touch a hot plate, a reflex action occurs in which the sensory receptor in the body responds to the stimulus which in this case is heat. Then the signal is transmitted via sensory neuron to the spinal cord. Multiple Interneurons are present in the Spinal Cord which activate on receiving signal. The interneurons then activate the Motor neuron which then sends the response signal back to the muscles to produce a reflexive response. The person will automatically remove his/her hand from the plate.

Reflex Action Diagram

The labelled diagram of reflex action is shown below:


Types of Reflex Action

Following are the different types of reflex actions:

  • Monosynaptic Reflex: This type of reflex involves a single synapse and the knee jerk reaction is an example of it.
  • Polysynaptic Reflex: An example of this type of reflex is the withdrawal reflex that involves multiple synapses and interneurons.
  • Conditioned Reflex: This is an acquired kind of relex based on experience. E.g Pavlov’s experiment.
  • Abdominal Reflex: The abdomen automatically starts to flex which allows the movement of feces through the intestines.
  • Blink Reflex: The eyes blink automatically without the brain knowing about it.
  • Sucking Reflex: This is seen in newborns where they automatically learn how to suckle on their mother’s nipples.

Reflex Action Example

Some common examples of reflex action are:

  • A hungry mouth started watering upon seeing food
  • Body parts moving in response to touching a flame, touching a needle, or touching a cold object
  • The change is size of the eye pupil when light acts as stimulus
  • Sudden withdrawal of leg when pricked by a pin
  • Coughing or sneezing because of irritation in nasal passages, etc.

How does our body respond to these actions? All these questions arise the concept of  ‘Reflex arc’.

Definition of Reflex Arc

The process that controls reflex action is known as the reflex arc.

The process of detecting the signal- input, and response to it by output action completely quickly; such connections are called reflex arcs. Reflex arcs are formed in the spinal cord, and the input information in the form of signals goes to the brain.

Reflex Action Pathway                                                  

Stimulus ——> Receptor (skin) —-Sensory neurons—-> Spinal Cord —-Motor neurons—-> Effectors (like Muscle and Glands)

Action of Neuron 

In a reflex action, two types of nerves are included – the efferent (excitatory) and afferent nerves(receptor). Both nerves work together to make any reflex action. Reflex action occurs in a series of events which are mentioned below:

  1. Any reflex action starts when the afferent nerve receives any signal due to any sudden change in the surrounding. Stimulus is received by the receptor nerves.
  2. Afferent nerves become active and pass the information to the relay neves after getting the stimulus.
  3. The relay nerve passes the information to the motor neurons.
  4. Motor neurons send the signal or activate the efferent nerves.
  5. The effector’s nerves react according to the information. 

Afferent nerves become active after receiving signals from the sensory organ, which transfers the information via signals to the Central Nervous System. Efferent nerves transmit signals to the muscles that react according to the signal. Here Spinal cord gives information to react or behave instead of the brain in Reflex action.

Also Read,

FAQs on Reflex Action

1. Which part of brain controls reflex action?

The brain is not involved in the reflex action but the spinal cord has a major role in the reflex action.

2. Which neuron is responsible for reflex?

The sensory neuron is the one responsible for detecting the signal and the motor neuron transmits the response signal.

3. What is the origin of the reflex action?

The Reflex Arc acts as the origin of Reflex action. It is a nervous system pathway that activates when the recptor receives signal.

4. What is a Reflex Arc?

The reflex arc is a way that controls the reflexes. 

5. What is the aim of reflex action?

The main aim of the reflex action is to protect an organism in case of adverse situations. E.g Pulling out your leg in case of hot utensil lying around.

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