Reflex Action

What is Reflex Action?

An involuntary or instantaneous action by the human body parts in response to a stimulus is called reflex action. It is because of numerous neural pathways that are known as reflex arcs that act on an impulse before it reaches the brain. Reflex action doesn’t need any conscious thought or awareness about the automatic response. 


What Happens in Reflex Action?

When a specialized tissue receives a stimulus, it may either directly/indirectly alter the relation of other tissue or also the whole individual to the environment from where stimuli arise. Let’s understand by a few examples of the mechanism of the reflex action. The pupil of the eye changes its size when light acts as a stimulus; when a pin pricks our hands or legs or we touch something very hot, we suddenly withdraw them; we cough or sneeze when foreign irritants go to our nasal passages. In these situations, our reactions are instantaneous, involuntary, and quick. It doesn’t require much of a thinking process and conscious brain control, therefore, the action is called the reflex action in scientific terms. And here, the major role is of the spinal cord and the nerve pathway which is involved in this action including a sensory nerve, a synapse in between, and a motor nerve is called a reflex arc. The pathway of reflex action (reflex arc) can be clearly understood below in the diagram.

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Types of Reflex Action

To understand reflex action, we should understand all parts of the reflex arc responsible to cause a reflex action. Types of reflex action can be myotatic reflexes, tendon reflex, or reflexes observed only in human infants such as sucking reflex, and other reflexes such as abdominal reflexes or cough reflex.


The reflex arc is the neural pathway controlling the reflexes and acts on an impulse even before it reaches the brain. The two types of reflex arcs are:

  1. Autonomic Reflex Arc: It affects the functioning of inner organs.

  2. Somatic Reflex Arc: It affects the functioning of muscles.


The Various Parts of the Reflex arc are Described as Follows -

  • Receptor

It is the part of the reflex arc responsible for detecting the stimulus. A specialized receptor cell or a particular dendrite has this receptor end in a sensory organ. It is highly sensitive to any kind of internal or external change resulting from the stimulus.

  • Sensory Neuron

It conveys the sensory information to the brain or the spinal cord. Dendrite, cell body and axon of a sensory neuron are present to assist it in accomplishing its function. Its function is to transmit nerve impulses from the receptor into the spinal cord or brain.

  • Interneuron 

Also known as relay neurons, it serves as a processing center and conducts nerve impulses from the sensory neuron to a motor neuron. Interneurons are the central nodes of neural circuits, responsible for communicating between sensory or motor neurons and the central nervous system (CNS). It is the dendrite, cell body, and axon of a neuron within the brain or spinal cord.

  • Motor Neuron

It conducts motor output to the periphery and it is a nerve cell forming part of the pathway along which impulses travel from the brain or spinal cord to a gland or muscle. It transmits nerve impulses from the brain or spinal cord out to an effector.

  • Effector 

Effector cells are muscle, organ, or gland that acts in response to a stimulus. It responds to stimulation by the motor neuron and produces a behavioral response called a reflex.


What is the Significance of Reflex Action

Reflex action is an involuntary response of effectors to the stimulus and it helps us in protecting us from any sudden stimulus which may harm us and thus takes care of the survival of an organism. It is the major point that explains the importance of reflex action.


The importance of reflex action is due to the fact that reflex arcs are composed of different components that are significant to create a reflex. The function of each component is explained below -

  1. Receptor - It receives the information and assists in generating impulses. 

  2. Sensory Nerve - It carries information from the receptor to the interneurons in the spinal cord. 

  3. Interneuron - It processes the information and generates effective responses. 

  4. Motor Nerve - It carries the information from the spinal cord to the effector organ. 

  5. Effector Organ - It receives information from effector neurons and results in the appropriate response (reflex). 


List Down 10 Examples of Reflex Action

Reflex Action Examples in Humans Include-

  1. Closing of eyes when a bright light hits our eyes

  2. Sudden withdrawing hands or legs when they touch something hot or pricking

  3. Coughing or sneezing due to irritants in the nasal passage

  4. Batting of eyelids frequently

  5. Blinking eyes when insects come in contact 

  6. Rooting reflex in infants

  7. Sucking reflex in infants

  8. Grasp reflex in infants

  9. The reflex of abdominal muscles to contract upon any force to the abdomen (Muscular defense)

  10. Knee-jerk reflex is known as a patellar reflex: when the patellar tendon is stretched, the contraction of quadriceps takes place.

FAQ (Frequently Asked Questions)

1. What do you Mean by Monosynaptic and Polysynaptic Reflex Action?

A monosynaptic reflex action is when a reflex arc consists of only one sensory neuron and one motor neuron where a single chemical synapse occurs. Example: Patellar reflex. Polysynaptic reflex action occurs when one or more sensory and motor signals are connected i,e, interneurons connect afferent and efferent signals.

2. What is a Reflex Arc?

A reflex arc is a nerve pathway through which different components like receptor, sensory neuron, interneuron, motor neuron, and effector function altogether to produce a reflex action. These components act in a five-step process to generate a reflex action that is initiated by a stimulus. It can be diagrammatically represented to make it more comprehensible. A reflex arc governs all the operations of reflexes. The types of reflex actions are also based on their functionalities and types. A reflex arc makes it possible for reflexes through the neural pathways that act on an impulse prior to reaching the brain.