[Biology Class Notes] on Reflex Action Pdf for Exam

A reflex is an involuntary and rapid response to the stimulus. It is a crucial component of the famed survival instinct. Depending on our previous experiences and understanding, we all have different instincts. A reflex is a response that is triggered by an instinct. Sometimes we don’t know if the pan is hot or not until it’s too late. To put it another way, reflex has little to do with instinct. In this article, you will understand reflex action, types of reflex action, the significance of reflex action, and some FAQs. So, let us start by understanding reflex action in the coming section.

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 tissues or also the whole individual to the environment from where stimuli arise. Let’s understand 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 called a reflex arc. The pathway of reflex action (reflex arc) can be clearly understood below in the diagram.

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 reflexes, or reflexes observed only in human infants such as sucking reflexes, and other reflexes such as abdominal reflexes or cough reflexes.

Reflex Arc

The reflex arc is the neural pathway controlling the reflexes and acts on an impulse even before it reaches the brain. Some stimuli require an automatic, quick response that does not involve conscious thought. 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 –

The reflex arc consists of a receptor, sensory neuron, interneuron, motor neuron, and effector.

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 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 centre and conduct 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 muscles, organs, or glands that act in response to a stimulus. It responds to stimulation by the motor neuron and produces a behavioural 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.