Reflex Action And Sense Organs

Introduction

Reflex action is a process that every living organism experiences, and it is bound quite intimately with the sense organs. There are multiple kinds of sense organs that help us perceive the material world by helping us experience external stimuli. In order to respond to the external stimuli, the body needs five sets of organs–the receptor, sensory neurons, relay neurons, motor neurons, and effector, and the sense organs often act as the receptor in case of reflex action. While external stimuli are often pleasing, there are dangerous external stimuli as well. 

Reflex Action

Reflex is a sudden and rapid response to external stimuli. It is also a huge part of any animal’s survival instinct. It is through reflex that reflex action takes place. This response is different in each animal because external stimuli depend on our nervous system.

This reaction to sudden or unexpected external stimuli is called reflex action. Reflex action does not need any conscious thought or effort, and it can take place even in sleep.

Reflex Action Working

Every tissue in the human body is designed to feel and express specific simulations. These tissues receive signals from external occurrences and send them to our brain, which in turn gives us instruction on how to react. This whole process happens really fast and involuntarily.

The trajectory of reflex action works in six broad stages:

1. The stimuli are received by a sensory organ.
2. The stimulation(pain or discomfort primarily) is generated where the stimuli make contact.
3. The signal is sent along and through the sensory neuron.
4. The sensory neuron sends the signal to the brain via relay neurons.
5. The brain then sends the instruction to act via a motor neuron.
6. Once the motor neuron passes the instruction along the receptor muscle, it responds accordingly.

So there are five parts of our body involved in the process of reflex action–receptor, sensory neuron, interneuron or relay neuron, motor neuron, and effector. 

Few examples of reflex action:

• The pupils of the eyes contract when a bright light is flashed upon them
• Our eyelids close when someone blows on them
• We sneeze when foreign elements(harmful or not) enter our bodies through the nose
• When our skin touches something very hot or cold, we instantly contract our muscles

Significance of Reflex Action

Reflex action is a way to protect our bodies from unwanted or dangerous external phenomena. Reflex action has significant benefits for our body–

• Reflex action is quick and immediate, so it prevents accidents from happening
• It prevents unwanted external elements from entering our bodies
• Our body understands its need to protect itself; hence it designs reflex action

Primary Sense Organs of the Body and Their Function

Sense organs are an important part of reflex action because they can act as the receptor of the reflex action, i.e., they receive external stimuli. These are specialised organs built by the body to work in limited and specific ways. They are built for us to experience and feel the environment in different ways. There are five primary sense organs.   

The primary sense organs of the body are– the eyes, ears, nose, tongue, and skin.

• Eyes

The eyes are a part of the sensory system and are responsible for vision. Lights pass through the complex mechanism of eyes to create an image. The images are projected on the yellow spot called the retina; these are what our brain perceives.

The main parts of an eye are– eyelids, eyelashes, pupil, lens, retina, and iris. The eyelids and eyelashes are there to protect the more sensitive portions of the eye. The light passes through the pupil to the lens where the image is formed. 

• Ears 

Ears, as we all know, help us in hearing things or audioception. Ears are separated into three sections–outer ear, middle ear, and inner ear. The outer ear consists of an eardrum enclosed by a tympanic membrane.

The middle ear is a narrow air-filled cavity located in the temporal bone. It is surrounded by three tiny bones called anvil, hammer, and stirrup. The inner ear is where the sensory cells for hearing are located. 

• Nose

The nose contains olfactory receptor cells, which are primarily responsible for the sensation of smell. These cells are seen in the olfactory epithelium. The olfactory epithelium can be seen in the hollow nasal chambers. These receptor cells function when any gaseous element enters the nose-canal. 

• Tongue

The tongue is the sense organ that helps us perceive taste. It consists of multiple taste buds which contain gustatory receptors. Gustatory receptors are what help us taste things. So the sensory system for taste is called Gustaoception. The tongue can also feel heat, cold, and touch.  

• Skin

Skin is the sensory system for touch. The skin has multiple kinds of receptor cells which can feel heat, cold, pressure, pain, and touch. Skin chiefly has three layers–Epidermis, Dermis, and Hypodermis. The epidermis is the outer layer.

The dermis is just beneath the epidermis, made mainly of papillae. It consists of fat, collagen, and fibres and makes skin strong. The hypodermis is the layer underneath the dermis, it helps protect the internal organs.

Conclusion

The primary sense organs are also the primary receptors in the process of reflex action. But the organs have manifold functions other than being a part of the reflex action process. The path or the trajectory of the reflex action is called the reflex arc. We must remember that the reflex action stems from the animal instinct or reflex. Reflexes can be improved and sharpened with practice and innovative sensory organs. Hope this reflex action and sense organs study material helps understand the relationship and function of various sense organs.