What is a Sensory system?– An overview and important solved questions

Sensory system

What is a Sensory system ?

The sensory system is a part of the nervous system responsible for processing sensory information. A sensory system consists of sensory receptors, neural pathways, and parts of the brain involved in sensory perception.

What are the Sense organ of the body ?

Commonly recognized sense organ are those for seeing, hearing, smell, taste and touching or feeling. In short, senses are transducers from the physical world to the realm of the mind where we interpret the information, developing our perception of the world round us.

Inability of sense organ
  • Eye (for seeing) – Blindness is the inability to see.
  • Ear (for hearing) – Deafness is the inability to hear.
  • Nose (for smell) – Anosmia is the inability to smell.
  • Tounge (for taste) – Ageusia is the inability to taste.
  • Skin (for touching or feeling)– Tactile anesthesia is the inability to feel anything physically.

What is the sensory system function ?

Sensory system is a functional system of neurons which enables perception of external or internal environment changes, conduction of impulse to central nervous system and formation of sensation.

Sensory Receptors

The sensory system consists of simple to complex structures called sensory receptors. The sensory receptors enable us to detect changes in our own body and in objects and events in the world around us. The information about the changes within the body is used to maintain homeostasis. The sensory receptors which report sight, sound and chemicals in the outer world are used to find food, shelter, mate, safety from enemies, and other adaptive responses to environment.


All sensory receptors are similar in basic structure. The simplest and most primitive type of sensory receptor is a single unspecialised sensory neuron whose terminal end is capable of detecting stimuli. It is called primary sense cell. Olfactory cells belong to this category. The more complex sensory receptors are modified epithelial cells able to detect stimuli. These receptors are termed secondary sense cells. They form synaptic connections with the sensory neurons which transmit impulses to the CNS. Mammalian taste buds are receptors of this type. The most complex sensory receptors consist of numerous sense cells, sensory neurons and associated accessory structures. They are known the sense organs. Eye and ear have a level of complexity of sense organs. The accessory structures may have a double role : eliminating the effect of unwanted stimuli and amplifying the effects of desired stimuli.

Working of Sensory Receptors

All sensory receptors resemble in mode of working too. The receptors receive particular stimuli and set up appropriate electrical impulses in the nerves. A stimulus is some form of energy: light, sound, pressure, heat, osmotic potential, electric current, and chemical changes. Each type of receptor is sensitive to a particular kind of stimulus. An animal responds to a stimulus in a four-step process-

(i) Sensory Transduction Sensory receptors transduce (transform) the energy of a stimulus into a localized nonpropagated electrical response which initiates nerve impulses in the neuron leaving the receptor.

(ii) Transmission The sensory neuron relays the impulse to the brain directly or through the spinal cord.

(iii) Integration  Nerve impulses (action potentials, often called receptor potentials) that reach the brain via sensory neurons are termed sensations. In the brain, the sensations are analysed and interpreted as perceptions, and we come to know of the stimuli acting on the receptors. The brain transmits motor impulses to appropriate effectors- muscles or glands.

(iv) Response Effectors produce suitable response . Muscles contract,or glands secrete chemicals, in response to the information sent to the brain by the receptors. 

The sensory receptors, thus, merely receive the stimuli and set up similar nerve impulses. They cannot interpret the impulses generated in them by the stimuli. This power lies with the brain. Actually, therefore, we feel, taste, smell, see and hear with the help of specific functional areas of the brain. Of course, the brain without sensory receptors cannot detect environmental changes. Similarly, the sensory receptors alone are of no use. Hence, what actually matters is where the nerve impulses reach, and not what generates them. 

What is the difference between the general senses and the special senses?

The receptors for sight, hearing, smell and taste are localized in specific organs and are, therefore, called special sensory receptors, and these senses are termed special senses. The sense of touch has receptors scattered all over the skin. Hence, it is termed a general sense.

Sensory Adaptation If a stimulus once noted by the receptors remains constant, it becomes less noticeable. This mechanism is called sensory adaptation. It checks the nervous system from becoming too sensitive. We quickly note a strange odour, but we also cease to perceive it quickly. For example, you soon cease to smell a perfume applied to the body or clothes, but others approaching you can still note its fragrance. Without sensory adaptation, you would be distinctly aware of the touch of your clothes and of every sound reaching your ears. Concentrating on a single stimulus, such as a person talking to you, would be difficult. 

Types of Receptors

The receptor cells are of many types. They may be classified according to their position in the body or regarding the form of stimulus energy they can detect.

A. Regarding their location, the receptors are of 3 types : exteroceptors, proprioceptors and visceroceptors or interoceptors. 

1. Exteroceptors or External Receptors These are located at or near the body surface, and are stimulated by changes in the environmental factors. They include the receptors for touch, taste and smell, and sense organs for sight and hearing. 

2. Proprioceptors The proprioceptors are located in the skeletal muscles, joints, tendons, etc. It is from these receptors that we know the position of our arm or leg without having to look at it.

 3. Visceroceptors or interoceptors or Internal Receptors

These are located in the viscera. They are affected by stimuli originating within the body itself and cause sensations, such as pain, hunger, thirst, fatigue, nausea, sex, etc. They also monitor blood pressure, carbon dioxide level, body temperature, osmotic relationships, pH, etc. 

B. According to the form of the stimulus energy they detect and transform (transduce), the receptors are of 5 main types. These are given in table –

Type of receptors

Important Solved Questions for Exams

1. What are the 5 sensory organs ?
Ans.  The 5 sense organs are eyes, ears, tongue, skin, and nose. They help to protect the body. The human sense organs contain receptors that relay information through sensory neurons to the appropriate places within the nervous system. Each sense organ contains different receptors.
2. What sensory system develops first ?
Ans. Touch , this is the  first sense organ to form, with development starting at around 8 weeks. The sense organ of touch initially begins with sensory receptor development in the face, mostly on the lips and nose.
3. What are the structures in and the functions of the sensory system?
Ans. A sensory system consists of sensory receptors, neural pathways, and parts of the brain involved in sensory perception. Commonly recognized sensory system organs are those for vision, hearing, touch, taste, smell, and balance. The main function of the sensory nervous system is to inform the central nervous system about stimuli impinging on us from the outside or within us.
4. Which sense organ tells you that someone crying?
Ans. Skin , sense organ use when someone crying .
5. Which is the largest sense organ?
Ans. Skin is the largest sense organ of human body.Various receptors are used for different situations like pain, temperature, pressure, etc
6. What happens when you lose one of your five senses?
Ans. If one sense is lost, the areas of the brain normally devoted to handling that sensory information do not go unused — they get rewired and put to work processing other senses.
7. What will happen if one of the sense organs is not working properly?
Ans.  When these senses begin to dim or are lost as we age, we face challenges dealing with everyday life. Losing one’s senses can also cause serious health problems such as – difficulty performing their daily activities, difficulty staying physically active, difficulty staying sharp mentally, overall worse health
, unhealthy weight loss and increased risk for dying.
8. How many sense organs are there in pair?
Ans. There are two sense organs are there in pair i.e. Eye and Ear.
9. Which body part controls our sense organs?
Ans. Brain is the control our sense organs. In brain the parietal lobe gives you a sense of ‘me’. It figures out the messages you receive from the five senses . This part of the brain tells you what is part of the body and what is part of the outside world.
10. How many sense organs are present in our body?
Ans. There are the BIG FIVE sense organs present in our body and according to some several others.
Humans have a multitude of senses if you expand the definition slightly. Sight (ophthalmoception), hearing (audioception), taste (gustaoception), smell (olfacoception or olfacception), and touch (tactioception) are the five traditionally recognized senses.

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