Types of sense organs

• The organs which enable us to perceive the undergoing changes in the external environment and body’s internal environment and make aware of them are called sense organs.
• These sense organs are responsible for senses in the human body.
• They are provided with specialized receptor cells or sensory receptors.
• A receptor is the part of the nervous system that has become adapted to receive stimuli.
• The receptors receive a particular stimulus and initiate the transmission of impulses to the brain through the sensory nerves.
• The receptors that detect changes in the outside world are positioned at or near the body surface.
• The sense organs can be classified in many ways. Some of them are as follows.

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A) Classification based on their location within the body

They are of two types. They are:

i) Exteroreceptors (external receptors)

• These are usually found outside the body and may also found inside the body.
• They receive stimuli from the external environment.
• They are organs for touch, smell, taste, sight and hearing.

ii) Interoreceptors (internal receptors)

• These are found within the body and are responsible for the changes of the internal environment of the body.
• They can detect internal pain, thirst, hunger, temperature and fatigue.

B) Classification based on the type of stimulus

They are classified on the following ways based on the type of stimulus. They are:

i) Photoreceptors

• These sense organs respond to the changes in intensity or wavelength of the light.
• e.g., eyes.

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ii) Chemoreceptor

• These sense organs respond to changes in concentration of specific chemical substances.
• e.g., taste buds, sensory cells of smell.

iii) Thermoreceptor

• These receptors respond to changes in the temperature.
• e.g., skin.

iv) Mechanoreceptor

• These respond to mechanical stimuli.
• e.g., nerve fibres around hair.

v) Gustatoreceptors

• These receptors respond to taste.

vi) Phonoreceptor

• These receptors respond to hearing.

vii) Olfactoreceptor

• These receptors respond to smell.

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C) Classification based on their specialized functions

They are as follows:

i) Proprioreceptors

• These sense organs respond to the movements of the muscles.
• They are found in muscles, tendons and joints.

ii) Nociceptors

• These are deep pain receptors.
• They respond to injury or any damaging stimuli.

iii) Telereceptors

• They are responsible to changes in distances and hearing.
• These are the receptor organs for the special senses such as vision, smell or hearing.

References: 

i) https://study.com/learn/lesson/5-senses-functions-examples.html

ii) https://humanbiology.pressbooks.tru.ca/chapter/10-7-human-senses/

Types of sense organs