Sense organs are the organs through which we sense or detect changes in the external environment. Each sense organ has special sensory cells, which receive the stimuli and transmit the impulses produced through the concerned nerve to the brain or the spinal cord. The brain sorts out the impulses, interprets them and transmits message for the required response.
In human, there are five sense receptors:
- Eyes for seeing
- Ears for hearing
- Nose for smelling
- Tongue for taste
- Skin for sensing touch, pain, or heat
The eye is nearly spherical in shape, bulging a little in front, and is able to rotate freely in the bony socket. The wall of the eyeball is made up of three layers: the sclera, choroid and retina.
The ear serves two sensory functions: hearing and maintaining balance of the body. The ear has three main parts: external ear, middle ear, and internal ear.
Tongue and Nose
The tongue perceives the taste and the nose perceives the smell. The perception depend upon the nature of chemical substance coming in contact with the sensory cells. For taste there is a direct contact of the substance with the sensory cells located in the taste buds on the tongue. For smell, the molecules of the chemical are carried inward by the air inhaled and they stimulate the sensory epithelium of the nose.
There are a variety of nerve endings in the skin. Some of these are concerned with touch (gentle pressure), some with deep pressure and others with cold, heat and pain.
The sense of hunger is due to receptors in the stomach wall. The sense of thirst is due to stimulation of nerves in the pharynx. The sense of fatigue is located in the muscles.