Receptors are the gateways to information. Our body has eight kinds of receptors, such as visual receptors (eyes), auditory receptors (ears), olfactory receptors (nose), gustatory receptors (tongue), tactual receptors (skin), labyrinthine receptors (cochlea in inner ear giving us sensation about our position of the body in space), kinesthetic receptors (deep joints and muscles) and visceral receptors (about internal organic sensation). Thus, receptors are divided into eight types according to sense modalities.
Any event, which causes the sense organs to be active, is termed as stimulus. Receptors are those sense organs of the body by which we receive the stimulation of various kinds from the environment. These receptors are sensitive to stimulation. What is stimulation? Stimulation is physical energy.
Our eyes, ears, tongue etc. are sensitive enough to notice stimulation through our receptors. Without these receptors, we would sense nothing, feel nothing, would see nothing and would have no information about the world.
Specific stimulation are received by specific receptors. For example, visual stimuli (color, people, light, books etc.) are received by only visual receptors i.e., eyes only. Similarly, auditory stimulations (music, shout, noise, chirping etc.) are received by pairs of ear only. We also receive combined stimulation from the environment and these are integrated in the brain. Thus, receptors being the sensitive parts of our body detect any changes in stimuli present in the environment. The cells in our sense organs are built to receive information in special ways. All receptors are able to produce impulses as a result of changes in some form of energy. There are mainly 3 categories of receptors, such as: (a) exteroceptors, (b) interoceptors, and (c) proprioceptors.
ADVERTISEMENTS:
The exteroceptors receive stimulus information from external sources but only when the source of information comes in direct physical contact with the receptors. Such receptors are found in the sense organs like eyes, ears, nose, skin and tongue.
The interoceptors receive stimulus information form internal sources. Such receptors are found in organic sense organs such as lining of the stomach, bladder, viscera etc. These receptor cells may be called as organic receptor celis. When our stomach is empty for example, the organic receptor ceils, which are present in the stomach boundary wall, receive this information.
The proprioceptors do not require either an external or internal stimulus to be stimulated. These receptor cells are stimulated by themselves. These are found in the kinesthetic sense organs, which constitute muscles, tendons, joints, etc., and the static or vestibular sense organ (semicircular canal of the inner ear). These receptor cells are also called as kinesthetic and static or vestibular receptor cells, respectively. Kinesthetic receptor cells receive information form our muscles and joints when they move. Vestibular receptor cells receive such information as when our body is lifted, moving, falling down or speeding up.