Sensory receptors on our bodies are responsive to different stimuli and they provide the brain and spinal cord with vital information about our surroundings and our internal environment. By use of different techniques we can learn how the sensory system works and how it affects the motor output from the brain and how it gives the correct information on our external world. The sensory receptors functions as the very first component in sensory system and they respond to specific stimulus modalities. By initiating transduction the sensory receptor responds to the stimulus. This is accomplished by a net shift in the initial states of a receptor.
Special senses are senses of smell, taste, vision and hearing. The taste buds on the tongue allow people to taste their food and the sense of smell is attributed to olfactory organs in the nose. Some sensory receptors are tonic this means that they fire action potentials as long as the stimuli is present. Other senses are phasic which means they adapt.
We are able to see objects near us or far because the processes are automatically carried out depending on the distance we look and operate in. our eyes are in a position to adapt the new surroundings be it dark or light. During this adaptation process, seeing in the dark and light is made possible by adjusting the degree of vision and increasing and decreasing it one million times. The activities of the photoreceptors (in the shape of rod and cone) are carried out by an amazing knowledge and power. Adaptation in tasting happens whenever we put something on our mouth. After tasting any food you can be in position to explain how the food tastes.
Adaptation in temperature makes the receptors to be stimulated in sudden temperature changes. When you put your hands in lukewarm water (both hands) that were subjected to different temperatures you will feel totally different. This is because the receptors sense both the sudden changes and constant situations. Both extreme hot and cold are harmful to the body. (Omer Avifagaoglu,2008)
The following experiment well explains how sensory nerve works.
Sensory receptors involved in taste contain receptor molecules which bind specific chemicals. Taste receptors in taste buds interact with chemicals in food to produce what we call action potential. Some receptors such as mechanoreceptors and photoreceptors are responsible for physical stimuli. They contain special proteins such as rhodopsin to transducer the physical energy. After rubbing the index finger on sandpaper for a while, the courses lessened which indicates that the body became somewhat accustomed to the coarseness. Thus it appears less coarse. Nerve endings throughout the body respond to a particular stimulate and in this case, the body responds due to adaptation. Nerve endings throughout the body respond to particular stimuli and send critical messages to the spinal cord and brain. Using these signals, the brain develops "a map" of the external world which is used for every movement that we make.
Thermoception is the sense of heat and cold by the skin and the heat flux around the skin area. Thermoceptors in the skin are different from homeostatic thermoceptors in the brain which provides feedback on internal body temperature. According to Fechner's s law, quantity's, brightness is related to the physical quantity energy flux or intensity logarithmically. If you cast a shadow on a piece of paper, though different illumination the surrounding does not change. The old system of classifying stars by magnitude in a uniform series of equal steps of brightness was found to be logarithmic, the ratio of intensities being about 2.5 in each step. This explains why the light began to look brighter(Glyde,1968)
Sweetness is usually regarded as a pleasurable sensation and it is produced by presence of sugars and few proteins. Aldehydes and ketone are connected to sweetness and they contain a carbonyl group. G protein coupled receptors coupled to G protein gustducin found on the taste buds are responsible for detecting sweetness. Sweetness receptors are activated for the brain o register the presence of sugar.TIR+3 and TIR3 are responsible for detecting two different thresholds of two different sweetness. After tasting water full of sugar and later tasting fresh water, the water tastes as if it had some sugar (semi sweet). This is because the average threshold for sucrose is 10 millimoles per litre and for lactose it is 30 millimoles per litre.
Thermoception is the sense of heat and cold by the skin and the heat flux around the skin area. Thermoceptors in the skin are different from homeostatic thermoceptors in the brain which provides feedback on internal body temperature. (Martin, 1964)
Adaptation in temperature makes the receptors to be stimulated in sudden temperature changes. When you put your hnds in lukewarm water (both hands) that were subjected to differenttemparatures you will feel totally different. This is because the receptors sense both the sudden changes and constant situations. Both extreme hot and cold are harmful to the body.
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