This article throws light upon the top five senses of the sensory system. They are: 1. Taste and Smell or the Chemical Sense 2. Organic Senses 3. Static Sense or the Sense of Equilibrium and Movement 4. Kinesthetic Sense 5. Skin Senses or Cutaneous Senses.
1. Taste and Smell or the Chemical Sense:
Taste and smell are often considered together for two reasons. They are very much inter-related. For example, coffee and quinine are both bitter in taste. But coffee tastes pleasant because of its smell. Further, these two sensations depend on chemical action or chemical changes rather than mechanical and electrical stimulation, as in the case of the other senses.
Taste is known as the gustatory sense and smell is known as the olfactory sense. Both taste and smell decline in accuracy with age. The receptors for smell are the olfactory cells in the nasal cavity or the nose. So far six primary smells have been identified. These are resinous, spicy, putrid, burned, fruity and flowery. In actual experience, however, smells are often mixed. The olfactory sense also shows very rapid adaptation.
The receptors for the sensation of taste are located in the tongue. The basic tastes are salt, sweet, bitter and sour. The receptors for these different tastes are distributed differently in different part of the tongue. These are known as papillae. Taste and smell also interact with our sense of temperature and touch. For example, hot coffee tastes different from cold coffee. Similarly, a spongy or gelatinous food like jelly tastes different from other food items.
2. Organic Senses:
Organic senses refer to the sensory experiences connected with conditions like hunger, thirst, and so on. In the case of hunger, these are caused by contractions of the internal muscles. Thirst is caused by a feeling of dryness and stickiness in the mouth. Our knowledge about the organic sense is relatively little compared to the other senses.
3. Static Sense or the Sense of Equilibrium and Movement:
We all feel strange when our head gives a reeling sensation. Similarly, we also experience a sensation of movement or sensations of remaining stationary. The receptors for these are the vestibules in the semi-circular canal in the inner part of the ear. Normally we are not conscious of our balanced position but when our balance is disturbed we experience some sensations.
An important phenomenon here is motion sickness. Extreme rotation and continuous up and down movement Cause dizziness. Of course, psychological factors like anxiety, and emotional factors also contribute to this. For instance, some people suffer from car-sickness, sea-sickness etc.
4. Kinesthetic Sense:
The sense is also referred to as the muscle sense. While muscles are connected to motor nerves they are also connected to sensory nerves. Kinesthetic impulses play a very important role in our experiences of walking, running, and all other types of physical movements. We also experience muscular tension. For example, even when it is dark we are able to climb flights of stairs.
This is because of the muscle sense. Kinesthetic senses perform the very important function of providing cues to our movements. For example, our ability to judge weights is dependent on our kinesthetic senses. Kinesthetic senses are very important in helping us to maintain smooth and continuous action.
5. Skin Senses or Cutaneous Senses:
Another major sensation operates through our skin. The skin sense cannot be placed in a single category of sensory experiences. In fact there are four categories of sensations which can be grouped under the skin sensation or cutaneous sense. The four sensations are pain, pressure, cold and warmth.
When our skin is pressed slightly by contact with some other object, we experience the sensation of pressure. The sensitivity to pressure is not uniform in all parts of the skin. Lips, fingertips, earlobes and hands are more sensitive to pressure than the other regions. This is because the pressure spots which are the receptors for the pressure sensation are greater in number in these regions.
The application of a very intense stimulus to any sensory nerve or sense organ, produces a pain sensation. Our experience of pain is, therefore, a consequence of a very strong stimulation. But there are certain parts of the skin known as ‘free nerve endings’ where even a mild stimulation can produce a sensation of pain.
The pain sensation biologically performs a warning function. Whenever there is pain we withdraw from the stimulus situation. Pain can be produced by any type of stimulus-mechanical, electrical or chemical. What matters is the intensity of the stimulus.
Warmth and cold constitute the other two categories of cutaneous sensory experience. The receptors for these are also found on the skin called cold and warmth spots. These spots are also called ‘temperature spots’. The number of such spots varies from one part of the body to the other.
In view of this some parts of the body are more sensitive to temperature than others. It has been estimated that there are more cold spots than warmth spots. When a cold spot is stimulated by a warm stimulus the resulting sensation is one of cold. Such phenomenon is called paradoxical cold. Similarly we have paradoxical warmth.
Skin sensations also show qualities of adaptation. If the intensity of the stimulus remains constant and it is continuously applied the felt experience gradually becomes less and less intense. For example, if a piece of ice is kept on one’s palm, the initial experience is very cold. Gradually, the cold sensation becomes less intense. This phenomenon is called temperature adaptation.
Another interesting phenomenon relating to the temperature sense is as follows. If a person dips one hand into hot water and the other into cold water simultaneously and then removes his hands and dips them both into lukewarm water, there results an interesting experience.
The hand which was earlier dipped into cold water now feels warm and the hand which was earlier dipped into warm water now feels cold. This is a demonstration of the phenomenon of contrast in temperature sense.