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The Amazing Sense of Touch
The sense of touch is due to the very sensitive neurons that respond to any deformation of the plasma membrane. In certain animals, like the cockroach, hairs are produced which act as receptor sites to pick up stimuli. Contact receptors in Man can be found under the skin in the form of nerve endings.
Sensitivity to touch is greatest around the lips, nipples, eyes and fingertips. In Man, touch sensitivity is particularly great around hairy areas including the hairline around the face and the genitals. Whiskers, which are found on cats and dogs and many other animals, are especially sensitive to touch. Human body hairs are also good sense organs. Keratin, found on the surface of the skin, has a piezoelectric effect. That is, whenever the epidermis is bent or folded, detectable electric discharges are produced which are picked up by the free nerve endings and translated in the brain.
Man's heat receptors are found deeper in the skin then the cold receptors. We cannot accurately distinguish between cold or hot and whether our brain perceives as hot or cold depends on the previous feeling. That is, if the body feels cold at first and is then subjected to something warm, the brain interprets it as such but if the skin had been warm and sense something less warm, it will interpret the object as cool. In other words, our feeling of coldness and warmth is basically a relative comparison.
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Different kinds of nerve endings are in charge of picking up different kinds of stimuli. The Krause's end picks up feelings of cold while the Ruffini endings are in charge of heat. Pacinian corpuscles are encapsulated nerve endings which pick up senses of pressure while the Meissner's corpuscles picks up light and touch. Baroreceptors are special tactile receptors what detect changes in the blood pressure within the blood vessel.