Touch and somatosensory perception

When we speak of somatosensory perception we do not only mean the system of skin sensibility but also the sensory system of a skeletomuscular apparatus. They both are ca­pable of responding to touch and perceiving heat, cold, pres­sure, vibration, and pain.

Hairs covering the human skin also contribute to tactile perception. They have the follicles that are set deeply enough in the skin to be nourished and preserved. Fine rierVe fibers intertwine these follicles, and.wrap around an individual hair from beneath. Because of these nerve terminations hair is very sensible to touch. The so-called Merkel’s disks (the touch cells) are also thought to be receptors for touch. They are particularly numerous in the skin of finger tips.

It is only through physical contact and touch with the objects that we can ascertain their peculiar features, such as I heir size, shape, surface texture and temperature. This con­tact is realized through different means in various parts of I lie body. The skin contains thousands of specialized cells, as well as nerve endings that respond to external stimuli (heat, cold, etc.). They differ in structure, are located at a different depth in the skin, and are differently dispersed on I ts surface.

In the dermal papillae of the fingers, toes, palms, soles, tongue, lips, nipples of the breasts, and genitals there are many tactile corpuscles (Meissner’s corpuscles) that are complicated in st ructure, and contain nerve terminations. They are held to be end organs of touch, and help in performing the function of tactile perception. Receptors with nerve terminations for perceiving pressure and vibration (the Pacinian corpuscles) have still deeper localization in the skin.

There are many contradictory theories related to skin sen- sitivity. The widely known one is that acknowledging the presence of specific receptors for the skin sensibility. Some skin receptors consist of several layers of cells attached to the nerve fiber, Others contain several nerve fibers arranged in a loop or coil. Several varieties of receptors, probably, play a part in each touch modality. Therefore, perhaps, we can distinguish between tactile reception, temperature recep­tion and pain reception.

Some characteristic features of the skin receptors should be mentioned. The majority of the skin receptors can be divided into rapidly and slowly adapting receptors accord* ing to how quickly they adapt themselves to the acting stimuli. Owing to adaptation of skin receptors, people do not feel constant pressure of their clothes, etc. The absolute I actile sensibility differs essentially in different parts of the skin. These differences are mainly associated with a various size of skin receptive fields. Thermal receptors of heat and cold are concentrated in the skin, on the cornea, in mucous membranes, and in the hypothalamus. Heat receptors are I ewer in number and located deeper than cold receptors. I'he skin of the face and neck contains most of the thermal receptors. Nociceptive sensation (the sensation of pain), as well as the problem of existence of the specific pain receptors still remains unsolved in spite of great scientific efforts.

General sensation including the tactile ones are perceived at specific points within the brain’s cerebral cortex.

Task 28. Fill in the blanks with the terms that follow, and translate the sentences:

1. Cells in the hair root produce horny cells which move upward through the ... . 2. The tongue is covered with many small projections called ... . 3. ... receptors respond to touch. 4. The sense concerned with the perception of ... is called smell. 5. The epidermis is the outermost layer of the ... . 6. Bauman’s gland is ... gland. 7. We distinguish the sweet, sour, bitter, or salty quality of substances by taste buds on the ... . 8. ... are sensitive to the chemical nature of food consumed.

(a — taste buds; b — ordour; c — olfactory; d — tongue; e — papillae; f — hair follicles; g — skin; h — tactile)

Task 29. Read the abridged article from U.S. News & World Report and comment upon it. Use the expres­sions suggested in unit one, task 18 and in unit nine, task 20. Say why you consider the article to be dull or interesting: