Touch

Touch is a complex feeling arising from the irritation of the receptors of the skin, external surfaces of the mucous membranes and muscular-articular apparatus. The main place in the formation of touch belongs skin analyzer, which provides the perception of external mechanical, thermal, chemical and other skin irritations.
Feel, being the most ancient form of sensation, comes from a tactile, temperature, pain and physical sensations.
The main role in touch belongs tactile sensations - touch and pressure. Receptors (see) of feeling in the skin are tree-like branched available end of nerve fibers, end twigs which penetrate between connective and epithelial cells, embraced external root vagina hair. Oscillation long outer part of the hair is transmitted to the root of and causes the excitation of nerve fibers. When increasing the intensity of touch starts to feel a sense of pressure. This means that affected receptors in the muscles, fascia and ligaments. One nerve fiber, branching out, can go up to 300 skin receptors. Touch divided into active and passive. Active sense of touch is manifested in the active actions of the body that contribute to a more complete perception of the subject (the person is manifested in the manipulation of the subject and the feeling it). Passive touch occurs when the simple action of irritant to skin and not accompanied by specific reactions of the body, usually aimed at clarifying the nature of the stimulus.
Cm. also the senses.

Touch is a complex feeling that occurs when skin irritation, the outer surface of the mucous membrane and muscle. This feeling is the result of comprehensive work of nervous structures, who receive information from exteroreceptors skin, mucous membranes, and kinesthetic receptors in the muscles and joints.
The main place in the formation of touch is a skin analyzer engaged exteroception mechanical, thermal, chemical and other skin irritations, falling on the skin. Receptors (see), perceiving the effects on the body environmental factors are called exteroceptors (exteroreceptors). The function of the skin analyzer is carried out with the participation letniskowa and spinothalamic CNS systems. The first consists of nerve fibers that carry tactile information from the skin through the dorsal columns of the spinal cord to tender and wedge-shaped; the nuclei of medulla oblongata. Through the system of medial lemniscus they reach ventro-basal nuclei of the thalamus. Spinothalamic system engaged mainly temperature and pain information, goes through anterolateral columns of the spinal cord in the medial geniculate body, i.e., dorsal to ventro-basal complex of the thalamus. Spinothalamic system, unlike letniskowa, modal less specific: 60% of the cells at the level of the thalamus respond to tactile, nociceptive and sound of annoyance. In a bark of the big hemispheres skin analyzer presents two somatosensory areas. The first zone is located in postcentral gyrus; here come the fibre from ventro-basal nuclei of the thalamus. Second somatosensory area is located in front of ectocervical gyrus. An important part of skin analyzer are efferent way, going from precentral.net, postcentral brains and posterior parietal cortex to wedge and tender kernels; these paths are one of the mechanisms touch feedback.
In the sense of feeling produce sensations of touch and pressure, heat and cold, pain, itching, and other mixed feelings. O. light touch and pressure - a consequence of signaling in the nervous with tactile receptors in the skin, which occupies the main place in the sense of feeling. Specific stimuli tactile receptors are mechanical impact in the wide range of intensity from light touch to pressure. The most superficially, in the epidermal layer of the skin, are bezmalinovic free nerve endings responsible for the perception of light touch. Located deeper in the skin around the hair bulbs thick nerve plexus are tactile receptors with high sensitivity to light touch and curl hair (deviation of hair at the back of the hand of man only 5 degrees leads to pulse in a single afferent fibers and a corresponding sense of touch). In animals the most sensitive special tactile hair - whiskers, located on special tubercle skin on his upper lip, on the wrist of the front legs. Whiskers perceive the most minor fluctuations in the air and allow animals (cats, mice and other) to navigate in the dark. The skin contains a large number of specialized tactile receptors (bullock, Pacini and Meissner, disks Merkel and others).
According to Dogiel (1900), in human skin there are at least 14 different types of nerve termination.
Originally touch studied psycho-physical method is by measuring the sensations of a man. Blix (M Blix), Frei (M. Frey), Goldsheider (A. Goldscheider) found that touch unevenly distributed on the surface of the skin where it is possible to allocate a highly sensitive point, perceiving certain type of irritation. Irritation of such points had always led to the appearance of the same feelings. So, irritation "cold" points on the skin caused the feeling of cold regardless of the quality of irritation. Were found tactile, points, heat and cold, and even pain, although the existence of the latter being questioned. On different parts of the body contains a different number of sentient points. So, on the falcons fingers, their number is so great that it is beyond calculation: 1 cm2 skin exaltation thumb there are more than 100; on the wrist - 40, in the middle of the forearm - 15; in the Shin 7-10. The density of the points in this area of the skin is the basis of the distinctive character of touch. The number of points on a particular area of skin may vary depending on the functional state of an organism under the influence of factors of an environment (functional mobility, by P. G. Snakin).
Skin areas, within which two simultaneous touch perceived as one, are called tactile circles Weber. Border tactile circle is the minimum distance at which the two touch felt separately. These borders (they are measured with the help of a compass Weber) is: on the tongue - 1.1 mm, at the ends of the fingers - 2,2, cheek to 11.2, on the upper back - 53, at the hip and back of the neck - 67,5 mm visual acuity touch (also compasses Weber) shows the spatial-distinctiveness of the skin - so-called differential threshold of tactile sensitivity. Acuity touch is also characterized by an absolute threshold of sensitivity, i.e. the minimum force pressure, causing a sensation. To measure this last value using a set hairs of different diameter (hairs Freya, the device Ryazanov). Absolute thresholds of tactile sensitivity for the person close coincide with differential thresholds and are (in gram-millimeters) on the tongue - 2, at your finger tips - 3, on the Palmar surface of the forearm - 8, calves - 15, on the back surface of the forearm - 35, on the back - 48, on the soles of the feet - 250. Finally, to determine the ability of the skin to the discernment of time two consecutive touches to the same point skin serves as temporary threshold of tactile sensitivity. Its value coincides with the value of the aforementioned thresholds. The highest sensitivity is celebrated on the tips of the fingers and tongue.


A careful study of touch electrophysiological techniques showed that innervation tactile receptors is usually thick nerve fibers with high speed (group a - alpha-, beta - and Delta-fiber and fiber group S. Tactile receptors anatomically interrelated and form a receptive field, innerved individual nerve fiber. Receptive field may overlap. At the distal parts of the body they have an elongated length form; their sizes vary from frogs from 2 to 105 mm2 and cat 3 to 185 mm2. Each receptive field contains from 2 to 29 individual receptors. In the center of the field is usually the most sensitive point; distance from the centre of only 1 mm results in the decrease of sensitivity twice. In the process of perception of adequate stimulus tactile receptors interact with each other, which helps to underline the spatial contrast.
To excite receptors need some speed deformation, called the critical slope offset the stimulus. It varies for different receptors of the skin from 0,8 up to 40 mm/sec. Perception and differentiation of different forms of feeling connected with the existence of rapidly adapting and slowly adapting receptors.
The feeling of heat and cold is carried out with the participation of specialized heat and cold receptors. For each of these groups receptors has its optimum sensitivity. For cold sensitivity, it lies in the 28 - 38 degrees. Optimum sensitivity of thermal receptors is shifted towards higher temperatures (35 - 43 degrees). Innervation temperature receptors are, as a rule, Delta-made fibres (group a) and fiber group C. the density of the thermal receptors varies in different parts of the skin: the largest it on the face, especially the eyelids and lips, and the lowest on the soles of the feet. Average depth of the skin cold receptors - 0.17 mm, heat - 0,3 mm Cold receptors in the skin significantly greater than the heat.
There is a significant group of the tactile-temperature receptors respond as a mechanical and thermal irritation (cold). It is possible that the activation of these receptors is the physiological basis of the so-called illusions Weber: chilled the subject seems to be more severe. Morpho-physiological basis of the pain and itching are not yet sufficiently understood.
According Frejus each type of skin sensitivity meet certain specific receptors in the skin. However, a great variety of these receptors, surpassing the number of different forms of touch, comparability of these sensations with defined structures of skin receptors. Moreover, the existence of receptors dual specificity shows that the perception of different stimuli can be associated with different types of activity same receptor structures (hence, for example, different frequency of nerve impulses in response to certain stimuli).
Based on these and other data of the Weddell and Sinclair (G. Weddell, D. Sinclair) has been hypothesized "sample discharge", according to which each type of skin sensitivity corresponds to the particular character of discharge impulses in nerve fiber originating from the skin receptors. However, these ideas need further experimental testing, as pulses transmitted from receptors in the brain, may be hindered or strengthened throughout the sensory pathways, interact with impulses coming from other receptors, etc. are of Great importance in the formation of feelings with the skin has the reticular formation (see) of the brain stem, which is able to regulate the passage of afferent impulses in the higher departments of a CNS and facilitate caused responses in the cortex of the brain. A significant role in regulation of activity of skin receptors plays a sympathetic nervous system.
The sense of touch is active, accompanied by the actions of the body (the feeling, manipulation of an object)and passive. In the process of labour great importance instrumental feeling (O. object, through the instrument of labor: a hammer, pliers, and so on); the main role in this kind of O. play receptury of muscles and joints. When loss of vision O. becomes the main way of understanding the world.
Disorders O. - see Sensitivity.
Cm. also, the Skin, the Organs of sense.