One of the most important purposes of the nervous system is sensitivity. The brain sends and receives impulses from any contact of the body with the external environment or due to the processes of the internal work of the whole organism. All sensations are recognized by the brain and enter into the general conscious sensitivity of a person. Almost all parts of the body can perceive all kinds of irritations. And tactile sensitivity receptors are present not only in the surface layers - the skin, mucous membranes, but also in the deeper areas - muscles, ligaments, joints, tendons, bones.
Origin of the concept
The property of the nervous system to perceive external and internal irritating effects with the help of special cells (receptors) and to respond to them is referred to a generalized concept - sensitivity. Moreover, it is characteristic of both man and animal. In turn, tactile sensitivity is a type of susceptibility of the skin. It is interconnected with sensations of touch and response to stimuli, pressure, vibration. Tactile receptors are part of the tactile system. They are located on the mucous membranes and the surface of the skin.
The very concept of "tactile sensitivity" comes from the Latin tactilis - tactile, touch, tango - touch, touch, denotes a variety of sensations that arise after exposure to the skin of various mechanical stimuli (touching, squeezing, pressing, vibration, stroking, tingling, pricking, touching objects and other things).
Essence and specificity
Specialized receptor cells have a high selective susceptibility to various stimuli. Along with the main types: pain, muscular-articular, temperature, internal organs, there is tactile sensitivity. Human physiology allows you to receive data from sensory receptors that are on the skin, muscles, joints, and in the inner ear. Receive information about the outside world and form an idea of the position of the body in space, about surfaces and textures. The main and integral part of interpersonal communication is tactile sensitivity. It is she who plays an important role in physical proximity.
In English, there is a similar concept - tactile sensitivity. It also acts as a way of knowing the world. Scientists have proven that touch is one of the first feelings that arises in an embryo. The development of tactile sensitivity plays a paramount role in the life of infants, since children with deviations in touch indices exhibit problems with survival even with the ability to hear and see.
Tactile receptors
The concept of “receptor” itself implies an apparatus of the nervous system capable of perceiving the actions of stimuli. Tactile sensitivity is carried out by two receptor systems:
- encapsulated nerve endings (Meissner bodies, Fater-Pacini, Merkel discs);
- nerve plexuses around the hair follicles.
These are sensitive points distributed throughout the body with varying degrees of density. Average values - 25 points per 1 square centimeter. In different parts of the body, the degree of density differs, respectively, the higher the density, the higher the acuity of susceptibility. The surface of the tongue has the greatest degree of sensation of sensations, and the sensitivity of the fingertips is still pronounced.
Primary sensations
After exposure to receptors, there are several types of sensations:
- Vibration.
- Touch.
- Tickling.
- Pressure.
Usually they are presented as different degrees of sensation of the same effect, since they arise in cases of deformation of the skin surface under the influence of mechanical irritants.
Description of tactile sensitivity receptors
Our body is extremely interesting! For example, each receptor is responsible for a specific reaction to external stimuli. There are encapsulated nerve endings (coated on the outside with a special capsule of connective tissue), these include:
- Meissner bodies are located in the shallow layers of the skin. These are the free endings of nerve fibers localized near the smallest vessels, the thinnest nerve fibers around the hair bag in those areas where hair is present. The greatest number of this type of receptors are on the surface of the palms of the hands, fingertips, feet, border of the lips, tip of the tongue. These receptors help to know the outside world.
- Merkel disks - are located in small groups in the deep layers of the epidermis and mucosa. These receptors are responsible for the feeling of pressure. They give a reaction to the bending of the skin under the action of mechanical stimulation, perceive the tactile irritations that occur when the skin comes into contact with objects. The bodies are located in particularly sensitive areas and are surrounded by the finest sensitive nerve endings.
- Vater-Pacini plate bodies respond to vibrational actions. They are located in the deeper layers of the dermis, adipose tissue, mucous membranes, in parts without hairline. They serve as detectors of short mechanical stresses. A sensation of vibration appears after irritation and deformation of several bodies of Vater-Pacini.
Unencapsulated nerve endings are located on the surface of the skin, which convey a feeling of tickling and moving around the skin.
Localization of tactile sensations, measurement of sensitivity
The person determines the place of sensation of touch or pressure very accurately. Localization is developed under the control of other organs of vision, muscle receptivity and experience gained in the development process.
Tactile sensitivity in different parts of the skin is notable for its acuity. Lips, nose, tongue are characterized by a high degree of susceptibility compared to other parts of the body. Sensitivity measurement is carried out using a Frey esthesiometer. The device determines the pressure force necessary for irritation of the receptors and the appearance of sensations.
Space threshold
Sometimes, when you instantly touch several points close to each other at once, you get the impression of just one common touch. The smallest distance between these points, giving a reaction of several touches, is called the threshold of space. It is measured using a Weber esthesiometer, similar to a compass with a millimeter scale.
Depending on the area on the body, sensations of touch occur at different distances and have different values of the threshold of space. Minimum values at the fingertips, tongue and lips, maximum values prevail on the shoulder, thigh, back. Thresholds depend on the branching of nerve fibers and the number of tactile receptors in this area.
Tactile Analyzer Departments (TA)
The receptors located on the surface of the body and mucous membranes are responsible for recognizing the effects on the skin and form a TA consisting of two departments:
- Conduction - consisting of sensitive nerve fibers coming from receptors to the spinal cord, optic tubercles and a network of neurons that activate the brain and control the reflex activity of the spinal cord.
- The brain department of the analyzer, represented by the posterior central gyrus, where similar sensations arise.
To check the state of health and tactile sensitivity of a person, various devices are used. The simplest of them is the Mochutkovsky taxiometer. It consists of eight surfaces with different textures, starting from the first - perfectly smooth in the eighth with deep notches. With reduced sensitivity, a person can distinguish only a few rough surfaces by roughness.