The sense of touch is a collection of special receptors that are located in the muscles, joints and tendons, skin and mucous membrane of the genitals, tongue, lips. The human touch organs perceive every action mechanically. For example, we can feel some pressure, touch, pain and temperature changes. As for the afferent innervation of our skin, it is carried out by special nerve fibers, which in turn come from neurons of the spinal ganglia. Tactile receptors located in the skin are formed by dendrites of sensitive neurons. In general, as already mentioned, such skin receptors are able to perceive not only chemical and mechanical irritations, but also electrical, as well as thermal.
Receptors, as a sense of touch, can be not only temperature or tactile, but also painful. According to physiologists, each of them acts as a perceiving apparatus. Nerve endings are divided into two types: non-free and free. Their difference lies in the presence of an axial cylinder in the second and glia cells in the first.
The organ of touch is, first of all, the free nerve endings. In human skin there are a huge number of such. There are many in the field of vibrissa. In human skin, which is covered with hair, not only free nerve endings are detected, but also mechanoreceptors, which are considered highly specialized. For example, Meissner bodies are located in the skin of fingers on the palms and soles of the feet, and Krause flasks are located on the mucous membranes of the lips, nipples, and genitals, which in turn provide increased sensitivity to these areas. As far as the process of touch itself is concerned, muscle spindles or proprioceptors of muscles, fascia, joints and tendons participate in it. One of the factors of the versatility of all tactile sensations of a person is considered to be the diversity of the organs of touch themselves, as well as the features of their temporal and spatial arousal.
The thickness of the epidermis is pierced by numerous free nerve endings. It is they who perceive pain irritations. This process is called nociception. The most delicate touches are perceived primarily by the nerve endings that braid the hair roots. In addition, the epidermis has many Merkel cells that are directly involved in the perception of any touch. In addition, they synthesize neuronal molecules, neurofilaments and many other markers specific for such nerve cells. Met-enkephalin stimulates almost all the immune responses of the human body. And this despite the fact that the substance is produced by the same Merkel cells. Another organ of touch is the Meissner body, which was mentioned above. They are located mainly in the papillary layer of the skin of the genitals, fingers, eyelids and lips. Their diameter is not more than 100 microns. In addition, each of these bodies is surrounded on the outside with a special connective tissue capsule. They include neuroglial cells, which in turn form an inner flask around the terminal thickening of each sensory nerve fiber.
A touch organ such as a pressure receptor is a Vater – Pacini plate body. A huge number of these bodies lies in the subcutaneous layer in the region of the external genitalia, fingers, capsule of internal organs, and the walls of the bladder. The diameter of one body does not exceed a millimeter. In general, they are characterized by the presence of an inner and outer bulb, while in the center of the first there is a branch of nerve fiber, which is very sensitive.
The human brain receives a huge amount of information about the world. In this case, of great importance in the process of perceiving the world for each of us is just touch. Sensory organ - tactile receptors, located on the entire surface of the human body. Thanks to this, we feel warmth, pain, touch and much more.