The receptor - specific nervous education, which ends sensitive (afferent) nerve fibers that can get excited when the effects of the stimulus. Receptors perceive irritations from the external environment, called exteroceptors; perceiving irritation of the internal environment of the body - interoceptors. Allocate a group of receptors located in the skeletal muscles and tendons and signaling tone muscles - proprioceptor.
Depending on the nature of the irritant receptors are divided into several groups.
1. Mechanoreceptors, which include tactile receptors; baroretseptorov located in the walls of blood vessels and reacting to changes in blood pressure; anoreceptive that responds to vibrations in the air, created a sound stimulus; receptors otolith system, perceiving changes in body position in space.
2. Chemoreceptors that respond to the impact of any chemical substances. These include osmoreceptors and glucoraphanin perceiving respectively change osmotic pressure and blood sugar levels; gustatory and olfactory receptors perceive the presence of chemicals in the environment.
3. Thermoreceptors, perceiving the temperature changes within the body and the body environment.
4. The photoreceptors, located in the retina perceive light stimuli.
5. Pain receptors are allocated in special group. They can be instituted mechanical, chemical and thermal stimuli such force that are destructive of their action on the tissues or organs.
Morphologically receptors can be as simple free nerve endings or be in the form of hairs, coils, plates, synochek, balls, cones, sticks. The structure of the receptors is closely connected with the specificity of adequate stimuli to which the receptors are high absolute sensitivity. For excitation of photoreceptors are enough 5-10 light quanta, for excitation of olfactory receptor - one molecule odorous substances. With long-term impact of the stimulus is adaptation receptors, resulting in a decrease their sensitivity to adequate stimulus. There are rapidly adapting (tactile, baroretseptorov and slowly adapting receptors (chemoreceptors, anoreceptive). Vestibulometry and proprioceptor, in contrast, is not adapted. The receptors under the action of an external stimulus occurs depolarization the surface of the membrane, which is designated as the receptor or generating potential. Having reached the critical value, it calls the afferent discharge pulse excitation in the nerve fibers extending from the receptor. Perceived by receptors information from internal and external environment of the organism is transmitted via afferent nerve pathways in the Central nervous system, where it is analyzed (see Analyzers).