The receptor is intended not only for the perception of stimulus signals, but also for the primary analysis of these signals. The receptor is located on the periphery of the nervous system.

Receptor functions:

1. Signal about the actions of external and internal stimuli on the body.

2. At the level of the receptor, the physical energy of the stimulus is converted into the physiological process of nervous excitation. The result of this excitation is the formation of a nerve impulse.

3. A primitive analysis of incoming stimuli begins at the receptor level.

Receptor classifications:

Due to the large amount of incoming information, there is the same number of receptors.

I. Depending on how many stimuli the receptor can perceive:

Monomodal (perceive 1 type of stimulus);

Polymodal (perceive several stimuli).

An example of monomodal ( hearing organs, visual receptors).

II. Depending on the source of information, all receptors are divided into 3 large groups:

1. Exteroreceptors perceive signals from the external environment.

2. Interoreceptors receive information from the internal environment of the body.

3. Proprioreceptors are found in ligaments, muscles, periosteum. Thanks to them, the central nervous system receives information about the state of the musculoskeletal system.

Exteroreceptors include:

Distact, for the excitation of which contact is not needed with irritant, they are excited at a distance .

Contact, excited by direct contact with the stimulus.

III. By the nature of the emerging sensations, receptors are divided into:

1. visual;

2. taste;

3. auditory;

4. olfactory.

IV. Depending on the energy of the stimulus that the receptor encounters, the following are distinguished:

1. chemoreceptors (if the irritant is a chemical);

2. mechanoreceptors (if the stimulus is a mechanical substance);

3. photoreceptors;

4. pain receptors.

V. By functioning, all receptors are divided into 2 groups:

1. primary perception (primary);

2. secondary perceiving (secondary).

The primary receptors come into contact with the stimulus directly, i.e. under the action of an irritant on the membrane of such a receptor, the generation (formation) of the receptor potential (RP) begins first. It is associated with a change in the permeability of the membrane for sodium ions. Sodium begins to actively enter the internal environment and depolarization occurs (a change in the charges of the membrane). When the RP reaches a certain value, it gradually develops into a generator potential (GP). This process occurs on the membrane of the primary receptor, HP is the cause of the action potential (AP) = nerve impulse. AP carries information to the CNS about the stimulus acting on the receptor. Proprioreceptors and olfactory receptors work according to this principle.

Secondary receptors differ from the primary in structure and physiology. The primary receptor is the end of the nerve fiber, the secondary in its composition, in addition to the nerve fiber, has a special specialized cell, which is called the receptor. The secondary receptor receives information secondarily. Primary information goes to the receptor cell. Under the action of a stimulus, RP occurs on the membrane of the receptor cell. The receptor cell contacts the sensing fiber via the synapse. There is a synoptic gap between the receptor cell and the sensory fiber. A mediator is released into this gap. The released neurotransmitter binds to the receptors of the membrane of the sensitive fiber and causes depolarization of the membrane, which leads to the formation of HP. Thus, in the secondary receptor, RP is formed on the receptor cell, and GP on the sensitive fiber. HP is the cause of the primary impulse on the receptor membrane.

Receptor Properties

1. Specificity. In the process of evolution, a more effective response reaction has been developed for certain types of receptor stimuli. Many of them have become specialized; capable of responding to their own type of stimulus (rods and cones to light). Those stimuli to which receptors are evolutionarily adapted are called adequate. In addition to adequate stimuli, inadequate stimuli can also act on receptors. In this case, in order for the receptors to respond to them, it is necessary that their strength be very large (for example, a small stimulus is enough for the reaction of shelves and cones; when a person is hit on the eyes, a person also sees flashes of light).

2. Wide range of sensitivity. It has been established that the human ear perceives the range from 16 to 20 thousand Hertz.

3.Adaptation. It is related to the protective function. It has been established that under the action of a constant stimulus, the sensitivity of the receptor decreases. The receptor has the highest sensitivity at the beginning of the action of the stimulus and at the end. Adaptation has a protective value for the nervous system, as it filters out unnecessary, redundant signals.

Receptor(from the Latin word - receiving) in biology has two meanings. In the first sense, receptors are called sensitive nerve endings or specialized cells that perceive irritations from the external or internal environment and convert them into nervous excitation, transmitted in the form of a stream of nerve impulses to the central nervous system of the body.

There are primary receptors, which are simple nerve endings of the processes of centripetal nerve cells - neurons, and secondary receptors, which have specialized cells for the perception of a certain irritation. Primary receptors include, for example, nerve endings in the skin that perceive tactile and pain stimuli, and secondary receptors include the olfactory cells of the nasal cavity, cones and rods of the retina that perceive light. Rods are modified epithelial cells containing substances that can disintegrate under the influence of light. The resulting decay products cause changes in the activity of these cells, which are recorded and processed by retinal neurons. Depending on the degree of excitation of cones and rods, neurons increase or decrease the flow of nerve impulses sent to the brain. Other secondary receptors that perceive sound vibrations, pressure on the skin, and the position of the body in space work according to a similar principle.

There are extrareceptors (exteroceptors) that perceive external stimuli: temperature, touch, light, sounds, taste, smell, etc.; intrareceptors (interoceptors) that register the state of the internal environment of the body: the chemical composition of the blood, its pressure on the walls of the vessel, the work of internal organs; proprioceptors (proprioceptors) that perceive tendon tension, changes in the length of muscle fibers, ligamentous apparatus. Receptors that perceive mechanical influences are called mechanoreceptors, chemical irritations are called chemoreceptors, and pressure is called baroreceptors.

In the second meaning of this term, receptors are called sections of the cell membrane that are sensitive to certain substances and transmit information about such a signal into the cell. In fact, membrane receptors are special protein molecules capable of recognizing molecules of certain compounds - proteins, peptides, low molecular weight hormones, growth factors and other substances. In most cases, the connection of the receptor with the signal molecule activates a special enzyme. The receptors are arranged in such a way that the molecules they recognize, or parts of these molecules, are able to enter the receptors, like a key in a keyhole. At the same time, the state and activity of the cell change. For example, muscle fiber receptors that provide automatic cardiac activity are sensitive to hormones - adrenaline and acetylcholine. The first hormone enhances the activity of the heart, the second slows it down.

Membrane receptors also function at the junctions of two nerve cells - synapses. The nerve ending of one cell releases a special substance - a mediator (for example, acetylcholine). Receptors on the surface of another cell perceive this signal and excite the second cell.

There are several classifications of receptors:

By position

• Exteroreceptors (exteroceptors) - located on or near the surface of the body and perceive external stimuli (signals from the environment)

  Interoreceptors (interoceptors) - located in the internal organs and perceive internal stimuli (for example, information about the state of the internal environment of the body)

  • Proprioreceptors (proprioceptors) are receptors of the musculoskeletal system, which make it possible to determine, for example, the tension and degree of stretching of muscles and tendons. They are a type of interoreceptors.

Ability to perceive different stimuli

• Monomodal - responding to only one type of stimulus (for example, photoreceptors - to light)

  Polymodal - responding to several types of stimuli (for example, many pain receptors, as well as some invertebrate receptors that respond simultaneously to mechanical and chemical stimuli).

According to the appropriate stimulus

• Chemoreceptors- perceive the impact of dissolved or volatile chemicals.

  Osmoreceptors- accept change osmotic concentration liquid (usually the internal environment).

  Mechanoreceptors- perceive mechanical stimuli (touch, pressure, stretching, vibrations of water or air, etc.)

  Photoreceptors- perceive visible and ultraviolet light

  thermoreceptors- perceive a decrease (cold) or an increase (thermal) temperature

  pain receptors whose stimulation results in pain. There is no such physical stimulus as pain, therefore, their selection into a separate group according to the nature of the stimulus is somewhat arbitrary. In fact, they are high-threshold sensors for various (chemical, thermal, or mechanical) damaging factors. However, a unique feature of nociceptors, which does not allow them to be classified, for example, as “high-threshold thermoreceptors,” is that many of them are polymodal: the same nerve ending can be excited in response to several different damaging stimuli. .

  Electroreceptors- perceive changes in the electric field

  Magnetic receptors- perceive changes in the magnetic field

Humans have the first six types of receptors. Taste and smell are based on chemoreception, touch, hearing and balance, as well as sensations of body position in space, on mechanoreception, vision is based on photoreception. Thermoreceptors are found in the skin and some internal organs. Most of the interoreceptors trigger involuntary, and in most cases unconscious, vegetative reflexes. Thus, osmoreceptors are included in the regulation of kidney activity, chemoreceptors that perceive pH, carbon dioxide and oxygen concentrations in the blood are included in the regulation of respiration, etc.

Sometimes it is proposed to single out a group of electromagnetic receptors, which includes photo-, electro- and magnetoreceptors. Magnetoreceptors have not been accurately identified in any group of animals, although some avian retinal cells, and possibly a number of other cells, presumably serve as them. .

26gmanhole (lat. oculus) - touch organ(organ visual system) of humans and animals, with the ability to perceive electromagnetic radiation in light wavelength range and providing the function vision. A person through eye receives about 90% of the information from the outside world .

Eye vertebrates is the peripheral visual analyzer, in which the photo receptor function is performed neurons- photosensory cells ("neurocytes") retina. Internal structure

1. rear camera 2. jagged edge 3. Eyelash ( accommodative) muscle 4. Ciliary (ciliary) girdle 5. Schlemm's channel 6. Pupil 7. Front camera 8. Cornea 9. Iris 10. Bark lens 11. Core lens 12. ciliary process 13. Conjunctiva 14. Inferior oblique muscle 15. Inferior rectus 16. medial rectus muscle 17. Arteries and veins of the retina 18. blind spot 19. Dura mater 20. Central artery retina 21. Central vein retina 22. optic nerve 23. Vorticose vein 24. Vagina of the eyeball 25. Yellow spot 26. Fossa centralis 27. Sclera 28. Vascular membrane of the eye 29. superior rectus muscle 30. Retina

The eyeball consists of shells that surround the inner core of the eye, representing its transparent contents - vitreous body, lens, aqueous humor in the anterior and posterior chambers.

The nucleus of the eyeball is surrounded by three shells: outer, middle and inner.

Outer - very dense fibrous membrane of the eyeball ( tunica fibrosa bulbi) to which are attached external muscles of the eyeball, performs a protective function and, thanks to turgor, determines the shape of the eye. It consists of a front transparent part - cornea, and the back of the opaque part of a whitish color - sclera.

Middle, or vascular, shell of the eyeball ( tunica vasculosa bulbi), plays an important role in metabolic processes, providing nutrition to the eye and excretion of metabolic products. It is rich in blood vessels and pigment (pigment-rich cells choroid prevent the penetration of light through the sclera, eliminating light scattering). She is educated iris, ciliary body and proper choroid. In the center of the iris there is a round hole - the pupil, through which the rays of light penetrate into the eyeball and reach the retina (the size of the pupil changes as a result of the interaction of smooth muscle fibers - sphincter and a dilator enclosed in the iris and innervated parasympathetic and sympathetic nerves). The iris contains a different amount of pigment, on which its color depends - " eye color».

The inner, or reticular, shell of the eyeball ( tunica interna bulbi), - retina- the receptor part of the visual analyzer, here there is a direct perception of light, biochemical transformations of visual pigments, a change in the electrical properties of neurons and the transfer of information to central nervous system.

With functional From the point of view of the shell of the eye and its derivatives, they are divided into three apparatuses: refractive (refractive) and accommodative (adaptive), which form the optical system of the eye, and the sensory (receptor) apparatus.

Human receptors) the stimulus is directly perceived by specialized cells of epithelial origin or modified nerve cells (sensitive elements of the retina), which do not generate nerve impulses, but act on the nerve endings innervating them, changing the secretion of the mediator. In other cases, the only cellular element of the receptor complex is the nerve ending itself, often associated with special structures of the intercellular substance (for example, Pacini's body).

How receptors work

Stimuli for different receptors can be light, mechanical deformation, chemicals, temperature changes, and changes in electric and magnetic fields. In receptor cells (whether they are not just nerve endings or specialized cells), the corresponding signal changes the conformation of sensitive molecules - cell receptors, which leads to a change in the activity of membrane ion receptors and a change in the membrane potential of the cell. If the receiving cell is directly a nerve ending (the so-called primary receptors), then the membrane usually depolarizes, followed by the generation of a nerve impulse. specialized receptor cells secondary receptors can both de- and hyperpolarize. In the latter case, a change in the membrane potential leads to a decrease in the secretion of an inhibitory mediator acting on the nerve ending and, ultimately, to the generation of a nerve impulse anyway. Such a mechanism is implemented, in particular, in the sensitive elements of the retina.

Cellular receptor molecules can be either mechano-, thermo-, and chemosensitive ion channels, or specialized G-proteins (as in retinal cells). In the first case, the opening of channels directly changes the membrane potential (mechanosensitive channels in Pacini bodies), in the second case, a cascade of intracellular signal transduction reactions is triggered, which ultimately leads to the opening of channels and a change in the potential on the membrane.

Types of receptors

There are several classifications of receptors:

• By position in the body

• • Exteroreceptors (exteroceptors) - located on or near the surface of the body and perceive external stimuli (signals from the environment)
  • Interoreceptors (interoceptors) - located in the internal organs and perceive internal stimuli (for example, information about the state of the internal environment of the body)
    • Proprioreceptors (proprioceptors) are receptors of the musculoskeletal system, which make it possible to determine, for example, the tension and degree of stretching of muscles and tendons. They are a type of interoreceptors.

• Ability to perceive different stimuli
  • Monomodal - responding to only one type of stimulus (for example, photoreceptors - to light)
  • Polymodal - responding to several types of stimuli (for example, many pain receptors, as well as some invertebrate receptors that respond simultaneously to mechanical and chemical stimuli).

Humans have the first six types of receptors. Taste and smell are based on chemoreception, touch, hearing and balance, as well as sensations of body position in space, on mechanoreception, vision is based on photoreception. Thermoreceptors are found in the skin and some internal organs. Most of the interoreceptors trigger involuntary, and in most cases unconscious, vegetative reflexes. Thus, osmoreceptors are included in the regulation of kidney activity, chemoreceptors that perceive pH, carbon dioxide and oxygen concentrations in the blood are included in the regulation of respiration, etc.

Sometimes it is proposed to single out a group of electromagnetic receptors, which includes photo-, electro- and magnetoreceptors. Magnetoreceptors have not been accurately identified in any group of animals, although some avian retinal cells, and possibly a number of other cells, presumably serve as them.

The table shows data on some types of receptors

Human receptors

Skin receptors

• pain receptors.
• Pacinian corpuscles are encapsulated pressure receptors in a round multilayered capsule. They are located in the subcutaneous fat. They are fast-adapting (they react only at the moment of the beginning of the impact), that is, they register the force of pressure. They have large receptive fields, that is, they represent rough sensitivity.
• Meissner bodies are pressure receptors located in the dermis. They are a layered structure with a nerve ending passing between the layers. They are fast adapting. They have small receptive fields, that is, they represent subtle sensitivity.
• Merkel bodies are nonencapsulated pressure receptors. They are slowly adapting (they respond to the entire duration of exposure), that is, they record the duration of pressure. They have small receptive fields.
• Hair follicle receptors - respond to hair deflection.
• Ruffini's endings are stretch receptors. They are slowly adapting, have large receptive fields.
• The Krause flask is a receptor that reacts to cold.

Muscle and tendon receptors

• Muscle spindles - muscle stretch receptors, are of two types:
  • with nuclear bag
  • with nuclear chain
• Golgi tendon organ - receptors for muscle contraction. When the muscle contracts, the tendon stretches and its fibers pinch the receptor ending, activating it.

Ligament receptors

They are mostly free nerve endings (Types 1, 3 and 4), a smaller group are encapsulated (Type 2). Type 1 is similar to Ruffini's endings, Type 2 is similar to Paccini's bodies.

receptors in the retina

Under the influence of light in the receptors occurs discoloration- a visual pigment molecule absorbs a photon and turns into another compound that absorbs light waves worse (of this wavelength). In almost all animals (from insects to humans), this pigment consists of a protein attached to a small molecule close to vitamin A. This molecule is the part chemically transformed by light. The protein part of the faded visual pigment molecule activates transducin molecules, each of which deactivates hundreds of cyclic guanosine monophosphate molecules involved in opening the membrane pores for sodium ions, as a result of which the flow of ions stops - the membrane hyperpolarizes.

The sensitivity of the rods is such that a person who has adapted to complete darkness is able to see a flash of light so weak that no single receptor can receive more than one photon. At the same time, rods are not able to respond to changes in illumination when the light is so bright that all sodium channels are already closed.