What is anatomy? It is a science that studies the characteristics of the human body. The classification of receptors and stimuli also belongs to the questions of this discipline. How are the first related to the second? Everything is very simple. The body is constantly exposed to a large number of various stimuli, our receptors respond to them selectively, it all depends on their location and structure. Nervous formations are also called the sensory system, transmitting sensations from the sense organs to the central nervous system.
There are different types of receptors, but first you need to identify the sense organs:
- Eyes.
- Ears.
- Gravity sense organs.
- Language.
- Nose.
- Leather.
Why do we need receptors
Everyone needs the kind of information that the environment provides. First of all, this is necessary in order to provide oneself with food and an individual of the opposite sex, to protect oneselffrom danger and for orientation in space. All this is provided by these nerve formations. The classification of receptors is, of course, an important issue, but before that, we will analyze the types of signals acting on them.
Irritants
They are classified according to the following features:
- Modality.
- Adequacy.
As for the first point, external stimuli distinguish between thermal, electrical, mechanical, osmotic, chemical, light and many others. They are transmitted directly with the help of various types of energy, for example, thermal, as you might guess, are transmitted with the help of temperature and so on.
Besides all this, they are divided into adequate and inadequate stimuli, it is worth talking about this in a little more detail.
Adequacy
It is important to note the incredibly clever idea of Friedrich Engels, who believed that the sense organs are the main tool of the brain. He is certainly right, because everything that we see, feel and hear is the merit of the sense organs and receptors, and the irritation of the latter is the very initial link in the knowledge of the external world. For example, we feel the work of taste buds when we feel the taste of food (bitter, s alty, sour or sweet), irritation of the eye receptors gives us a feeling of light or its absence.
The stimulus to which the receptor is adapted is called adequate. The tongue receptors are a good example. When hit inthe mouth of a substance we experience a taste, such as bitter, s alty, sweet, or sour. The retina of the eye picks up light waves, so we understand that the light is on.
Inadequacy
The properties of receptors are quite diverse, but speaking about the inadequacy of stimuli, we can distinguish the following: when exposed to energy to which the receptor is not adapted, an insignificant part of sensations is caused, such as when stimulated adequate. An example would be electric shock or chemical irritation.
If the retina of the eye has received mechanical irritation, then there will be a sensation of light, this phenomenon is commonly called "phosphene". Or when we receive an electric shock in the ear, we can hear a noise, but a mechanical shock can cause a taste sensation.
Classification of receptors: physiology
We figured out the issue of irritants, now we have an equally important question left. To understand the mechanism of action, the classification of receptors is important. To begin with, we will analyze the question of the principle of the structure of human sensory systems, highlight the main functions, and talk about adaptation. First of all, the classification of receptors by type includes the following:
- Pain receptors.
- Visual.
- Receptors that determine the position of the body and its parts in space.
- Auditory.
- Tactile.
- Olfactory.
- Flavourful.
This is not the only classification of receptors, in addition to these types, there is a division according to othersqualities. For example, by localization (external and internal), by the nature of contact (distant and contact), primary and secondary.
External are the receptors responsible for hearing, sight, smell, touch and taste. The internal ones are responsible for the musculoskeletal system and the condition of the internal organs.
As the second point, we identified the following types of receptors: distant, that is, those that pick up a signal at a distance (vision or hearing), and contact, which need direct contact, for example, taste.
As for the division into primary and secondary, the first group includes those that convert irritation into an impulse in the first neuron (example: smell), and the second - those with a receptor cell (example: taste or vision).
Building
If we consider the structure of human receptors, it is possible to highlight the basic principles, such as:
- Many layers of cells, that is: the nerve receptor is connected to the first layer of cells, and the last layer is a conductor to the cerebral cortex, or rather to its motor neurons. This feature allows you to process incoming signals at a very high speed, processed already at the first layer of the system.
- For the accuracy and reliability of the transmission of nerve signals, multi-channel is provided. As described in the previous paragraph, the sensory system has many layers, and they, in turn, have from several tens of thousands to several million cells that transmit information to the next layer. In addition to reliability, this feature also provides detailedsignal analysis.
- Funnel formation. For example, consider the receptors of the retina of the eye. In the retina itself, there are one hundred and thirty million receptors, but in the layer of ganglion cells there are already one million three hundred thousand, which is a hundred times less. We can state that a narrowing funnel is observed. What is its meaning? All unnecessary information is filtered out, but at the next stages an expanding funnel is formed, which provides advanced signal analysis.
- Vertical and horizontal differentiation. The first contributes to the formation of departments consisting of layers and performing any one function. The second is needed in order to divide the cells into classes within the same layer. For example, let's take vision, there are two channels working at once, which carry out their work in different ways.
Receptor functions
An analyzer is a part of our nervous system, which consists of several elements: the perceiver, nerve pathways and parts of the brain.
There are three components in total:
- Receptors.
- Conductors.
- Department of the brain.
Their functions are also individual, that is, the first seize signals, the second escort them to the brain, and the third analyzes the information. This whole system works synchronously to ensure, first of all, the safety of humans and other living beings.
Table
We propose to highlight the main functionsoperation of the entire sensory system, for this we present a table.
| Functions | Explanation |
| Detection | Over time, the sensory system evolves, at the moment the receptors are able to capture a very large number of signals, both adequate and inadequate. For example, the human eye is able to capture light, and also distinguishes both mechanical and electrical shock. |
| Distinguishing incoming signals | |
| Transfer and transformation | All receptors are a kind of converters, since they receive a completely different one from one energy (nervous irritation). In no case should they distort the signal. |
| Encoding | This feature (function) is described above. Coding the signal into the form of nerve stimulation. |
| Detection | The receptor, in addition to picking up the signal, must also highlight its sign. |
| Ensuring image recognition | |
| Customization | |
| Interaction | It is this important function that shapes the scheme of the world, in order to adapt, we need to relate ourselves to it. No organism can exist without the perception of information, this function ensures the struggle for existence. |
Properties of receptors
Dealing further. Now it is necessary to highlight the main properties of receptors. The first we will call selectivity. The thing is that most human receptors are aimed at receiving only one type of signal, for example, light or sound, they are very susceptible to such types of signals, the sensitivity is unusually high. The receptor is excited only if it detects the minimum signal, for this the concept of “excitation threshold” has been introduced.
The second property is directly related to the first, and it sounds like a low threshold value for adequate stimuli. For example, let's take vision, which picks up such a minimum signal that it takes to heat a milliliter of water by one degree Celsius for sixty thousand years. Thus, responses to inappropriate stimuli, such as electrical and mechanical, are only possible for these species, respectively, and the threshold is much higher. In addition to all that has been said, there are two types of thresholds:
- absolute,
- differences.
The former determine the smallest value felt by the body, and the latter allow us to distinguish degrees of illumination, shades of different colors, and so on, that is, the difference between two stimuli.
Another very important property of all living organisms on earth is adaptation. This is how our sensory systems adapt to external conditions.
Adaptation
This process covers not only the receptors of sensory systems, but also all its layers. How does this happen? It's simple, the threshold of arousal, which wesaid earlier, this is not a constant value. With the help of adaptation, they change, become less sensitive to a constant stimulus. Do you have a clock at home? You do not pay attention to their eternal ticking, because your receptors (in this case, auditory) have become less sensitive to this stimulus. And to other long and monotonous irritations, we have developed immunity.
Adaptation processes cover not only receptors, but all parts of sensory systems. Adaptation of peripheral elements is manifested in the fact that the excitation thresholds of receptors are not a constant value. By raising the thresholds of excitation, that is, by reducing the sensitivity of the receptors, adaptation to prolonged monotonous stimuli occurs. For example, a person does not feel constant pressure on the skin of his clothes, does not notice the continuous ticking of the clock.
Phase and tonic receptors
Note that all receptors are divided into:
- quickly adaptable,
- slow to adapt.
Moreover, the first, they are also called phasic, give a reaction to stimuli only at the very beginning and at the end of its action, but the second (tonic) send continuous signals to our central nervous system for a rather long period of time.
It is also necessary to know that adaptation can be accompanied by both an increase and a decrease in the excitability of the receptor. For example, let's imagine that you are moving from a bright room to a dark one, in which case there is an increase in excitability, firstyou see illuminated objects, and only then darker ones. The opposite case, if you move from a dark room to a bright one, everyone knows the expression “light hurts the eyes”, we squint because our receptors are being rebuilt, namely, the excitability of our photoreceptors decreases, now the so-called dark adaptation is taking place.
Regulation
It is important to know that a person's nervous system is capable of regulation, it all depends on the needs at a given time. If, after a state of rest, a person abruptly begins physical work, then the sensitivity of the receptors (motor apparatus) increases sharply. Why is this necessary? To facilitate the perception of information related to the state of the musculoskeletal system. In addition, the adaptation process is capable of affecting other formations in addition to receptors. For example, let's take hearing, if there is an adaptation, then the mobility of such parts as:
- hammer,
- anvil,
- Stirrup.
That is, the ossicles of the middle ear.
Conclusions
Summing up all of the above, we will once again highlight the main functions of our sensory systems: signal detection, discrimination, conversion of one type of energy into another (nerve impulse), transmission of the converted signal to other layers of sensory systems, pattern recognition. The main properties are the following points: selectivity, low response threshold for adequate stimuli, the ability to adapt to the environment. We also considered such important points as the structure andclassification of sensory systems, classification according to different characteristics of stimuli, adaptation.
