Receptor classification Taste, visual, pain receptors

What is anatomy? This is a science that studies the characteristics of the human body. The classification of receptors and stimuli also relates to issues of this discipline. How are the former related to the latter? 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. Nerve formations are also called the sensory system, transmitting sensations from the senses to the central nervous system.

There are various types of receptors, but first you need to highlight the sensory organs:

• Eyes.
• The ears.
• Sensory organs of gravity.
• Tongue.
• 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 yourself with food and an individual of the opposite sex, to protect yourself from 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 using various kinds of energies, for example, thermal, as you might guess, transmitted through temperature and so on.

In addition to all this, they are divided into adequate and inadequate stimuli, it is worth talking about this in more detail.

Adequacy

It is important to note the incredibly clever thought of Friedrich Engels, who believed that the senses are the main tool of the brain. He is certainly right, because everything that we see, feel and hear is the merit of the senses and receptors, and the irritation of the latter is the very initial link in the knowledge of the outside world. For example, we feel the work of taste buds when we feel the taste of food (bitter, salty, sour or sweet), irritation of the eye receptors gives us a feeling of light or its absence.

The irritant to which the receptor is adapted is called adequate. A good example is language receptors. If a substance enters the mouth, we taste, for example, bitter, salty, sweet or sour. The retina catches light waves, so we understand that light is on.

Inadequacy

The properties of the receptors are quite diverse, but, speaking about the inadequacy of stimuli, the following can be distinguished: when exposed to energy to which the receptor is not adapted, a small part of the sensations is caused, such as those with adequate stimulation. An example is 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 usually called “phosphene”. Or when we get an electric shock in the ear, we can hear a noise, but mechanical damage can cause a taste sensation.

Receptor Classification: Physiology

We sorted out the question of stimuli; now we still have an equally important question. To understand the mechanism of action, classification of receptors is important. To begin with, we will examine 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.
• Flavoring.

This is not the only classification of receptors, in addition to these species, there is a separation in other qualities. For example, by localization (external and internal), by the nature of the contact (distant and contact), primary and secondary.

External are receptors responsible for hearing, sight, smell, touch and taste. Internal ones are responsible for the musculoskeletal system and the condition of internal organs.

The second item 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: sense of smell), and the second - having a receptor cell (example: taste or vision).

Structure

If we consider the structure of human receptors, it is possible to highlight the basic principles, such as:

1. 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, and more precisely to its neurons in the motor regions. This feature allows you to process incoming signals processed on the first layer of the system with a very high speed.
2. For accuracy and reliability of transmission of nerve signals, multichannel is provided. As described in the last 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 provides detailed signal analysis.
3. Funnel formation. For example, consider retinal receptors. 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 one hundred times less. We can state that a narrowing funnel is observed. What is its meaning? All unnecessary information is screened out, but in the next steps an expanding funnel is formed, which provides advanced signal analysis.
4. Differentiation vertically and horizontally. The first contributes to the formation of departments consisting of layers and performing any one function. The second is needed in order to divide cells into classes within one layer. For example, take vision, two channels work there at once, which carry out their work in different ways.

Receptor functions

An analyzer is called a part of our nervous system, which consists of several elements: the perceiving, nerve paths and parts of the brain.

In total, three components can be distinguished:

1. Receptors.
2. Conductors.
3. Department of the brain.

Their functions are also individual, that is, the former capture the signals, the latter escort them to the brain, and the third analyzes the information. This entire system works synchronously to ensure, first of all, safety for man and other living beings.

Table

We suggest highlighting the basic functions of the entire sensor system, for this we give a table.

Receptor properties

We understand 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 picks up the minimum signal, for this the concept of “threshold of excitation” is introduced.

The second property is directly related to the first, and it sounds like a low threshold for adequate stimuli. For example, take vision that picks up such a minimal signal, which is needed to heat a milliliter of water by one degree Celsius for as many as sixty thousand years. Thus, a reaction is possible to inadequate stimuli, such as electrical and mechanical, only for such species, respectively, and the threshold is much higher. In addition to all of the above, two types of thresholds are distinguished:

• absolute
• differential.

The former determine the smallest amount felt by the body, while the latter allow us to distinguish between the degrees of illumination, the shades of various colors, and so on, that is, the difference between the two stimuli.

Another very important property of all living organisms on earth is adaptation. So our sensor systems adapt to external conditions.

Adaptation

This process covers not only the receptors of sensory systems themselves, but also all its layers. How does this happen? It's simple, the threshold of excitation, which we talked about earlier, is not a constant. With the help of adaptation, they change, become less sensitive to a constant irritant. Do you have a watch at home? You do not pay attention to their eternal ticking, because your receptors (in this case, the auditory ones) have become less sensitive to this stimulus. And to other long and monotonous irritations we have developed immunity.

Adaptation processes encompass not only receptors, but also all links of sensory systems. The adaptation of peripheral elements is manifested in the fact that the thresholds of excitation of receptors are not a constant value. By increasing the excitation thresholds, i.e., reducing the sensitivity of the receptors, adaptation to long-term monotonous irritations occurs. For example, a person does not feel constant pressure on the skin of his clothes, does not notice the continuous ticking of watches.

Phase and tonic receptors

Note that all receptors are divided into:

• quickly adaptable
• slowly adapting.

Moreover, the first, they are also called phase, 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 receptor excitability. For example, imagine that you are switching from a bright room to a dark one, in which case there is an increase in excitability, first you see illuminated objects, and only then darker. The opposite case, if we turn from a dark room to a light one, everyone knows the expression “light hurts our eyes”, we squint because our receptors are rearranged, namely, the excitability of our photoreceptors decreases, now the so-called dark adaptation is taking place.

Regulation

It is important to know that in humans, the 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 (of the motor apparatus) increases sharply. Why is this needed? To facilitate the perception of information related to the condition of the musculoskeletal system. In addition, the adaptation process is capable of affecting other formations in addition to receptors. For example, let’s take a rumor, if adaptation takes place, then the mobility of such parts as:

• hammer,
• anvil,
• stapes.

That is, the auditory ossicles of the middle ear.

conclusions

To summarize the foregoing, we will once again highlight the main functions of our sensory systems: signal detection, discrimination, the 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 as follows: selectivity, low response threshold for adequate stimuli, the ability to adapt to the environment. We also examined such important points as the structure and classification of sensory systems, classification according to various signs of stimuli, and adaptation.