Tasks such as when standing with your eyes closed, you need to touch the tip of the nose with your index finger, or turn the steering wheel of a car smoothly enough and in the right direction to make a maneuver on the road, are solved with the help of the debugged work of proprioceptive systems.
But what it feels like when the system is not working at full capacity, a healthy person can feel it as a result of using local anesthesia, for example, in dentistry. Then the treated area feels like a stranger. In such conditions, not only the pain ceases to be felt, but also problems arise with the perception of one's body.
What it is
The ability of the body to sense the location of its parts relative to each other and space, to make precise and coordinated movements is called proprioception. It is also responsible for balance and agility, is one of the conditions for the normal functioning of the vestibular system and is divided into:
- interception, which sends data about internal organs to the brain;
- exterception, which conveys information about the outside world.
A person whose proprioceptive abilities are in order is able to move the limbs, while correctly calculating in which direction and how far they move. Usually, this process is complemented by automatic movements to correct body position.
In addition, there is the concept of "kinesthesia", which is sometimes equated with proprioception, but more often they nevertheless, they are divided, referring the first to the conscious reaction of the organism to the situation, and the second to unconscious. Also, kinesthesia is considered a behavioral sense responsible for body movement and sensation of movement, based on data obtained from the vestibular apparatus and vision.
An example is muscle memory formed by repeated repetition of physical exercises in sports or when working on computer keyboard, when you first need to look for the correct key with your eyes, and having gained experience, a person is able to type quickly and Blindly.
Types of muscle feelings
A healthy person, even with closed eyes, is able to determine whether he is standing, sitting or lying, whether his legs and arms are bent, his head is lowered or turned to the side. The following components of proprioception help the body in this:
- Sense of Position - Determines the angles between joints, forming an idea of the position and posture of the whole body.
- Sense of movement - determines the direction and speed of movement of the joints.
- Sense of Strength - Measures the muscle force applied to move or hold a joint.
Muscular sensation is closely related to other types of perception, most often with the feeling of touch and pressure. Interacting with hearing and sight, it underlies the sensation of time.
How it works
Motor neurons send information to the brain about the external environment and about the position of each member of the body, then the brain processes the data and, as a result, gives orders to the muscles. There are many 
proprioceptors, sensory receptors located in different parts of the body:
- in ligaments, joints and skin;
- in the neck and labyrinth apparatus of the inner ear;
- in muscles and tendons.
The receptors on the skin are called mechanoresetors, and they send data about the location of the limbs. Also proprioceptors include:
- Neuromuscular spindles - fusiform structures covered with a connective tissue capsule, located between muscle fibers, providing data on changes in muscle length, muscle contractions and sprains.
- The Golgi tendon organ (or Golgi apparatus) reports a change in the degree of muscle and tendon tension and is located in the tendons, between muscles and bones. In structure, these are nerve filaments surrounded by thin muscle fibers and enclosed in separate capsules, due to which they are also called "tendon spindles".
Skeletal muscle contractions cause muscle fibers to contract inside the spindles. Nerve impulses are formed, which are sent to the centers of the spinal cord, and then, if necessary, to the brain. Thus, a continuous flow of data on the position of the body in space, the degree of flexion and extension of the joints and muscle tension is organized. This data is processed and ultimately allows you to determine the exact position of the limbs and send the necessary commands to the muscles.
By themselves, everyone has proprioceptors, but the speed of their reaction is different for each of us. A good example of the work of proprioceptors is the "tendon reflex". Exposure to the knee tendon results in a reflex contraction of the quadriceps muscle of the leg.
What is it for
All this suggests that during any physical exercise, a huge number of impulses sent by receptors from various organs and muscles are sent to the central nervous system. This leads to an increase in the excitability of the central nervous system and normalizes the body's performance.
In other words, the nerve signals that the muscles send serve to maintain vigor, excellent tone, and therefore health.
Also, the processing of such a volume of information stimulates the development of the brain, which is why special attention is paid to fine motor skills in the development of children. An active lifestyle has been proven to improve learning in all areas. And this is directly related to the normal functioning of the proprioceptive system.
"Rubber Hand Illusion"
Visual, tactile, kinesthetic and auditory modalities send information to the brain. He, in turn, analyzing the totality of the received data, forms the image of the body in the mind. Scientists have experimentally found out that the body image is mobile, it can be changed, and in just a few minutes. We also found out that the ability to control the limbs is closely related to the awareness of the integrity of the body. This is well demonstrated by an experiment called the rubber hand illusion.
The procedure is carried out in different variations, but the common thing is that the subject's hand is taken at a distance and hidden under a blanket, a box or behind a partition, and then place an artificial hand on the table in front of him as if it were his own. After that, the subject must fix his hand in a similar position with the requisite one. When the preparation process is completed, synchronous actions are performed on the hands, most often stroking with a brush is chosen. This continues on average from two to four minutes and leads to the fact that at some point a person begins to perceive the rubber hand as his own. This suggests that the human brain, receiving visual and tactile information, gradually produces proprietary transference and changes the perception of its body.
Scientists using special sensors during experiments measured the intensity of electrical pulsations sent by the brain to hidden limb, and found that at the moment when a person has the feeling that the rubber hand is his own, the flow is significantly is shrinking. This proves that not only at the level of perception, but also at the physical level, the brain for some time ceased to perceive its own hand as its own.
Potential opportunities
People with impaired muscle sensations lose the accuracy of movements, with age this process occurs naturally, but sometimes a disease can cause this. Including many of those who have survived a stroke, stop perceiving paralyzed limbs as their own, as if they no longer belong to them. This is precisely the reason for active research on this issue.
The body compensates for the loss of proprioception through vision.
But scientists hope that by thoroughly studying this issue, they can develop a diagnostic tool that helps to find out:
- to what extent a person's perception of his body coincides with the real image;
- how soon is it brain adopts a new image of himself;
- what exactly is distorted in the perception of the body.
This knowledge will allow solving therapeutic problems, creating restorative procedures for patients.
But first it is necessary to find out how the brain forms and stores an internal idea of its body and why, if the sensation of owning its body formed based on proprioception, the brain becomes confused when it receives conflicting data from other modalities, in particular from vision.
