With preserved consciousness, a person accurately feels the relationship of parts of his body, controls every movement in the joints. Also, when performing any action, information about the intensity of the resistance put on it is sent to the brain.
This human ability is called proprioception, which is carried out with the help of specialized sensitive cells. The synonym for proprioception is deep sensitivity, since the receptor apparatus of this system is located on the structures lying below the subcutaneous fatty tissue.
General understanding of proprioceptors
Proprioceptors are highly differentiated nerve cellslocated in the structures of the musculoskeletal system, which are included in the work when the functional state and the interposition of muscle fibers and tendons change. These structures belong to one of the varieties of mechanoreceptors, therefore, they are characterized by general nonspecific properties:
- A high level of sensitivity, measured by the response threshold and associated with it in an inversely proportional relationship.
- Sensory adaptation, which manifests itself as a decrease in sensitivity to a background stimulus that has a long-term effect on the receptor.
In addition, they play a dominant role in the definition and functioning of the following senses:
- strength, manifested in the assessment of the necessary effort to perform a certain movement or hold a pose;
- positions - drawing up an idea of the relative position of all parts of the body at each moment in time;
- movement, due to which the vector and rate of change in the position of the joints is realized.
Mechanism of work
The principle of reaction to irritation of all receptors is similar to each other, but depending on the type, the nuances of the mechanism may change.
The stimulus for activation of muscle sense receptors is mechanical deformation, as a result of which a change in the conformation of molecules, leading to the activation of membrane mechanosensitive ion channels and a change rest potential.
Since proprioceptors are the primary receptor structures, as a result of mechanical action, the cell membrane is depolarized and an electrical impulse is generated.
Classification of the receptors of this system
Depending on the most typical localization and structural features, it is customary to divide proprioceptors into 2 types.
- Neuromuscular spindles, the activation of which occurs when the length of the muscle changes.
- Golgi receptors are typical of tendons, responding to force of contraction and changes in tension.
Muscle spindles
Located parallel to the fibers of skeletal muscle, they are receptor formations with a high degree of differentiation, which communicate with afferent and efferent nerves. Intrafusal fibers are spindle-shaped structures up to 10 mm long and about 100 microns in diameter with a capsule consisting of connective tissue.
From a histological point of view, each individual fiber consists of a central part, with nuclei located in it, and movable peripheral sections. This feature is the basis for the separation of proprioceptors of this type. V
They distinguish fibers with a nuclear bag, functionally subdivided into dynamic and static, and with a nuclear chain.
The structure of each spindle is not uniform: it consists of 6-13 fibers of both types.
The endings receiving afferent innervation are divided into primary (annulospiral, in the form of a spiral around the neuromuscular fibers) and secondary (prone to branching). Thick fibers depart from the primary with a low (12-70 m / s) speed of excitation, the secondary ones are characterized by a smaller diameter and higher speed (40-70 m / s).
The static response develops with a gradual stretching of the spindles, manifests itself on both types of afferent fibers, and depends on the degree of change in the length of the central part. With a quick unexpected impact, a dynamic response is characteristic only in the annulospiral endings.
Gamma motor neurons serve for efferent innervation and are distinguished by the lowest conduction speed (15-40 m / s). They are also divided into static, nuclear-chain feeding fibers, and dynamic, characteristic of nuclear-buried fibers.
Golgi tendon receptors
The Golgi bodies located in the tendons are characterized by a higher threshold of excitation during contraction. They are collagen filaments with a thin-walled capsule up to 1 mm long, sequentially connected with 10-15 muscle fibers. Knowing this, we can say that the excitation of the receptor occurs on muscle tension. An afferent impulse is sent to the spinal cord, causing the activation of inhibitory motor neurons, which relax the innervated muscle.
