PROPRIOCEPTORS (Latin proprius own, special + [re] tseptor) — touch devices of a musculoskeletal system (muscles, sinews, fastion, joints, etc.). Sometimes carry to P. also receptors of a vestibular mechanism and cardiovascular system.
Originally the term «proprioceptors» entered by Ch. Sherrington (1906) designated all touch devices of an organism. Now P. usually consider as one of groups of interoceptors (see. Interoception ). Items participate in all acts, work-related muscles, joints and sinews (movement of a body and its parts in space, breath, processes of speech production, etc.). By means of P. the organism obtains information on the nature of movements of a body, on features of the incentives (their size, duration, speed, the direction, etc.) operating on a musculoskeletal system. Thanks to P.'s activity there are feelings called by I. M. Sechenov «dark muscle sense».
Among P. there are as usual receptor educations (free nerve terminations, the encapsulated receptors like Ruffini and Pachini's little bodies and their version), and very specific touch devices, e.g. tendinous receptors of Golgi and muscle spindles.
Free nerve terminations (see) are the most widespread type of the Item. The encapsulated receptors meet in muscular and tendinous connections and in tissues of joints more often (see. Mechanioreceptors ). Tendinous receptors are located in sinews usually on border of a muscular and tendinous part of a muscle, in basic sites of joint capsules, in not capsular and intra capsular sheaves; have the extended form. Thick afferent pulpy fibers, and also thinner myelinized fibrils which are coming to an end according to a number of scientists, the free nerve terminations braiding a receptor and, perhaps, participating in emergence of the nociceptive alarm system approach them.
Muscle spindles have the extended structure extending in a middle part at the expense of the capsule, edges gives it the spindle-shaped form that found reflection and in the name of a receptor. At mammals, including at the person, these receptors are the most difficult after specialized sense bodys. The greatest density estimated on number of receptors on a weight unit of a muscle (Bokki's index) is found in small muscles of the hands making the thin, high-coordinate movements. As well as in all other receptors, in muscle spindles there are auxiliary structures presented by specialized cross-striped muscle fibers (so-called intrafusal muscle fibers), and also the capsule, contents the cut on structure, apparently, differs from a usual intercellular lymph. In the center of intrafusal fiber there is a nonreducible site (area of a nuclear bag). It is adjoined on both sides by zones of the changed muscular tissue (so-called miotrubk), for to-rymi usual muscular structures begin. Touch nerve terminations of a muscle spindle are localized in the field of a nuclear bag and a miotrubka. Allocate two types of muscle spindles: muscle spindles of one type in the central area of intrafusal fibers have a large number of kernels (so-called fiber with a nuclear bag); at fibers of other type (usually thinner and short) concentration of kernels in the equatorial zone is less, they are rowed, forming a chain (so-called fibers with a nuclear chain). This type of fibers meets at the animals possessing thinner coordination of movements more often.
Intrafusal fibers contain three types of nerve terminations. Two of them touch (primary, or annulospiral, and secondary, or uviform), and one — motor. Primary endings are localized in the equatorial part of fibers, secondary are located in the field of a miotrubka. The motor terminations are disseminated through other parts of intrafusal fibers. Primary endings occur at mammals in fibers of both types and are formed by branchings of the myelinized nerve fibrils which are the largest in an organism (diameter to 20 microns) and belong to fibers of the That group. Secondary endings are located usually only in fibers with a nuclear chain and formed by branchings of more fine pulpy fibers of group P. Distinctions in the diameter of nerve fibrils, and also in the speed of carrying out impulses on them are the main criteria of distinguishing of the signals going from primary and secondary endings. Fine structure of primary and secondary endings in general is identical. The efferent fibers (fusimotor) going to a muscle are presented by two basic groups: the thick pulpy fibers (alpha group) innervating preferential extrafusal muscle fibers and the fine fibers (gamma group) innervating intrafusal fibers. Intrafusal fibers can sometimes receive a motive innervation and from fibers of other type.
Items belong to type of aresnitchaty mechanioreceptors. Deformation of the terminations of not myelinized branchings of nerve fibrils is the cornerstone of the mechanism of their excitement, the cut is a consequence change of ion permeability of a superficial membrane of mechanoreceptor bombways. Between the size of a static phase of receptor potential and frequency of impulses there is directly proportional dependence. The picture of distribution of impulses at P.'s irritation is defined by a number of their properties, such as mechanical characteristics of auxiliary structures of receptors, features of receptor substrate and the related system of generation of the local electric phenomena (receptor, or generating, potential) and, at last, features of afferent nerve fibrils (first of all, properties of their initial segment where under the influence of generator potential there is an emergence of action potentials). At one P. (e.g., muscle spindles of tendinous receptors, Ruffini's little bodies) the tonic component of the answer is well-marked, and these P. are slowly adaptive receptors perceiving static components of irritants. Other P. (e.g., Pachini's little bodies) have only a dynamic component of reaction, and they are quickly adaptive receptors which are well perceiving such influences as the bystry movement and vibration. Muscle spindles are located in fabric parallel to extrafusal muscle fibers whereas tendinous receptors — it is consecutive. Therefore at the time of muscular contraction load of muscle spindles decreases, and on tendinous receptors increases. At a muscle strain load of both types of receptors increases, and all of them are excited. These features in an arrangement of receptors lead to the fact that muscle spindles send to c. N of page information on length of a muscle, and tendinous receptors — about its tension (active or passive). Respectively, they are called sensors of length and tension.
Efferent regulation plays very large role in work of the Item. By efficiency of a feed-back muscle spindles hold exclusive position among other fabric receptors that is defined by their role in implementation of the fast-proceeding, strictly coordinate motive acts (see. Movements ). Activation of efferent fibers leads to reduction of intrafusal muscle fibers and, respectively, to excitement of the receptor. All efferent gamma fibers are subdivided into two types: dynamic and static. Fibers of the first group have ability to excite a muscle spindle during dynamic action of irritation (muscle strain). Fibers of the second group work excitingly in the period of a static phase of stretching. With a constant length of a muscle the irritation of fibers of both types causes initiation of the receptor terminations. Static fusimotor fibers have similar effect on primary and secondary endings. Influence of dynamic fibers, apparently, is limited only to primary endings. Gamma fibers usually have background activity that leads to fluctuation of excitability of nerve terminations of a muscle spindle. At the same time the primary endings subject to a greater influence of a fusimotor innervation show big variability of excitability.
Items are the major link in processes of implementation of the most different motive acts (see. Movements ), in maintenance muscle tone (see), preservation poses (see), balances of a body (see), etc. At section of afferent ways from P. tonic influence of an impulsation keeps from P. on motor-neurons of a spinal cord, disappearance of a muscle tone is a consequence of what. The short-term muscle strain (e.g., at blow by a hammer on her sinew) causes surge in activity of P. and leads to emergence of the myostatic reflex answer of this muscle. Tendon jerks (see) have the shortest (monosinaptichesky) reflex arc and are caused by activation of primary nerve terminations of muscle spindles. These reflexes are of great importance in a wedge. to practice at diagnosis of diseases spinal cord (see). Static reactions concern to other group of the reflexes caused by P.'s activation (see. Postural reflexes ). They are local, segmented and generalized. Local reaction is the response of a muscle to activation of own Items. At a long muscle strain (tens of seconds) the tonic answer is observed. So, the muscle strain for 1% increases tension of muscle fibers on 2 kg. Segmented static reactions are answers of c. N of page and contralateral muscles on P.'s activation other muscles of this segment of a spinal cord. The ex-tensor crossed reflex at the decerebrated animals is a typical example of these reactions. Segmented reflexes play an important role in processes of locomotion. Generalized static reactions are widely irradiating answers. At the same time reaction of muscles of one segments to P.'s irritation of other segments can be modulated by the reflex influences caused by P.'s irritation of muscles of a neck and receptors of a webby labyrinth of an inner ear. Together with P. in assessment of movements, in formation so-called muscular, or kinaesthetic, feelings participate also tangoreceptors of skin (see. Skin , physiology). All these touch structures usually consider as a peripheral part somato-kinaesthetic, or motive, the analyzer (see. Motor analyzer ). At different damages of peripheral and central parts of the nervous system of feature of disturbance of muscular and skin sensitivity have important diagnostic value and are, as a rule, investigated in parallel. At peripheral defeats of a zone of disturbance there is enough lokalna; at spinal pathology they can have segmented character. So, at hemilesions of a spinal cord Broun-Sekar's paralysis is observed (see. Broun-Sekara syndrome ), at Krom on the party of defeat loss of a myesthesia, and on the opposite side — skin takes place. One of the most constant signs of defeat of back roots of spinal nerves at early stages back tabes is considerable decrease in a myesthesia at minor changes of tactile and temperature feeling. Very considerable disturbances of kinaesthetic and tactile sensitivity arise at defeat of parietal area of a cerebral cortex.
P.'s studying is carried out by various methods (by means of light and a submicroscopy, methods of an electrophysiology, biochemistry, etc.). At P.'s studying at the person began to use a method of assignment of biopotentials from single fibers by means of the microelectrodes entered into a nervous trunk. Widely apply methods of computer facilities to the analysis of pulse flows.
Bibliography: Granite P. Bases of regulation of movements, the lane with English, M. 1973; Ilyinsky O. B. Physiology of touch systems, the p. 3 — Physiology of mechanioreceptors, L., 1975; Sherrington H. Integrative activity of a nervous system, the lane with English, L., 1969; Handbook of sensory physiology, ed. by C. C. Hunt, v. 3/2, B., 1974; Matthews P. Century of C. Mammalian muscle receptors and their central actions, Baltimore, 1972.
O. B. Ilyinsky.