Tonus

TONUS, the elastic-viscous properties of muscles, a known degree of involuntary constant muscular tension. There are three different understandings of the term T.: 1) resistance of the muscle to forces stretching it (Rieger, Spiegel), 2) ability of the muscle to long maintain a certain degree of contraction (Foix) and 3) the consistency of the muscle is taken as the criterion of T. In this respect, the muscle is characterized, besides the state of shortening or lengthening, by its elastic and plastic properties. Elasticity is understood as the ability of the muscle to resist deforming forces and to return to its lost shape (contractile T.), while plasticity is the degree of pliability and the tendency of the muscle to long maintain each newly given position, to fix each deformation of its length, thickness, etc. (plastic tonus). Some authors (Ricsser) define plastic T. as the ability of the muscle to change the degree of tension independently of length, while in contractile tonus this is achieved only by shortening and lengthening the muscle. Regarding the role of T. in the life of the organism, some think that it consists mainly in creating favorable conditions facilitating the performance of tetanus (Pie-ron), while others (Rieger) pay special attention to the moment of delay of movement. In general, tonic functions play an enormous role both in maintaining the body and its parts in a certain position, and in movement. Further development of these concepts requires consideration of some peculiarities of T. of smooth musculature and tonic functions of invertebrate muscles. Unlike striated musculature, in which each single contraction is automatically followed by relaxation, the smooth muscle has the property of freezing in a contracted state, and special innervational influences are required for the contracted smooth muscle to relax. Thus, the smooth muscle, besides the ability to shorten and relax, also has the function of long fixation of the contracted state. In the musculature of bivalve shells, these functions are separated also by substrate. The transparent ligament by its contraction closes the valves, while the white one maintains them in the closed state. In snails, the innervation is also separate. The supraganglionic node regulates the clonic functions, while the pedal ganglion has the role of inhibiting T. In the smooth musculature of the spines of sea urchins, we encounter the ability not only to long maintain the contracted state, but also to vary the degree of tension depending on the resistance overcome. This function is denoted by the term "sliding tension" (Uexkull). The tonic function of smooth muscles differs in its peculiarities compared to the tetanus of striated muscles. It does not, like the latter, involve an increase in oxidative processes, is not connected with loss of weight, does not give the typical for tetanus fluctuations of action current, proceeds without formation of lactic acid. In the striated musculature of vertebrates, two types of fibers are distinguished: 1) red fibers, containing hemoglobin, rich in sarcoplasm and granular on cross-section, and 2) those not containing hemoglobin, having fewer granules on cross-section, poor in sarcoplasm. Muscles of the first category are rich mainly in those muscles that produce prolonged and strong contractions. If one compares, for example, the m. pectoralis of a falcon, a goose, and a domestic chicken, it will turn out that red fibers are most numerous in this muscle in the falcon and least in the chicken. In the rabbit we encounter muscles consisting almost entirely of red fibers. Such muscles by their function belong to the tonic category. To the latter can also be attributed such muscles as the t. tenzor tympani. In most animals, however, in the same muscle there are fibers of both kinds. In accordance with this, each muscle has both clonic and tonic functions. Some authors consider it possible to speak of division of functions within a single muscle fiber and attribute to the sarcoplasm the ability to contract extremely long-lasting, while the myofibrils give rapid contractions (Bottazzi). Regarding tonic functions, plasticity is supposedly conditioned by the properties of sarcoplasm, while the fibrils are elastic bodies (Riesser). Others attribute plastic and contractile tonus to different muscle fibers. Still others consider sarcoplasm the carrier of tonic functions in general; plastic tonus supposedly depends, in the opinion of these authors, on the relaxed state of sarcoplasm, contractile on its active state (Langelaan). In parallel with this, evidence is also brought for the separateness of tonic and clonic functions of striated musculature on the basis of other data. It is believed that the former are characterized by the creatine phase of metabolism in the muscle, unlike the lactic acid phase typical for clonic functions (Pekelharing). To this is added that T. is connected with the transformation of free potassium into bound potassium. Potassium supposedly enhances T., while calcium causes clonic functions. Gas exchange and action currents in both types of functions also differ sharply. If some authors find a fundamental difference in gas exchange and action currents in tonic and clonic functions and believe, for example, that the influence of tonic functions on gas exchange equals zero, and action currents are either completely absent or give extremely slow long-wave oscillation of the string, others find only a quantitative difference and reduce negative results to shortcomings of methodology. Thus, there are two fundamentally different viewpoints on this basic question: 1) the mechanism of T. and tetanus is the same; 2) T. and tetanus differ both in metabolism and in their reflection in electrical processes and are even separate by anatomical substrate. Finally, proponents of the latter viewpoint speak of different innervation of these functions of striated muscle. Some (de Boer) in general connect T. with the autonomic nervous system, others (Hunter, Langelaan) believe that only plastic T. depends on the latter, while contractile T. is innervated, in their opinion, by cerebrospinal fibers. There is also a dispute as to whether tonic functions are connected only with the sympathetic system (n. sympathicus) or also with the parasympathetic (n. vagus). In this, proponents of the latter viewpoint differ in that some (de Boer) attribute to the sympathetic nerve an increase in T., to the vagus a decrease, while others (Frank) on the contrary. It should be noted that recently a theory (Orbeli) is being developed, according to which both contractile and plastic T. are conditioned by cerebrospinal innervation, while the sympathetic innervation has the role of adaptation of the muscle to one or another state of T. in the sense of creating certain favorable conditions ("topotropic" influence of n. sympathici according to the terminology of this school). More and more facts speak in favor of this latter viewpoint. In the whole organism, T. is under the influence of a number of neuro-humoral influences. The result of these is that displacement to which tendons are subjected during their in vivo severance. On the other hand, destruction of the spinal cord or interruption of afferents or efferents of the muscle leads to cessation of this tense state and to flabbiness of the musculature. If in a decapitated frog the posterior roots innervating one of the paws are severed on one side, it will turn out that in the preparation suspended by a hook this paw will hang lifelessly, while the second will be somewhat drawn up. Such tension, caused by constantly incoming along the posterior roots innervational influences, in this case originating from proprioceptors of stretched muscles, is designated as reflex T. (Brondgeest). However, the musculature of spinal animals is still comparatively relaxed even with complete preservation of all parts of the reflex pathway. This already testifies that the innervational influences coming from the brain to the cells of the anterior (and lateral) horns of the spinal cord play a dominant role in creating muscle T. In decerebrated animals, the state of the musculature (especially of extensor groups) becomes extremely tense (see Decerebration, decerebrational rigidity). If in such an animal the posterior roots innervating any limb are severed, rigidity in it sharply weakens (mainly due to exclusion of proprioceptors). This proves the reflex nature of decerebrational rigidity. For the latter to arise, it is necessary that the pyramidal and rubrospinal tracts be interrupted (according to data of some authors only the rubrospinal tracts). Preservation of the cerebellum or its exclusion has no decisive significance. With destruction of the cerebellum, decerebrational rigidity even increases, and with its irritation it somewhat weakens (at least in extensors; in flexors sometimes an increase in T. is observed). Destruction of the labyrinth also causes a decrease in T. of extensors of the decerebrated animal on the corresponding side. Any attempt to bring a limb of such an animal out of its initial position encounters sharp resistance.

In this case, we encounter an increase in contractile T., in the origin of which a dominant role is attributed to the so-called myostatic reflexes (Sherrington). The latter are conditioned by stimuli coming from proprioceptors of stretched muscles. Parallel to this, in decerebration rigidity, the tonic neck and labyrinthine reflexes (Magnus) are sharply expressed, regulating posture and participating in the distribution of T. by means of proprioceptors of the neck and balance apparatuses in the inner ear. Part of them is connected with the cervical region of the spinal cord (neck reflexes), the localization of others (tonic labyrinthine reflexes) is attributed to the pons Varolii, and finally the third ones (Stellreflexe) require the preservation of the red nucleus. A significant role in conditions increasing T. is also played by the so-called postural reactions of decerebrated animals upon irritation of a transverse section at the level of the red nuclei (Graham Brown). In this case, a prolonged, persistent contraction of the muscles extending and turning the head to the same side is obtained, which continues after the cessation of irritation, flexion of the homolateral forelimb and extension of the contralateral one. The contralateral hind limb is flexed, the homolateral one is extended, the back is slightly convex on the side opposite to the irritation. The tail straightens and bends toward the side of irritation. The pyramidal phase functions are in antagonism with this postural reaction. Stimulation of the corticospinal tract ceases the latter. In decerebration that preserves not only the midbrain but also the area of the optic thalamus, an increase in plastic T. is observed. In such decerebrated animals, the extensor and flexor reflexes are sharply expressed, manifesting themselves in the fact that if the attachment points of tendons are brought closer together or moved apart, the muscle always freezes in this new shortened or lengthened position (Sherrington). In these reactions as well, proprioceptors play the main role. The section of the posterior roots innervating one or another limb eliminates its participation in the extensor and flexor reflexes, which proves their reflex nature. If one approaches the question of the conducting pathways and nerve centers of muscle T. and its manifestations (contractility and plasticity) as a whole, much will still be undeveloped (in particular: 1) the role of vegetative centers in the regulation of plastic properties of the muscle, 2) the relationship of the cerebellum to contractile tonus, etc.). Therefore, one still has to be content with certain schemes developed on the basis of pathological data, which are to a significant extent inaccurate in regard to their accuracy.

L. Fidelgolts. Pathology. Many methods are used in the clinic to examine Tonus. Some of them have only an indirect relation to Tonus. Thus, Tonus is judged by the state of tendon reflexes and the state of active movements. This especially includes the studies of Lewy, who used the technique proposed by Isserlin for recording finger movements (Weiler apparatus), accurately calculating the speed of active movements in their various phases and determining the occurrence of action currents in agonists and antagonists during this. Of course, much can be clarified in this way as well. However, the primary significance belongs to other methods: methods of studying muscle resistance and methods of studying muscle resistance during passive movements. A whole series of apparatuses has been proposed for studying muscle resistance: the apparatus of Exner and Tandler; the apparatus of Noyons and Uexkull, which determines the depth of indentation produced in a muscle by a weight supported by an electromagnet when the circuit is broken; the spring sclerometer of Wertheim-Salomonson, which measures both the depth of indentation and the degree of tension of the spring pressing on the pelotte; the ballistic sclerometer of Noyons, built on the principle of a pendulum, the swings of which are damped less the harder the object the pendulum strikes; the apparatus of Mangold, consisting of a two-armed lever equipped with a pelotte: the depth of muscle indentation produced by this pelotte is determined by a millimeter scale by the displacement of the lever; the apparatus of Gildemeister, which determines the time of the impact of a weight falling on a muscle. The method of Lewy also belongs to this group, although it registers not the resistance of the muscle, but the degree of its thickening during passive movement. The second group of methods investigating Tonus in the clinic consists of methods for measuring muscle resistance during their stretching during passive movements. Uexkull asserts that the state of tension (Sperrung) of muscles corresponds to their resistance. Then resistance is indeed a measure of Tonus. On the contrary, Gildemeister considers the parallelism of both phenomena doubtful; Lewy establishes only "some" correlation between Tonus, resistance, and muscle elasticity; Spiegel considers resistance only a "side effect" and believes that it gives only an approximate idea of the state of tonic function (Haltefunktion), while the state of resistance to stretching is the actual measure of Tonus. The significance of resistance to stretching as an expression of the function of "internal muscle tension" was already emphasized by Fick; Weizsäcker regards as a measure of Tonus the force that is necessary to perform a passive movement at a given speed, and defines the Tonus index by the formula I = K/C (K = force, C = speed). On the whole, it should be recognized that both methods—the method of measuring resistance and the method of measuring resistance to stretching—do not yield fully comparable results, since the states they investigate are qualitatively different; therefore, such a comparison should be treated with great caution. In this regard, it is necessary to follow the example of Förster, who, when characterizing extrapyramidal rigidity, considers in separate categories the state of plastic Tonus that gives shape to the muscle, the increase in resistance to stretching, and the phenomena of fixation rigidity. Unfortunately, a global characterization of Tonus changes is encountered much more often. In clinical practice, the first place among all methods belongs to the determination of the state of Tonus by examining resistance to stretching. Instrumental examination, requiring the use of complexly constructed apparatuses, a large expenditure of time, etc., is used very rarely, essentially only for clarifying special pathophysiological questions. As a rule, for diagnosis, the usual manual examination is used: the patient is made not to actively tense the muscle groups being examined, not to exert active resistance, and a passive movement is performed, determining by one's own sensation the degree of resistance encountered. This examination is one of the most difficult in the series of neurological examinations; it places great demands on the experience of the examiner, who must be well acquainted with the normal state of Tonus, which comes only with great practice, must be able to make the patient refrain from active resistance, and must be able to isolate purely functional (neurotic) changes and differentiate them from organic changes, which is especially difficult in those very frequent cases where neurotic changes exist simultaneously with organic ones and mask them to one degree or another. Changes in Tonus that interest the clinician can go in two directions: towards a decrease (hypotonia, atonia) and towards an increase (hypertonia). Since Tonus, as has been shown long ago, is a reflex, its decrease or loss can be caused primarily by disturbances of the reflex arc in one place or another. What role the autonomic nervous system plays in this has not yet been clarified with complete certainty; various researchers have attributed a certain participation in the realization of Tonus to both the sympathetic and parasympathetic systems; with some probability, tonic function is attributed to the sarcoplasm, while the myofibrillar system is supposed to manage only purely motor functions. It is a firmly established fact that damage to both efferents (anterior horn cells, anterior roots, motor peripheral nerves) and afferents (peripheral nerves, posterior roots) of the spinal arc leads to hypotonia or atonia. This state is revealed, firstly, by an increase in the volume of passive movements in the corresponding joints, and secondly, by a decrease in resistance. In the normal state, a stretched muscle tenses at the beginning of its stretching, as if striving to preserve the initial length it has at rest [braking (Bremsung) of Rieger], which is of very great importance for motor functions, for their smoothness, measuredness, and for their entire dynamics. With damage to the spinal arc (a particularly illustrative example here are cases of posterior radiculitis, tabes dorsalis, where the paralyses and amyotrophies characteristic of damage to the effector system, which mask to a greater or lesser extent the role of the loss of the tonigenic moment itself, are absent), the loss of this braking finds its clear expression not only in passive movements but also in the voluntary motor activity of patients, in the excessive volume of their movements, in the classic throwing of the legs in the knee joints when walking, in stamping the ground with the heels, etc.; tabetic ataxia is to a significant extent explained by disturbances of Tonus, by the loss of the Rieger mechanism. But hypotonia can also be observed in the absence of a direct interruption of the spinal reflex arc. As is known, strokes affecting the pyramidal system in the region of the internal capsule, etc., lead to hemiplegias, which in the initial phases of the disease are usually characterized not by an increase in Tonus, as happens later, but by its fall. In essence, however, here too it is a matter of damage to the same spinal arc, specifically its effector neuron (anterior horn cell), the function of which is deeply, although only dynamically, damaged due to diaschisis (see). When the phenomena of diaschisis are overcome, hypotonia is replaced by hypertonia, which is in essence characteristic of the pyramidal symptom complex. In some cases, however, hemiplegia remains permanently flaccid, and here it is a matter of prolonged diaschisis due to the weakness of the protoneuron itself (general exhaustion, etc.), which is unable to recover at all from the shock sustained. Flaccid paraplegias arising from high total damage to the spinal cord (Bastian's law) apparently have the same genesis, although besides diaschisis, other moments (circulatory disorders, etc.) may also be of significance here. Finally, hypotonia can be a consequence of damage to the cerebellum. The mechanism of the occurrence of hypotonia of such origin is not yet fully clear; experiment generally yields largely contradictory results, but the clinical significance of the decrease in Tonus on the side of the cerebellar lesion is beyond any doubt. The second large group of tonus disorders consists of hypertonias. Experiments with decerebrate rigidity show that in the region below the level of the red nuclei there is a strong tonigenic center, which is under the influence of impulses originating from the general proprioceptive system, especially from the proprioceptors of the neck musculature and from the labyrinths (see Magnus-de Kleijn reflexes). The red nuclei have primary significance for the regulation of Tonus, as is shown especially by the experiments of Rademaker. With sections oral to the red nuclei, no significant changes occur in the Tonus of animals, while the separation of the red nuclei from the underlying sections or the destruction of the Forel decussation leads to general hypertonia.

On the basis of these experiments, as well as an analysis of the literature relating to clinical practice, Rademaker considers it necessary to recognize the primary importance of the red nuclei in the regulation of tonus even in humans, disputing traditional views regarding the significance of the pyramidal system, pallidum, and substantia nigra here: "the significance of complete or partial destruction of the pyramidal tract for the emergence of hypertension in humans has been estimated too highly until now," "the role which the striatum plays in the regulation of tonus in humans"

TOHS

is still unknown, and it is not yet certain that it plays any role at all in this," "the existence of a tonus-regulating center in the substantia nigra is very doubtful." How correct this revision of conventional views is, the future will show; for now, the prevailing position is the doctrine of hypertension as a consequence of damage to both the pyramidal and extrapyramidal systems. The symptom complexes arising in one case or the other possess characteristic features and differ quite significantly from each other. Hypertension arising from damage to the pyramidal system, or spastic hypertension, is characterized first of all by the unevenness of its distribution in agonists and antagonists, affecting only specific muscle groups (selective type): in the upper limb, hypertension usually affects the muscles that lower the shoulder joint, the adductors of the shoulder, the flexors and pronators of the forearm, and the flexors of the hand and fingers; in the lower limb, the adductors of the thigh, the extensors of the thigh and lower leg, and the dorsal extensors of the foot. In some cases, this formula may be distorted, but the basic principle—the unevenness of hypertension in antagonists—always remains in force. The next characteristic sign of spastic hypertension consists in the fact that the increase in resistance to muscle stretching is uneven in different phases of passive movement: for example, during knee flexion, the examiner encounters sharp resistance from the very beginning, after overcoming which further flexion proceeds more or less freely; during forearm extension, the same jerky resistance is encountered approximately in the middle phase of movement (about 90°), etc. Furthermore, its "springy" character is typical for spastic hypertension: upon completion of passive movement, the corresponding limb segment returns with force to its initial position (rebound phenomenon). Finally, a strong dependence of spastic hypertension on external stimuli is characteristic: the lower limb may present, for example, phenomena of the strongest extensor hypertension of irresistible force, and yet a nociceptive stimulus (forced flexion of the fingers according to Marie and Foix, a prick to the sole, its thermal stimulation) immediately changes the entire picture; shortening of the limb occurs, i.e., its flexion in the hip, knee, and ankle joints. The influence of the speed of passive movements on the increase of hypertension is also typical: the faster the movement, the stronger the tension; slow passive movement overcomes this tension with much greater ease. Hypertension observed in extrapyramidal lesions, or rigidity, has a completely different character. Here, first of all, there is no such selective coverage of specific muscle groups by hypertension and no such contrast between the state of protagonists and antagonists, which are so characteristic of spastic hypertension. Furthermore, the uniformity of resistance in all phases of passive movement, the "waxy" character of hypertension, is extremely typical for extrapyramidal rigidity. The "cogwheel" phenomenon is often encountered, i.e., the overcome tension has a saccadic character. However, the jerks here are also distributed more or less evenly in all phases of passive movement and thus differ sharply from the jerk that is characteristic of spastic hypertension. The rebound phenomenon is absent; the exact opposite phenomenon is observed: muscles exhibit the property of adapting, during the passive bringing together of their attachment points, to this approximation by active tension (adaptation tension) and tonically freezing in this tension (fixation tension, O. Forster). These properties are revealed especially clearly in the Westphal phenomenon and in the postural reflexes of Thevenard and Foix. The influence of the speed of passive movement on the degree of rigidity is not always noted and, in any case, does not reach such a degree as in spastic hypertension. Finally, in extrapyramidal rigidity, there is an absence of the dependence of hypertension on nociceptive stimuli, which is noted in spastic hypertension.

I. Filimonov. Tonus—nervous, psychic, vital—is a conventional designation for the functional state in which a person is at a given time. This concept, despite its approximation and, strictly speaking, lack of scientific rigor, has won the right to wide application as an indicator of the psychophysiological "energy" of the organism, its readiness for certain manifestations of healthy activity, and the possibility of overcoming certain influences. The content of the concept of tonus usually also includes moments associated with a certain mood, its elevation, excitement, depression [euphoria (see), depression (see)], etc. At the same time, a change in tonus is usually evaluated not only as a pathological phenomenon characteristic of various somatic and neuropsychiatric diseases, but also as a subtle detection of the general reactivity of the organism, which gives certain fluctuations in different periods of the life of completely normal people (for example, age-related changes). In diseases, tonus plays a very large role as a negative or positive factor. Numerous clinical observations show that when an infectious agent enters an organism with a weakened or "lowered" tonus, the course of the disease often proceeds significantly more acutely and severely, accompanied by various complications. It has been noticed that during epidemics, fearful and confused subjects fall ill more often. Likewise, in surgical practice, the preoperative state of a patient with "lowered" tonus usually causes anxiety for the surgeon, because according to clinical observations, a person with such altered tonus is more susceptible to operative shock or is less resistant in the postoperative period. From a neuropsychiatric point of view, the behavior of a person with "lowered" tonus presents a picture of indecisiveness, fearfulness, lack of will, or indifference and depression. For some psychoses and "psychoneuroses," a lowering of tonus is a characteristic sign. Thus, for example, cyclothymic depression, some forms of schizophrenia, arteriosclerosis of the brain, etc., among other symptoms, give a more or less sharply expressed lowering of nervous-psychic tonus. This or that state of tonus depends on moments of an endogenous nature, for example, on a disturbance of physiological balance due to insufficient or improper nutrition, on sleep disorders, sexual excesses, fatigue, etc. A large role must be attributed to endocrinological moments (e.g., G. 98 sharp lowering of tonus in hypothyroidism, etc.). The general state of the autonomic nervous system is of enormous importance. Thus, at the basis of the variability of tonus lie psychophysiological, humoral, and neurotrophic influences, and therefore the substrate of tonus is strictly material, starting from the type of the entire structure of the organism and the nervous system (asthenic type) and ending with complex moments of a biochemical nature. Changes in the behavior of animals (protozoa) under the influence of a number of physiological moments—see Depression in biology. Artificial raising or lowering of a person's tonus under the influence of alkaloids (caffeine, morphine, nicotine, strychnine, etc.) clearly indicates the enormous importance of intoxication moments in the origin of pathological changes in tonus. Finally, it should be pointed out that purely psychic factors, both negative and positive, are capable of sharply changing the general picture of neuropsychic tonus both in the direction of depression (psychic traumas, unfavorable situations) and in the direction of elevation (successes, achievements, skillful psychotherapeutic influence).

L. Brusilovsky.