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Biomedical subjects

U Proske

Publications and source records attributed to U Proske.

At least 127 records · Page 7Linked to original sources
PubMed1984

Mechanical properties of toad slow muscle attributed to non-uniform sarcomere lengths.

Tension changes have been measured during shortening or stretching movements applied to actively contracting motor units of the tonus bundle of the iliofibularis muscle of the toad Bufo marinus. During a slow, constant-velocity release tension fell, initially rapidly and then more slowly. The size of the fall, particularly later in the movement, depended on a number of factors including the duration of the isometric contraction before the onset of shortening, the amount of tension developed by the motor unit and the length of the muscle. When an isometrically contracting motor unit was rapidly shortened, the rate of rise on re-development of tension following the release was significantly slower than at the onset of the contraction. This effect was more marked if the release was preceded by a longer period of isometric contraction, if the experiment was carried out at shorter muscle lengths or if a smaller motor unit was used. If, following a period of isometric contraction, stimulation was interrupted, and a release-stretch movement applied to quickly bring the level of force down to near zero, and then stimulation recommenced , the final level of re-developed tension was less than that immediately before the release. The size of the tension deficit following re-development was larger for small motor units and at short muscle lengths. When the duration of the contraction before release was increased the size of the deficit also increased. A deficit could be prevented if the muscle was allowed to relax passively before the shortening movement was commenced. Stretch of actively contracting slow muscle produced an initial steep tension rise followed at times by a transient fall before tension slowly rose again. The transient fall became larger at short muscle lengths, and after long-duration contractions before stretch. Its tension dependence was less easy to establish because of complications involving changes in the relative series compliance. All of the above observations could be accounted for by an explanation based on the development of sarcomere non- uniformities in slow muscle fibres, produced as a result of non-uniform activation of the fibre membrane through the distributed nerve supply.

Animals↗
PubMed1984

Cortical projection of afferent information from tendon organs in the cat.

In cats anaesthetized with chloralose, evidence has been sought for the projection of information from tendon organs to the sensory receiving areas of the cerebral cortex. Selective stimulation of afferent fibres from tendon organs has been achieved by raising the threshold to electrical stimulation of the fibres from primary endings of muscle spindles. The method uses longitudinal vibration at 200-250 Hz to elicit, over a period of 20 min, one impulse for each excursion of the vibrator from all of the spindles in the test muscle, soleus or medial gastrocnemius. The accumulated post-spike positivities following passage of the impulses are thought to be responsible for the rise in threshold. Segmental monosynaptic reflex testing after a bout of vibration was used to confirm that the residual Group I volley no longer contained impulses from muscle spindles. The volley in response to stimulating the nerve of the test muscle was timed to facilitate the monosynaptic reflex of a synergist. Before vibration 5- to 10-fold facilitation of reflex amplitude could be produced; however, after vibration, if all the spindle primary endings had been effectively engaged by the stimulus, no detectable facilitation remained. This test was found to be sensitive and reproducible. An afferent volley containing only activity of tendon organ afferents evoked small-amplitude potentials from the post-sigmoid gyrus of the contralateral pericruciate cortex. The field was highly localized and lay caudal to the main receiving area for activity from the sural nerve and from afferents of hip flexor muscles. Recordings with tungsten micro-electrodes revealed that the surface-evoked activity took origin in cellular discharges in the internal pyramidal layer of area 3a. Recent psychophysical experiments have provided evidence for a sense of muscle tension, as distinct from a sense of effort, and the tendon organ has been suggested as the likely receptor of origin. Our electrophysiological observations now provide a firm experimental basis for such a proposal.

Animals↗
PubMed1984

The after-effects of stretch and fusimotor stimulation on the responses of primary endings of cat muscle spindles.

These experiments explore the after-effects of repetitive movements and dynamic fusimotor stimulation on the responses of primary endings of soleus muscle spindles in the anaesthetized cat. If immediately following a series of conditioning stretch and shortening movements, the muscle was held at the stretched length for 3 s before being returned to its rest length, the subsequent response to a brief dynamic fusimotor tetanus given during a slow test stretch produced only a small increase in spindle firing. If, on the other hand, the muscle was returned to its rest length immediately after the movements, the fusimotor tetanus evoked a much larger afferent burst. This difference in the size of the burst could only be observed if the fusimotor tetanus was given soon after onset of the test stretch. If it was delayed and given at a time when the test stretch passed through the length at which the muscle had been held stretched after the movements, there was no difference in the size of the afferent burst. If following the movements the muscle was held stretched for less than 3 s, the response to the subsequent tetanus was not fully depressed. Once the depressed condition had been achieved, the muscle had to be left undisturbed for up to half an hour before the response had recovered its original fully undepressed size. Conditioning repetitive stimulation of the fusimotor fibre was just as effective as using alternating movements in producing the effects. If the test tetanus, which was normally ten shocks in 50 ms, was made longer, the change in size of the impulse burst became a change in latency of onset of the response to the tetanus. Holding the muscle stretched at the end of the conditioning movements/tetanus produced a delay in onset of the response to the test tetanus without significantly altering its size. These observations have been interpreted as arising from development of stable cross-bridges between actin and myosin filaments in the intrafusal fibres. During repetitive movements or fusimotor stimulation, stable bridges become detached and during the subsequent 3 s they re-attach, at the length at which the muscle is being held after conditioning.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

Stiffness of cat soleus muscle and tendon during activation of part of muscle.

Experiments have been carried out on the soleus muscle and its tendon in the anesthetized cat. Measurements of isometric tension and muscle stiffness were made during contraction of whole or part of the muscle in response to stimulation of ventral root filaments. In an attempt to determine the distribution of tension in different portions of the tendon during activation of only part of the muscle, the free tendon of insertion was split longitudinally into two halves and a strain gauge attached to each piece. From a large number of measurements, it was found that the mean fraction of tension recorded in one-half of the tendon remained about the same, over a wide range of tensions. However, the scatter of values, which increased as the portion of muscle contracting was reduced, was greater than expected if muscle fibers were randomly distributed throughout the muscle. Measurements of muscle and tendon stiffness were made from length and tension changes during stretch of the actively contracting muscle. Ventral root stimulation that engaged 20% or more of the muscle yielded a value for tendon compliance (0.09 mm/N), which was the same as for stimulating the whole muscle. This result suggested that for contraction of portions as small as 20% of the muscle, fibers were effectively attached to the whole tendon, indicating that tendinous attachments of individual muscle fibers ran independent of one another over only a short distance and were bound together over most of their remaining course. It was concluded that groups of muscle fibers selected by stimulation of ventral root filaments are not entirely randomly distributed throughout the muscle. However, for groups representing larger fractions of the total tension, (greater than 20%) the distribution is uniform enough and the connections between their tendinous attachments firm enough for the force applied by such a group to act through a tendon compliance, which is the same as that seen by the whole muscle.

Achilles Tendon↗
PubMed1982

The responses of frog muscle spindles during stimulation of slow motor axons.

Responses of muscle spindles of the iliofibularis muscle of frog Litoria aurea have been recorded during single shock and repetitive stimulation of single functional motor axons. Repetitive stimulation of axons which innervated slow muscle, and on four occasions, axons which innervated twitch muscle, produced a large increase in the dynamic response of the spindle to a ramp-and-hold stretch. While extrafusal slow muscle did not respond to a single motor volley, some spindles did, especially if at the same time the muscle was being stretched. In an explanation of the effect of muscle stretch on responses of spindles to slow motor volleys it was proposed that stretch acted to reduce the internal motion in muscle fibres produced by a non-uniform distribution of sarcomere lengths. It was proposed that this kind of effect may account for dynamic fusimotor actions in all vertebrate spindles.

Animals↗
PubMed1982

Effect of fusimotor stimulation on ia discharge during shortening of cat soleus muscle at different speeds.

1. In barbiturate-anaesthetized cats, the L7 and S1 dorsal and ventral roots were dissected to isolate functionally single afferents identified as primary endings of soleus muscle spindles, and motor filaments which exerted a fusimotor action on the afferents with limited action on extrafusal muscle. Up to seven filaments, with an action on a given primary ending, could be isolated and each was classified as exerting either a predominantly dynamic or static action.2. Combined stimulation of these filaments, at rates up to 200 impulses/s could maintain afferent firing during muscle shortenings at speeds up to 200 mm/s.3. Fusimotor stimulation could also maintain afferent firing at a target frequency of 100 impulses/s during muscle shortenings up to 200 mm/s. The timing, in relation to the onset of shortening, and the rates of fusimotor stimulation were found to be critical in achieving the target frequency.4. Sinusoidal modulation of the frequency of fusimotor stimulation was used to study the conditions required to achieve constant afferent firing in the face of imposed sinusoidal length changes.5. For given depths of modulation, the phase advance of fusimotor stimulation needed to produce minimum modulation of afferent firing (best compensation) increased with increasing frequency of the sinusoids. The compensation deteriorated with an increase in the frequency of the sinusoids and a change in the mean muscle lengths, although in some cases it could be restored by adjustments to the depth of modulation of fusimotor rate. This suggests that for movements of varying speeds and amplitudes, settings which are appropriate for shortening at a given velocity and mean muscle length, do not apply if either of these two variables are altered.6. These findings demonstrate that the fusimotor system is potentially capable of eliciting constant afferent firing as envisaged in the ;servo-assistance' hypothesis (Matthews, 1964, 1972; Stein, 1974). This, and the fact that constant afferent firing is not seen during normal unobstructed shortenings at velocities greater than 0.2 resting length/s (Prochazka, 1981), are used to argue that it is by choice rather than necessity that ;servo-assistance' (as defined above) is not employed during normal movements. However, servo-assistance of a different form (involving modulated spindle afferent feed-back from both agonists and antagonists) remains a viable alternative.

Animals↗
PubMed1982

Muscle receptors in the cross-reinnervated soleus muscle of the cat.

1. Discharges have been recorded from afferents of the soleus muscle following reinnervation by the nerve of a fast twitch muscle, extensor digitorum longus. Recordings were made 227-449 d post-operatively.2. The gross afferent discharge from the cross-reinnervated soleus suggested the presence of fewer mechanosensitive receptors than in normal muscles, as judged by discharges seen during a maximal muscle twitch.3. A comparison of receptors in the cross-reinnervated muscle with afferents from a self-reinnervated muscle showed that many of the responses in the self-reinnervated muscle were also abnormal. It was concluded that much of the disruption resulted from the surgical interference and that rather less could be attributed to the foreign nerve.4. A detailed analysis of response characteristics of receptors in cross-reinnervated soleus muscles of five cats showed that afferent conduction velocities of identified spindles and tendon organs were generally lower than normal and responses to muscle stretch or vibration were often atypical. A large number of afferents which could not be classified as muscle spindles or tendon organs included a group called contraction receptors. These responded generally only during maximal muscle contractions and with a rather feeble discharge. A second group consisted of afferents in which impulses could be elicited by electrical stimulation of the nerve but not by any mechanical activity in the muscle.5. In a further five animals a detailed study was made of the motor supply of muscle spindles. A fusimotor innervation was common, but invariably stimulation of the gamma fibre had a static action on the spindle. No purely dynamic fusimotor fibres were encountered. There were many static beta fibres (skeletofusimotor) no dynamic betas and three axons conducting in the alpha range, which developed no tension, yet produced specific intrafusal effects. Two of these had a mixed static-dynamic action while the third was purely static.6. It was concluded that in the cross-reinnervated soleus muscle the majority of afferents were abnormal in one or other respect. The central action of such abnormal receptors would have to be taken into account when seeking explanations of the transformation of a muscle's mechanical properties following reinnervation by a foreign nerve.

Action Potentials↗
PubMed1981

Motor unit contractions initiating impulses in a tendon organ in the cat.

1. Responses, identified as coming from Golgi tendon organs, were recorded in afferent nerve fibres supplying the cat soleus muscle. 2. Receptor discharge was recorded during stimulation of single, selected motor units. The degree of summation of responses to combined stimulation of pairs of motor units was compared with the effect of stimulating each motor unit separately. Whenever individual response frequencies differed by a large amount there was little summation on combined stimulation. 3. The response of tendon organ to the second of a pair of closely spaced tetanic contractions of a motor unit showed adaptation of the discharge. Adaptation could also be induced by a conditioning contraction from another motor unit. The amount of 'cross-adaptation' could be correlated with the difference in individual response frequencies of the two motor units and with the degree of summation on combined stimulation. 4. A mechanical model is proposed to account for these observations. The muscle fibre from each motor unit is envisaged to pull on a collagen strand which supports one of the receptor terminals. The non-linear summation of responses on combined stimulation and the phenomenon of cross-adaptation are accounted for by mechanical cross-links between collagen strands such that one muscle fibre pulls on more than one receptor terminal.

Action Potentials↗
PubMed1980

The discharge rate: tension relation of Golgi tendon organs.

Tendon organs are preferentially sensitive to activity in a small selected number of motor units. We have isolated single tendon organ afferents and the motor units exerting effects on them in the soleus muscle of the cat. Using the method of distributed stimulation it has been possible to grade motor unit tension over a wide range and record the corresponding firing rates of the receptor. The plot of firing rate against tension was found to be highly non-linear and did not conform to the simple power function previously attributed to the relation.

Action Potentials↗
PubMed1979

The responses of Golgi tendon organs to stimulation of different combinations of motor units.

1. Afferent discharges were recorded from stretch receptors identified as Golgi tendon organs, in the medial gastrocnemius and soleus muscles of the cat. 2. The response of a tendon organ was recorded during stimulation of one or more motor units selected for the intensity of discharge elicited from the receptor during twitch and tetanic contractions. 3. Repetitive stimulation of a single motor unit could evoke in a tendon organ a firing rate of up to 174 impulses/sec. The mean rate for a total of 90 motor units was 65 (+/- 32 S.D.) impulses/sec. No significant difference in effectiveness could be detected between motor units covering a wide range of contraction speeds, tetanic tensions and susceptibility to fatigue. 4. The response of a tendon organ to contraction of several motor units in combination was greater than from stimulating any one motor unit alone but less than predicted from the algebraic sum of individual responses. 5. The relation between firing rate and tension was plotted for combined stimulation of up to ten motor units. The relation was found to be a straight line provided the size of the response elicited by each motor unit in the stimulated bundle was similar or when responses were ranked according to their intensity. When one motor unit evoked a much more powerful response than others it tended to dominate the discharge and disturb the linearity. 6. Evidence is provided that the sites of stimulus transduction for motor units which exert their effect directly on the receptor can be relatively independent of one another. It is argued that on such occasions summation of responses may be attributed to mechanisms operating at the level of impulse generation.

Action Potentials↗
PubMed1979

Properties of motor units of the frog iliofibularis muscle.

The tension developed by single motor units of the iliofibularis muscle of the frog Litoria aurea was recorded in response to single-shock and repetitive stimulation of motor axons. The majority of units in each muscle, 13 on the average, were of the twitch type; an additional 4 units were slow or tonic. It appeared that slow units comprised a single homogeneous population, but two types of twitch units could be recognized: small fatigue-resistant units with long twitch times to peak (20--40 ms) and larger, fatigable units with briefer times to peak (16--27 ms). Evidence from a comparison of unit tetanic tensions indicated the presence of polyneuronal innervation of both slow and twitch muscle fibers. The relatively low incidence of polyneuronal innervation of twitch fibers in iliofibularis, when compared with a muscle like sartorius (9), was attributed to the difference in lengths of muscle fibers in the two muscles. It was argued that slow muscle fibers probably receive a multiterminal as well as polyneuronal innervation, with the terminals of any one axon lying widely spaced along the muscle fiber.

Animals↗
PubMed1978

Afferent fibres from muscle receptors in the posterior nerve of the cat's knee joint.

The properties of some receptors with afferent fibres in the cat's posterior knee joint nerve have been examined, especially those discharging tonically with the joint in intermediate positions between full flexion and extension. Some of these receptors behave like muscle spindles, and respond to manoeuvres which stretch popliteus muscle. Both in single unit and whole nerve recordings their discharge pauses during a popliteus twitch, and can be strikingly augmented by tetanic stimulation of a number of popliteus fusimotor fibres isolated from ventral root filaments. The action of succinylcholine on these receptors closely resembles its effect on popliteus spindle units with fibres sited normally in the popliteus nerve. Other units with properties suggesting origin from popliteus tendon organs were also observed; their fibres and those of the spindle units conducted at Group I velocity. It is concluded that some afferent fibres from popliteus spindles and possibly tendon organs commonly pursue an aberrant course in the posterior articular nerve of the knee joint.

Afferent Pathways↗
PubMed1978

The stiffness of amphibian slow and twitch muscle during high speed stretches.

Experiments were carried out to compare the stiffness of cross-bridges in amphibian slow and twitch muscle. An isolated iliofibularis muscle was subjected to rapid, small stretches during contraction of either slow or twitch fibres at a number of different isometric tensions. The method of analysis allowed the compliance of the cross-bridges to be distinguished from other sources of compliance. Provided that the muscle was stretched sufficinetly rapidly to obtain limiting values of stiffness, little difference was found between the mechanical properties of the cross-bridges in slow and twitch muscle. It is concluded that the difference in observed stiffness of the two muscle types is due to a lower turnover rate of cross-bridges and a smaller number of sarcomeres in slow fibres.

Animals↗
PubMed1978

Measurements of muscle stiffness and the mechanism of elastic storage of energy in hopping kangaroos.

1. A kangaroo hopping above a certain speed appears to consume less oxygen than a quadrupedal mammal, of similar weight, running at the same speed (Dawson & Taylor, 1973). This is thought to be achieved by storage of elastic energy in tendons and ligaments. 2. Energy can be stored in a tendon by stretching it, but only if the muscle fibres in series with it are stiff enough to resist most of the length change. We have measured length and tension changes in the contracting gastrocnemius muscle of the wallaby Thylogale during rapid, controlled stretches, and from this determined the amount of movement in muscle fibres and tendon (method of Morgan, 1977). 3. When the muscle was developing close to its maximum isometric tension, up to eight times as much movement occurred in the tendon as in the muscle fibres. This is made possible by the wallaby having a long and compliant tendon. 4. Measurement of work absorption by the muscle with a full length of free tendon and when the tendon had been shortened, showed that with the shortened tendon a larger proportion of movement occurred in the muscle fibres, producing a steep rise in work absorption by the muscle and a consequent increase in energy loss.

Animals↗