Biomedical subjects

U Proske

Publications and source records attributed to U Proske.

At least 109 records · Page 6Linked to original sources

PubMed1987

Tendon stiffness: methods of measurement and significance for the control of movement. A review.

An appraisal of the role of tendons in transmitting muscle tension to skeletal parts during posture and movement requires accurate knowledge of the mechanical characteristics of the tendon. Here the most important property is tendon stiffness. While it is relatively easy to measure the stiffness of an isolated segment of tendon, more sophisticated methods must be sought to take into account the whole length of tendon, including its intramuscular portion. Two methods are currently available for measurement of whole tendon stiffness: each has a limited range of muscle tensions over which it appears to provide reliable values, one method being better at low tensions, the other at high tensions. Some controversy remains about the precise values obtained in the mid-tension range covered by both methods. Nevertheless it is now possible to achieve reasonable estimates of tendon stiffness over the whole working range of the muscle. An important consideration which has emerged from the discussion is that at low tensions the tendon is much less stiff than at higher tensions.

Animals↗

PubMed1987

Changes in size of the stretch reflex of cat and man attributed to aftereffects in muscle spindles.

1. This is a report of experiments carried out on the cat and on man, which demonstrate that conditioning of a muscle by contraction and movement can lead to changes in amplitude of stretch reflexes elicited in that muscle. 2. In triceps surae of the cat, the reflex response to a brief stretch was recorded after conditioning with a whole-muscle contraction followed by a pause at a length either 5 mm longer or shorter than the length at which the reflex was elicited. Following conditioning at the long length the reflex response was less than half as large as that following conditioning at the short length. 3. The changes in reflex amplitude could be correlated with an altered stretch responsiveness of muscle spindles in the soleus muscle. When the muscle had been held long during conditioning, a subsequent brief stretch applied at an intermediate length elicited fewer impulses in primary endings of spindles than after conditioning at a short length. 4. The same kind of experiment was then carried out on adult human subjects. When a tendon tap was applied to the Achilles tendon after a voluntary contraction and relaxation of triceps surae with the muscle at a long length, (foot dorsiflexed) the reflex was frequently less than half the size it had been after a contraction at a short length (foot plantarflexed). It was concluded that the same kind of spindle aftereffects as observed for cat soleus spindles were responsible for the changes in reflex amplitude. 5. It was found both in the cat and in human subjects that the changes in reflex amplitude after conditioning became progressively less as the test length was made longer. 6. The explanation put forward to account for these observations is that stable cross-bridges form between actin and myosin filaments of passive intrafusal (and extrafusal) fibers. When the muscle is shortened several seconds after a contraction at a long length, the intrafusal fibers, stiffened by the presence of cross-bridges, fall slack. Slack does not develop after a contraction at a short muscle length, as the fiber is stretched to the test length. Since any slack must first be taken up by the test stretch, there is a smaller afferent response and consequently a smaller reflex contraction in response to a tendon tap after conditioning at a long length.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1986

Conduction velocity in peripheral nerve of foetal, newborn and adult sheep.

Measurements have been made of conduction velocity in tibial and peroneal divisions of the sciatic nerve in foetal, newborn and adult sheep. Foetal age ranged from 91 days after mating to term, at 145 days. Measurements on foetuses used chronically implanted electrodes in 6 animals and direct nerve recordings in two acute preparations. For chronic recordings, two pairs of stimulating electrodes were placed as far apart along the nerve as possible and recording electrodes measured the electromyogram of the lateral gastrocnemius muscle. In the nerve recordings stimulating electrodes were placed at several different sites and the latency of the nerve action potential at each site was plotted against electrode separation. Values of maximum conduction velocity in foetal tibial nerve ranged from 24 m/s at 91 days to 60 m/s at term. Conduction velocity increased by 0.6 m/s per day. In the newborn lamb conduction velocity was more than half of the adult value of 96 m/s, indicating the relative maturity of the sheep at birth compared with other mammals.

Animals↗

PubMed1986

Vibration-evoked responses from lamellated corpuscles in the legs of kangaroos.

A group of lamellated corpuscles are present in the interosseous region of the legs of macropod marsupials. Structurally, they are similar to, but simpler than the Pacinian corpuscles of eutherian mammals, in having fewer lamellae. Responses of mechanoreceptors with axons coursing in the interosseous nerve were recorded from filaments, containing single functional units, dissected from the sciatic nerve of the wallaby Thylogale billardierii. The receptors were all maximally sensitive to stimuli applied in the interosseous region, where the cluster of lamellated corpuscles is located. Most units had low mechanical thresholds and were sensitive to sinusoidal vibration over a wide range of frequencies. Functional properties generally resembled those of eutherian Pacinian corpuscles, but the marsupial receptors were less rapidly adapting. The afferent nerve fibres conducted at 45 to 60 ms-1, while the diameter of axons in the osmium-stained interosseous nerve ranged between 7.5 and 12 micron. It is suggested that one important function of the receptors might be the detection of ground-borne vibration.

Adaptation, Physiological↗

PubMed1986

Aftereffects in the responses of cat muscle spindles.

Responses have been recorded from primary endings of muscle spindles in the cat soleus muscle. Changes in spindle responsiveness were measured following a period of conditioning that consisted of a series of rapid stretches or of tetanic ventral root stimulation. In the testing procedure the response of a single spindle afferent was recorded to stimulation of a dynamic fusimotor axon during a slow stretch. Changes in gross afferent discharge coming from the muscle were measured by integrating the activity recorded in dorsal roots. If, after conditioning stretches, the muscle was immediately returned to its initial length, the spindle responded to the test fusimotor stimulation with a high-frequency burst of afferent impulses. If the muscle was held stretched for 3 s after conditioning the response to the brief test tetanus was small or "depressed." It has been suggested that conditioning stretches result in detachment of stable crossbridges in intrafusal fibers and that these bridges then reform over the next few seconds at whatever length the muscle happens to have at the time. When it is long, shortening the muscle back to the initial length leads to the development of slack in intrafusal fibers because of the passive stiffness they have acquired from the presence of the stable bridges. Under these conditions a brief test fusimotor tetanus will lead to a depressed response because the slack must first be taken up before a full response can be generated. It was possible to reverse the depression by interposing an extrafusal contraction during the period between the conditioning and test sequences. It is suggested that lateral compression from the contracting extrafusal fibers and the stretch they impose as they relax reduces any intrafusal slack and thereby reduces the depression. A more quantitative measure of intrafusal slack than the test for depression is to determine the delay in onset of the afferent response to a longer fusimotor tetanus. The delay was short a long initial muscle lengths where, if the muscle was left undisturbed, it soon disappeared completely and spontaneously. It is suggested that at long lengths passive tension in the muscle tends to remove any slack in intrafusal fibers and therefore removes any after effects. The rise in resting discharge of muscle afferents after a conditioning tetanus applied to the ventral root ("postcontraction sensory discharge") can be accounted for by the same hypothesis.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗

PubMed1986

Fusimotor axons in the kitten.

In kittens 1- to 23-days old growth of axons in the soleus nerve has been studied using the structural parameters nerve length, internodal length, and axonal diameter. In addition, single functional fusimotor axons were isolated in lumbosacral ventral roots, and the responses of muscle spindles in soleus were studied during fusimotor stimulation. While nerve length over the soleus nerve to lumbar spinal root increased from 41 to 76 mm during the 22 days, mean internodal length increased from 250 to 410 microns. Mean axon diameter increased from 2.1 to 4.1 microns. In the youngest animals values for both internodal length and axon diameter were distributed uniformly about the mean. From day 11 onward the distributions became bimodal, including a growing number of new axons in the small-myelinated range. Filaments of ventral root were isolated that on repetitive stimulation had a specific excitatory effect on the discharge of muscle spindles. The responses could be attributed to axons that were not associated with measurable tension and were therefore likely to be fusimotor fibers. Measurements of the conduction velocity of skeletomotor and fusimotor axons showed that conduction speed increased progressively with age for both groups, but the rate of increase was more than three times faster in the most rapidly conducting skeletomotor axons compared with the fusimotor axons. The distribution of conduction velocities for fusimotor fibers showed two peaks, one in the range typical for conduction in unmyelinated fibers, 0.5-1.0 m/s, the second at 3-4 m/s. The small number of values in the range of 1-2 m/s was attributed to the process of myelination. It is suggested that conduction speed increases discontinuously over this part of the range as impulse conduction changes from continuous propagation to saltatory transmission. Eighteen fusimotor axons could be classified as having either a static or a dynamic action on spindle discharge. Repetitive stimulation of fusimotor fibers during a ramp-and-hold stretch of the muscle produced a characteristic response. Fibers classified as dynamic had little effect on the response of the spindle when the muscle was held at a particular length but greatly increased the response during a length change. Static fusimotor fibers, on stimulation, increased the response of the spindle at constant length but did not evoke a selective increase during the length change. Both kinds of fusimotor effects were characterized by overall low firing rates.

Aging↗

PubMed1985

Lack of summation of dynamic and static components in the responses of cat tendon organs.

Discharges of single tendon organs of cat peroneus tertius muscle were recorded during tetanic contractions of motor units. On combined stimulation of several motor units activating the same tendon organ, the static components of responses sum, although not linearly, whereas the dynamic component of a response superimposed on a pre-existing discharge does not sum at all with this discharge.

Animals↗

PubMed1985

The discharge of cat tendon organs during unloading contractions.

Tendon organs respond preferentially to contractions of a select set of motor units. If a tendon organ is given a resting discharge by raising the passive tension in the muscle, other motor units can be identified which on contraction interrupt the discharge, presumably by unloading the passive tension. These experiments investigate the possibility that stimulation of motor units with unloading effects can reduce the response of a tendon organ to a loading contraction. We find that over most of the range of muscle lengths the unloading contraction produces only a transient lowering of the firing rate. Only at short muscle lengths where further shortening is accompanied by a steep fall in tension is the unloading contraction able to induce a sustained reduction of afferent discharge.

Action Potentials↗

PubMed1985

After-effects of stretch on the responses of cat soleus muscle spindles to static fusimotor stimulation.

Mammalian muscle spindles show persistent after-effects following conditioning stretch or fusimotor stimulation. Most previous observations have been carried out on primary endings of spindles and using dynamic fusimotor stimulation. We report here observations on after-effects produced either by conditioning stretch or by static fusimotor stimulation on the responses of primary and secondary endings to a slow test stretch during which a brief burst of static fusimotor stimulation is applied. We find that the response to the test burst is large if the muscle is kept short after conditioning but it becomes depressed if the muscle is held stretched for 3 s following conditioning. We attribute these effects to the presence of stable cross-bridges between actin and myosin filaments in intrafusal fibres. We conclude that, qualitatively, after-effects using static fusimotor testing are the same as with dynamic fusimotor testing and this must be taken into account when providing an explanation for the phenomenon.

Animals↗

PubMed1985

Action of single dynamic fusimotor neurones on cat soleus Ia afferents during muscle shortening.

The ability of single dynamic fusimotor (gamma d) fibres to sustain the firing of muscle spindle primary (Ia) afferents during shortening was investigated in soleus muscles of anaesthetised cats. Of 11 gamma d fibres, 10 could maintain Ia firing during 10 mm/s shortening. Of the 7 tested at greater velocities, 5 could maintain Ia firing during shortening at velocities greater than 50 mm/s. This ability was, however, critically dependent upon the timing of the stimulation. In particular, it rapidly reduced with increasing duration of stimulation before the onset of shortening. Furthermore, if appreciable stretch occurred between the onset of gamma d stimulation and the onset of shortening, this could greatly reduce the ability of gamma d fibres to sustain Ia discharge. If gamma d neurones are on occasion phasically activated during voluntary shortening movements, their action could be an important determinant of Ia firing, even in the presence of weak gamma s action. Therefore in chronic recordings, observation of Ia firing during muscle shortening is not an adequate criterion for inferring gamma d activity.

Action Potentials↗

PubMed1985

Responses of muscle receptors in the kitten.

Responses have been recorded in single functional afferents supplying muscle receptors of the soleus muscle in kittens aged between 1 and 23 days. Recordings of nerve volleys in whole dorsal or ventral roots in response to muscle nerve stimulation showed that conduction velocity for afferent and motor fibres was similar and increased from 9 m s-1 in a 2-day-old animal to 33 m s-1 in a 23-day-old animal. Of a total of 215 single functional axons isolated from 28 animals, 82 showed responses typical of tendon organs and 103 resembled muscle spindles, leaving 30 unidentified units. Both muscle spindles and tendon organs were characterized by having an over-all low firing rate compared with responses of adult receptors. The most immature receptors also lacked a maintained response to the hold phase of a ramp-and-hold stretch. Spindles in animals over the whole range of ages, including the youngest animals could be shown to be supplied with a fusimotor innervation. On a few occasions it was possible to isolate single fusimotor axons to a spindle; such axons were sometimes found to conduct impulses at a speed characteristic of non-myelinated fibres. Evidence was obtained for the existence of a beta-(skeletofusimotor) innervation of spindles. On four occasions it was possible to isolate single functional beta-axons in the ventral root. The incidence of beta-innervation appeared to be higher than in the adult.

Action Potentials↗

PubMed1985

The initial burst of impulses in responses of toad muscle spindles during stretch.

The responses of muscle spindles in the iliofibularis muscle of the cane toad Bufo marinus were examined during constant velocity stretch of the passive muscle. Spindles were found to show an 'initial burst' of high frequency impulses at the onset of stretch. Associated with the initial burst was a steep passive tension rise in the whole muscle, the short-range elastic component (Hill, 1968), called here the passive stiffness. The size of the initial burst was found to depend on muscle length in a similar way as whole-muscle tetanic tension. Repetitive stretch was found to reduce both the initial burst and passive stiffness. The time taken for both to return to their control values was 3 and 10 s respectively. If immediately following repetitive stretch the muscle, and hence the spindle, was held stretched for 3 s, the initial burst in response to a subsequent stretch from a shorter length remained reduced in size for 300 s. The depression could be reversed by a brief period of fusimotor stimulation. Hypertonic Ringer solutions were found to increase the initial burst and passive stiffness, while both were reduced in hypotonic solutions. Low concentrations of caffeine (1.5 mM) produced a similar decrease in both the initial burst and the passive stiffness. Calcium-free Ringer solution left the stiffness unchanged, and increased the whole dynamic response of the spindle. Metabolic exhaustion and poisoning of the muscle caused the initial burst to increase while decreasing the active tension. It is concluded that the initial burst is an intrafusal manifestation of the passive short-range stiffness of extrafusal muscle which is thought to be due to the formation of stable cross-bridges between the actin and myosin filaments of myofibrils.

Action Potentials↗

PubMed1985

Pathway to the cerebral cortex for impulses from tendon organs in the cat's hind limb.

In cats anaesthetized with alpha-chloralose, extracellular, recordings were made from neurones lying in nucleus Z. All cells could be excited by electrical stimulation of ipsilateral hind-limb muscle nerves at group I strength. Many cells showed an irregular background discharge. In response to graded contraction of hind-limb muscles, including lateral gastrocnemius, soleus and flexor digitorum longus, cell discharge changed in a manner suggesting that it was driven by input from muscle spindles or from tendon organs. Responses of individual nucleus Z cells were always specific to one kind of receptor and there was no evidence of convergence of afferent impulses from spindles and tendon organs. Nucleus Z neurones excited by muscle group I input could be antidromically driven by stimulation of the contralateral thalamus identifying them as bulbo-thalamic projection neurones. The same cells could be driven trans-synaptically by stimulation of the ipsilateral anterior lobe of the cerebellum. It was possible using a collision test to show that afferent fibres synapsing on nucleus Z cells were collaterals of dorsal spinocerebellar tract cells. It is concluded that nucleus Z is a brain stem relay for afferent information from muscle spindles and tendon organs which is destined for the cerebral cortex.

Action Potentials↗

PubMed1985

Responses of tendon organs to unfused contractions of single motor units.

The discharges of individual tendon organs of peroneus longus and tertius muscles were examined in anesthetized cats during stimulation of single motor units at frequencies that elicit unfused contraction (5-50/s). At these frequencies nearly all the fast-contracting motor units activating a tendon organ elicited responses whose discharge rates reproduced the stimulation frequency ("1:1 driving"), whereas slow-contracting motor units elicited responses in which the discharge rate was higher than the stimulation frequency. When a motor unit stimulated at 40/s developed a gradually potentiating tension, the tendon organ discharge could remain locked on stimulation frequency over an appreciable range of the increasing tension as if the receptor responded to the tension oscillations rather than to the mean level of tension. The only visible effect of the gradual increase in mean tension on the tendon organ response was a gradual decrease of the delay between each stimulus and the corresponding impulse. Driving of tendon organ discharge at the stimulation frequency occurred not only when relatively large oscillations were superimposed on a low level of static tension but also when the static component of the tension was quantitatively preponderant. These observations suggest that during unfused contractions the dynamic component of the stimulus (i.e., oscillation of tension) exerts a prevailing influence on the discharge pattern of tendon organs. Computed simulations of tendon organ responses confirmed that a relatively strong dynamic sensitivity could account for the observed behavior of the receptor.

Animals↗

PubMed1985

Site of impulse initiation in tendon organs of cat soleus muscle.

A continuing controversy surrounds the question of whether Golgi tendon organs are examples of receptors in which impulses may be generated at more than one site. This paper reports a systematic examination of a number of models incorporating single or multiple impulse generators and of the compatibility of their predictions with experimental observations. Two phenomena, in particular, that must be accounted for are nonlinear summation and cross-adaptation. When two motor units each with a direct effect on the tendon organ are stimulated together, the rate of discharge is greater than either individual rate but is less than their sum. In cross-adaptation a conditioning response elicited by one motor unit contraction produces adaptation of the discharge associated with stimulation of a second motor unit. A model with a central impulse generator can be modified to account for nonlinear summation by postulating a nonlinear transformation in the generator current-to-impulse rate conversion. Experiments measuring summation of responses to stimulation of three inputs produced results that did not support this model. Another variation of the model, which had a nonlinearity in the tension-to-current step and cross-connections (mechanical or neural) between tendon strands stressed by contracting muscle fibers, was able to account for the observations. A second model that provided the right predictions was a multiple impulse generator with cross-connections. Which of the two models best fits the experimental observations can be decided by comparing the calculated summation coefficients and cross-adaptation coefficients. A central impulse generator predicts a negative correlation, the multiple impulse generator a positive correlation. All of the observations were made using tendon organs of cat soleus muscle. Responses were recorded to stimulation of filaments of ventral root. In a comparison between 20 pairs of responses from six tendon organs the correlation between summation and cross-adaptation coefficients was found to be significantly positive. We conclude that the tendon organ model that accurately predicts all of the experimental observations incorporates multiple generators.

Adaptation, Physiological↗

PubMed1984

Can fusimotor activity potentiate the responses of muscle spindles to a tendon tap?

Experiments on the cat soleus muscle have determined the effect of selective activation of the fusimotor system on the responses of muscle receptors to a simulated tendon tap. Primary endings of spindles responded in the passive muscle with an average 4.3 impulses at a mean instantaneous rate of 502 impulses/s. Static fusimotor stimulation at 100 pulses/s increased the number of impulses during the tap to 4.8 but dropped the mean instantaneous rate to 400 impulses/s. Dynamic fusimotor stimulation increased the number of impulses to 6.3 and the instantaneous rate to 557 impulses/s. Combined stimulation of the two axons gave intermediate values. We consider these effects as rather feeble. The tendon jerk in man shows a large increase in reflex amplitude following a reinforcement manoeuvre (Jendrassik manoeuvre). Based on our animal experiments we conclude that such increases cannot be accounted for simply in terms of selective engagement of the fusimotor system.

Action Potentials↗

PubMed1984

The transformation of cross-reinnervated slow-twitch muscle after deafferentation in the cat.

Cross-reinnervations were effected between the extensor digitorum longus and soleus muscles in the cat hind limb. At the same time dorsal root section or ganglionectomy was performed over segments L6-S1. Completeness of the deafferentation was subsequently confirmed either by dissection or by dorsal root recording. The isometric and force-velocity properties of the muscles were measured. In animals with a unilateral cross plus deafferentation the conversion of the contractile properties of the normally slow-twitch soleus to those resembling a fast-twitch muscle was typical of that seen with an intact afferent supply. In cats with a bilateral cross-reinnervation and unilateral deafferentation there was no significant difference in the degree of transformation between the two sides. It is concluded that at least for the conversion of a slow-twitch to a fast-twitch muscle afferent feedback does not play a major role.

Afferent Pathways↗

PubMed1984

Non-linear summation of tension in motor units of toad slow muscle.

Tension developed by single motor units and bundles of motor units has been recorded from the slow, non-twitch portion of the iliofibularis muscle of the toad Bufo marinus. Evidence was sought for the presence of individual muscle fibres within a motor unit which remained less than fully activated when the axon was maximally stimulated, i.e. at a rate and duration sufficient to produce maximum tension. When two motor units were stimulated separately and together, one at a low rate and the other at a maximal rate, the tension recorded on combined stimulation was greater than the sum of individual tensions, i.e. combined stimulation acted to 'facilitate' tension in a proportion of fibres. Adding the anticholinesterase eserine to the solution bathing the muscle produced a large increase in individual motor unit tensions but a rather smaller increase during combined stimulation of several axons. This suggested that in normal solution, maximally stimulating a single axon left many muscle fibres less than fully activated. When the local anaesthetic lignocaine was added to the bathing solution, tension in response to nerve stimulation fell, presumably because of impulse blockade in small terminal branches of the axon. However tension fell more steeply for single motor units than for combinations of motor units, again, we propose, because single motor units contain a larger fraction of incompletely activated fibres whose tension output depends critically on the level of activation. Overlap between two motor units is a measure of the proportion of fibres innervated by both axons. When overlap was measured over a range of different muscle lengths and using contractions of different durations, evidence was obtained in support of the notion that tension output of some muscle fibres was less than maximum not only because the fibre received too sparse an innervation to achieve a sufficient over-all level of depolarization but because they had been non-uniformly activated, leading to internal motion within the fibre and a consequent further drop in tension.

Animals↗