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Biomedical subjects

M Hulliger

Publications and source records attributed to M Hulliger.

At least 37 records · Page 2Linked to original sources
PubMed1991

The dependence of the response of cat spindle Ia afferents to sinusoidal stretch on the velocity of concomitant movement.

1. The responses of de-efferented soleus muscle spindle primary afferents to 1 Hz sinusoidal stretches, which were superimposed on triangular background movements of intermediate amplitude (1.2 mm, half peak-to-peak) and widely varying speed, were recorded in anaesthetized cats. 2. Compared with control responses to the same sinusoids applied at fixed mean muscle length, the sensitivity to small (50 and 100 microns, half peak-to-peak), but not to large (1000 microns), sinusoidal movements was dramatically reduced during concomitant stretching, unless the background movements were extremely slow (well below 0.005 resting lengths per second). 3. For small stretches (50 and 100 microns) the reduction of sensitivity caused by background movement depended on the speed of this movement. For the highest velocity studied (1.6 mm s-1, corresponding to about 0.03 resting lengths per second) sensitivity dropped to below 10% of the control values. 4. The functional implication is that the sensitivity of spindle Ia afferents to small irregularities of voluntary movements (of any but the slowest speeds) may well be very much lower than it has hitherto been inferred from the striking sensitivity to minute disturbances at fixed mean muscle length. The present finding clearly puts extra demands on the gain of any spinal or central reflex actions of the sensory feedback from spindle afferents. 5. The effect is interpreted in terms of the widely accepted cross-bridge hypothesis of spindle small-movement sensitivity. The result suggests that in de-efferented intrafusal muscle fibres, which are subjected to imposed stretches, connected cross-bridges (conveying a friction-like property to the contractile fibre poles) may exist not only in a state of permanent attachment, but also in a dynamic equilibrium between stretch-induced detachment and reattachment. Indirect evidence further suggests that the duration of this disruption and reattachment cycle is of the order of 1 s.

Action Potentials↗
PubMed1990

In-series compliance of gastrocnemius muscle in cat step cycle: do spindles signal origin-to-insertion length?

1. It has been claimed that stretch in the non-contractile (extramysial) portion of muscles is substantial, and may produce large discrepancies between the origin-to-insertion muscle length and the internal length variations 'seen' by muscle spindle endings. 2. In eight pentobarbitone-anaesthetized cats, we estimated stretch in the extramysial portion of medial gastrocnemius (MG) muscle with a method similar to the spindle null technique. 3. Length variations of MG previously monitored in a normal step cycle were reproduced with a computer-controlled length servo. The responses of test MG spindle endings were monitored in dorsal root filaments. Distributed stimulation of ventral root filaments, rate-modulated by the step-cycle EMG envelope, served to reproduce step-cycle forces. The filaments were selected so as to have no fusimotor action on the test spindle. 4. Spindle responses in active cycles were compared with those in passive cycles (stretch, but no distributed stimulation). In some cases concomitant tonic fusimotor stimulation was used to maintain spindle responsiveness throughout the cycle, both in active and passive trials. Generally, small discrepancies in spindle firing were seen. The passive trials were now repeated, with iterative adjustments of the length function, until the response matched the spindle firing profile in the active trial. The spindle 'saw' the same internal length change in the final passive trial as in the active trial. Any difference between the corresponding length profiles was attributed to extramysial displacement. 5. Extramysial displacement estimated in this was was maximal at short mean muscle lengths, reaching about 0.5 mm in a typical step cycle (force rising from 0 to 10 N). At longer mean muscle lengths where muscle force rose from say 2 to 12 N in the cycle, extramysial displacement was in the range 0.2-0.4 mm. 6. Except at very short lengths, the displacement was probably mainly tendinous. On this assumption, our results suggested that the stiffness of the MG tendinous compartment was force related, and about double that of cat soleus muscle at any given force. Calculations indicated that though the stretch was small, the MG tendon would store and release enough strain energy per cycle to contribute significantly to the E3 phase of the step cycle. The discrepancies in spindle firing were generally quite subtle, so we reject the claim that extramysial stretch poses a serious difficulty for inferences about fusimotion from chronic spindle afferent recordings.

Action Potentials↗
PubMed1989

Ensemble proprioceptive activity in the cat step cycle: towards a representative look-up chart.

Analysis of the control of movement in tasks such as stepping is severely restricted by the lack of quantitative data on the ensemble activity of afferents in the numerous muscles involved. We have started to build up a quantitative "look-up-chart" of the ensemble afferent and efferent profiles in the cat step cycle. To this end, we have developed software which allows us to digitize afferent firing, muscle length and electromyogram (EMG) activity, and to align segments for averaging by choosing one or more reference points in the step cycle. The ensemble firing of triceps surae Ia afferents showed lower than expected mean and peak rates, whereas triceps group II and Ib afferents were more active than predicted. There were small but significant transients in Ia firing at foot-off and touch-down which could not be explained in terms of origin-to-insertion length lone. They were most likely caused by propagated mechanical transients or tendon compliance effects giving rise to small differences between the origin-to-insertion length and the intramuscular length "seen" by spindles. Net ensemble Ia rates, based on previous estimates of spindle populations, probably exceed 25 kilo-impulses/second (ki.p.s.) in some muscles. Inputs as large as this are likely to contribute significantly to reflex control.

Animals↗
PubMed1989

Flexible fusimotor control of muscle spindle feedback during a variety of natural movements.

A refined version of an experimental iterative simulation method is described, which was used to infer, from chronic spindle afferent recordings, type and time course of static and dynamic fusimotor activation during a variety of voluntary movements. When used to estimate overall fusimotor drive (without distinction between static and dynamic action) the method provides unique solutions. However, when generating independent gamma s and gamma d activation profiles, the solutions no longer are strictly unique. Yet the boundary conditions imposed by the type specific characteristics of gamma-action nevertheless permit detection of powerful activation, especially of dynamic efferents. Extending the finding of selective dynamic fusimotor activation during unpredictably imposed and resisted stretches, evidence for powerful, often transient activation of dynamic efferents has now been obtained for three additional motor paradigms. First, initiation of walking was accompanied by mixed fusimotor action. Static drive was stepped up and then maintained, whereas dynamic drive declined after an initial abrupt peak. Second, corrective balancing on a narrow walk beam was characterized by largely maintained static background drive, whilst dynamic activation profiles often exhibited powerful surges or transients, when the animal crouched to regain balance. These preceded subsequent EMG bursts during the stretch phase of crouching by about 300 ms. Third, preparation for landing from rapid lowering featured prominent and possibly selective activation of dynamic fusimotor neurones, which peaked while the animal was in mid-air and declined upon landing, and which preceded the sharp onset of EMG after landing by several hundred milliseconds. In all cases the fusimotor activation profiles were unrelated to the parent muscle EMG and difficult to reconcile with the notion of alpha-gamma linkage or coactivation. These findings then clearly support the concept of flexible central control, particularly of dynamic gamma-motoneurones during certain motor tasks.

Animals↗
PubMed1989

Muscle afferent contribution to control of paw shakes in normal cats.

1. The discharge of various hindlimb muscle afferents was recorded during paw shakes in normal cats with the use of floating dorsal root electrodes. 2. Muscle spindle group Ia-afferents and tendon organ group Ib-afferents fired during muscle lengthening, reaching very high peak discharge rates and then silencing at or shortly after the onset of shortening. The timing of Ia firing was consistent with the predictions of a linear model as well as the responses of Ia endings subjected to identical length variations in separate anesthetized cats. 3. In the latter "reconstruction" experiments, waxing and waning dynamic fusimotor action straddling whole paw-shake sequences gave the most consistent matches with the data from the normal cats. The reproducibility of the inferred fusimotor action justifies the inclusion of paw shakes as a class of movement in which fusimotor set is high. 4. The peak ensemble Ia activity from single hindlimb muscles was estimated to be approximately 20 kiloimpulses/s (Kips). Ankle extensor and hamstrings length variations were nearly in phase in the first cycles of a paw-shake sequence. From published data on spindle populations in these muscles, this indicated that peak Ia input to the spinal cord exceeded 0.2 megaimpulses/s (Mips). 5. The phase relationship between origin-to-insertion muscle length and Ia firing during paw shakes was little affected by doubling or tripling the moment of inertia of the foot. We argue that this refutes the notion that in paw shakes phase reversals occur between muscle fibers and tendons in the muscles studied. 6. Inertial loading of the foot led to small but significant reductions in mean paw-shake frequency. This is consistent with an afferent contribution to the generation of these movements. 7. We conclude that in paw shakes in normal cats, the CNS "chooses" to sensitize Ia-afferents to muscle length variations by increasing dynamic fusimotor action. The resulting ensemble Ia input is very large and is likely to play a significant role in reflexly shaping the alpha-motoneuronal activity responsible for the paw shakes.

Action Potentials↗
PubMed1987

An experimental simulation method for iterative and interactive reconstruction of unknown (fusimotor) inputs contributing to known (spindle afferent) responses.

A simulation technique, combining chronic recordings in freely moving alert cats with acute experiments on a nerve muscle preparation, has been designed to estimate fusimotor activity profiles underlying chronically recorded muscle spindle afferent responses to movements. Fusimotor stimulation patterns are iteratively generated and tested for their ability to simulate a target response during reproduction of the movement. The error between a simulated and the target response is incorporated into the current stimulation pattern, to generate the stimulation profile for the next cycle of iteration. The procedure is semi-automatic and offers a number of interactive features. For instance, the user has the choice to redraw manually critical segments of a given stimulation profile. The procedure converges rapidly, and solutions are unique, since target responses (first produced with known inputs) could be reconstructed by virtually identical, iterated, profiles. The method opens up the possibility of investigating complex transient adjustments of fusimotor drive, e.g. during adaptive motor performance.

Animals↗
PubMed1985

'Fusimotor set': new evidence for alpha-independent control of gamma-motoneurones during movement in the awake cat.

The discharge activity of single muscle spindle receptors was recorded in freely moving cats. Large changes in responsiveness to length variations was observed in different types of movement. In separate stimulations on anaesthetised cats, the activity of the gamma-fusimotor neurones responsible for these changes was reconstructed. The results suggested that fusimotor action on a given spindle afferent during the movements studied was not rigidly alpha-linked, but 'set' by the CNS to steady levels, and that it could switch from largely static (gamma s) to largely dynamic (gamma d) according to the motor tasks performed.

Animals↗
PubMed1985

Discharge in muscle spindle afferents related to direction of slow precision movements in man.

Single-unit activity was recorded with needle electrodes in eighteen muscle spindle afferents (eleven primaries, seven secondaries) from finger extensor muscles in the radial nerve of awake human subjects. The discharge rate of the afferents was determined during precisely controlled voluntary movements. The subjects performed a standardized visual ramp-and-hold tracking task, which included very slow finger extension and flexion movements (2.5 deg/s) with an amplitude of 20 deg. Throughout the tracking task a constant torque load of small or intermediate size, i.e. less than 30% of maximum voluntary contraction force, opposed finger extension. Altogether, 131 trials were studied. For most units the discharge rate was lower during shortening compared with active position holding, and it was higher during lengthening contractions. Thus, the majority of units responded to phasic stretch during the active movements, although the size of the movement response varied considerably between units and was never large. A few units even exhibited a reversed stretch response pattern. Hence, when estimated from pooled data, movement responses of the unit sample as a whole were small, around 1 impulse/s. The over-all response pattern of an individual afferent during the tracking task was very similar between successive tests. Although the discharge rate of most units increased with the load during movements as well as during position holding, the presence as well as the magnitude of movement responses depended only little on the size of the load. However, a few afferents exhibited a stretch response pattern with small loads and a reversed stretch response pattern with larger loads. In spite of the predominant increase of afferent firing during muscle lengthening there was no systematic modulation of the discharge rate in relation to the joint angle during the active movements, either in the primary or in the secondary afferents. The present findings suggest that human muscle spindles provide information about the occurrence as well as the direction of slow isotonic movements at low velocities in a precision motor task. This is in contrast to the lack of accurate position response which has previously been demonstrated.

Action Potentials↗
PubMed1984

Fusimotor reflexes in triceps surae muscle elicited by extension of the contralateral hind limb in the cat.

Experiments were performed in thirty-two cats anaesthetized with chloralose. The aim of the study was to investigate the reflex effects of flexion or extension of the contralateral hind limb on ipsilateral fusimotor neurones, to compare these effects with the effects elicited by stretch of the ipsilateral posterior biceps and semitendinosus (p.b.s.t.) muscles (Appelberg, Hulliger, Johansson & Sojka, 1982) and to clarify the interactions between the reflexes elicited from the ipsilateral and the contralateral side. Activity in fusimotor neurones was studied indirectly by recording from primary and secondary muscle spindle afferents of the triceps surae muscle. The mean rate of firing and the modulation of the afferent response to sinusoidal extension of the triceps surae was determined. Control measurements were made with the ipsilateral p.b.s.t. muscles relaxed and the contralateral hind limb in resting position. Tests were made with stretch of the ipsilateral p.b.s.t. and/or extension/flexion of the contralateral hind limb. With extension of the contralateral hind limb 64 out of 210 primary afferents (30.5%) showed predominantly dynamic reflexes (41 out of 134 in spinalized preparations: 30.6%), 25 (11.9%) showed mixed or predominantly static effects (1 spinalized: 0.7%), 121 (57.6%) showed no effect (92 spinalized: 68.7%). Flexion of the limb gave, with only two exceptions, no observable effect. Thirty-three secondary afferents were investigated. Five responded to extension of the contralateral hind limb with excitatory reflex effects. Flexion did not influence the secondary afferents. Mostly the reflex effects were not accompanied by detectable electromyogram (e.m.g.) activity in the ipsilateral triceps (surface recordings), indicating that the reflexes mainly involved gamma-motoneurones. A comparison was made between the reflexes elicited by stretch of the ipsilateral p.b.s.t. and extension of the contralateral hind limb. The percentage of responsive units was higher for the contralateral stimulus. Spinalization almost abolished the statis reflex responses to both ipsi- and contralateral stimulation, and it increased the number of dynamic responses to ipsilateral stimulation. The ipsilaterally elicited reflexes also seemed more dependent upon background activity. Ipsilateral stimulus could facilitate or reduce a contralaterally evoked response, even when the ipsilateral stimulus alone gave no effect. The reflexes could also summate. Quite often combined stimuli changed the character of the reflex from dynamic to static or vice versa.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1983

The variability of inter-spike intervals of human spindle afferents in relaxed muscles.

The impulse discharge in single afferent units was recorded in waking human subjects. Tungsten needle electrodes were percutaneously inserted in the left radial nerve, and activity in muscle spindle afferents from the extensor muscles of the forearm were studied while the subjects remained relaxed. Thirty-six spontaneously discharging single units were studied, 16 primaries, 10 secondaries and 10 non-classified. The regularity of afferent discharge and the shape of the inter-spike interval histograms was assessed by off-line statistical analysis of stationary segments of afferent discharge. The mean discharge rate of both primary and secondary afferents was generally low. Secondaries predominantly fired with low variability, whereas primaries showed high as well as low variability, but the median values for the two groups differed significantly. However, the individual unit values of coefficient of variation showed a considerable overlap between the two groups. The size of the coefficient of variation in the human spindle afferents was between that of de-efferented and of intact afferents in decerebrated cats. Determination of the coefficient of variation may therefore help, as a complementary criterion, to differentiate between primary and secondary afferents in man.

Adult↗
PubMed1983

A new simulation method to deduce fusimotor activity from afferent discharge recorded in freely moving cats.

Direct recordings from identified and classified fusimotor gamma-motoneurons in freely moving animals have not so far been achieved, and present knowledge on fusimotor activity during natural movements is based on qualitative inferences made from spindle afferent discharge. In order to put such deductions on a firmer basis, a simulation method has been developed, which provides quantitative estimates of the fusimotor drive that shaped the spindle afferent discharge, as recorded in chronically implanted cats during voluntary or imposed movements. Simulations are performed in acute experiments on anesthetized cats, whereby variations in muscle length and EMG envelopes are reproduced by an electromagnetic servo from digitally stored segments of the original records. The responses of spindle afferents to the simulated movements are then examined, both in the absence of fusimotor action and during concomitant stimulation of functionally single gamma-motoneurons, rate modulated according to a variety of stored functions (including the original EMG envelope).

Afferent Pathways↗
PubMed1983

Actions on gamma-motoneurones elicited by electrical stimulation of group I muscle afferent fibres in the hind limb of the cat.

The reflex actions, elicited by graded electrical stimulation of hind-limb muscle, skin and joint nerves were studied in an extended series of experiments in extra-and intracellular recordings from 120 lumbar gamma-motoneurones of cats anaesthetized with chloralose. The present report deals with the action of group I muscle afferent fibres, which was examined in ninety-five gamma-cells. Of the gamma-cells 83% were classified as either static or dynamic by stimulation in the mesencephalic area for dynamic control. The general responsiveness (i.e. number of input nerves with effect/number of input nerves tested) of the cells was very high (89.9%). The responsiveness to stimulation of group I muscle afferent fibres was extremely low, both in flexor and extensor gamma-motoneurones and irrespective of whether they were static or dynamic. There was no difference, as regards the low incidence of group I muscle reflex action, between stimulation of autogenetic and heteronymous nerves. Among the rare reflex effects elicited from group I muscle fibres inhibition was four times as frequent as excitation. Inhibitory effects could be provoked from the autogenetic as well as from the heteronymous nerves. In contrast, excitatory effects were almost always autogenetic. The scarcity of group I muscle action on gamma-motoneurones is in striking contrast to the well known and powerful reflex actions of Ia and Ib fibres on alpha-motoneurones. These findings are discussed in relation to the concept of alpha-gamma linkage, and it is concluded that skeletomotor and fusimotor activity cannot be rigidly linked under all conditions.

Action Potentials↗
PubMed1983

Actions on gamma-motoneurones elicited by electrical stimulation of group II muscle afferent fibres in the hind limb of the cat.

The reflex effects elicited by electrical stimulation of group II muscle afferent fibres were recorded with micro-electrodes in ninety-eight hind-limb gamma-motoneurones of cats anaesthetized with chloralose. Eighty-one of the gamma-cells were classified as either static or dynamic by means of stimulation in the mesencephalic area for dynamic control known to influence dynamic gamma-motoneurones selectively. A high responsiveness to activity in group II muscle fibres was found for the whole sample of gamma-cells. Group II muscle action on dynamic gamma-motoneurones was found to be more frequent than that on static ones. Excitation from group II fibres outweighed inhibition. This was clear cut for flexor gamma-motoneurones. In extensor gamma-cells, excitation prevailed by a small margin only. However, for both static and dynamic extensor gamma-cells, excitation prevailed from both posterior biceps--semitendinosus and the gastrocnemius--soleus nerves, whereas inhibition was more frequent from the deep peroneal and quadriceps nerves. All the reflex effects studied were likely to be mediated via oligosynaptic pathways. The shortest latencies of excitatory effects were compatible with a disynaptic coupling. The fastest inhibitions were presumably trisynaptic. The present findings, supported by a parallel study of reflexes evoked by group III muscle afferents, strongly suggest that the reflexes on gamma-motoneurones are not organized in accordance with the concept of flexion reflex afferents as conceived for alpha-motoneurones. The interpretation of the results suggests a particularly independent position for dynamic gamma-cells in relation to alpha- and static gamma-motoneurones. Hence, the results also furnish an argument against the concept of alpha-gamma linkage.

Action Potentials↗
PubMed1983

Actions on gamma-motoneurones elicited by electrical stimulation of group III muscle afferent fibres in the hind limb of the cat.

The reflex actions evoked by electrical stimulation of group III muscle afferent fibres were investigated with micro-electrode recordings from ninety-three gamma-motoneurones projecting to hind-limb muscles of cats anaesthetized with chloralose. For seventy-eight of the ninety-three gamma-cells the frequency of occurrence and types of effects mediated via group II and group III muscle fibres were compared. Seventy-seven of the cells tested at intensities which excited group III and seventy-five of the cells tested at intensities which excited both group II and group III afferent fibres were classified as either static or dynamic, using the method of mesencephalic stimulation (Appelberg, 1981). The responsiveness of the whole sample of gamma-motoneurones to inputs from group III muscle fibres was high and comparable to that found with group II fibres. It was found that group III muscle fibres acted preferentially on static gamma-motoneurones. In contrast, group II fibres acted preferentially on dynamic gamma-motoneurones. Both excitatory and inhibitory effects were provoked by stimulation of group III fibres. Generally excitation was more frequent than inhibition. A strong dominance of excitation over inhibition was found in flexor muscles, and a weaker prevalence of excitation was also encountered in extensor muscles. This prevalence of excitation in extensor gamma-motoneurones is in contrast to the striking predominance of group III-evoked inhibition of extensor alpha-motoneurones as described by the flexion reflex afferents concept. A comparative survey is also given of the patterns of responses elicited in individual posterior biceps-semitendinosus and gastrocnemius-soleus gamma-cells by stimulation of group II and group III fibres. These data further corroborate the view that reflexes from high-threshold muscle afferent fibres to gamma-motoneurones are organized differently from those to alpha-motoneurones. The functional implications of these findings are discussed. It is proposed that the pools of gamma-motoneurones should be considered as integrative systems intercalated between descending and reflex pathways on the one hand and the skeletomotor neurones on the other. The descending messages and the multisensory peripheral information, integrated in the fusimotor neurones, undergo final adjustment in the muscle spindle. The link to the skeletomotor neurones is formed by the primary spindle afferents. These constitute a final common input, conveying integrated detailed polymodal feed-back, to the central nervous system. This new concept is referred to as the 'final common input' hypothesis.

Action Potentials↗
PubMed1983

Recurrent actions on gamma-motoneurones mediated via large and small ventral root fibres in the cat.

Effects on single lumbar gamma-motoneurones, mediated via fibres running in the ventral roots, were studied by micro-electrode recording in cats anaesthetized with chloralose. Graded electrical stimulation of ventral roots or of peripheral nerves was used. The cells were identified as gamma-motoneurones by antidromic stimulation and by measurement of their axonal conduction velocity. Some of the cells were classified as static or dynamic. The findings confirm the previously demonstrated existence of low-threshold, presumed recurrent, inhibition of both static and dynamic gamma-motoneurones. Strong evidence for the occurrence of high-threshold recurrent inhibition of gamma-motoneurones is also presented. In addition, excitatory effects on gamma-cells, also mediated via fibres in the ventral roots, are described. The low-threshold effects from ventral root fibres are attributed to recurrent alpha-collateral activity and the high-threshold effects to gamma-collateral activity. The significance of recurrent inhibition of gamma-motoneurones is discussed in relation to the 'gain regulator' concept proposed by Hultborn, Lindström & Wigström (1979).

Action Potentials↗