PubMed Health⌕ Search

Biomedical subjects

M Hulliger

Publications and source records attributed to M Hulliger.

63 records · Page 4Linked to original sources
PubMed1977

Static and dynamic fusimotor action on the response of Ia fibres to low frequency sinusoidal stretching of widely ranging amplitude.

1. Single fusimotor fibres were stimulated repetitively to test their action on the responsiveness of muscle spindle primary endings in the cat soleus to sinusoidal stretching of both large and small amplitude. Frequencies of 0.06-4 Hz were used at amplitudes from 10 mum to 3 mm.2. The response was assessed by fitting a sinusoid to the cycle histogram of the afferent firing throughout the course of the cycle; this linear approximation measures the fundamental of the response and ignores any harmonics. The sine was allowed to project to negative values and any empty bins in the histogram were ignored when fitting.3. With small amplitudes of stretching the histograms were reasonably sinusoidal, but with large amplitudes they showed appreciable distortion of the wave form for the passive ending and during dynamic fusimotor stimulation. Non-linearity of response manifested itself also, with increasing amplitude of stretching, by an increase in the phase advance of the response, by increasing r.m.s. deviation of the histogram points from the fitted sine and (for dynamic stimulation) by an increase in the mean value of the fitted sine.4. With increasing amplitude the response modulation ceased to increase proportionately with the stimulus, so that the sensitivity of the ending to a large stretch (defined as afferent modulation/stretch amplitude) was appreciably less than for a small stretch. This effect was most pronounced for the passive ending.5. Whatever the amplitude of movement the modulation during static stimulation was less than that for the passive or during dynamic stimulation. For small amplitudes the response during dynamic stimulation was less than that of the passive, but for large amplitudes the response during dynamic stimulation was always the greater. At some intermediate cross-over amplitude the two responses were the same size, though still differing slightly in other respects. The value of the cross-over amplitude was usually about 200 mum at 1 Hz, and increased on lowering the frequency. Thus dynamic fusimotor action does not uniformly produce either an increase or a decrease in the sensitivity of the ending in relation to the passive.6. Bode plots, for each amplitude, of sensitivity and phase against frequency suggested that(a) under all conditions the ending is relatively insensitive to frequency in the range studied, for the slope of the log-log sensitivity lines was only 0.15-0.2 (3.5-6 db/decade);(b) the mechanism which makes for non-linearity is not particularly frequency sensitive;(c) static fusimotor stimulation does not change the frequency sensitivity of the ending;(d) dynamic fusimotor stimulation very slightly increases the frequency sensitivity of the ending for large amplitudes.In reaching these conclusions more attention was paid to the slope of the sensitivity lines than to the values of phase.7. It appears that the major effect of fusimotor action, whether static or dynamic, is to regulate the sensitivity of the primary ending to stretching for all amplitudes of movement (i.e. gain) rather than to control the relative values of its sensitivity to length and to velocity (i.e. crudely, the damping in a feed-back loop).

Action Potentials↗
PubMed1977

Effects of combining static and dynamic fusimotor stimulation on the response of the muscle spindle primary ending to sinusoidal stretching.

1. A pair of fusimotor fibres, one static and the other dynamic, were stimulated simultaneously to test their combined action on the response of muscle spindle primary endings in the cat soleus to sinusoidal stretching. A frequency of 1 Hz was chiefly used, with a wide range of amplitudes (10 micronm-2 mm). The response of the ending was assessed from the parameters of the sine fitted to its firing averaged throughout the course of the cycle; this was felt useful even though the responses to the larger stretches showed certain non-linear features. 2. With small stretches (up to about 50 micronm amplitude) static action dominated, and the modulation of firing during conbined stimulation was little or no larger than that found during the static stimulation on its own, and much smaller than that found during the static stimulation on its own, and much smaller than that found during the dynamic stimulation. The phase of the response was, however, much the same for all three conditions. 3. With larger stretches the modulation with combined stimulation was intermediate between the values found on stimulating either fusimotor fibre on its own; the dynamic contribution increased progressively with the amplitude of stretching. 4. With larger stretches the phase of the response during combined stimulation was appreciably closer to that for static action than to that for dynamic action. But the differences between the various conditions were small (below 20 degrees) and seem attributable to various distortions of the response wave from away from a true sinusoid, rather than betokening a difference in the ratio of velocity to length sensitivity under the various conditions. This view was supported by the effects on phase of grading the rate of stimulation of one fusimotor fibre while holding that of the other constant. 5. Detailed comparison of the cycle histograms obtained under different conditions showed an interestingly asymmetrical pattern of summation and occlusion of the effects of the two kinds of fusimotor fibre. At the peak of the response to a large stretch static action summed with dynamic action, which was here the stronger, so that at this phase of the cycle the firing was greater with the combined stimulation than with either fibre on its own. But, in the trough of the response to the same stretch static action occluded any dynamic action, which was now the weaker, so that at this phase of the cycle the firing with combined stimulation was virtually the same as that with static stimulation on its own. With a small stretch, static action normally occluded dynamic action throughout the cycle; this is in line with the firing during static action now usually being greater than that during dynamic action for all phases of the cycle.

Action Potentials↗
PubMed1977

Effects of fusimotor stimulation on the response of the secondary ending of the muscle spindle to sinusoidal stretching.

1. The responsiveness of the spindle secondary ending to sinusoidal stretching has been studied using the soleus muscle of the anaesthetized cat. The sensitivity (impulses/sec firing per mm stretching) and the phase of the response were determined by computer averaging. The small linear range was studied at frequencies of 0.5-500 Hz, and also the larger non-linear range at 1 Hz.2. In the linear range, stimulation of single fusimotor fibres (which were presumed to be static axons) approximately halved the sensitivity of the ending to low frequency stretching (up to 30 Hz), but did not produce any change in the phase of the response. Thus, from the point of view of motor function, fusimotor activity provides control of gain and a biasing signal, but not control of the relative sensitivity of the secondary ending to length and velocity.3. In contrast, such stimulation slightly increased the responsiveness of the secondary ending to high-frequency stretching (100-500 Hz) and slightly advanced the phase of the response above that of the passive ending.4. The results are discussed in relation to the effect of static fusimotor stimulation on the primary ending, and to findings on secondary endings in the decerebrate cat.

Action Potentials↗
PubMed1975

The effects of fusimotor stimulation during small amplitude stretching on the frequency-response of the primary ending of the mammalian muscle spindle.

Single fusimotor fibres to the de-efferented soleus of the anaesthetized cat were stimulated repetitively while recording the response of single primary afferents to small amplitude sinusoidal stretching at frequencies of 0-5--500 HZ. The response of the ending was determined by averaging its firing for many cycles to construct a 'cycle histogram'. When small enough, the stretching modulated the firing sinusoidally; as the frequency increased the requisite amplitude fell to a fraction of a micron. The amplitude of the modulation (in impulses/sec) divided by be amplitude of stretchin (in mm) gave the sensitivity of the ending for the particular frequency in question. 2. The passive frequency--response curve obtained in the absence of fusimotor stimulation agreed with those obtained before...

Action Potentials↗