Correlation analysis of muscle spindle responses to single motor unit contractions.

SUMMARY1. The proportion of muscle fibres innervated by more than one motoneurone (polyneuronal innervation) was measured in the fourth deep lumbrical muscle of young rats following either unilateral deafferentation or spinal cord isolation (cord transaction combined with bilateral deafferentation).2. Unilateral deafferentation at 7 days of age did not affect the subsequent time course of synapse elimination in the developing muscle.3. Spinal cord isolation at 7 days led to a prolongation of the time course of synapse elimination in the muscle, levels of polyneuronal innervation approaching zero beyond about 30 days (about 20 days in normal animals). The raised levels of polyneuronal innervation in these animals were not associated with significant terminal sprouting at end-plates, but were associated with multiple axonal inputs to end-plates as is found in younger normal animals. This was shown by zinc iodide and osmium staining. Also some muscle fibres had two and sometimes three separate end-plates.4. Spinal cord isolation in rats 19 or more days old resulted in a reappearance of multiple innervation. This was largely due to ultraterminal sprouting. 5. It is concluded that unilateral deafferentation alone causes no change in the time course ofsynapse elimination. The multiple innervation caused by total deafferentation and spinal transaction is attributed to the lack of activity of these muscles.

Section: Deafferentationmentioning

confidence: 99%

The effects of deafferentation and spinal cord transection on synapse elimination in developing rat muscles.

Caldwell¹,

Ridge²

1983

“…During a voluntary contraction spindle endings are subjected not only to fusimotor influences but also to the modulating effect of asynchronous twitch contractions of anatomically related muscle units (Binder, Kroin, Moore, Stauffer & Stuart, 1976;Windhorst & Meyer-Lohmann, 1977;Binder & Stuart, 1978). From the present results, it seems likely that asynchronous twitching of adjacent muscle fibres can affect the variability of spindle discharge significantly.…”

mentioning

confidence: 99%

The regularity of muscle spindle discharge in man.

Burke¹,

Skuse²,

Stuart³

1979

Self Cite

SUMMARY1. The variability of discharge of thirty-nine muscle spindle afferents from the pretibial muscles of normal human subjects was determined for spike train sequences recorded with the ankle joint fixed in 250 plantar flexion, during further stretch and during graded voluntary contractions of the receptor-bearing muscle.2. In non-contracting muscles with the ankle joint in 250 plantar flexion, a sustained discharge was maintained by twenty-four of the thirty-nine endings. The mean discharge frequency for the active endings was 11-1 Hz (range 4-8-22-1 Hz), the mean coefficient of variation 0-073 (range 0*021-0 183). With further stretch, the discharge of endings maintaining frequencies below 10-12 Hz became more regular. For endings maintaining higher frequencies, changes in the coefficient of variation were small and occurred in either direction. All secondary endings maintained a highly regular discharge, but, at these frequencies, there was no statistically significant difference in the variability of primary and secondary endings.3. It is considered that these findings are comparable to those of Matthews & Stein (1969) for de-efferented feline spindle endings, and support the view that there is no functionally effective background fusimotor drive to non-contracting muscles of normal human subjects. 4. A voluntary contraction sufficient to accelerate a spindle ending invariably decreased the regularity of its afferent discharge. During voluntary contractions, coefficients of variation up to 0*345 were recorded. However, coefficients as low as 01 were not uncommon, and thus the absence of fusimotor drive cannot necessarily be inferred from a regular afferent discharge pattern.5. With contractions of different strength, the increase in the coefficient of variation did not parallel the increase in discharge frequency. It is concluded that not all fusimotor influences acting on a spindle ending are translated into variability, and that measurements of the variability of discharge do not accurately reflect the level of fusimotor drive.6. The discharge frequency of some spindle endings decreased slightly in some contractions and this was accompanied by an increase in the variability of discharge. It is suggested that contracting extrafusal muscle fibres can modulate the discharge pattern of spindle endings and contribute to the variability of discharge during a voluntary contraction.

“…Our computational techniques have been detailed in another report (Binder et al 1976). For each spike train, the time of every pulse event is determined (to nearest 0.1 msec) and entered into a computer file.…”

Section: Methodsmentioning

confidence: 99%

“…Cross-correlation histograms are then compiled between the afferent and efferent channels. Eighteen motor unit twitches were selected at random throughout each run and averaged for display (Stein, French, Mannard & Yemm, 1972;Binder, Rosenberg, McWilliams & Moore, 1974;Binder et al 1976). The correlograms (cross-correlation histograms) show the 338 Ib RESPONSES TO MOTOR UNIT CONTRACTIONS 339 frequency of occurrence of a sensory spike as a function of time following the e.m.g.…”

Section: Methodsmentioning

confidence: 99%

The response of Golgi tendon organs to single motor unit contractions.

Binder

Kroin

et al. 1977

Self Cite

163

SUMMARY1. Cross-correlation analysis has been used to quantify the responses of cat soleus tendon organs to repetitive twitch contractions of: (a) different motor units within the muscle, (b) single motor units at different muscle lengths, and (c) single motor units when the pulse-train pattern of stimulation delivered to the motor unit axon was altered.2. lb afferents were observed which responded to each of several hundred successive motor unit twitches with identical numbers of spikes and with relatively invariant latencies.3. The present results show that tendon organs are sensitive to subtle alterations in motor unit twitch wave form and amplitude, and that this sensitivity is reflected in the precise timings of their afferent discharge.4. Examination of these tendon organ responses indicates that the forces produced by single motor units coupled to the receptor capsule are well above threshold. Calculations based on these results, and earlier soleus motor unit and muscle fibre data, suggest that the absolute force threshold for tendon organs may be as little as 4 mg, which is less than the estimated minimum twitch force generated by individual soleus muscle fibres.5. Considering the number oftendon organs in a muscle, and the likelihood that every motor unit is connected with at least one receptor, the sensitivity of tendon organs ensures that every twitch of every motor unit will be reflected in the population of afferent signals projecting to the spinal cord,