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R M Reinking

Publications and source records attributed to R M Reinking.

34 records · Page 2Linked to original sources
PubMed1975

Tendon organs of cat medial gastrocnemius: responses to active and passive forces as a function of muscle length.

The responses of 13 Golgi tendon organs to graded force development of 29 motor units in medial gastrocnemius of the cat have been studied in five experiments. Of the 13 tendon organs, 11 were responsive to passive stretch within the physiological range of muscle length and 5 were "spontaneously" active at very short lengths where no passive tension could be recorded. The relationship between passive force and the firing rates of the various afferents ranged from a linear one to a power relation (Y = Axb + c) with b, a widely varying exponent. Results support the general conclusion that although many Ib afferents respond to passive force within the physiological range of muscle stretch, this form of stimulus is not a particularly effective one. The statis responses of Golgi tendon organs to active force development produced by single motor units was studied at different muscle lengths. In all cases the apparent sensitivity (change in firing rate per active force developed) decreased as muscle length approached Lo. The static responses of Golgi tendon organs to force developed by single motor units were also studied during fatiguing contractions. The data suggest a sigmoid relationship between force developed at the tendon and the Ib response. The collective response of all 13 tendon organs to active and passive forces at different muscle lengths was also examined. This analysis offered further support for the viewpoint that active motor unit contractions provide themost significant excitatory input to tendon organs and that changes in passive force during muscle stretch have comparatively little effect on the collective tendon organ response. The interaction between active and passive force inputs to the Golgi tendon organs is discussed in relation to the complicated nature of the relationship between forces measured at the tendon and those acting within the receptor capsule. When these complications were taken into account it was possible to explain the differences in responsiveness of a given tendon organ to active contraction of several motor units and to passive force in terms of a single force-firing rate curve for the receptor. It is concluded that changes in the force of contraction of single motor units result in relatively small changes in Ib afferent firing and that during normal muscle contractions, changes in the number of motor units acting on a single receptor must produce far more significant changes in firing rate than changes in the amount of force developed by any single unit. Changes in dynamic Ib sensitivity to single motor unit contractions are also shown to depend on length and in a similar way to the changes in static Ib sensitivity. During fatiguing contractions, a sigmoid relation was found between the dynamic Ib response and the rate of force development by single motor units.

Animals↗
PubMed1975

Interface unit for on-line measurements of motor unit properties with a small laboratory computer.

Some simple circuitry is described which has been successfully used in conjunction with a small laboratory computer for "on-line" measurements of the force of contraction of single motor units in cat gastrocnemius and soleus muscles. Our approach emphasizes use of a sample and hold device to allow high amplification of small forces developed during single motor unit contractions which are often superimposed on relatively large whole muscle passive forces. Two digitally controlled selectable gain amplifiers are used to ensure proper modulation of the computer's ADC and to enable automatic scaling of the measured variables. An analog peak detector is incorporated into the unit such that peak force measurements can be made with the minimum of computer software. The principles governing the present design are directly applicable to the measurement of intracellularly recorded postsynaptic potentials and a variety of other physiological variables which require accurate measurement of a small transient signal superimposed on a large "control" or "resting" signal.

Animals↗
PubMedDate not supplied

Electromyographic responses of mammalian motor units to a fatigue test.

Evidence is presented that marked changes in the electromyographic (EMG) activity of single motor units often occur during a fatigue-test paradigm (12) widely used for the classification of mammalian motor units into fast-fatigable (FF), fast-intermediate-fatigable, fast-fatigue-resistant and slow categories (11), particularly in type FF units. Force output and EMG activity were measured in single motor units of the tibialis posterior muscle of anasthetized cats, while each unit was subjected to a fatigue test consisting of 4 min of motor-axon stimulation, using 1 Hz 330 ms trains of 0.1 ms shocks at 40 Hz. As a measure of the temporal characteristics of the EMG waveform, the reciprocal of the interval between first positive and subsequent negative peak was measured. For parameters of EMG magnitude, peak-to-peak amplitude and area were measured. The fatigue test was shown to produce, on average, significantly greater alterations in the values of the EMG parameters of FF units than of the other unit types. There were no significant EMG alterations among the other unit types. The results are discussed in relation to the interpretation of EMG depression as an indication of excitation failure and the relative fatigability and EMG depression of different motor unit types.

Animals↗