Slowly adapting muscle receptors in man.
TL;DR: It was concluded that the motor cortex exerts a very powerful control of the intrafusal muscle fibres of the majority of the muscle spindles.
Abstract: Unitary nerve impulses originating from slowly adapting muscle receptors were recorded with percutaneously inserted tungsten electrodes from the median and the tibial nerves in awake human subjects. Discharges from 72 receptors located in the wrist flexor muscles and the ankle extensor muscles were analysed. The possibilities to derive criteria of muscle spindles and Golgi tendon organs were tested by means of a number of experimental procedures. A differentiation between these two types of receptors could, for technical reasons, not be achieved by electrically induced muscle twitches. For the majority of the endings muscle spindle characteristics could be demonstrated. In relaxed muscles, a number of the muscle spindle afferents exhibited a high dynamic sensitivity to passive joint movements whereas a smaller proportion of them had a low dynamic sensitivity. A steady state discharge as a function of the muscle length could be demonstrated for some of them. During weak voluntary contractions without external muscle shortening, the majority of the units responded with a sustained impulse discharge which started and stopped almost simultaneously with the onset and the cessation of the extrafusal contractions. It was concluded that the motor cortex exerts a very powerful control of the intrafusal muscle fibres of the majority of the muscle spindles. For a few units the relation between the muscle force and the impulse frequency was very striking but for the majority of them this relation was poor. It was concluded that the former units were Golgi tendon organs.
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TL;DR: Evidence for "central" fatigue and the neural mechanisms underlying it are reviewed, together with its terminology and the methods used to reveal it.
Abstract: Muscle fatigue is an exercise-induced reduction in maximal voluntary muscle force. It may arise not only because of peripheral changes at the level of the muscle, but also because the central nervous system fails to drive the motoneurons adequately. Evidence for “central” fatigue and the neural mechanisms underlying it are reviewed, together with its terminology and the methods used to reveal it. Much data suggest that voluntary activation of human motoneurons and muscle fibers is suboptimal and thus maximal voluntary force is commonly less than true maximal force. Hence, maximal voluntary strength can often be below true maximal muscle force. The technique of twitch interpolation has helped to reveal the changes in drive to motoneurons during fatigue. Voluntary activation usually diminishes during maximal voluntary isometric tasks, that is central fatigue develops, and motor unit firing rates decline. Transcranial magnetic stimulation over the motor cortex during fatiguing exercise has revealed focal cha...
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TL;DR: The responses of primary endings to tendon taps were reduced during muscle vibration, a reduction which probably contributes to vibration‐induced suppression of tendon jerks.
Abstract: 1. In micro-electrode recordings from the human peroneal and tibial nerves, the responses of thirty-two primary spindle endings, thirteen secondary spindle endings and three Golgi tendon organs were studied during vibration of the tendons of the receptor-bearing muscles in the leg. The amplitude of the applied vibration was 1-5 mm and the frequency was varied from 20 to 220 Hz. As checked with e.m.g. and torque measurements, the muscles of the leg were relaxed during the sequences analysed. 2. Providing that the vibrator was accurately applied, all endings responded with discharges phase-locked to the vibration cycles, the discharge rates being at the vibration frequency or at subharmonics of that frequency. The response to vibration was of abrupt onset and offset, was maintained for the duration of vibration, and was not subject to fluctuation with changes in attention or with remote muscle contraction. 3. The maximal discharge rate that could be achieved varied from one ending to the next, and increased with the length of the receptor-bearing muscle. For endings driven at their maximal rate an increase in vibration frequency produced a decrease in discharge rates as the ending changed to a subharmonic pattern of response. The converse occurred on decreasing vibration frequency. 4. For any given muscle length, primary endings could generally be driven to higher rates than secondary endings but there was a wide range of responsiveness within each group and a significant overlap between the groups. At medium muscle length, the most responsive primary endings could be driven up to 220 Hz but secondary endings did not reach discharge rates higher than 100 Hz. 5. With combined vibration and passive movements, primary endings exhibited maximal vibration responsiveness during the stretching phases, sometimes firing twice per vibration cycle. During the shortening phases, however, they usually ceased responding to the vibratory stimulus. The vibration responsiveness of secondary endings was not potentiated to the same extent by on-going muscle stretch or reduced to the same extent by on-going muscle shortening. Thus, during shortening, secondary endings may be more responsive than primary endings. 6. The responses of primary endings to tendon taps were reduced during muscle vibration, a reduction which probably contributes to vibration-induced suppression of tendon jerks. Additionally, as the muscle shortened after tendon percussion, there was a transient pause in the response to vibration.
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Cites background or result from "Slowly adapting muscle receptors in..."
...The greater vibrationresponsiveness of human primary endings agrees with previous findings in the cat (Bianconi & Van der Meulen, 1963; Brown et al. 1967), but the extent to which human secondary endings respond to vibration applied to the muscle tendon could not have been anticipated from these earlier studies. Differences in technique may account for much ofthe discrepancy. In man the effective amplitude of vibration is unknown and the mode of application is probably less efficient than directly attaching a severed tendon to the vibrator. Nevertheless, the conclusion of Brown et al. (1967) that 'In man, vibration applied to a tendon in the absence of muscle contraction can be presumed to be a specific stimulus for the primary endings' is not supported by the present findings....
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...1C and D, 5 B) they have not differentiated between endings that are truly unresponsive to vibration and those which although unable to follow the vibration frequency one-to-one are capable of subharmonic activation. Indeed in their Fig. 5B, a 'non-responsive' slowly conducting fibre appears to more than double its firing rate with increase in vibration frequency from 60 to 150 Hz. Subharmonic activation of secondary endings was recognized by Brown et al. (1967), and also by McGrath & Matthews (1973), but with the higher vibration frequencies and lower amplitudes which they used they considered such activation minor compared with the extreme sensitivity of primary endings....
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...Of the two studies, that of Bianconi & Van der Meulen (1963) is more comparable with the present since they applied vibration by a stylus to the muscle overlying the appropriate ending or to the muscle tendon. Bianconi & Van der Meulen (1963) describe two types of response: 'either an ending was capable of following the vibra-...
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...Of the two studies, that of Bianconi & Van der Meulen (1963) is more comparable with the present since they applied vibration by a stylus to the muscle overlying the appropriate ending or to the muscle tendon....
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TL;DR: The sections in this article are: Methodological Considerations, General Summary and Epilogue, Ascending Pathways that Monitor Segmental Interneuronal Activity, and Evidence That Ascending FRA Pathways Monitor Activity in interneurons of Reflex Pathways.
Abstract: The sections in this article are:
1
Methodological Considerations
1.1
Selective Stimulation of Primary Afferents
1.2
Stimulation of Central Motor Systems
1.3
Methods for Investigation of Convergence at Interneuronal Level
2
Spinal Neuronal Circuits Used in Common by Segmental Afferents and Supraspinal Motor Centers
2.1
Recurrent Inhibition
2.2
Pathways From Ia-Afferents and Their Control by γ-Motoneurons
2.3
Reflex Pathways From Group Ib Tendon Organ Afferents
2.4
Reflex Pathways From Cutaneous and Joint Afferents and From Groups II and III Muscle Afferents
2.5
Propriospinal Neurons
2.6
Presynaptic Inhibition of Transmission From Primary Afferents
3
Reticulospinal Inhibition of Segmental Reflex Transmission
3.1
Dorsal Reticulospinal System
3.2
Ventral Reticulospinal Pathways
3.3
Monoaminergic Reticulospinal Pathways
3.4
Decerebrate Preparation
4
Direct Projections of Descending Pathways to α-Motoneurons
5
Ascending Pathways that Monitor Segmental Interneuronal Activity
5.1
Evidence That Ascending FRA Pathways Monitor Activity in Interneurons of Reflex Pathways
5.2
Information Via Ascending Collaterals of Interneurons
5.3
Ventral Flexor Reflex Tracts
5.4
Ventral Spinocerebellar Tract
6
General Summary and Epilogue
6.1
General Summary
6.2
Epilogue
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773 citations
TL;DR: A technique is described which allows recording of multi-fiber discharge and single-unit activity from intact peripheral nerves of awake human subjects and it was possible to judge when afferent nerve fibers of cutaneous origin lay close to the electrode tip by the quality of the insertion paresthesias and the type of peripheral stimuli required to induce afferent responses.
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TL;DR: The present work has been undertaken to see what can be learnt of these nerve endings by -direct observation, and this paper is a general survey of the subject, as the work has raised many new problems which have not been fully examined.
Abstract: SINCE Ruffini [1898] gave us his beautiful drawings of muscle spindles, and Sherrington [1894] showed that they were sensory end-organs, our knowledge of their function and importance has been steadily growing owing to the observations of physiologists in many parts of the world, and particularly to those of Sherriington and his co-workers. Until recent years our knowledge of the behaviour of the sense organs in muscle was obtained by inference and indirect observations. The only direct observations on mammalian proprioceptors made hitherto are those of Forbes, Campbell and Williams [1924], and Mc Couch, Forbes and Rice [1928], who, using a string galvanometer, were able to show that sensory action currents occurred after a muscle had contracted. But now the methods pioneered by Adrian have made direct observation of the response of these nerve endings possible, and it has only been necessary to adapt the technique to the pecularities of the problem for the behaviour of mammalian muscle spindles to be studied directly. A considerable amount of work has already been done oin the nerve endings in frog's muscle [Adrian and Zotterman, 1926a; Bronk, 1929a and b; Matthews, 1929b, 1931a and b], but the histology of the' nerve endings in mammalian muscle is far more complex than that of the muscle spindles in the frog, and does not justify the assumption that they behave in exactly the same way. The present work has been undertaken to see what can be learnt of these nerve endings by -direct observation, and this paper is a general survey of the subject, as the work has raised many new problems which have not as yet been fully examined. The tecbnique employed is essentially the same as that by which muscle spindles in the frog were studied [Matthews, 1931 a, b], but many modifications in details have been necessary.
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