Gamma‐motoneurone discharge patterns during fictive locomotion in the decerebrate cat

Pr, Murphy; Gr, Hammond

doi:10.1113/expphysiol.1990.sp003376

Cited by 8 publications

(8 citation statements)

References 3 publications

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“…It is of considerable interest that in the present work the mean values of resting frequency of the modulated fusimotor fibres was very significantly higher than that of the tonic ones. This agrees with the findings of Murphy et al (1984) and of Murphy & Hammond (1990) in their triceps surae studies. The difference between the two groups of experiments therefore still lies in the identification of the two classes of fusimotor fibres as static or dynamic.…”

Section: Discussionsupporting

confidence: 92%

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The use of midbrain stimulation to identify the discharges of static and dynamic fusimotor neurones during reflex jaw movements in the anaesthetized cat

Donga

Taylor²,

Jüch³

1993

Experimental Physiology

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SUMMARYIn anaesthetized cats, it was possible to enhance the dynamic sensitivity to stretch ofjaw muscle spindle primary afferents by electrical stimulation in the midbrain. This effect was taken to be due to excitation of dynamic fusimotor neurones and was used to identify fusimotor fibres as static or dynamic in recordings from the masseter nerve. During reflex movements, some fusimotor fibres fired tonically, while others were markedly modulated with increases in firing corresponding approximately to muscle shortening. The modulated group had a significantly higher mean resting firing frequency than the tonic group. Midbrain stimulation at points shown to produce dynamic effects on muscle spindle primary afferents increased the discharge frequency of the tonic fusimotor units, but did not significantly affect the modulated fusimotor units. We conclude that the fusimotor fibres in the masseter nerve which fire tonically during reflex jaw movements are probably of the dynamic type, while those which show strongly modulated increases in firing are probably static.

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Section: Discussionsupporting

confidence: 92%

“…The question as to the extent to which the observed fusimotor patterns are reflex consequences of the active movements or are generated centrally has not been considered in the present work. However, the recent study by Murphy & Hammond (1990) indicates the latter to be the case in muscles involved in locomotion.…”

Section: Discussionmentioning

confidence: 97%

The use of midbrain stimulation to identify the discharges of static and dynamic fusimotor neurones during reflex jaw movements in the anaesthetized cat

Donga

Taylor²,

Jüch³

1993

Experimental Physiology

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“…Some of the earliest observations of spindle discharge in hindlimb and forelimb muscles in decerebrate animals (Perret & Busser, 1972;Perret & Berthoz, 1973) strongly suggested the presence of static fusimotor modulation in parallel with á_activity. Later, more detailed studies involving recording from hindlimb extensor ã-axons (Murphy, 1982;Murphy et al 1984;Murphy & Hammond, 1990) or spindles (Taylor, Stein & Murphy, 1985;Bennett, De Serres & Stein, 1996) have supported the idea that one group of ã_motoneurones fires tonically whilst another group fires in a modulated fashion, but identified the latter as dynamic. Evidence from chronic recordings from cat hindlimb spindles has been interpreted as indicating that the observed behaviour could be explained by essentially tonic levels of static and dynamic fusimotor firing, though with the possibility of some additional static modulation approximately in parallel with á-activity (Prochazka et al 1987).…”

Section: Discussionmentioning

confidence: 99%

Fusimotor Influence on Jaw Muscle Spindle Activity during Swallowing‐Related Movements in the Cat

Taylor

Hidaka

Durbaba

et al. 1997

The Journal of Physiology

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The activity patterns of muscle spindle afferents in jaw‐closer muscles were studied during reflex swallowing movements in anaesthetized cats. Simultaneous records were made of the electromyogram (EMG) in masseter and anterior digastric muscles and of the unloaded jaw movements. The underlying patterns of fusimotor activity were deduced by comparing afferent discharges occurring during active swallowing with those occurring when exactly the same movements were imposed passively. The interpretation of spindle behaviour was greatly facilitated by characterizing the afferents according to the evidence for their contact with the various intrafusal muscle fibres, derived from testing with succinylcholine. It was also valuable to have two different types of afferent recorded simultaneously. There was clear evidence of fusimotor activity occurring during active jaw closing so as to oppose the spindle silencing. This effect was most marked in b2c‐type afferents (probably secondaries) and was therefore attributed to a modulation of static fusimotor discharge approximately in parallel with α‐activity. Afferents with evidence of bag1 fibre contacts (primaries) showed much greater sensitivity to muscle lengthening during active movement than when the movement was imposed. This difference was exaggerated when anaesthesia was deepened for the passive movements. This was interpreted as evidence for a higher level of dynamic fusimotor activity maintained during active movements than at rest. The results support the view that for a variety of active jaw movements, static fusimotor neurone firing is modulated roughly in parallel with α‐activity but leading it so as to counteract spindle unloading. Dynamic fusimotor neurone firing appears to be set at a raised level during active movements. Anaesthesia appears to depress activity in the α‐motoneurones more than in γ‐motoneurones.

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“…During stance, the net result of sural/medial plantar inputs on dynamic y-activity is unknown and will depend on the dominant effect under natural conditions. Indeed, it is possible that, depending on the influence of other afferents, the net effect of peripheral feedback is zero and that background dynamic y-rate is normally predetermined and set to a high level by central drives (Murphy & Hammond, 1990). The possible presence of a degree of cancellation of cutaneous fusimotor reflexes (see also Johansson & Sojka, 1985;Johansson, Sjolander, Sojka & Wadell, 1989;Gandevia, Wilson, Cordo & Burke, 1994;Murphy & Martin, 1995 a) may partly explain their apparent scarcity in intact cats, as inferred from spindle afFerent recordings (e.g.…”

Section: A)mentioning

confidence: 99%

“…However, at this time, plantar cutaneous activity will facilitate ankle extensor dynamic y-efferents (due to reflex reversal), augmenting the effect of sural afferent feedback and the I a support of muscle contraction. In this context, the prevailing excitatory pattern of cutaneous reflex control of dynamic fusimotor neurones may be functionally appropriate in compensating for a low, centrally set background level of discharge (Murphy & Hammond, 1990). …”

Section: A)mentioning

confidence: 99%

Reversal of fusimotor reflex responses during locomotion in the decerebrate cat

Pr¹,

Gr²

1997

Experimental Physiology

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SUMMARYThe effect of brief trains of electrical stimulation, at 2, 3 and 20 x threshold (T), of cutaneous afferents in the medial plantar nerve on the discharges of single medial gastrocnemius static and dynamic y-efferents has been investigated at rest and during locomotion in a decerebrate cat preparation. The units were classified as dynamic (10 units) or static (10 units) indirectly on the basis of their resting and locomotor discharge characteristics. Responses were assessed by calculating the change in mean y-rate during the 100 ms after stimulus onset compared with a control period. At rest, most dynamic neurones were inhibited by stimulation at 2T (9 of 10 units) and above. In contrast, the resting responses of most static neurones were excitatory at 2T (9 of 10 units) and 3T, while 20T produced static y-effects that varied in sign. During locomotion the responses of both types of y-efferent were phase related. Two patterns were observed with dynamic units. For seven dynamic neurones, at stimulus levels of 2T (7 units) and above, responses during electromyogram (EMG) bursts were inhibitory while those between bursts were not significantly different from zero. However, for three other dynamic units, a phase-related reversal of reflex responses was observed at some stimulus intensities (always 2T, 3 units) comprising inhibition during, and excitation between, EMG bursts. For static neurones, inhibitory (never excitatory) responses occurred during walking at stimulus intensities of 2T (10 units) and above. The locomotor responses of static units were maximum during (3 units) or between (7 units) EMG bursts and were minimum in the opposite phase of EMG activity. A task-related reversal of reflex responses was thus generally apparent (9 of 10 units) to low intensity stimulation (2T) for static y-efferents during locomotion (inhibition) compared with rest (excitation). During locomotion there was a significant linear relation between the magnitude of response and the background y-rate for static units and those dynamic units that did not exhibit phase-related reflex

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Gamma‐motoneurone discharge patterns during fictive locomotion in the decerebrate cat

Cited by 8 publications

References 3 publications

The use of midbrain stimulation to identify the discharges of static and dynamic fusimotor neurones during reflex jaw movements in the anaesthetized cat

The use of midbrain stimulation to identify the discharges of static and dynamic fusimotor neurones during reflex jaw movements in the anaesthetized cat

Fusimotor Influence on Jaw Muscle Spindle Activity during Swallowing‐Related Movements in the Cat

Reversal of fusimotor reflex responses during locomotion in the decerebrate cat

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