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

Taylor, Anthony R.; Hidaka, Osamu; Durbaba, Rade; Ellaway, P H

doi:10.1111/j.1469-7793.1997.157bi.x

Cited by 14 publications

(12 citation statements)

References 38 publications

(30 reference statements)

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“…If the additional spindle activity were sufficient it might alert the animal to the unexpected obstruction and cause a change in the strategy of the movement. Similar conclusions were derived from studies of rhythmic jaw movements in the lightly anaesthetized cat (Taylor et al 1997). The significance of the interrupted pattern of dynamic fusimotor firing in rhythmic movements has been suggested to be that it primes the primary spindle afferents to provide a very distinct signal to the central pattern generator indicating the onset of muscle lengthening.…”

Section: Discussionsupporting

confidence: 79%

Static and dynamic γ‐motor output to ankle flexor muscles during locomotion in the decerebrate cat

Taylor

Durbaba

Ellaway

et al. 2006

The Journal of Physiology

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In locomotion, the flexor muscles of the leg are mainly concerned with the relatively constant task of raising the foot, whereas the extensors have the more variable task of support and propulsion at different speeds. This suggests that the way in which the fusimotor system works may differ between the two muscle groups. Observations previously made of the static and dynamic γ-motor firing patterns in the ankle extensor medial gastrocnemius (MG) have therefore been repeated in the flexor tibialis anterior (TA). One or more single γ-motor axons, dissected from a small filament of TA nerve, were recorded simultaneously with a number of single spindle afferents in dorsal rootlets. Cats were decerebrated and locomoted spontaneously on a treadmill. Identification of each γ-motor axon depended on relating the changes in firing caused by midbrain stimulation to the changes in static and dynamic behaviour of the spindle afferents in response to repetitive ramp and hold stretches. Static γ axons all showed a smooth modulation in frequency, increasing in phase with muscle shortening, superimposed on a minimum frequency of about 20-30 impulses s −1 . Dynamic γ axons showed interrupted firing with the frequency rising abruptly from zero at the onset of shortening, and falling again to zero shortly after the onset of lengthening. The frequency during the active periods was relatively constant, even when movement amplitudes varied. The basic similarity in the static and dynamic gamma discharge patterns for the two muscles suggests that the strategy of γ-motor control is common to both flexors and extensors. The static γ pattern is thought to be a 'temporal template' of the expected movement, effectively expanding the dynamic response range of the spindles in active movements. The dynamic γ pattern sensitizes the primary afferents to detect the onset of muscle lengthening and to detect departures from the intended movement trajectory.

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Section: Discussionsupporting

confidence: 79%

Static and dynamic γ‐motor output to ankle flexor muscles during locomotion in the decerebrate cat

Taylor

Durbaba

Ellaway

et al. 2006

The Journal of Physiology

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“…Although the possibility remains that these different discharge patterns were caused by the dissimilar jaw movements induced, the firing patterns could also result from a difference in fusimotor activity. In support of this proposal, a very irregular discharge of the spindle afferents was noted during active movements, whereas spindle firing was more regular when the same movements were reproduced passively (Taylor et al 1997). It seems therefore that the fusimotor drive is more active in CRJMs than in reflexively evoked rhythmic jaw movements.…”

Section: Behavior Of Muscle Spindle Afferents During Crjmsmentioning

confidence: 79%

Behavior of Jaw Muscle Spindle Afferents During Cortically Induced Rhythmic Jaw Movements in the Anesthetized Rabbit

Hidaka

Morimoto²,

Kato³

et al. 1999

Journal of Neurophysiology

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The regulation by muscle spindles of jaw-closing muscle activity during mastication was evaluated in anesthetized rabbits. Simultaneous records were made of the discharges of muscle spindle units in the mesencephalic trigeminal nucleus, masseter and digastric muscle activity (electromyogram [EMG]), and jaw-movement parameters during cortically induced rhythmic jaw movements. One of three test strips of polyurethane foam, each of a different hardness, was inserted between the opposing molars during the jaw movements. The induced rhythmic jaw movements were crescent shaped and were divided into three phases: jaw-opening, jaw-closing, and power. The firing rate of muscle spindle units during each phase increased after strip application, with a tendency for the spindle discharge to be continuous throughout the entire chewing cycle. However, although the firing rate did not change during the jaw-opening and jaw-closing phases when the strip hardness was altered, the firing rate during the power phase increased in a hardness-dependent manner. In addition, the integrated EMG activity, the duration of the masseteric bursts, and the minimum gape increased with strip hardness. Spindle discharge during the power phase correlated with jaw-closing muscle activity, implying that the change in jaw-closing muscle activity associated with strip hardness was caused by increased spindle discharge produced through insertion of a test strip. The increased firing rate during the other two phases may be involved in a long-latency spindle feedback. This could contribute to matching the spatiotemporal pattern of the central pattern generator to that of the moving jaw.

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“…Studies in the jaw‐closing muscles, from both spindle afferent and γ‐motor recordings, have been consistently in favour of modulated patterns of firing in γ s neurones (e.g. Taylor & Appenteng, 1981; Taylor et al 1997). Although jaw muscles serve very different functions from hindlimb extensor muscles, it would be surprising if there were to be such a basic difference in the way in which the fusimotor system is used in the two cases.…”

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confidence: 99%

Patterns of fusimotor activity during locomotion in the decerebrate cat deduced from recordings from hindlimb muscle spindles

Taylor

Durbaba

Ellaway

et al. 2000

The Journal of Physiology

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The part played by muscle spindles in the control of natural movements must depend on how the static and dynamic gamma (ãs and ãd) fusimotor systems are activated. However, their patterns of activity have been difficult to elucidate, because technical problems severely limit the possibilities for directly recording from ã_motoneurones. The alternative approach of deducing ã-patterns from spindle afferent records has been used in a variety of reduced preparations Journal of Physiology (2000), 522.3, pp. 515-532 515 Patterns of fusimotor activity during locomotion in the decerebrate cat deduced from recordings from hindlimb muscle spindles 1. Recordings have been made from multiple single muscle spindle afferents from medial gastrocnemius (MG) and tibialis anterior (TA) muscles of one hindlimb in decerebrate cats, together with ankle rotation and EMG signals, during treadmill locomotion. Whilst the other three limbs walked freely, the experimental limb was denervated except for the nerves to MG and TA and secured so that it could rotate only at the ankle joint, without any external load. Each afferent was characterised by succinylcholine testing with regard to its intrafusal fibre contacts. Active movements were recorded and then replayed through a servo mechanism to reproduce the muscle length changes passively after using a barbiturate to suppress ã-motor firing. 2. The difference in secondary afferent firing obtained by subtracting the discharge during passive movements from that during active movements was taken to represent the profile of static fusimotor activity. This indicated an increase before the onset of movement followed by a strongly modulated discharge in parallel with muscle shortening during locomotion. The pattern of static firing matched the pattern of unloaded muscle shortening very closely in the case of TA and with some phase advance in the case of MG. The same effects were observed in primary afferents. 3. Primary afferents with bagÔ (b1) contacts in addition showed higher firing frequencies during muscle lengthening in active than in passive movements. This indicated increased dynamic fusimotor firing during active locomotion. There was no evidence as to whether this fluctuated during the movement cycles. 4. When the mean active minus passive difference profile of firing in bagµ-chain (bµc) type primary afferents was subtracted from that for b1bµc afferents, the difference was dominated by a peak centred on the moment of maximum lengthening velocity (v). 5. The component of the active minus passive difference firing due to b1 fibre contacts could be modelled by f(t) = av (where a is a constant) during lengthening and by f(t) = 0·2av during shortening. The remainder of the difference signal matched the predictions of the static fusimotor signal derived from secondary afferents. 6. The findings are discussed in relation to the concept that the modulated static fusimotor pattern may represent a 'temporal template' of the expected movement, though the relationship of the results to locomot...

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

Cited by 14 publications

References 38 publications

Static and dynamic γ‐motor output to ankle flexor muscles during locomotion in the decerebrate cat

Static and dynamic γ‐motor output to ankle flexor muscles during locomotion in the decerebrate cat

Behavior of Jaw Muscle Spindle Afferents During Cortically Induced Rhythmic Jaw Movements in the Anesthetized Rabbit

Patterns of fusimotor activity during locomotion in the decerebrate cat deduced from recordings from hindlimb muscle spindles

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