Elastic Fibres and Reticulin of Mammalian Muscle Spindles and Their Functional Significance

Cooper, Sybil; Gladden, M. H.

doi:10.1113/expphysiol.1974.sp002280

Cited by 31 publications

(17 citation statements)

References 23 publications

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“…No such additional contraction was observed, however, and the additional stretch was confined to the region of the sensory endings. It is concluded, therefore, that this additional stretch was the result of mechanical coupling between the intrafusal fibres at the spindle equator, due to connective tissue or elastic elements (Cooper & Gladden, 1974). Such coupling in the sensory region is not uncommon even though the nuclear bag and nuclear chain fibres slide easily past each other elsewhere in the spindle fluid space.…”

Section: Motor Control Of Isolated Spindlesmentioning

confidence: 98%

Motor control of nuclear bag and nuclear chain intrafusal fibres in isolated living muscle spindles from the cat.

Boyd¹

1975

The Journal of Physiology

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SUMMARY1. The behaviour of nuclear bag and nuclear chain intrafusal fibres in isolated cat muscle spindles was studied by direct observation during repetitive stimulation of the muscle nerve at different stimulus strengths. Contraction of intrafusal fibres and stretch of sensory endings was recorded on film.2. Tenuissimus spindles are usually operated by a total of four or five fusimotor axons, and the individual action of all of them was studied in many cases.3. The great majority of fusimotor axons produce activity at one spindle pole only.4. In about 60 % of spindles nuclear bag and nuclear chain intrafusal fibres are selectively controlled by different fusimotor axons, while in one third of these spindles the individual nuclear bag fibres are themselves controlled independently. The remaining 40 % of spindles, in addition to some selective innervation, receive one non-selective axon which operates both nuclear chain and nuclear bag fibres though usually only one of the nuclear bag fibres is involved. Selective control is demonstrated in photographs.5. The thresholds of fusimotor axons selectively innervating nuclear bag and nuclear chain fibres, and of non-selective fusimotor axons are not significantly different.6. It is suggested that in spindles in which the nuclear bag fibres are controlled by the same axon, it is a 'dynamic' y, or occasionally /J, axon.Where one nuclear bag fibre is operated along with the nuclear chain fibres it is controlled by 'static' y axon(s), and the other nuclear bag fibre is selectively controlled by 'dynamic' y, and perhaps fi, axon(s). Where two nuclear bag fibres are separately operated one may be controlled by I. A. BOYD AND J. WARD 'dynamic' axon(s) and the other by 'static' y axon(s). Nuclear chain fibres are always controlled by 'static' y axons.

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Section: Motor Control Of Isolated Spindlesmentioning

confidence: 98%

Motor control of nuclear bag and nuclear chain intrafusal fibres in isolated living muscle spindles from the cat.

Boyd¹

1975

The Journal of Physiology

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“…In the case of the static nuclear bag fibre it seems likely that the extension of its primary sensory spiral is limited by the elastic and collagen tissue which braces the nuclear bag region (Cooper & Gladden, 1974). If so, then the extension of the spiral produced by the passive stretch will decrease progressively as the frequency of static y stimulation is increased.…”

Section: Glycogen Depletion In Intrafusal Fibresmentioning

confidence: 99%

Control of dynamic and static nuclear bag fibres and nuclear chain fibres by gamma and beta axons in isolated cat muscle spindels.

Boyd¹,

Gladden²,

McWilliam³

et al. 1977

The Journal of Physiology

189

132

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SUMMARY1. The behaviour of nuclear bag and nuclear chain intrafusal fibres in isolated cat muscle spindles with a blood supply, during stimulation of dynamic y axons, dynamic f axons, or static y axons in ventral root filaments was observed and recorded on still and moving film.2. Most spindles were controlled by one dynamic y axon (sometimes a f axon) and three static y axons, one of which was often non-selective in distribution. A large majority of fusimotor axons controlled one pole of the spindle only.3. Dynamic y and ft axons produced focal contraction in only one of the two nuclear bag fibres in any spindle and this fibre was never activated by static y axons. Maximal tetanic contraction was attained slowly and the primary sensory spiral on this fibre was stretched by a small amount only. This fibre has been named the 'dynamic nuclear bag fibre'.4. Static y axons produced either: (a) focal contraction in the second of the two nuclear bag fibres only; (b) local contraction in the bundle of nuclear chain fibres only; or (c) contraction in one nuclear bag fibre and the nuclear chain fibres together. Maximum tetanic contraction of this nuclear bag fibre stretched its primary sensory spiral considerably and the time to plateau was relatively short. This fibre has been named the 'static nuclear bag fibre'.5. 'Driving' of the Ia afferent discharge could always be produced by non-selective static y axons, frequently by static y axons controlling nuclear chain fibres alone, and was probably due to mechanical oscillation in nuclear chain fibres. It was never produced by dynamic y axons and on one occasion only by a static y axon controlling a nuclear bag fibre alone.6. The conduction velocities of dynamic y and static y axons overlapped extensively, though dynamic y axons were absent from the lower end, and I. A. BOYD AND OTHERS static y axons innervating nuclear chain fibres only were absent from the upper end, of the range of velocities.7. The observations are correlated with spindle structure and histochemistry. Dynamic and static nuclear bag fibres are shown to correspond with 'bag1 fibres' and 'bag2 fibres', respectively (Ovalle & Smith, 1972).8. The possible origin of the dynamic and static actions of fusimotor axons and the role of the dynamic and static intrafusal systems in motor control are discussed.

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“…Bessou and Pages [1975], also, observed that there was no mechanical interaction at all between individual nuclear bag fibres or between nuclear bag fibres and the bundle of nuclear chain fibres in the same spindle pole. There is always some mechanical linkage between the fibres in the equatorial region, however, which may be due either to connective tissue elements [Cooper and Gladden, 1974], or to the sensory terminations themselves. This mechanical coupling is most evident when one pole of a nuclear bag fibre or bundle of nuclear chain fibres pulls the entire primary sensory ending towards the active pole.…”

Section: Effect Of Intrafusal Activity On the Sensory Endingsmentioning

confidence: 99%

The Response of Fast and Slow Nuclear Bag Fibres and Nuclear Chain Fibres in Isolated Cat Muscle Spindles to Fusimotor Stimulation, and the Effect of Intrafusal Contraction on the Sensory Endings

Boyd

1976

Exp Physiol

111

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CONTENTS2. Mammalian intrafusal muscle fibres are of three functional types. Most spindles contain one slow nuclear bag fibre, one fast nuclear bag fibre, and four or five nuclear chain fibres. 3. Contraction in slow nuclear bag fibres is characterized by a long latency and very slow initial velocity, whereas the latency for the other intrafusal fibres is short and the initial velocity rapid. The mean time for maximum contraction (at 75 Hz to 100 Hz) and relaxation is significantly longer for slow nuclear bag fibres (0-8 s) than for other intrafusal fibres (0 5 s). The contraction time of fast nuclear bag fibres is sometimes longer than that of nuclear chain fibres but the mean values are not significantly different; a difference in the time to attain 90% contraction is more obvious. 4. At low stimulation frequencies (10 Hz) contraction in slow nuclear bag fibres and in most fast nuclear bag fibres is smooth whereas nuclear chain fibres exhibit marked oscillations. Single stimuli elicit small local twitches in nuclear chain fibres and occasionally in fast nuclear bag fibres but produce no visible effect in slow nuclear bag fibres. 5. Maximum contraction of slow and fast nuclear bag fibres at body temperature is attained at a stimulation frequency of 75 Hz to 100 Hz, whereas a frequency of 150 Hz or more is required for maximum contraction of nuclear chain fibres. At 50 Hz at body temperature contraction in nuclear bag fibres is at least half the maximum, whereas in many spindles nuclear chain fibres show only a very small contraction at this frequency. 6. Contraction in slow nuclear bag fibres occurs at one or two discrete foci, most of which lie in the intracapsular region beyond the end of the fiuid space. Weak contraction extends the primary sensory spiral by a small amount (2 %-8 %) at a low velocity (5 %-10% s-1). When the fibre is passively stretched the spiral opens and then creeps back to about 75 % of the extension at the end of the stretch due to yielding in the poles of the fibre; creep is complete in 0-5 s to 2-5 s. 7. Contraction in fast nuclear bag fibres also occurs at one or two discrete foci, most of which lie in the intracapsular region beyond the end of the fluid space. Shortening of sarcomeres at the foci and extension of the sensory spiral are, however, up to eight times greater (up to 25 %) than in slow nuclear bag fibres, and the velocity of stretch of the spiral is three to eight times greater (25 %-40 % s-1). Fast nuclear bag fibres exhibit little or no creep following passive stretch. 8. Contraction in the nuclear chain fibre bundle is localized to the intracapsular region, centred on a point in the intracapsular region between 0 9 mm and 1-6 mm from the spindle equator. Maximal contraction stretches primary and secondary sensory endings by 15 % to 20%, at 30% to 40 % s-l. Nuclear chain fibres follow length changes of the spindle faithfully and rarely exhibit creep following passive stretch. 9. The resting sarcomere length of nuclear bag fibres is significantly greater in the contractin...

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Elastic Fibres and Reticulin of Mammalian Muscle Spindles and Their Functional Significance

Cited by 31 publications

References 23 publications

Motor control of nuclear bag and nuclear chain intrafusal fibres in isolated living muscle spindles from the cat.

Motor control of nuclear bag and nuclear chain intrafusal fibres in isolated living muscle spindles from the cat.

Control of dynamic and static nuclear bag fibres and nuclear chain fibres by gamma and beta axons in isolated cat muscle spindels.

The Response of Fast and Slow Nuclear Bag Fibres and Nuclear Chain Fibres in Isolated Cat Muscle Spindles to Fusimotor Stimulation, and the Effect of Intrafusal Contraction on the Sensory Endings

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