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At least 19 recordsLinked to original sources
PubMed1976

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.

1. The mechanical behaviour of intrafusal muscle fibres during fusimotor stimulation and passive stretch was observed directly in muscle spindles isolated from the cat tenuissimus muscle. 2. 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 inital velocity rapid. The mean time for maximum contraction (at 75 Hz to 100 Hz) and relaxation is significantly longer for slow nuclear bag fibres (0-8s) 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 fluid 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 fibre; creep is complete in 0-5s to 2-5s. 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, centered 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-1...

Animals↗
PubMed1992

Effects of cigarette smoke on the clearance of short asbestos fibres from the lung and a comparison with the clearance of long asbestos fibres.

Long asbestos fibres are generally considered to have greater disease-producing potential than short asbestos fibres. However, recent reports have suggested that short fibre asbestos appears to be as effective an inducer of macrophage growth factors and toxic oxygen species as long fibre asbestos, but that short fibres are readily removed from lung and do not gain access to tissues. Because smoke is believed to impair the clearance of asbestos fibres from lung, we examined the clearance of a short (geometric mean length 1.3 microns) amosite preparation administered by intratracheal instillation to guinea-pigs. Half the animals in each group were exposed to the smoke of 10 cigarettes daily. Animals were sacrificed 1 day, 1 week, or 1 month later, the macrophages recovered by lavage, and fibre concentrations and sizes determined by analytical electron microscopy in macrophages and lung tissue. A 30-fold increase was seen in total numbers of fibres retained in macrophages in smokers compared to non-smokers by 1 month, and there was an eightfold increase in retention of short fibres in the lung tissue by 1 month. By contrast, a long fibre amosite preparation (geometric mean length 8.9 microns) showed approximately the same increase in fibre retention in macrophages, but only a twofold increase in tissue retention. We conclude that (1) cigarette smoke markedly impairs the clearance of short amosite fibres from the lung with enhanced retention of fibres in both macrophages and tissue; (2) the effects of smoke on short fibre tissue retention appear to be greater than those on long fibre retention; (3) with the long fibre preparation, smoke causes increased tissue retention of relatively shorter fibres; (4) for both fibre size experiments, the increase in total fibres in macrophages in smoke-exposed animals reflects an increase in the total number of fibre-containing macrophages, rather than an increase in the number of fibres phagocytized per macrophage; (5) enhanced short fibre retention markedly increases total fibre surface area, a parameter which has been suggested as a measure of fibre toxicity, to the point where short fibres might under some circumstances have roughly the same potential toxicity as long fibres. These observations suggest that short asbestos fibres could play an important role in the pathogenesis of some types of asbestos-related disease in cigarette smokers.

Animals↗
PubMed1977

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

1. The behaviour of nuclear bag and nuclear chain intrafusal fibres in isolated cat muscle spindles with a blood supply, during stimulation of dynamic gamma axons, dynamic beta axons, or static gamma axons in ventral root filaments was observed and recorded on still and moving film. 2. Most spindles were controlled by one dynamic gamma axon (sometimes a beta axon) and three static gamma 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 gamma and beta axons produced focal contraction in only one of the two nuclear bag fibres in any spindle and this fibre was never activated by static gamma 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 gamma 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 gamma axons, frequently by static gamma axons controlling nuclear chain fibres alone, and was probably due to mechanical oscillation in nuclear chain fibres. It was never produced by dynamic gamma axons and on one occasion only by a static gamma axon controlling a nuclear bag fibre alone. 6. The conduction velocities of dynamic gamma and static gamma axons overlapped extensively, though dynamic gamma axons were absent from the lower end, and static gamma 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.

Action Potentials↗
PubMed1992

Variability of muscle fibre composition and fibre size in the horse gluteus medius: an enzyme-histochemical and morphometric study.

To determine the variability in fibre types and fibre sizes in the equine gluteus medius muscle, biopsy specimens were removed from 5 sites, at 4 different depths, within the right and left muscles of 3 Andalusian stallions. The percentage, lesser fibre diameter and cross-sectional area of the various fibre types were measured systematically in myosin ATPase and NADH-tetrazolium reductase-stained, serial cryostat sections of these multiple samples. Significant differences in muscle fibre type composition were recorded, with a lower percentage of type I fibres (high myosin ATPase activity at pH 4.5) being observed towards superficial regions of the muscle and a greater percentage towards the deep areas. Type II B fibres (moderate myosin ATPase activity at pH 4.5), including both II B nonoxidative (low NADH-TR activity) and II B oxidative (moderate NADH-TR activity), displayed the opposite tendency, and the percentage of type II A fibres (low myosin ATPase activity at pH 4.5) did not change with depth. Types I and II A fibres in the deep regions were larger than superficially, whereas the II B fibres in the deep regions were smaller than in the superficial parts of the muscle. The results also imply that type I fibres tend to be larger than type II fibres in the deep regions. The size of type I fibres is more homogeneous in the deep parts than in the superficial regions of the muscle, while II B fibres vary more in size in the peripheral portions than in deep regions. A single biopsy taken from the gluteus medius muscle of the horse is therefore a poor representative of the whole muscle and care should be exercised in sampling and interpreting data obtained from limited biopsy of this muscle. The pattern of variation in fibre types and fibre sizes between the different depths of the muscle probably reflect different functional demands on the gluteus medius muscle.

Animals↗
PubMed1978

Significance of fibre length in the clearance of asbestos fibres from the lung.

Rats were exposed by inhalation to radioactive anthophyllite asbestos. Animals were then killed serially over a period of 205 days and the fibre content of the lungs measured radiometrically. The lungs were subjected to selective bronchopulmonary lavage and the mean fibre content determined of free cells recovered from the alveolar spaces. The length distributions of fibres recovered from the lungs by lavage, and of those remaining in the lungs following lavage, were measured. Short (less than 5 micrometer) fibres are cleared from the lung via the conducting airways more efficiently than longer fibres and fibres exceeding 50 micrometer in length are not removed from the lungs by this route. Although fibres of about 200 micrometer in length were present in all the lungs examined, the longest which could be recovered by lavage, once fibre deposited in the airways had been cleared, was only about 100 micrometer decreasing to 60-70 micrometer after 205 days. It is suggested that long fibres are more liable than short to penetrate the alveolar wall as they tend to bridge the alveolar ducts and alveoli.

Animals↗
PubMed1979

Fibre number and fibre size in a surgically overloaded muscle.

Soleus muscles of male and female mice were overloaded by surgical resection of parts of gastrocnemius and plantaris. The effects of overloading were examined histologically after 7, 55 and 208 post-operative days, and also in teased preparations. Animals studied after 7 post-operative days showed a marked increase in muscle weight, but no significant change in mean fibre diameter or fibre number. Animals studied after 55 and 208 post-operative days showed an increase in soleus muscle weight, with fibre hypertrophy (but no increase in fibre number) proximally, while distally there was an increase in the number of fibre profiles in cross sections, some being wider, some thinner than normal. The small diametered fibres seem to persist indefinitely. From the evidence, both direct and indirect, it was concluded that surgically overloaded fibres split longitudinally into unequal parts, and that this explains the increase in fibre profiles in distal cross sections as well as their variation in size. It is clear that, because of the splitting, a surgically overloaded muscle is a difficult model on which to study fibre hypertrophy.

Animals↗
PubMed1976

Different toxic effects of ouabain and 16-epi-gitoxin on Purkinje fibres and ventricular muscle fibres.

Action potentials of isolated Purkinje fibres and ventricular muscle fibres of canine hearts treated with ouabain and 16-epi-gitoxin were recorded by microelectrodes. Under the influence of both glycosides, Purkinje system fibres became inexcitable earlier than ventricular muscle fibres. Being exposed to 0.125 muM ouabain and 2.5 muM 16-epi-gitoxin, both Purkinje and ventricular muscle fibres became poisoned in the same time as ventricular muscle fibres exposed to 0.1 muM ouabain and 1.5 muM 16-epi-gitoxin. At the lower 16-epi-gitoxin concentration Purkinje fibres had 2.5 times the survival time of that exposed to the lower ouabain concentration. Compared to 16-epi-gitoxin the inexcitability of Purkinje fibres after ouabain remained irreversible. The semisynthetic glycoside 16-epi-gitoxin exerts a weaker effect on the specialized conducting system.

Action Potentials↗
PubMed1979

Quantitative studies of the regeneration of rat myelinated nerve fibres: variations in the number and size of regenerating fibres after repeated localized freezings.

The number and size of myelinated nerve fibres were determined in the nerve to the medial head of the gastrocnemius muscles of rats whose left sciatic nerve was repeatedly frozen (one to five times at three weekly intervals). The contralateral nerve was used as a control. Results varied according to the number of freezings performed and, for a given number of freezings, according to the period of regeneration. When measurements were completed 1 month after the last of several localized freezings, the number of regenerating myelinated nerve fibres increased regularly up to the third freezing, reaching to about 220% of the control value, but no higher values were recorded after four or five freezings. The nerve fibre distribution was unimodal in all the nerves studied. The mean diameter of all myelinated fibres decreased with the number of freezings from 50% of the control value after the first to 36% after the fifth. When measurements were made 1, 3, 6, 12 and 18 months after the third and final freezing, the number of regenerating myelinated nerve fibres decreased by about 30% between the first and third month and then stabilized at 190% of the control value. Nerve fibre distribution became bimodal from the third month onwards, and the mean diameter of all myelinated fibres increased regularly. However, by the eighteenth month, the size of regenerated myelinated nerve fibres had only reached 70% of the normal contralateral value.

Animals↗
PubMed1976

Variability of inter-spike intervals of cat's on-center optic tract fibres activated by steady light spot: a comparative study on X- and Y-fibres.

Extracellular recordings were made from single on-center optic tract fibres in cats. Light spots of 10sec duration were focussed on the center of the receptive field under 1cd/m2 adaptation luminance by diffuse light. In the maintained discharges at 1 cd/m2, the shape of inter-spike interval histograms (IH) tended to be more skewed in X-fibres than in Y-fibres. As the luminance of the light spot increased, corresponding with the decrease in irregularity of length of inter-spike intervals, the shape of the IHs from X-fibres became symmetrical without noticeable shift of the modal interval peaks. This change was not clear in Y-fibres. The first order serial correlation coefficients showed small negative values in the case of the maintained discharges. These negative values increased with the decrease of the mean intervals of the discharges induced by the light spots, commonly in X- and Y-fibres. The negative correlation of adjacent inter-spike intervals was associated with a change of the shape of some IHs at lower luminances.

Animals↗
PubMed1992

Torque-velocity relation and muscle fibre characteristics of foot dorsiflexors after long-term overuse of residual muscle fibres due to prior polio or L5 root lesion.

Isokinetic foot dorsiflexion strength and muscle biopsy data from eight patients with overuse of tibialis anterior muscle (TA) fibres due to weakness after prior polio or L5 root lesion were compared to data from age and sex matched, healthy subjects. Concentric peak torque at an angular velocity of 30 degrees/s was 6-24 Nm in the patients and 15-34 Nm in the controls (p < 0.01). Muscle biopsies from TA showed a significantly higher proportion of type 1 fibres in the patients as compared to the controls (p < 0.005). The type 1 fibres in the patients had a significantly larger cross-sectional area than in the controls (p < 0.005). The type 1 fibre proportion and relative area were inversely correlated to the relative concentric torque produced at 180 degrees/s (p < 0.05) and 240 degrees/s (p < 0.05) compared to that produced at 30 degrees/s in the controls but not in the patients. However, the relative concentric torque produced at 180 degrees/s and 240 degrees/s compared to that produced at 30 degrees/s was not significantly different in the patients and the controls. This indicates that the contractile properties of the overused muscle fibres do not change in parallel with the histochemical fibre type.

Aged↗
PubMed1975

Motor unit fibre density in the extensor digitorum communis muscle. Single fibre electromyographic study in normal subjects at different ages.

A single fibre EMG study is presented from extensor digitorum communis muscle in sujbects aged 10 to 89 years. The average number of single muscle fibre action potentials generated by muscle fibres in the same motor unit within the uptake area of the electrode is used as a measure of the motor unit fibre density. The fibre density increases slowly during life with a faster progression after the age 70 years. The number of recordings indicating impaired nerve or neuromuscular impulse transmission increases at the same time. The findings indicate degenerative loss of motor neurones with aging, compensated for by reinnervation. The changes are relatively slight in the extensor digitorum communis muscle as compared with other muscles, permitting early pathological changes in this muscle to be recognized independently of age factors.

Action Potentials↗
PubMed1976

The rabbit optic nerve: fibre diameter spectrum, fibre count, and comparison with a retinal ganglion cell count.

This electron microscopic study indicates that the rabbit optic nerve contains 394,000 +/- 20,000 (p less than 0.05) nerve fibers, of which at least 98% are myelinated. The fibre diameter spectrum of the nerve is unimodal and ranges from 0.25-7 mum with its peak at 0.75 mum. The projection of the visual streak fibres is not apparent in local diameter spectra near the optic nerve head. Integration of a ganglion cell density map of the retina from another rabbit indicates a total ganglion cell count lying between 455,000 and 547,000. The optic nerve fibre and ganglion cell counts are both substantially greater than the maximum fibre count previously reported.

Animals↗
PubMed1979

Metabolic substrates, muscle fibre composition and fibre size in late walking and normal children.

In 10 children with delayed walking, muscle specimens were obtained by needle biopsy from the vastus lateralis muscle for determination of ATP, creatine phosphate (CP), glycogen and lactate concentration, as well as fibre composition and fibre size. The values obtained are compared with corresponding results for a control group of 25 children aged 2 months--11 years. Details of the control series are given and its validity as a reference group is discussed. Six children (group I) who showed minor gross motor delay but otherwise normal development at follow-up were found to have lowered ATP, CP and glycogen concentrations, compared to 4 children (group II) who had general developmental delay, and to the control group. The children in group I were shown to have smaller fibre size and a greater difference between type 1 and 2 fibres than the children in group II and in the control group. No differences in the concentrations of metabolic substrates or the morphometric values could be detected between group II and the control group.

Adenosine Triphosphate↗
PubMed1992

Differentiation of oxytalan fibres from elastic fibres with reagents for detection of magnesium.

Elastic fibres in various human and animal tissues revealed positive results with reagents for the detection of magnesium. By contrast, no Mg could be detected in oxytalan fibres or in zonular fibres of the ciliary body, which are composed of microfibrils not containing elastin. Mg is therefore concluded to be associated with the elastin core of elastic fibres. Its antagonism to calcium is speculated to play a protective role in maintaining the extensibility of elastin.

Animals↗
PubMed1978

Properties of two unmyelinated fibre tracts of the central nervous system: lateral Lissauer tract, and parallel fibres of the cerebellum.

1. Monoplar tungsten micro-electrodes were used to stimulate and platinun plated tungsten micro-electrodes to record from single, unmyelinated cerebellar parallel fibres and lateral Lissauer tract axons in cats. 2. Stimulation of the lateral Lissauer tract resulted in the activation of a narrow, longitudinal 'beam', much as on the cerebellar surface. 3. Following impulse conduction, parallel and Lissauer tract fibres showed a supernormal conduction velocity (up to 25% increase) and increased excitability (up to 40% increase). No subnormality was encountered following supernormality. Some Lissauer tract fibres had prolonged relative refractory periods and no supernormal periods. 4. Chronaxies ranged from 155 to 380 microseconds. 5. Single fibres exhibited a remarkable increase in conduction velocity (up to 18% and excitability (up to 40%) following a single subthreshold stimulus. The duration of this effect (up to 20 msec) was much longer than expected from membrane time constant estimates.

Action Potentials↗
PubMed1978

Dietary fibres, fibre analogues, and glucose tolerance: importance of viscosity.

To define the type of dietary fibre of fibre analogue with the greatest potential use in diabetic treatment, groups of four to six volunteers underwent 50-g glucose tolerance tests (GTT) with and without the addition of either guar, pectin, gum tragacanth, methylcellulose, wheat bran, or cholestyramine equivalent to 12 g fibre. The addition of each substance significantly reduced blood glucose concentration at one or more points during the GTT and generally reduced serum insulin concentrations. The greatest flattening of the glucose response was seen with guar, but this effect was abolished when hydrolysed non-viscous guar was used. The reduction in the mean peak rise in blood glucose concentration for each substance correlated positively with its viscosity (r = 0.926; P less than 0.01), as did delay in mouth-to-caecum transit time (r = 0.885; P less than 0.02). Viscous types of dietary fibre are therefore most likely to be therapeutically useful in modifying postprandial hyperglycaemia.

Adult↗