scholarly journals Polyneural innervation: mechanical properties of overlapping motor units in a small foot muscle of Xenopus laevis.

1980 ◽  
Vol 306 (1) ◽  
pp. 29-39 ◽  
Author(s):  
R M Ridge ◽  
A M Thomson
Keyword(s):  
Mechanical Properties ◽  
Xenopus Laevis ◽  
Motor Units

Intrafibre distribution of succinate dehydrogenase in cat tibialis anterior motor units

1992 ◽  
Vol 70 (7) ◽  
pp. 970-976 ◽  
Author(s):  
Thomas P. Martin ◽  
V. R. Edgerton
Keyword(s):  
Mechanical Properties ◽  
Enzymatic Activity ◽  
Succinate Dehydrogenase ◽  
Dehydrogenase Activity ◽  
Tibialis Anterior ◽  
Radial Distance ◽  
Motor Units ◽  
Computer Assisted ◽  
Mitochondrial Enzymes ◽  
Succinate Dehydrogenase Activity

Using isolated ventral root filament stimulation and glycogen depletion techniques, 14 motor units from the cat tibialis anterior were studied. Based on their mechanical properties, the units were classified as either slow-fatigue resistant, fast-fatigue resistant, fast-fatigue intermediate, or fast-fatigable. Quantitative histochemical and computer assisted image analysis techniques were used to determine the activity of succinate dehydrogenase in a population of fibres in each unit. In addition, the intrafibre distribution of succinate dehydrogenase activity was measured in those same fibres by calculating the enzymatic activity of circumferential layers every 0.5 μm starting from the fibre edge to its centre. It was established that enzymatic activity and radial distance were linearly related in the fibres. A range in succinate dehydrogenase activity (mean coefficient of variation, 29%) was observed among the fibres of a unit. In contrast, the intrafibre distribution of that activity was rather consistent (mean variation, 4%) across the fibres of a unit. Further, the intrafibre distribution was similar among the fibres of units classified as the same type. However, the intrafibre distribution was disparate among the different unit types. These data suggest that the intrafibre distribution of mitochondrial enzymes may contribute to the mechanical properties of a motor unit. In this regard, a hypothesis is proposed that describes how the absolute activity of a mitochondrial enzyme, and the intrafibre distribution of that activity, may interactively contribute to the fatigue resistance of a unit.Key words: mitochondria, quantitative histochemistry, fatigue.

scholarly journals Properties of motor units in a small foot muscle of Xenopus laevis.

1980 ◽  
Vol 306 (1) ◽  
pp. 17-27 ◽  
Author(s):  
R M Ridge ◽  
A M Thomson
Keyword(s):  
Xenopus Laevis ◽  
Motor Units

scholarly journals Directly probing the mechanical properties of the spindle and its matrix

2010 ◽  
Vol 188 (4) ◽  
pp. 481-489 ◽  
Author(s):  
Jesse C. Gatlin ◽  
Alexandre Matov ◽  
Gaudenz Danuser ◽  
Timothy J. Mitchison ◽  
Edward D. Salmon
Keyword(s):  
Mechanical Properties ◽  
Xenopus Laevis ◽  
Metaphase Plate ◽  
Constant Length ◽  
Spindle Matrix ◽  
Microtubule Motors ◽  
Egg Extracts ◽  
Length Regulation ◽  
Length Determination ◽  
Poleward Flux

Several recent models for spindle length regulation propose an elastic pole to pole spindle matrix that is sufficiently strong to bear or antagonize forces generated by microtubules and microtubule motors. We tested this hypothesis using microneedles to skewer metaphase spindles in Xenopus laevis egg extracts. Microneedle tips inserted into a spindle just outside the metaphase plate resulted in spindle movement along the interpolar axis at a velocity slightly slower than microtubule poleward flux, bringing the nearest pole toward the needle. Spindle velocity decreased near the pole, which often split apart slowly, eventually letting the spindle move completely off the needle. When two needles were inserted on either side of the metaphase plate and rapidly moved apart, there was minimal spindle deformation until they reached the poles. In contrast, needle separation in the equatorial direction rapidly increased spindle width as constant length spindle fibers pulled the poles together. These observations indicate that an isotropic spindle matrix does not make a significant mechanical contribution to metaphase spindle length determination.

Mechanical Properties and Behaviour of Motor Units in the Tibialis Anterior During Voluntary Contractions

1997 ◽  
Vol 22 (6) ◽  
pp. 585-597 ◽  
Author(s):  
Michaël Van Cutsem ◽  
Patrick Feiereisen ◽  
Jacques Duchateau ◽  
Karl Hainaut
Keyword(s):  
Mechanical Properties ◽  
Tibialis Anterior ◽  
Motor Units ◽  
Voluntary Contraction ◽  
Recruitment Threshold ◽  
Time To Peak ◽  
Spike Triggered Averaging ◽  
The Mean ◽  
Voluntary Contractions ◽  
Mean Time

The present work was carried out to analyse the properties and behaviour of Tibialis anterior motor units (MUs) during voluntary contractions in humans. A total of 528 single MU mechanical properties was recorded in 10 subjects by means of the spike-triggered averaging (STA) technique. MU recruitment thresholds and discharge frequencies were recorded during linearly increasing maximal voluntary contraction (MVC). The results indicate a mean (±SD) MU torque of 25.5 ± 21.5 mN•m. and a mean time-to-peak of 45.6 ± 13.6 ms. A comparison of the average MU twitch torque with that of the muscle allowed an estimate of about 300 MUs in the Tibialis anterior. A positive linear relationship was recorded between the MU twitch torque and the recruitment threshold. The mean minimal and maximal discharge frequencies of MUs were 8.4 ± 3.0 Hz and 33.2 ± 14.7 Hz, respectively. The results of the present work indicate that MU behaviour during voluntary contractions is different in the tibialis anterior and in the adductor pollicis. Key words: discharge frequency, recruitment threshold, motor unit count

scholarly journals Effect of ageing on the electrical and mechanical properties of human soleus motor units activated by the H reflex and M wave

2003 ◽  
Vol 548 (2) ◽  
pp. 649-661 ◽  
Author(s):  
G Scaglioni ◽  
M V Narici ◽  
N A Maffiuletti ◽  
M Pensini ◽  
A Martin
Keyword(s):  
Mechanical Properties ◽  
Motor Units ◽  
H Reflex ◽  
M Wave

scholarly journals Intrinsic Properties and Reflex Compensation in Reinnervated Triceps Surae Muscles of the Cat: Effect of Activation Level

2003 ◽  
Vol 90 (3) ◽  
pp. 1537-1546 ◽  
Author(s):  
Clotilde M.J.I. Huyghues-Despointes ◽  
Timothy C. Cope ◽  
T. Richard Nichols
Keyword(s):  
Mechanical Properties ◽  
Stretch Reflex ◽  
Full Range ◽  
Motor Units ◽  
Triceps Surae ◽  
Type I ◽  
Initial Stiffness ◽  
Decerebrate Cat ◽  
Reflex Action ◽  
Triceps Surae Muscles

The manner in which activation levels influence intrinsic muscular properties and contributions of the stretch reflex were studied in homogeneous soleus (SOL) and heterogeneous gastrocnemius (G) muscles in the decerebrate cat. Intrinsic mechanical properties were represented by the initial stiffness of the muscle, measured prior to reflex action, and by the tendency of the muscle to yield during stretch in the absence of the stretch reflex. Stiffness regulation by the stretch reflex was evaluated by measuring the extent to which reflex action reduces yielding and the extent to which stiffness depends on background force. Intrinsic mechanical properties were measured in muscles deprived of effective autogenic reflexes using the method of muscular reinnervation. Reinnervated muscles were recruited to force levels comparable to those achieved during natural locomotion. As force declined during crossed-extension reflexes in reinnervated and intact muscles, initial stiffness declined according to similar convex trajectories. The data did not support the hypothesis that, for a given force level, initial stiffness is greatest in populations of predominantly type I motor units. Incremental stiffness (Δ f/Δ l) of both G and SOL increased in the presence of the stretch reflex. Yielding of SOL (ratio of incremental to initial stiffness) substantially decreased in the presence of the stretch reflex over the full range of forces. In reflexive G, yielding significantly decreased for low to intermediate forces, whereas at higher forces, yielding was similar irrespective of the presence or absence of the stretch reflex. The stretch reflex regulates stiffness in both homogeneous and heterogeneous muscles.

Mechanical properties of muscle spindles in Xenopus laevis

1974 ◽  
Vol 15 (2) ◽  
pp. 91-98 ◽  
Author(s):  
R. S. Smith ◽  
Z. J. Koles
Keyword(s):  
Mechanical Properties ◽  
Xenopus Laevis ◽  
Muscle Spindles
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