scholarly journals Neuromuscular organization of avian flight muscle: architecture of single muscle fibres in muscle units of the pectoralis (pars thoracicus) of pigeon (Columba livia)

1999 ◽  
Vol 354 (1385) ◽  
pp. 917-925 ◽  
Author(s):  
A. J. Sokoloff ◽  
G. E. Goslow
Keyword(s):  
Motor Unit ◽  
Cross Sections ◽  
Unit Length ◽  
Muscle Length ◽  
Motor Units ◽  
Columba Livia ◽  
Muscle Fibres ◽  
Cross Sectional ◽  
Total Length ◽  
Fast Twitch

The M. pectoralis (pars thoracicus) of pigeons ( Columba livia ) is comprised of short muscle fibres that do not extend from muscle origin to insertion but overlap ‘in-series’. Individual pectoralis motor units are limited in territory to a portion of muscle length and are comprised of either fast twitch, oxidative and glycolytic fibres (FOG) or fast twitch and glycolytic fibres (FG). FOG fibres make up 88 to 90% of the total muscle population and have a mean diameter one-half of that of the relatively large FG fibres. Here we report on the organization of individual fibres identified in six muscle units depleted of glycogen, three comprised of FOG fibres and three comprised of FG fibres. For each motor unit, fibre counts revealed unequal numbers of depleted fibres in different unit cross-sections. We traced individual fibres in one unit comprised of FOG fibres and a second comprised of FG fibres. Six fibres from a FOG unit (total length 15.45 mm) ranged from 10.11 to 11.82 mm in length and averaged (±s.d.) 10.74±0.79 mm. All originated bluntly (en mass) from a fascicle near the proximal end of the muscle unit and all terminated intramuscularly. Five of these ended in a taper and one ended bluntly. Fibres coursed on average for 70% of the muscle unit length. Six fibres from a FG unit (total length 34.76 mm) ranged from 8.97 to 18.38 mm in length and averaged 15.32 ±3.75 mm. All originated bluntly and terminated intramuscularly; one of these ended in a taper and five ended bluntly. Fibres coursed on average for 44% of the muscle unit length. Because fibres of individual muscle units do not extend the whole muscle unit territory, the effective cross-sectional area changes along the motor unit length. These non-uniformities in the distribution of fibres within a muscle unit emphasize that the functional interactions within and between motor units are complex.

Histology of allometric growth in hindlimb muscles of pigs

1982 ◽  
Vol 98 (3) ◽  
pp. 629-632
Author(s):  
H. J. Swatland
Keyword(s):  
Cross Sections ◽  
Muscle Length ◽  
Biceps Femoris ◽  
Longitudinal Growth ◽  
Muscle Fibres ◽  
Allometric Growth ◽  
Cross Sectional ◽  
Relative Growth ◽  
Limb Bones ◽  
Hindlimb Muscles

SUMMARYHindlimbs of pigs were dissected at 4-week intervals from 9 to 29 weeks after birth. Allometric growth ratios of the gluteal muscles, biceps femoris and semitendinosus were calculated relative to gastrocnemius. Relative growth in weight of the proximal limb muscles was greater than that of the distal muscle, gastrocnemius. The greater relative growth of proximal muscles was not due to greater relative growth of muscle fibre diameters, nor to greater relative growth of muscle cross-sectional areas. In biceps femoris and gluteal muscles, growth in the area of musole cross sections did not keep pace with the radial growth of muscle fibres. The relative longitudinal growth of proximal limb bones exceeded that of distal bones, and the relative longitudinal growth of biceps femoris and semitendinosus exceeded that of any of the limb bones. New sarcomeres were added to muscle length at a faster rate in biceps femoris and semitendinosus than in the peroneus longus located distally in the limb.

scholarly journals Variation in normalized isometric tetanic force of isolated fast-twitch muscle fibres of Rana temporaria.

1997 ◽  
Vol 200 (3) ◽  
pp. 523-529
Author(s):  
H P Buschman ◽  
W J van der Laarse ◽  
G J Stienen ◽  
G Elzinga
Keyword(s):  
Total Variation ◽  
Rana Temporaria ◽  
Unit Length ◽  
Force Production ◽  
Rest Period ◽  
Muscle Fibres ◽  
Sectional Area ◽  
Cross Sectional ◽  
Tetanic Force ◽  
Fast Twitch

The origin of the threefold variation found previously in isometric force normalized to cross-sectional area of single fast-twitch tibialis anterior muscle fibres of the frog Rana temporaria was studied by using (1) a strictly defined stimulus protocol, and (2) influencing the condition of the frog using artificial hibernation. Variation in normalized force was found to be influenced by the length of the rest period between tetani. After a long rest (> 6h), tetanic force production was less than for a tetanus produced after 1 h. The length of the rest period accounted for a factor of 1.24 of the total variation in normalized force. The condition of the frog also influenced normalized force production. Little variation in normalized force was observed between different fibres from the same animal, whereas a significant difference was found between animals. After artificial hibernation, force normalized to cross-sectional area remained unchanged, but force normalized to dry mass per unit length increased; the total variation increased from a factor of 1.37 to a factor of 1.64. Force normalized to muscle protein mass per unit length, however, was not affected by artificial hibernation. We conclude that variation in normalized tetanic force can be partly reduced by standardization of the stimulation protocol and normalization to protein content per unit length.

The motor unit

2016 ◽  
Author(s):  
David Burke ◽  
James Howells
Keyword(s):  
Motor Unit ◽  
Neuromuscular Junctions ◽  
Discharge Rate ◽  
Motor Units ◽  
Motor Unit Action Potential ◽  
Muscle Fibres ◽  
Reflex Gain ◽  
Active Motor ◽  
Motor Unit Action ◽  
Fast Twitch

The motor unit represent the final output of the motor system. Each consists of a motoneuron, its axon, neuromuscular junctions, and muscle fibres innervated by that axon. The discharge of a motor unit can be followed by recording its electromyographic signature, the motor unit action potential. Motoneurons are not passive responders to the excitatory and inhibitory influences on them from descending and segmental sources. Their properties can change, e.g. due to descending monoaminergic pathways, which can alter their responses to other inputs (changing ‘reflex gain’). Contraction strength depends on the number of active motor units, their discharge rate, and whether the innervated muscle fibres are slow-twitch producing low force, but resistant to fatigue, fast-twitch producing more force, but susceptible to fatigue, or intermediate fast-twitch fatigue-resistant. These properties are imposed by the parent motoneurons, and the innervated muscle fibres have different histochemical profiles (oxidative, glycolytic, or oxidative-glycolytic, respectively).

Organization of single motor units in feline sartorius

1994 ◽  
Vol 72 (4) ◽  
pp. 1885-1896 ◽  
Author(s):  
E. Smits ◽  
P. K. Rose ◽  
T. Gordon ◽  
F. J. Richmond
Keyword(s):  
Motor Unit ◽  
Cross Section ◽  
Cross Sections ◽  
Muscle Fibers ◽  
Motor Units ◽  
Single Motor Unit ◽  
Single Motor ◽  
Medial Head ◽  
Single Motor Units ◽  
Fast Twitch

1. We depleted single motor units in feline sartorius muscles of glycogen by stimulating their motoneurons intracellularly. We mapped the intramuscular distribution of depleted fibers by inspecting histological cross-sections throughout the length of sartorius. 2. We selected ten depleted motor units for detailed study and quantitative analysis. Nine motor units were located in the anterior head of sartorius. One was located in a muscle whose distal half appeared to have been damaged some time before the acute experiment. A single motor unit was located in the medial head of sartorius. 3. Five motor units were composed of fast-twitch glycolytic (FG) muscle fibers, two of fast-twitch oxidative glycolytic (FOG) muscle fibers, and three of slow-twitch oxidative (SO) muscle fibers. Estimates of the numbers of depleted fibers in motor units of anterior sartorius indicated that FG motor units were larger (mean 566 fibers) than FOG and SO motor units (SO mean 190, FOG mean 156 fibers). The SO motor unit in the damaged muscle had 550 fibers. One motor unit depleted in the medial head of sartorius had 270 fibers with FG profiles. 4. Muscle fibers belonging to each anterior motor unit were never distributed throughout the whole cross-section of anterior sartorius at any proximodistal level. Furthermore, fibers were distributed nonuniformly along the proximodistal axis of the muscle. In most muscles at least a few depleted fibers were found at all proximodistal levels. However, in one normal muscle and the damaged muscle, depleted fibers were confined to the proximal end. 5. The fibers in the medial motor unit were confined to a strip that did not extend across the whole cross-section of the muscle head. Fibers within this strip were scattered quite evenly from origin to insertion. This medial FG motor unit occupied a smaller territory and contained fewer fibers than anterior motor units of the same histochemical type. 6. These results show that sartorius motor units are not distributed uniformly in the mediolateral plane; those in anterior sartorius were distributed asymmetrically in the proximodistal axis as well. This finding has important functional implications for the way in which we model force development and transmission in sartorius and other long muscles.

Ageing and Human Muscle: Observations From Sweden

1993 ◽  
Vol 18 (1) ◽  
pp. 2-18 ◽  
Author(s):  
Jan Lexell
Keyword(s):  
Physical Activity ◽  
Motor Neurons ◽  
Cross Sections ◽  
Motor Units ◽  
Human Muscle ◽  
Activity Level ◽  
Physiological Adaptation ◽  
Muscle Fibres ◽  
Training Programmes ◽  
Fast Twitch

The purposes of this review are to summarize studies of cross-sections of autopsied whole muscles from previously physically healthy males and to focus on the cause of the ageing atrophy. The ageing atrophy begins around 25 years of age and thereafter accelerates. This is caused mainly by a loss of muscle fibres, and to a lesser extent by a reduction in fibre size, mostly of the proportion of the fibre area in the muscle cross-section occupied by type 2 (fast-twitch) fibres. In muscle from old subjects, there is a significant increase in the number of enclosed fibres, indicating an increased incidence of fibre type grouping, a loss of motor neurons in the spinal cord, and a reduction in the number of functioning motor units. These findings strongly suggest a combination of a progressive denervation process and an altered physical activity level as the two major mechanisms underlying the effects of normal ageing on human muscle. These changes have obvious implications for old individuals and their participation in physical activity and in sports, which must be accommodated in rehabilitation regimes or in training programmes. Key words: ageing, microscopy, muscles, physiological adaptation

Summation of motor unit tensions in the tibialis posterior muscle of the cat under isometric and nonisometric conditions

1991 ◽  
Vol 66 (6) ◽  
pp. 1838-1846 ◽  
Author(s):  
R. K. Powers ◽  
M. D. Binder
Keyword(s):  
Motor Unit ◽  
Muscle Fibers ◽  
Stimulus Frequency ◽  
Muscle Length ◽  
Motor Units ◽  
Force Transducer ◽  
Tibialis Posterior ◽  
Single Motor Units ◽  
Individual Motor ◽  
Stimulation Of

1. The tension produced by the combined stimulation of two to four single motor units of the cat tibialis posterior muscle was compared with the algebraic sum of the tensions produced by each individual motor unit. Comparisons were made under isometric conditions and during imposed changes in muscle length. 2. Under isometric conditions, the tension resulting from combined stimulation of units displayed marked nonlinear summation, as previously reported in other cat hindlimb muscles. On average, the measured tension was approximately 20% greater than the algebraic sum of the individual unit tensions. However, small trapezoidal movements imposed on the muscle during stimulation significantly reduced the degree of nonlinear summation both during and after the movement. This effect was seen with imposed movements as small as 50 microns. 3. The degree of nonlinear summation was not dependent on motor unit size or on stimulus frequency. The effect was also unrelated to tendon compliance because the degree of nonlinear summation of motor unit forces was unaffected by the inclusion of different amounts of the external tendon between the muscle and the force transducer. 4. Our results support previous suggestions that the force measured when individual motor units are stimulated under isometric conditions is reduced by friction between the active muscle fibers and adjacent passive fibers. These frictional effects are likely to originate in the connective tissue matrix connecting adjacent muscle fibers. However, because these effects are virtually eliminated by small movements, linear summation of motor unit tensions should occur at low force levels under nonisometric conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Ensemble discharge from Golgi tendon organs of cat peroneus tertius muscle

1990 ◽  
Vol 64 (3) ◽  
pp. 813-821 ◽  
Author(s):  
G. Horcholle-Bossavit ◽  
L. Jami ◽  
J. Petit ◽  
R. Vejsada ◽  
D. Zytnicki
Keyword(s):  
Motor Unit ◽  
Motor Units ◽  
Good Correspondence ◽  
Golgi Tendon Organs ◽  
Afferent Fibers ◽  
Slow Type ◽  
Tendon Organs ◽  
Fast Twitch ◽  
Force Profiles ◽  
Tendon Organ

1. The responses of individual tendon organs of the cat peroneus tertius muscle to motor-unit contractions were recorded in anesthetized cats during experiments in which all the Ib-afferent fibers from the muscle had been prepared for recording in dorsal root filaments. This was possible because the cat peroneus tertius only contains a relatively small complement of approximately 10 tendon organs. 2. Motor units of different physiological types were tested for their effects on the whole population of tendon organs in the muscle. Effects of unfused tetanic contractions were tested under both isometric and anisometric conditions. Each motor unit activated at least one tendon organ, and each tendon organ was activated by at least one motor unit. Individual slow-type units were found to act on a single or two receptors, whereas a fast-type unit could activate up to six tendon organs. 3. In one experiment, the effects of 8 motor units on 10 tendon organs were examined. One fast-twitch, fatigue resistant (FR)-type unit acted on six tendon organs, of which four were also activated by another FR unit. The contraction of each unit, on its own, elicited a range of individual responses, from weak to strong. The discharge frequencies of individual responses displayed no clear relation with the strength of contraction, nor did they accurately represent the shape of force profiles. But when all the discharges were pooled, a fairly good correspondence appeared between variations of contractile force and variations of averaged discharge frequencies.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in diaphragm motor unit EMG during fatigue

1990 ◽  
Vol 68 (5) ◽  
pp. 1917-1926 ◽  
Author(s):  
G. C. Sieck ◽  
M. Fournier
Keyword(s):  
Motor Unit ◽  
Fatigue Test ◽  
Motor Units ◽  
Evoked Force ◽  
Slow Twitch ◽  
The Right ◽  
Fast Twitch ◽  
Multiple Units ◽  
Motor Unit Emg ◽  
Stimulation Of

Fatigue-related changes in the waveform and root-mean-square (rms) values of evoked motor unit electromyographic (EMG) responses were studied in the right sternocostal region of the cat diaphragm. Motor units were isolated by microdissection and stimulation of C5 ventral root filaments and then classified as fast-twitch fatigable (FF), fast-twitch fatigue intermediate (FInt), fast-twitch fatigue resistant (FR), or slow-twitch (S) based on standard physiological criteria. The evoked EMG responses of S and FR units showed very little change during the fatigue test. The evoked EMG waveform and rms values of FF and FInt units displayed variable changes during the fatigue test. When changes were observed, they typically included a prolongation of the EMG waveform, a decrease in peak amplitude, and a decrease in rms value. The changes in EMG amplitude and rms values were not correlated. In more fatigable units, the decrease in force during the fatigue test generally exceeded the decrease in EMG rms values. Changes in the evoked force and EMG responses of multiple units innervated by C5 or C6 ventral roots were also examined during the fatigue test. The decrease in diaphragm force during the fatigue test closely matched the force decline predicted by the proportionate contribution of different motor unit types. However, the observed reduction in diaphragm EMG rms values during the fatigue test exceeded that predicted based on the aggregate contribution of different motor unit types. It was concluded that changes in EMG do not reflect the extent of diaphragm fatigue.

scholarly journals SLCV–a supervised learning—computer vision combined strategy for automated muscle fibre detection in cross-sectional images

PeerJ ◽  
2019 ◽  
Vol 7 ◽  
pp. e7053
Author(s):  
Anika Rettig ◽  
Tobias Haase ◽  
Alexandr Pletnyov ◽  
Benjamin Kohl ◽  
Wolfgang Ertel ◽  
...  
Keyword(s):  
Computer Vision ◽  
Supervised Learning ◽  
Muscle Fibre ◽  
Cross Sections ◽  
Reconstruction Error ◽  
Muscle Fibres ◽  
Dice Similarity Coefficient ◽  
Cross Sectional ◽  
Staining Methods ◽  
Combined Strategy

Muscle fibre cross-sectional area (CSA) is an important biomedical measure used to determine the structural composition of skeletal muscle, and it is relevant for tackling research questions in many different fields of research. To date, time consuming and tedious manual delineation of muscle fibres is often used to determine the CSA. Few methods are able to automatically detect muscle fibres in muscle fibre cross-sections to quantify CSA due to challenges posed by variation of brightness and noise in the staining images. In this paper, we introduce the supervised learning-computer vision combined pipeline (SLCV), a robust semi-automatic pipeline for muscle fibre detection, which combines supervised learning (SL) with computer vision (CV). SLCV is adaptable to different staining methods and is quickly and intuitively tunable by the user. We are the first to perform an error analysis with respect to cell count and area, based on which we compare SLCV to the best purely CV-based pipeline in order to identify the contribution of SL and CV steps to muscle fibre detection. Our results obtained on 27 fluorescence-stained cross-sectional images of varying staining quality suggest that combining SL and CV performs significantly better than both SL-based and CV-based methods with regards to both the cell separation- and the area reconstruction error. Furthermore, applying SLCV to our test set images yielded fibre detection results of very high quality, with average sensitivity values of 0.93 or higher on different cluster sizes and an average Dice similarity coefficient of 0.9778.

Maximal force as a function of anatomical features of motor units in the cat tibialis anterior

1987 ◽  
Vol 57 (6) ◽  
pp. 1730-1745 ◽  
Author(s):  
S. C. Bodine ◽  
R. R. Roy ◽  
E. Eldred ◽  
V. R. Edgerton
Keyword(s):  
Motor Unit ◽  
Tibialis Anterior ◽  
Periodic Acid ◽  
Muscle Fibers ◽  
Motor Units ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Periodic Acid Schiff ◽  
Cross Sectional ◽  
Single Motor Unit

In 11 tibialis anterior muscles of the cat, a single motor unit was characterized physiologically and subsequently depleted of its glycogen through repetitive stimulation of an isolated ventral root filament. Muscle cross sections were stained for glycogen using a periodic acid-Schiff reaction, and single-fiber optical densities were determined to identify those fibers belonging to the stimulated motor unit. Innervation ratios were determined by counting the total number of muscle fibers in a motor unit in sections taken through several levels of the muscle. The average innervation ratios for the fast, fatigueable (FF) and fast, fatigue-resistant (FR) units were similar. However, the slow units (S) contained 61% fewer fibers than the fast units (FF and FR). Muscle fibers belonging to S and FR units were similar in cross-sectional area, whereas fibers belonging to FF units were significantly larger than fibers belonging to either S or FR units. Additionally, muscle fibers innervated by a single motoneuron varied by two- to eightfold in cross-sectional area. Specific tensions, based on total cross-sectional area determined by summing the areas of all muscle fibers of each unit, showed a modest difference between fast and slow units, the means being 23.5 and 17.2 N X cm-2, respectively. Variations in maximum tension among units could be explained principally by innervation ratio, although fiber cross-sectional area and specific tension did contribute to differences between unit types.

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