Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “MUSCLES”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 361 records · Page 20Linked to original sources
PubMed2003

[Histochemical study of the sensory endings of muscle spindles in rat longissimus muscles].

Most studies concerning the structure and function of muscle spindles have utilized the hind limbs of experimental animals. However, little is known about muscle spindles of the back muscles. The purpose of this study was to investigate the sensory innervation of muscle spindles of the paravertebral muscle in the rat. The subjects were 10 normal male rats. The longissimus muscles were isolated and frozen in cooled isopentane (-160 degrees C), and serial transverse sections were made with a cryostat. Histochemical preparations were then made using nicotinamide adenine dinucleotide tetrazolium reductase (NADH-TR) stain and modified Gomori-trichrome stain. The muscle spindles in each segment were identified microscopically by observing the equatorial and polar regions. NADH-TR staining was employed to distinguish nuclear bag1, nuclear bag2, and nuclear chain intrafusal muscle fibers. A total of 20 spindle poles were surveyed. The mean polar length of intrafusal fibers as well as that of each region (A, B, and C) were measured. NADH-TR staining also demonstrated the terminal sites of sensory fibers along intrafusal fibers. All spindle poles surveyed were innervated by secondary sensory fibers in addition to primary sensory fibers. Eight spindle poles were intermediate type muscle spindles that were innervated by one primary sensory fiber and one secondary sensory fiber. Twelve spindle poles were complex type muscle spindles that were innervated by one primary sensory fiber and multiple secondary sensory fibers. The mean length of the A region was 223.1+/-37.9 microm (n=8) for intermediate type spindles and 493.8+/-157.0 microm (n=12) for complex type spindles. The length of the A region was significantly longer in the complex type spindles than in the intermediate type spindles (p<0.001). The results suggest that the innervations of secondary sensory fibers were well developed in the longissimus muscle spindles in the rat. The morphological features of muscle spindles of the longissimus muscle may represent the structural basis for qualitatively different afferent discharges that relate to the characteristic types of locomotion served by paravertebral muscles.

Animals↗
PubMed1983

Formation of neuromuscular junctions in transplanted peroneus longus muscles in the rat. A quantitative comparison with reinnervation of the muscle in situ.

The formation of neuromuscular junctions in free heterotopic muscle transplants in the rat has been studied quantitatively and compared with the reinnervation of the muscle in situ. The AChE-containing area and the nerve terminal were stained in the same longitudinal section and the length of end-plate, the average number of nerve terminal branch points within the end-plate and the terminal innervation ratio (TIR) were determined. In denervated muscles we noticed early disappearance of nerves whereas the AChE-stained end-plates were visible after eight weeks. The reinnervation of the muscle in situ and after transplantation showed considerable similarities. Early during reinnervation the number of AChE positive areas increased and many of them were innervated by more than one axon. Terminal axons were also seen innervating more than one end-plate situated on the same or on different muscle fibres. Later the number of end-plates decreased and they were innervated by only one axon. The end-plate length reached normal value in the reinnervated muscle in situ but remained smaller in the transplanted muscle. In all reinnervated muscles ultraterminal sprouting was found as indicated by an increased number of nerve terminal branch points within the end-plate area. The TIR was increased in all reinnervated muscles due to terminal and ultraterminal sprouting of the axon. No significant difference in reinnervation was noted between normal and predenervated transplants. The reinnervation of transplanted muscles obviously has similarities not only with the reinnervation of normal muscles but also with the development of muscular innervation during early postnatal growth. In spite of the plasticity of the peripheral nerve the transplanted muscles underwent considerable atrophy which may have been enhanced by the unphysiological placement of the muscles in the abdomen. However, this experimental model made it possible to study reinnervation of muscle fibres only originating from the graft.

Animals↗
PubMed2000

Muscle fiber types of human extraocular muscles: a histochemical and immunohistochemical study.

PURPOSE: To classify muscle fibers of human extraocular muscle (hEOM) and to compare them to previous studies on hEOM, as well as to nonhuman EOM classification schemes and skeletal muscle fiber types. METHODS: Muscle fibers cut in different muscle planes were followed on consecutive cross sections and typed with regard to their oxidative profile in combination with their myosin-immunohistochemical characteristics. RESULTS: Three zones were observed. In the global layer three muscle fiber types were observed: global layer singly innervated granular fibers, 79.4 +/- 8.1 microm (perimeter [values at midmuscle region] +/- SD); 59%; global layer singly innervated coarse fibers (80.3 +/- 10.8 microm; 21%); and global layer multiply innervated muscle fibers (4.1 +/- 9.7 microm; 21%). Two muscle fiber types were detected in the orbital layer: orbital layer singly innervated muscle fibers (54.1 +/- 8.5 microm; 83%) and orbital layer multiply innervated muscle fibers (53.5 +/- 7.6 microm; 17%). Three muscle fiber types were differed in the marginal zone: marginal zone singly innervated muscle fibers (83.1 +/- 15.8 microm; 56%), marginal zone multiply innervated low oxidative muscle fibers (84.4 +/- 23.3 microm; 7%), and marginal zone multiply innervated high oxidative muscle fibers (88.4 +/- 14.5 microm; 37%). Coexpressions of developmental myosin heavy chain isoforms and fast myosin heavy chain isoform were detected mainly in the marginal zone. CONCLUSIONS: hEOMs resemble mammalian EOM with regard to their organization. However, in addition to an inner global layer and an orbital layer an external marginal zone was described for the first time in hEOM in the present study.

Aged↗
PubMed1976

[Muscle spindles in denervated and reinnervated m. soleus of the rat. I. Changes in number, distribution and length of muscle spindles].

After a transient or permanent unilateral denervation of the soleus muscle of the rat the number, distribution and length of muscle spindles were determined. The results were compared with those of the contralateral innervated muscle and with the data received from investigating soleus muscles of normal uninjured rats. Denervation (with or without reinnervation) reduces the number of muscle spindles by nearly 50%. The typical uniform distribution of muscle spindles in the muscle remains almost unchanged. The remaining muscle spindles grow longer. The same findings are observed in the contralateral still innervated muscles, too. Consequently a comparison of the denervated (reinnervated) muscle exclusively with its contralateral muscle does not show different counts of muscle spindles. Therefore in such investigations the contralateral muscle is of dubious value as a mean of control. As regards number, distribution and length of muscle spindles there exist only small differences between the various strains of rats.

Animals↗
PubMed1980

[Tension and shortening velocity of slow muscle fibers of cat extraocular muscle (author's transl)].

Tension and shortening of the extraocular muscles were investigated with the aim to evaluate the contribution of the contraction of the slow muscle fibers to that of the whole muscle. The muscle was stimulated either massively (massive stimulation) or at one end (point stimulation). When the muscle was stimulated at one end, the slow muscle fiber would not develop the tension. Let the tension developed by the massive stimulation be M and that by the point stimulation be P, then (M-P)/M, slow fiber ratio, would indicate the degree of contribution of slow muscle fiber to the whole muscle. The slow fiber ratio in tetanus was, 8.1-23% for the inferior oblique muscle, 24-30% for the lateral rectus muscle and less than 5% for the retractor bulbi muscle. The shortening velocity under a small load was independent of the mode of stimulation. The evidence indicates that the resting slow muscle fibers do not act as the resistance against the shortening of the twitch muscle fibers. When the inferior oblique or lateral rectus muscle was stimulated for long time, the tension showed two peaks. The interval between them was 6-10sec and the amplitudes were nearly comparable.

Action Potentials↗
PubMed1998

Measurement of impaired muscle function of the gastrocnemius, soleus, and tibialis anterior muscles in spastic hemiplegia: a preliminary study.

Based on the results of several electrodiagnostic and biomechanical studies, the following classification of muscle dysfunction in spastic hemiplegia is proposed: changes in muscle activation (excess symptoms, e.g., spasticity, and deficit symptoms, e.g., paresis); changes in muscle stiffness; and changes in muscle length. The clinical significance of this classification is that different types of muscle dysfunction might require specific treatment. The authors have developed techniques to measure quantitatively each type of muscle dysfunction: free frequency repetitive movement (FFRM) and torque angle diagram (TAD). Surface EMGs of tibialis anterior, gastrocnemius, and soleus muscle are recorded during active (FFRM) and passive (TAD) ankle movements. EMG data are converted to parameters for abnormal muscle activation (excess and deficit symptoms). Parameters for muscle stiffness and muscle length are derived from the hysteresis curve of the TAD. This article describes the measurements and the results of a validation study. For the validation study, four hypotheses were formulated: 1) in nonimpaired control subjects, parameters expressing abnormal muscle activation are low; 2) in hemiplegic subjects, differences between the affected and the unaffected sides will be found for all types of parameters; 3) after local anaesthesia of the tibial nerve on the hemiplegic side, excess symptoms will decrease, while muscle stiffness remains unchanged; and 4) despite a uniform gait pattern, between-subject differences can be detected with regard to muscle activation, stiffness, and length. The first hypothesis was tested and confirmed in two controls; the remaining three were tested and confirmed in ten hemiplegic subjects (mean age 47.7 yrs, mean time since onset 10.7 yrs). However, the level of co-contraction of the gastrocnemius muscle was low, probably indicating that the clinical significance of this phenomenon might be limited. The results support the validity of the proposed classification and measurements.

Adult↗
PubMed2000

Neuromuscular specializations of the pharyngeal dilator muscles: II. Compartmentalization of the canine genioglossus muscle.

The genioglossus (GG) muscle is divided into horizontal and oblique compartments that are the main protrusor and depressor muscles of the tongue, respectively. In humans the GG plays an important role in speech articulation, swallowing, and inspiratory dilation of the pharynx. At present, little is known about the neuromuscular specializations of the GG in any mammal. This study examined the specializations of these compartments in the canine tongue using a variety of anatomical and histochemical techniques. Six canine GG muscles were sectioned and stained for myofibrillar ATPase to study muscle fiber types; five whole-mount GG muscles were stained for acetylcholinesterase (AChE) to study the distribution of motor endplates; and eight whole mount GG muscles were processed with Sihler's stain to study the entire nerve supply pattern. In addition, the arrangement of muscle fibers of the GG within the tongue was also determined (N = 3). The most notable difference between the compartments of the GG was their proportions of fast and slow twitch muscle fibers: the horizontal compartment contained 64% slow twitch muscle fibers compared to 41% in the oblique compartment. In addition, although the oblique compartment appeared to be grossly homogeneous, it could be divided into thirds by significant differences in the percentages of slow twitch fibers: posterior (23%), middle (15%), and anterior (56%; P < 0.05). The muscle fibers of the oblique GG within the tongue were found to be divided into medial and lateral layers that run vertically and transversely, respectively. The nerve supply to each third of the oblique GG formed a plexus with the anterior third being the densest. The innervation pattern of the oblique GG was also notable as terminal nerve branches coursing parallel to the muscle fascicles gave off perpendicular secondary branches along each motor endplate band. These secondary nerve branches connected the primary nerves and formed a regularly spaced grid throughout the compartment. Evidently, the two compartments of the GG exhibited different anatomical specializations. The horizontal had a slow muscle fiber profile and simple innervation pattern; these qualities are possibly related to its single force vector and respiratory related activity. The oblique compartment had a relatively fast muscle fiber profile with evidence for three separate functional subdivisions. The most anterior part was noticeably different, and was presumably specialized for fine motor control of the tip of the tongue. The vertically oriented fibers of the oblique GG within the tongue body may function as a midline depressor of the tongue, whereas its transversely oriented fibers could play a role in narrowing the tongue during other motor tasks.

Acetylcholinesterase↗
PubMed2000

Examination of intrafascicular muscle fiber terminations: implications for tension delivery in series-fibered muscles.

Mammalian skeletal muscles with long fascicle lengths are predominantly composed of short muscle fibers that terminate midbelly with no direct connection to the muscle origin or insertion. The manner in which these short fibers terminate and transmit tension through the muscle to their tendons is poorly understood. We made an extensive morphological study of a series-fibered muscle, the guinea pig sternomastoid, in order to define the full range of structural specializations for tension transmission from short fibers within this muscle. Terminations were examined in single fibers, teased small bundles of fibers, and in sections at both the light and electron microscopic level. In many cases, sites of fiber termination were defined by reactivity for the enzyme acetylcholinesterase, which also marks myotendinous junctions. Additionally, transport of the lipophilic fluorescent dye, DiI, or injection of Lucifer Yellow were used to visualize undisturbed fiber terminations in whole muscles using confocal and fluorescence microscopy. At the light microscopic level, we find that intrafascicularly terminating fibers end about equally often in either a long progressive taper, or in a series of small or larger blunt steps. Combinations of these two morphologies are also seen. However, when analyzed at higher resolution with confocal or electron microscopy, the apparently smooth progressive tapers appear also to be predominantly composed of a series of fine stepped terminations. Stepwise terminations in most cases join face-to-face with complementary endings of neighboring muscle fibers, some via an extended collagenous bridge and others at close interdigitating myomyonal junctions. These muscle-to-muscle junctions show many of the features of myotendinous junctions, including dense subsarcolemmal plaques in regions of myofibrillar termination and we suggest that they serve to pass tension from fiber to fiber along the longitudinal axis of the muscle. In addition, we observe regions of apparent side-to-side adhesion between neighboring fibers at sites where there is no apparent fiber tapering or structural specialization typical of myofibril termination. These sites show acetylcholinesterase reactivity, and large numbers of collagen fibers passing laterally from fiber to fiber. These latter connections seem most likely to be involved in lateral transmission of tension, either from fiber to fiber, or from fiber to endomysium. Overall, our results suggest that tension from intrafascicularly terminating fibers is likely to be passed along the muscle to the tendon using both in-series and in-parallel arrangements. The results are discussed in light of current theories of tension delivery within the series-fibered muscles typical of large, nonprimate mammals.

Acetylcholinesterase↗
PubMed2005

Responses of muscle spindles in feline dorsal neck muscles to electrical stimulation of the cervical sympathetic nerve.

Previous studies performed in jaw muscles of rabbits and rats have demonstrated that sympathetic outflow may affect the activity of muscle spindle afferents (MSAs). The resulting impairment of MSA information has been suggested to be involved in the genesis and spread of chronic muscle pain. The present study was designed to investigate sympathetic influences on muscle spindles in feline trapezius and splenius muscles (TrSp), as these muscles are commonly affected by chronic pain in humans. Experiments were carried out in cats anesthetized with alpha-chloralose. The effect of electrical stimulation (10 Hz for 90 s or 3 Hz for 5 min) of the peripheral stump of the cervical sympathetic nerve (CSN) was investigated on the discharge of TrSp MSAs (units classified as Ia-like and II-like) and on their responses to sinusoidal stretching of these muscles. In some of the experiments, the local microcirculation of the muscles was monitored by laser Doppler flowmetry. In total, 46 MSAs were recorded. Stimulation of the CSN at 10 Hz powerfully depressed the mean discharge rate of the majority of the tested MSAs (73%) and also affected the sensitivity of MSAs to sinusoidal changes of muscle length, which were evaluated in terms of amplitude and phase of the sinusoidal fitting of unitary activity. The amplitude was significantly reduced in Ia-like units and variably affected in II-like units, while in general the phase was affected little and not changed significantly in either group. The discharge of a smaller percentage of tested units was also modulated by 3-Hz CSN stimulation. Blockade of the neuromuscular junctions by pancuronium did not induce any changes in MSA responses to CSN stimulation, showing that these responses were not secondary to changes in extrafusal or fusimotor activity. Further data showed that the sympathetically induced modulation of MSA discharge was not secondary to the concomitant reduction of muscle blood flow induced by the stimulation. Hence, changes in sympathetic outflow can modulate the afferent signals from muscle spindles through an action exerted directly on the spindles, independent of changes in blood flow. It is suggested that such an action may be one of the mechanisms mediating the onset of chronic muscle pain in these muscles in humans.

Adrenergic alpha-Antagonists↗
PubMed2005

Controlled intermittent shortening contractions of a muscle-tendon complex: muscle fibre damage and effects on force transmission from a single head of rat EDL.

This study was performed to examine effects of prolonged (3 h) intermittent shortening (amplitude 2 mm) contractions (muscles were excited maximally) of head III of rat extensor digitorum longus muscle (EDL III) on indices of muscle damage and on force transmission within the intact anterior crural compartment. Three hours after the EDL III exercise, muscle fibre damage, as assessed by immunohistochemical staining of structural proteins (i.e. dystrophin, desmin, titin, laminin-2), was found in EDL, tibialis anterior (TA) and extensor hallucis longus (EHL) muscles. The damaged muscle fibres were not uniformly distributed throughout the muscle cross-sections, but were located predominantly near the interface of TA and EDL muscles as well as near intra- and extramuscular neurovascular tracts. In addition, changes were observed in desmin, muscle ankyrin repeat protein 1, and muscle LIM protein gene expression: significantly (P<0.01) higher (1.3, 45.5 and 2.3-fold, respectively) transcript levels compared to the contralateral muscles. Post-EDL III exercise, length-distal force characteristics of EDL III were altered significantly (P<0.05): at high EDL III lengths, active forces decreased and the length range between active slack length and optimum length increased. For all EDL III lengths tested, proximal passive and active force of EDL decreased. The slope of the EDL III length-TA+EHL force curve decreased, which indicates a decrease of the degree of intermuscular interaction between EDL III and TA+EHL. It is concluded that prolonged intermittent shortening contractions of a single head of multi-tendoned EDL muscle results in structural damage to muscle fibres as well as altered force transmission within the compartment. A possible role of myofascial force transmission is discussed.

Animals↗
PubMed1997

Expression of myosin heavy chain isoforms in regenerated muscle spindle fibres after muscle grafting in young and adult rats--plasticity of intrafusal satellite cells.

Satellite cells are the myogenic precursor cells of postnatal skeletal muscles. After muscle injury they can proliferate, differentiate, fuse and form myofibres. We have analysed regeneration of distinctly different types of intrafusal fibres in rat muscle spindles. We have introduced the new technique of heterochronous allotransplantation and compared it with the previously used standard autografting method. The allotransplantation method enables one to graft muscles from very young animals; we have used the extensor digitorum longus (EDL) muscles from 2- to 28-day-old rats, which were grafted into EDL muscles of adult inbred recipients. The regenerated "intrafusal" fibres did not express the spindle-specific slow tonic and alpha cardiac-like myosin heavy chain (MyHC) isoforms and they did not exhibit the dual mATPase reaction typical of the nuclear bag2 fibres and the characteristic regional differences in MyHC expression and in the mATPase reaction of nuclear bag1 and nuclear bag2 fibres. On the other hand, they expressed either fast twitch or slow twitch/beta cardiac MyHC isoforms and exhibited an alkali or acid stable mATPase reaction along their whole length, like extrafusal fast type 2 and slow type 1 muscle fibres, respectively. In all regenerated muscle spindles only motor, but no sensory axons were found. More than 85% of muscle spindles in our sample contained regenerated spindle fibres of the same extrafusal fibre type (either type 2 or type 1), in contrast to control muscle spindles, which always contained intrafusal fibres of three different intrafusal fibre types (nuclear bag1, nuclear bag2 and nuclear chain fibres). There were no differences in MyHC expression and mATPase activity between spindle fibres regenerated in grafts taken from young rats of various ages or between allotransplanted and autotransplanted EDL muscles. The present results demonstrate that regenerated "intrafusal" fibres resemble, according to MyHC expression, extrafusal fast or slow muscle fibres. It can thus be concluded that intrafusal satellite cells derived from distinctly different nuclear bag1, nuclear bag2 and nuclear chain fibres show great plasticity, as their MyHC expression can be respecified towards the extrafusal muscle fibre phenotype by foreign alpha-motor innervation.

Animals↗
PubMed2001

Comparative histochemical composition of muscle fibres in a pre- and a postvertebral muscle of the cervical spine.

References to histochemistry are extensive for human limb muscles but occur less frequently in relation to vertebral muscle. Most vertebral muscle literature has been concerned with muscle fibre characteristics in the lumbar and thoracic spine, due in large part to the incidence of low back pain and idiopathic scoliosis. However few studies have investigated the histochemical composition of neck muscles in humans: and, to our knowledge, no previous study has examined the antagonistic longus colli and multifidus muscle pair. In addition, while age-related segmental degeneration is most prominent between C5 and C7, it is not known whether these osteoligamentous changes are paralleled by changes in muscle fibre ratio. Tissue blocks comprising muscle and bone from C5-C7 segments were harvested at autopsy from 16 subjects with ages ranging from 4 to 77 years. The prevertebral longus colli and postvertebral multifidus muscle pairs were randomly selected from one or other side in each subject. The tissue was frozen, sectioned and histochemically stained for myofibrillar adenosine triphosphatase. Analysis of muscle fibre types was performed by light microscopy. Wilcoxon paired t-tests were used to ascertain whether intramuscular and intermuscular differences in fibre composition were significant. In addition, correlation and regression analyses were used to determine whether fibre type proportions changed in either muscle with increasing age. The present study has revealed histochemical differences between longus colli and multifidus at the level of the C5-C7 vertebral segments. Multifidus comprises a significantly greater proportion of type I than type II fibres. Longus colli comprises a significantly greater proportion of type II fibres than multifidus. Further there were no changes in fibre type proportion in either muscle with increasing age. These observations suggest that longus colli responds equally to postural and phasic demands, whereas multifidus is predominantly postural. Also it would appear that age-related structural alterations in lower cervical segments are not paralleled by changes in muscle fibre ratio.

Adenosine Triphosphatases↗
PubMed2002

Testosterone-induced increase in muscle size in healthy young men is associated with muscle fiber hypertrophy.

Administration of replacement doses of testosterone to healthy hypogonadal men and supraphysiological doses to eugonadal men increases muscle size. To determine whether testosterone-induced increase in muscle size is due to muscle fiber hypertrophy, 61 healthy men, 18-35 yr of age, received monthly injections of a long-acting gonadotropin-releasing hormone (GnRH) agonist to suppress endogenous testosterone secretion and weekly injections of 25, 50, 125, 300, or 600 mg testosterone enanthate (TE) for 20 wk. Thigh muscle volume was measured by magnetic resonance imaging (MRI) scan, and muscle biopsies were obtained from vastus lateralis muscle in 39 men before and after 20 wk of combined treatment with GnRH agonist and testosterone. Administration of GnRH agonist plus TE resulted in mean nadir testosterone concentrations of 234, 289, 695, 1,344, and 2,435 ng/dl at the 25-, 50-, 125-, 300-, and 600-mg doses, respectively. Graded doses of testosterone administration were associated with testosterone dose and concentration-dependent increase in muscle volume measured by MRI (changes in vastus lateralis volume, -4, +7, +15, +32, and +48 ml at 25-, 50-, 125-, 300-, and 600-mg doses, respectively). Changes in cross-sectional areas of both type I and II fibers were dependent on testosterone dose and significantly correlated with total (r = 0.35, and 0.44, P < 0.0001 for type I and II fibers, respectively) and free (r = 0.34 and 0.35, P < 0.005) testosterone concentrations during treatment. The men receiving 300 and 600 mg of TE weekly experienced significant increases from baseline in areas of type I (baseline vs. 20 wk, 3,176 +/- 186 vs. 4,201 +/- 252 microm(2), P < 0.05 at 300-mg dose, and 3,347 +/- 253 vs. 4,984 +/- 374 microm(2), P = 0.006 at 600-mg dose) muscle fibers; the men in the 600-mg group also had significant increments in cross-sectional area of type II (4,060 +/- 401 vs. 5,526 +/- 544 microm(2), P = 0.03) fibers. The relative proportions of type I and type II fibers did not change significantly after treatment in any group. The myonuclear number per fiber increased significantly in men receiving the 300- and 600-mg doses of TE and was significantly correlated with testosterone concentration and muscle fiber cross-sectional area. In conclusion, the increases in muscle volume in healthy eugonadal men treated with graded doses of testosterone are associated with concentration-dependent increases in cross-sectional areas of both type I and type II muscle fibers and myonuclear number. We conclude that the testosterone induced increase in muscle volume is due to muscle fiber hypertrophy.

Adolescent↗
PubMed1998

Potential targets for skeletal muscle impairment by hypogravity: basic characterization of resting ionic conductances and mechanical threshold of rat fast- and slow-twitch muscle fibers.

Prolonged hypogravity such as during space flights affects skeletal muscle function by inducing postural changes as well as reduced muscle strength and locomotion capacity. Also in rats, space flight as well as useful models of groundbased hypogravity induce marked atrophy in the slow-twitch soleus (SOL) muscle as opposed to slight or none in the fast-twitch ones such as extensor digitorum longus (EDL). Biochemical and histological studies on hindlimb suspended animals, showed a hypogravity-induced impairment of muscle function involving the transition of slow-twitch muscle type, responsible for postural control, toward the fast-twitch phenotype by modification of excitation-contraction pattern. In slow muscles of rats, hindlimb suspension induced upregulation of the fast isoform of myosin heavy-chain and increased expression of fast Ca2+ pump mRNA and protein, which is consistent with the increased Ca(2+)-dependent ATPase activity and the speeding of muscle relaxation, typical of fast muscles. Little is known about the modifications induced by hypogravity in the sarcolemmal ion channels function, which controls the pattern of muscle excitability and contractility. The normally high resting chloride conductance, which is required for the electrical stabilization of mammalian muscle fibers, may be a target of hypogravity modifications since a pharmacological block of this parameter determines, though an increase of excitability, the transition of the fast-twitch muscle phenotype toward the slow one either in adult or in developing rats. Hypogravity also induced increased expression of dihydropyridine receptors in soleus muscle, that are normally lower than that found in the fast ones. In this study, we characterized the electrical and contractile properties of rat extensor digitorum longus (EDL) and slow-twitch soleus SOL muscles fibers at the aim to better understand the molecular mechanisms leading to fiber transition.

Animals↗
PubMed2004

Human jaw muscle strength and size in relation to limb muscle strength and size.

The aim of the present study was to investigate to what extent general factors (e.g. genotype, hormones) and factors at the craniofacial level (e.g. craniofacial size, jaw muscle architecture) contribute to the size and strength of the jaw muscles. A strong relationship of jaw muscle size and strength with that of other muscles would argue for general influences, whereas a weak relationship would argue for craniofacial influences. In 121 adult individuals, moments of maximal bite force, arm flexion force and leg extension force were measured. In addition, thicknesses of jaw muscles, arm flexor muscles and leg extensor muscles were measured using ultrasound. Relationships were assessed by using a principal component analysis. In females, one component was found in which all force moments were represented. Bite force moment, however, loaded very low. In males, two components were found. One component loaded for arm flexion and leg extension moments, the other loaded for bite force moments. In both females and males, only one component was found for the muscle thicknesses in which all muscle groups loaded similarly. It was concluded that the size of the jaw muscles was significantly related to the size of the limb muscles, suggesting that they were both subject to the same general influences. Maximal voluntary bite force moments were not significantly related to the moments of the arm flexion and leg extension forces, suggesting that besides the general influence on the muscle size, variation in bite force moment was also influenced by local variables, such as craniofacial morphology.

Adolescent↗
PubMed1983

Electromyography of the opercularis muscle of Rana catesbeiana: an amphibian tonic muscle.

The opercularis muscle of Rana catesbeiana originates on the suprascapular cartilage of the shoulder girdle and inserts on the otic opercular element. It is part of the levator scapulae musculature and lies dorsomedial to the levator scapulae superior and inferior muscles. Bipolar electrode recordings from all three muscles show electrical activity linked to cyclical firing of the posterior intermandibularis muscle, an important ventilatory muscle. The opercularis muscle shows low amplitude, erratic signals when animals are submerged. Upon emergence of the snout region, the opercularis muscle shows rhythmic low amplitude activity at twice the rate of buccal pumping. Lung ventilation is synchronized with this rhythm and at ventilation the opercularis muscle shows higher amplitude activity. Upon submergence, opercularis activity again shows low level activity with no rhythmic pattern. Opercularis muscle activity has a major low frequency component (about 30 Hz) that probably corresponds to activity of tonic muscle fibers. Higher frequency signals (about 200-250 Hz) comparable to those of the levator scapulae muscles are also present and probably represent activity of phasic muscle fibers. Activity of the opercularis muscle is correlated with conditions in which aerial respiration is possible, and this pattern of activity supports an opercularis role in aerial hearing and/or detection of substrate vibrations. As far as we know, this is the first report of electromyographic analysis of a vertebrate tonic muscle.

Animals↗
PubMed1985

Morphogenesis of the human gluteus maximus muscle arising from two muscle primordia.

In human embryos and fetuses a supernumerary muscle was found situated on the distal margin of the gluteus maximus muscle and supplied by the most distal main branch of the inferior gluteus nerve. According to its origin and insertion it is being named the coccygeofemoralis muscle. In embryos and fetuses of up to 40 mm in CR length the coccygeofemoralis muscle is separated by loose connective tissue from neighbouring fetal muscles. Later on, close contact between the coccygeofemoralis and the distal margin of the fetal gluteus maximus muscle develops, and during the prenatal period both fetal muscles gradually fuse. Postnatally, the coccygeofemoralis muscle is incorporated into the gluteus maximus muscle of which the pars sacroiliaca corresponds to the fetal gluteus maximus itself and the pars coccygea represents the fetal coccygeofemoralis muscle. With respect to the general process of muscle morphogenesis, the developmental pattern described for the gluteus maximus muscle demonstrates that adult muscles may be formed by a fusion of several fetal muscles.

Buttocks↗
PubMed1997

Apparent contralateral inferior oblique muscle overaction after unilateral inferior oblique muscle weakening procedures.

BACKGROUND: Unilateral inferior oblique muscle weakening surgical procedures often lead to the appearance of inferior oblique muscle overaction in the contralateral eye. The purpose of this study was to determine how different types of unilateral inferior oblique muscle procedures affect the apparent function of the inferior oblique muscle in the contralateral eye. METHODS: A computer search was performed to locate all patients on the pediatric ophthalmology service at the Wilmer Ophthalmological Institute who underwent a unilateral inferior oblique muscle weakening procedure from 1980 to 1994. Only patients with a diagnosis of primary inferior oblique muscle overaction were included in the study. RESULTS: Fourteen patients met the inclusion criteria. One patient had undergone an anterior transposition of the inferior oblique muscle, seven patients had undergone a 10 mm recession of the inferior oblique muscle, and six patients had undergone a myectomy of the inferior oblique muscle. Before the operation,there was no difference in the inferior oblique muscle function of the contralateral eye among the three groups. However, after the operation apparent inferior oblique muscle overaction developed more frequently and to a greater degree in the contralateral eye among patients in the anterior transposition and 10 mm recession groups than among patients in the myectomy group. CONCLUSION: Either anterior transposition or 10 mm recession of the inferior oblique muscle may limit elevation in abduction in the eye on which inferior oblique muscle surgery was performed. The limitation of elevation in abduction may create apparent inferior oblique muscle overaction in the contralateral eye.

Adult↗