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PubMed1998

Influence of muscle morphometry and moment arms on the moment-generating capacity of human neck muscles.

STUDY DESIGN: The function of neck muscles was quantified by incorporating experimentally measured morphometric parameters into a three-dimensional biomechanical model. OBJECTIVE: To analyze how muscle morphometry and moment arms influence moment-generating capacity of human neck muscles in physiologic ranges of motion. SUMMARY OF BACKGROUND DATA: Previous biomechanical analyses of the head-neck system have used simplified representations of the musculoskeletal anatomy. The force- and moment-generating properties of individual neck muscles have not been reported. METHODS: A computer graphics model was developed that incorporates detailed neck muscle morphometric data into a model of cervical musculoskeletal anatomy and intervertebral kinematics. Moment arms and force-generating capacity of neck muscles were calculated for a range of head positions. RESULTS: With the head in the upright neutral position, the muscles with the largest moment arms and moment-generating capacities are sternocleidomastoid in flexion and lateral bending, semispinalis capitis and splenius capitis in extension, and trapezius in axial rotation. The moment arms of certain neck muscles (e.g., rectus capitis posterior major in axial rotation) change considerably in the physiologic range of motion. Most neck muscles maintain at least 80% of their peak force-generating capacity throughout the range of motion; however, the force-generating capacities of muscles with large moment arms and/or short fascicles (e.g., splenius capitis) vary substantially with head posture. CONCLUSION: These results quantify the contributions of individual neck muscles to moment-generating capacity and demonstrate that variations in force-generating capacity and moment arm throughout the range of motion can alter muscle moment-generating capacities.

Biomechanical Phenomena↗
PubMed2004

Continuous muscle stretch prevents disuse muscle atrophy and deterioration of its oxidative capacity in rat tail-suspension models.

OBJECTIVE: The purpose of this study was to evaluate the effect of continuous muscle stretch on disuse-atrophied muscles. DESIGN: Sprague-Dawley rats were used and divided into five groups: control group, hind limb suspended for 3 and 7 days, and hind-limb suspension plus strenuous continuous muscle stretch for 3 and 7 days. In the hind-limb suspension plus strenuous continuous muscle stretch groups, the gastrocnemius-plantaris-soleus muscles were stretched using a plastic plate that immobilized the ankle joint at the maximum dorsal flexed position during the hind-limb suspension period. The intracellular energy metabolism of the working muscle during electric stimulation was evaluated by phosphorus-31 magnetic resonance spectroscopy in vivo. Changes in phosphocreatine, inorganic phosphate, and the intracellular pH were monitored to evaluate intramuscular oxidative capacity. Maximum tension and muscle wet mass were also measured. RESULTS: The oxidative capacity, muscle wet weight, and maximum tension decreased after hind-limb suspension. The muscle oxidative capacity at control levels was maintained during the first 3 days in muscles subjected to continuous strenuous stretch. It was also effective to prevent the decrease in muscle mass and maximum twitch tension during the initial 3 days. However, the effects did not persist. CONCLUSION: Continuous strenuous stretch was effective to prevent disuse muscle atrophy and its functional deterioration; however, its effects did not last long.

Animals↗
PubMed2005

The anatomical relationship between the orbicularis oculi muscle and the levator labii superioris and zygomaticus muscle complexes.

OBJECTIVE: The purpose of this study was to define the anatomical relationship between the orbicularis oculi muscle and the levator labii superioris/zygomaticus major. METHODS: Forty-eight sides of 24 preserved cadaver heads were evaluated. The Frankfort plane, the lateral canthus, and the midpupillary line were marked on each hemiface as landmarks. Four parallel incisions were made perpendicular to the inferior orbital rim and the Frankfort horizontal line. The incisions were midpupillary, lateral canthus, 1 cm lateral to the lateral canthus, and 2 cm lateral to the lateral canthus. Within each incision, measurements were performed that included the depth of the zygomaticus major from the orbicularis oculi (i.e., how superficial is the orbicularis above the zygomaticus complex), the superior to inferior distance between the Frankfort line and the origin of the zygomaticus major, the height of the orbicularis oculi muscle above the levator labii muscle (i.e., how superficial is the orbicularis above the levator in the midpupillary line), and how inferior to the inferior orbital rim is the origin of the levator labii superioris. RESULTS: The orbicularis oculi muscle was on average 0.5 cm superficial to the zygomaticus major muscle group at 2 cm lateral to the lateral canthus. At this site, the female cadaver zygomaticus muscle depth was approximately 2 mm deeper versus the male cadavers (0.60 cm versus 0.41 cm). On average, the origin of the zygomaticus major was identified 1.40 cm and 1.50 cm inferior to the Frankfort horizontal line at 1 cm lateral to and at the lateral canthus, respectively. Of note, there were 14 instances (15 percent) in which the muscle group was found to be 1 cm or less from the Frankfort horizontal line. At 1 cm lateral to the lateral canthus and at the lateral canthus, the zygomaticus muscle was seen to interdigitate with the orbicularis muscle. On average, the orbicularis oculi muscle lies 0.80 cm superficial to the levator labii muscle complex. The superficial border of the malar eminence also lies at or near the Frankfort line. CONCLUSIONS: An exact understanding of the location of specific muscle groups can help prevent poor outcomes, such as the lip droop occasionally seen with Botox injections. The Frankfort line may be a more appropriately used landmark for the safe placement of Botox than the commonly used malar eminence.

Botulinum Toxins, Type A↗
PubMed2005

New insights into beta-adrenoceptors in smooth muscle: distribution of receptor subtypes and molecular mechanisms triggering muscle relaxation.

1. The beta-adrenoceptor is currently classified into beta(1), beta(2) and beta(3) subtypes and all three subtypes are expressed in smooth muscle. Each beta-adrenoceptor subtype exhibits tissue-specific distribution patterns, which may be a determinant controlling the mechanical functions of corresponding smooth muscle. Airway and uterine smooth muscles abundantly express the beta(2)-adrenoceptor, the physiological significance of which is established as a fundamental regulator of the mechanical activities of these muscles. Recent pharmacomechanical and molecular approaches have revealed roles for the beta(3)-adrenoceptor in the gastrointestinal tract and urinary bladder smooth muscle. 2. The beta-adrenoceptor is a G(s)-protein-coupled receptor and its activation elevates smooth muscle cAMP. A substantial role for a cAMP-dependent mechanism(s) is generally believed to be the key trigger for eliciting beta-adrenoceptor-mediated relaxation of smooth muscle. Downstream effectors activated via a cAMP-dependent mechanism(s) include plasma membrane K(+) channels, such as the large-conductance, Ca(2+)-activated K(+) (MaxiK) channel. 3. Beta-Adrenoceptor-mediated relaxant mechanisms also include cAMP-independent signalling pathways. This view is supported by numerous pharmacological and electrophysiological lines of evidence. In airway smooth muscle, direct activation of the MaxiK channel by G(s)alpha is a mechanism by which stimulation of beta(2)-adrenoceptors elicits muscle relaxation independently of the elevation of cAMP. 4. The cAMP-independent mechanism(s) is also substantial in beta(3)-adrenoceptor-mediated relaxation of gastrointestinal tract smooth muscle. However, in the case of the beta(3)-adrenoceptor, a delayed rectified K(+) channel rather than the MaxiK channel seems to mediate, in part, cAMP-independent relaxant mechanisms. 5. In the present article, we review the distribution of beta-adrenoceptor subtypes in smooth muscle tissues and discuss the molecular mechanisms by which each subtype elicits muscle relaxation, focusing on the roles of cAMP and plasma membrane K(+) channels.

Adrenergic Agonists↗
PubMed1973

The muscle spindles in slow and twitch skeletal muscle of the lizard.

1. Responses from stretch receptors, identified as muscle spindles, were recorded in filaments of the nerve supplying a twitch muscle, semimembranosus, and a slow muscle, semitendinosus in the lizard Tiliqua.2. While recording afferent discharges in one filament of the motor nerve, several adjacent filaments were each in turn stimulated repetitively until one was encountered which on stimulation produced a powerful increase in spindle firing. Such an effect of the motor stimulus was interpreted as resulting from intrafusal contraction. Any interference with spindle firing patterns from extrafusal contraction produced by the motor stimulation was removed by differentially blocking the contraction with the drug curare.3. Discharge patterns of spindles in response to a slow stretch of the muscle were compared with the response to the same stretch, but during repetitive stimulation of the motor nerve filament which produced an intrafusal contraction.4. At the initial length, the firing rate of spindles in the twitch muscle was greatly increased by the motor tetanus. There was little further increase in the response during and following stretch of the muscle.5. While the spindles in the slow muscle were only moderately excited by the motor tetanus at the initial length of the muscle, a large increase was recorded during the dynamic component of the stretch. At the new length, the steady-state firing continued at a rate well above that for the initial length.6. The effect of the motor tetanus on the response to stretch of muscle spindles in the slow muscle could be mimicked by adding succinyl choline (5 mug/ml.) to the perfusion solution. Spindles in the twitch muscle did not show a sustained sensitivity to the drug.7. It is suggested that while the different effects of motor stimulation on the responses to stretch of spindles in slow and twitch muscle can be explained by propositions based on the sliding filament theory of contraction, the sustained elevation, at the new length, of firing frequencies of spindles in slow muscle might require an additional explanation.

Action Potentials↗
PubMed2003

Presence of (phospho)creatine in developing and adult skeletal muscle of mice without mitochondrial and cytosolic muscle creatine kinase isoforms.

We assessed the relationship between phosphocreatine (PCr) and creatine (Cr) content and creatine kinase (CK) activity in skeletal muscle of mice. The PCr and total Cr (tCr) concentrations, as well as CK activity, in hindlimb muscles of mice, with or without the cytosolic and mitochondrial isoforms of muscle creatine kinase (wild-type or CK--/-- mice), were determined by in vivo magnetic resonance (MR) spectroscopy and by biochemical means during postnatal growth and adulthood. In wild-type muscle the [tCr], PCr/ATP ratio and CK activity increased rapidly in the first 4-7 weeks. Remarkably, CK--/-- mice showed a similar increase in the PCr/ATP ratio during the first month in the presence of only minor brain-type BB-CK activity. Uptake of Cr in muscle was seemingly unrelated to CK activity as tCr increased in the same way in the muscles of both mouse types. At older ages the PCr/ATP ratio decreased in CK--/-- muscles, in contrast to wild-type where it still slowly increased, whereas [tCr] was similar for muscle of both mouse types. Using a new in vivo MR approach with application of [4-13C]Cr, a lower PCr/tCr ratio was also observed in CK--/-- muscle. From these data it follows that in vivo global ATP levels at rest are similar in the presence or absence of CK. Although Cr could still be converted to PCr in mature CK--/-- muscle, the immediate availability of PCr decreased, and PCr became partly inconvertible at older ages. Apparently, catalysis of the CK reaction by BB-CK, although significant in muscles of newborn mice, gradually declines to very low levels in adulthood. Part or all of this BB-CK may arise from satellite cells fusing with myotubes, a process that is most active during the first months of life. Finally, our observation that the MR and chemical assessment of muscle [tCr] and PCr/tCr ratio were similar for all mice does not support the existence of a significant MR-invisible or immobile pool of Cr, with a role for CK in this phenomenon.

Adenylate Kinase↗
PubMed2006

Mechanism of insulin's anabolic effect on muscle: measurements of muscle protein synthesis and breakdown using aminoacyl-tRNA and other surrogate measures.

Despite being an anabolic hormone in skeletal muscle, insulin's anticatabolic mechanism in humans remains controversial, with contradictory reports showing either stimulation of protein synthesis (PS) or inhibition of protein breakdown (PB) by insulin. Earlier measurements of muscle PS and PB in humans have relied on different surrogate measures of aminoacyl-tRNA and intracellular pools. We report that insulin's effect on muscle protein turnover using aminoacyl-tRNA as the precursor of PS and PB is calculated by mass balance of tracee amino acid (AA). We compared the results calculated from various surrogate measures. To determine the physiological role of insulin on muscle protein metabolism, we infused tracers of leucine and phenylalanine into 18 healthy subjects, and after 3 h, 10 subjects received a 4-h femoral arterial infusion of insulin (0.125 mUxkg(-1)xmin(-1)), while eight subjects continued with saline. Tracer-to-tracee ratios of leucine, phenylalanine, and ketoisocaproate were measured in the arterial and venous plasma, muscle tissue fluid, and AA-tRNA to calculate muscle PB and PS. Insulin infusion, unlike saline, significantly reduced the efflux of leucine and phenylalanine from muscle bed, based on various surrogate measures which agreed with those based on leucyl-tRNA (-28%), indicating a reduction in muscle PB (P < 0.02) without any significant effect on muscle PS. In conclusion, using AA-tRNA as the precursor pool, it is demonstrated that, in healthy humans in the postabsorptive state, insulin does not stimulate muscle protein synthesis and confirmed that insulin achieves muscle protein anabolism by inhibition of muscle protein breakdown.

Adult↗
PubMedDate not supplied

Muscle flexibility as a risk factor for developing muscle injuries in male professional soccer players. A prospective study.

BACKGROUND: Muscular tightness is frequently postulated as an intrinsic risk factor for the development of a muscle injury. However, very little prospective data exist to prove this. HYPOTHESIS: Increased muscle tightness identifies a soccer player at risk for a subsequent musculoskeletal lesion. STUDY DESIGN: Prospective cohort study. METHODS: We examined 146 male professional soccer players before the 1999-2000 Belgian soccer competition. None of the players had a history of muscle injury in the lower extremities in the previous 2 years. The flexibility of the hamstring, quadriceps, adductor, and calf muscles of these players was measured goniometrically before the start of the season. All of the examined players were monitored throughout the season to register subsequent injuries. RESULTS: Players with a hamstring (N = 31) or quadriceps (N = 13) muscle injury were found to have significantly lower flexibility in these muscles before their injury compared with the uninjured group. No significant differences in muscle flexibility were found between players who sustained an adductor muscle injury (N = 13) or a calf muscle injury (N = 10) and the uninjured group. CONCLUSIONS: These results indicate that soccer players with an increased tightness of the hamstring or quadriceps muscles have a statistically higher risk for a subsequent musculoskeletal lesion. CLINICAL SIGNIFICANCE: Preseason hamstring and quadriceps muscle flexibility testing can identify male soccer players at risk of developing hamstring and quadriceps muscle injuries.

Athletic Injuries↗
PubMed1996

Mechanical power and work of cat soleus, gastrocnemius and plantaris muscles during locomotion: possible functional significance of muscle design and force patterns.

Electrical activity, forces, power and work of the soleus (SO), the gastrocnemius (GA) and the plantaris (PL) muscles were measured during locomotion in the cat in order to study the functional role of these ankle extensor muscles. Forces and electrical activity (EMG) of the three muscles were measured using home-made force transducers and bipolar, indwelling wire electrodes, respectively, for walking and trotting at speeds of 0.4 to 1.8 m s-1 on a motor-driven treadmill. Video records and a geometrical model of the cat hindlimb were used for calculating the rates of change in lengths of the SO, GA and PL muscles. The instantaneous maximum possible force that can be produced by a muscle at a given fibre length and the rate of change in fibre length (termed contractile abilities) were estimated for each muscle throughout the step cycle. Fibre lengths of the SO, GA and PL were calculated using a planar, geometrical muscle model, measured muscle forces and kinematics, and morphological measurements from the animal after it had been killed. Mechanical power and work of SO, GA and PL were calculated for 144 step cycles. The contribution of the positive work done by the ankle extensor muscles of one hindlimb to the increase of the total mechanical energy of the body (estimated from values in the literature) increased from 4-11% at speeds of locomotion of 0.4 and 0.8 m s-1 to 7-16% at speeds of 1.2 m s-1 and above. The relative contributions of the negative and positive work to the total negative and positive work done by the three ankle extensor muscles increased for GA, decreased for SO and remained about the same for PL, with increasing speeds of locomotion. At speeds of 0.4-0.8 m s-1, the positive work normalized to muscle mass was 7.5-11.0 J kg-1, 1.9-3.0 J kg-1 and 5.3-8.4 J kg-1 for SO, GA and PL, respectively. At speeds of 1.2-1.8 m s-1, the corresponding values were 9.8-16.7 J kg-1, 6.0-10.7 J kg-1 and 13.4-25.0 J kg-1. Peak forces of GA and PL increased and peak forces of SO did not change substantially with increasing speeds of locomotion. The time of decrease of force and the time of decrease of power after peak values had been achieved were much shorter for SO than the corresponding times for GA and PL at fast speeds of locomotion. The faster decrease in the force and power of SO compared with GA and PL was caused by the fast decrease of the contractile abilities and the activation of SO. The results of this study suggest that the ankle extensor muscles play a significant role in the generation of mechanical energy for locomotion.

Animals↗
PubMed1982

Relationship between muscle force and muscle area showing glycogen loss during locomotion.

This experiment was designed to study the relationship between the cross-sectional area of rat skeletal muscle showing glycogen loss and the muscle forces exerted during exercise. Muscular force exerted by the extensors of the elbows and ankle was increased by 24% by loading rats with 24% of their body mass while running them on a treadmill at 30 m.min-1. VO2 increased by 24% and stride frequency was unchanged when the rats ran with loads. Cross-sectional areas of the elbow and ankle extensor muscles showing glycogen loss were compared from rats running with and without the load. We found a nearly direct proportionality between the changes in force and the changes in muscle area showing glycogen loss, i.e. when the force of the extensors was increased by 24%, the cross-sectional area of the elbow extensors showing glycogen loss increased by 28%, and that of the ankle extensor group increased by 24%. The more peripheral muscles in each group accounted for a greater proportion of the increase in cross-sectional area of the group showing glycogen loss (i.e. lateral and long heads of triceps brachii muscle accounted for 91% of the increase in the elbow extensor group, and gastrocnemius muscle accounted for 84% of the increase in the ankle extensor group). Most of the increases in muscle area showing glycogen loss occurred in fast-twitch-glycolytic fibres (84% in the elbow and 88% in the ankle). The data suggest that increasing muscle force requirements by 24% by loading resulted in proportional increases in cross-sectional area of muscles recruited to produce the force, i.e. that spatial recruitment primarily accounted for the elevation in force. The relatively greater increases in cross-sectional area showing glycogen loss of peripheral muscles within a group indicate the importance of studying whole groups of muscles when considering muscular recruitment patterns during exercise.

Animals↗
PubMed2005

Muscle fiber and motor unit behavior in the longest human skeletal muscle.

The sartorius muscle is the longest muscle in the human body. It is strap-like, up to 600 mm in length, and contains five to seven neurovascular compartments, each with a neuromuscular endplate zone. Some of its fibers terminate intrafascicularly, whereas others may run the full length of the muscle. To assess the location and timing of activation within motor units of this long muscle, we recorded electromyographic potentials from multiple intramuscular electrodes along sartorius muscle during steady voluntary contraction and analyzed their activity with spike-triggered averaging from a needle electrode inserted near the proximal end of the muscle. Approximately 30% of sartorius motor units included muscle fibers that ran the full length of the muscle, conducting action potentials at 3.9 +/- 0.1 m/s. Most motor units were innervated within a single muscle endplate zone that was not necessarily near the midpoint of the fiber. As a consequence, action potentials reached the distal end of a unit as late as 100 ms after initiation at an endplate zone. Thus, contractile activity is not synchronized along the length of single sartorius fibers. We postulate that lateral transmission of force from fiber to endomysium and a wide distribution of motor unit endplates along the muscle are critical for the efficient transmission of force from sarcomere to tendon and for the prevention of muscle injury caused by overextension of inactive regions of muscle fibers.

Adult↗
PubMed1995

Effects of preslaughter muscle exercise on muscle metabolism and meat quality studied in anesthetized pigs of different halothane genotypes.

The influence of preslaughter muscle activity was studied on porcine muscle metabolism and meat quality, whereas other stress factors were minimized. Muscle exercise was stimulated by electrical pulses in anesthetized pigs of different halothane genotypes (NN, Nn, nn). A part of the LM and SM was stimulated during the last 15 min of a 45-min period of anesthesia. The contralateral part of each muscle was taken as a non-stimulated control. Antemortem blood and muscle biopsy samples were taken to study the muscle energy metabolism by measuring different metabolites. The same metabolites and certain meat quality characteristics were determined after slaughter. Stimulated muscle exercise led to lower (P < .01) antemortem glycogen and creatine phosphate concentrations and increased (P < .01) lactate and creatine values in pigs of all halothane genotypes. No difference was seen between the three halothane genotypes in the measured glycogen breakdown just before slaughter. Postmortem glycolysis differed between pigs of different halothane genotypes. This resulted in lower (P < .05) glycogen and creatine phosphate values and higher (P < .05) lactate and creatine concentrations for nn pigs than for NN pigs, with intermediate metabolite concentrations for Nn pigs. Water-holding capacity was lower (P < .05) in exercised muscles of NN and Nn pigs than in the muscles of controls. Meat color was only lighter (P < .05) after muscle stimulation in NN pigs. The exercise did not deteriorate the already light color and lower water-holding capacity in nn pigs. Muscle pH can already be low at slaughter and is not only the result of an increased postmortem glycolysis. Preslaughter muscle exercise is relatively more important in determining meat quality from NN and Nn pigs.

Animals↗
PubMed2000

Influence of muscle temperature on the contractile properties of the quadriceps muscle in humans with spinal cord injury.

Low muscle temperature in paralysed muscles of individuals with spinal cord injury may affect the contractile properties of these muscles. The present study was therefore undertaken to assess the effects of increased muscle temperature on the isometric contractile properties of electrically stimulated paralysed quadriceps muscles. When muscle temperature at a depth of 3 cm was increased from approximately 32 degrees C to approximately 36 degrees C by ultra-short-wave application, the half-relaxation time shortened and low-frequency force responses became less fused, but the maximal rate of increase in force remained unchanged. Heating had no effect upon either force decline or slowing of relaxation during fatiguing contractions. The force-frequency relationship of the paralysed quadriceps muscle was shifted to the right after the muscle was heated. Despite this shift, however, the relationship still resembled that in muscles of non-paralysed individuals, probably due to the unexplained high twitch forces. These results indicate that reduced muscle temperature in spinal-cord-injured individuals may lead to an underestimation of the changes in contractile properties in terms of relaxation rate or the degree of fusion with low-frequency stimulation. In addition, the force-frequency relationship of paralysed muscles does not accurately reflect the magnitude of these changes, even when the muscle is heated, and should therefore be treated with caution.

Adult↗
PubMed2001

Quantitative study of muscle spindles in suboccipital muscles of human foetuses.

The proprioceptive inputs from the cervical musculature play an important role in head-eye co-ordination and postural processes. Deep cervical muscles in humans are shown to have high spindle content. The density, distribution and morphology of muscle spindles were studied in superior oblique capitis, inferior oblique capitis and rectus capitis posterior major and minor three small suboccipital muscles. The muscles were obtained, post-mortem from stillborn human foetus. The spindle density was calculated as the ratio of mean spindle content to the mean wet weight of that muscle in grams. The distribution and arrangement of spindles within the muscle and their arrangement was studied. The spindle density of superior oblique muscle was found to be 190, that of inferior oblique was 242 and the rectus capitis posterior contained 98 spindles per gram of muscle. No tendon organs were seen. The serial transverse sections of inferior oblique muscle revealed muscle spindles of varying sizes, length varying between 100-650 microns and, diameter 50-250 microns. A complex parallel arrangements of group of large spindles were seen in the belly of the inferior oblique muscle, while the polar regions contain few small isolated spindles. The relevance of such high spindle receptor content in these tiny muscles is discussed.

Fetus↗
PubMed2006

[Changes in muscle satellite cells in denervated and innervated muscles].

OBJECTIVE: To explore the rule of changes in the myoblast stem cells (satellite cells) in the denervated and innervated muscles and to find out the cellular mechanism of the changes in the muscle morphology and function. METHODS: The denervated muscle-atrophy models were established from 27 Wistar rats aged 1 month. One to six months after operation, examinations of the histology, histochemistry, and morphology were performed on the specimens from the bilateral triceps muscle of the calves of 3 rats in each month. Meanwhile, examination of the cell biology was performed on the specimens from the bilateral triceps muscle of the calves of 1 rat 1, 2 and 3 weeks after operation, and monthly for 1-6 months after operation. The innervation models were established from 35 Wistar rats aged 1 month. Immediately after the denervation, and monthly for 1-6 months after operation, 5 denervated rats underwent the nerve implantation. The changes in the electrophysiological index were observed dynamically until 8 weeks after the nerve implantation. RESULTS: After the denervation, the muscle wet weight and the muscle cell area decreased rapidly, but the content of the collagen fibers increased gradually. The number of the nucleus in the period of proliferation was the greatest 3-4 months after the denervation, and then decreased rapidly. The muscle satellite cells began to increase obviously 3 weeks after the denervation, but 2 months later they decreased rapidly and 4 months later the number of the cells was the smallest. Four to five weeks after innervation, the muscle action potential could be induced, and the best innervation effect could be achieved in the implanted nerve after the 2-3 months on denervation, and at this time the differentiation ability of the satellite cells was the strongest. CONCLUSION: Four months after the denervation of the skeletal muscle, an extremely small number of the satellite cells can make the muscle enter the irreversible atrophy. However, when the innervation is performed 2-3 months after the denervation, the actively-growing satellite cells can promote a better functional recovery of the atrophic muscle.

Animals↗
PubMed1991

Regulation of putative muscle-derived neurotrophic factors by muscle activity and innervation: in vivo and in vitro studies.

The normal embryonic development of spinal cord motoneurons (MNs) involves the proliferation of precursor cells followed by the degeneration of approximately 50% of postmitotic MNs during the period when nerve-muscle connections are being established. The death of MNs in vivo can be ameliorated by activity blockade and by treatment with muscle extracts. Muscle activity and innervation have been suggested to regulate the availability of putative muscle-derived neurotrophic agent(s), and MNs are thought to compete for limited amounts of these trophic agents during normal development. Thus, activity and innervation are thought to regulate MN survival by modulating trophic factor availability. We have tested this notion by examining MN survival in vivo and ChAT development in spinal cord neurons in vitro following treatments with partially purified muscle extracts from normally active, paralyzed (genetically or pharmacologically), aneural, denervated, slow tonic, and fast-twitch muscles from embryonic and postnatal animals. Extracts from active and chronically inactive embryonic avian and mouse muscles were found to be equally effective in promoting the in vivo survival of MNs in the chick embryo. Similarly, extracts from fast-twitch and slow tonic postnatal avian muscles did not differ in their ability to promote both MN survival in vivo and ChAT activity in vitro. Although aneural and control embryonic muscle extract had similar effects on ChAT development in vitro, aneural muscle extract contained somewhat less MN survival-promoting activity when tested in vivo. By contrast, denervated postnatal muscle extract was more effective in promoting both MN survival in vivo and ChAT activity in vitro than age-matched control muscle extract.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Ultrastructural observations on muscle spindles in extraocular muscles of pig.

Human and some mammals such as the sheep, goat and domestic and wild pigs have more or less muscle spindles in the extrinsic eye muscles, especially the domestic pigs having abundant muscle spindles (Matsuyama, 1987). The muscle spindles play a large role in maintaining the stable visual posture of the eyeballs. To define the morphological properties of the muscle spindles relative to the eye movement, the ultrastructure of the spindles was investigated in 6 extraocular muscles of the pigs by electron microscopy. The muscle spindles in the pig extraocular muscles consist of 4 to 5 intrafusal muscle fibers, one of which is nuclear bag fiber and 3 to 4 are nuclear chain fibers. The outer capsule is thin, composing of few layers, and the inner capsule ramifying to enwrap the individual fiber, accompanied by the medullated and unmedullated nerve fibers and blood capillaries. The nuclear bag fiber, 14 micron in diameter, is innervated by the atypical annulospiral sensory terminals and the chain fiber by the typical annulospiral terminal packed with mitochondria and microvesicles. The intrafusal fibers are innervated by the flower-spray sensory terminals anchoring deeply into the sarcoplasma, having abundant neurotubules and few mitochondria. The gamma motor end-plates have a relatively smooth synaptic cleft with a width of 70 nm and synaptic boutons containing few synaptic vesicles, sometimes, revealing a shallow fold of postsynaptic sarcolemma and abundant synaptic vesicles. The alpha motor end-plates reveal a relatively smooth synaptic cleft with a width of 80 nm, sometimes with a rough postsynaptic infolding, and boutons containing few synaptic vesicles and small-sized mitochondria. The satellite cells are innervated by the sensory terminals in various ways. The muscle spindles in the pig extraocular muscles are found to be much simpler in structure than those in the other antigravity muscles of the body. Their ultrastructure seems to reflect the morphological adaptation relative to the eyebal movement.

Animals↗
PubMed1978

The properties of the extraocular muscles of the frog. II. Pharmacological properties of the isolated superior oblique and superior rectus muscles.

The pharmacological properties of the superior oblique and the superior rectus muscles of the frog's eye were investigated in comparison with those of a skeletal muscle (iliofibularis muscle) of the same animal. Acetylcholine causes sustained contractures of the extraocular muscles; this effect is increased by physostigmine and decreased or abolished by d-tubocurarine. Also the applications of succinylcholine, choline or caffeine are able to evoke contractures. There are no striking differences in pharmacological properties between extraocular and skeletal muscles of the frog. The time-course of the contractures and the sensitivity of the muscle preparations to the drugs which evoke contractures are identical in extraocular and iliofibularis muscles. In comparison with skeletal muscles there is no higher sensitivity of the extraocular muscles against curare-like drugs. The existence of adrenergic receptors could not be found neither in extraocular nor in skeletal muscles of the frog. It is concluded that in frogs no pharmacological differences exist between the muscle fibre types which compose the extraocular and the skeletal muscles.

Acetylcholine↗