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PubMed1988

Calcium concentration in the myoplasm of skinned ferret ventricular muscle following changes in muscle length.

1. Ferret ventricular muscles were skinned by prolonged application of Triton X-100. Aequorin was allowed to diffuse into the myoplasmic space and the resulting light emission was used to monitor the myoplasmic [Ca2+]. The muscle was then activated with a lightly buffered Ca2+ solution and the changes in myoplasmic [Ca2+] and tension in response to length changes were investigated. 2. A sudden reduction in muscle length led to a rapid increase in myoplasmic [Ca2+] to a new level which was maintained as long as muscle length was reduced and which was reversed when the muscle was stretched back to the control length. The rate of increase of [Ca2+] when the muscle length was reduced was greater than the rate of decrease in [Ca2+] when the muscle was stretched. 3. Increasing the concentration of EGTA in the activating solution, so as to increase its Ca2+-buffering capacity, eliminated the changes in myoplasmic [Ca2+] in response to a length change but had little effect on developed tension. 4. On stretching the muscle there was a slow component of recovery of tension with a time course broadly similar to the rate of decrease of myoplasmic [Ca2+]. The time course of tension redevelopment and of the accompanying reduction in myoplasmic [Ca2+] both decreased to a similar extent when the [Ca2+] used to activate the muscle was increased. 5. Step reductions of length of increasing amplitude caused increases in myoplasmic [Ca2+] which were larger in proportion to the size of the step. 6. Step reductions of length of equal size but from different starting lengths caused changes in myoplasmic [Ca2+] the amplitude of which correlated with the change in tension rather than the change in length. 7. The increase in myoplasmic [Ca2+] when muscle length is reduced suggests that Ca2+ is released from a site in the muscle, probably troponin C. The time course and magnitude of the changes in myoplasmic [Ca2+] correlate more closely with the changes in developed tension than muscle length.

Aequorin↗

PubMed1993

Skeletal muscle size: relationship to muscle function in heart failure.

Abnormalities of skeletal muscle function and metabolism are common in patients with congestive heart failure (CHF) and appear to contribute to systemic exercise limitation. Although the mechanism for these differences is unclear, one possibility is skeletal muscle atrophy. In 21 CHF patients and 12 sex- and age-matched sedentary control subjects, we quantified muscle size as maximal cross-sectional area (MCSA) of thigh muscles measured by magnetic resonance imaging and determined the relationship between muscle size and muscle function. Muscle strength was measured as maximum force developed during isometric contractions, and muscle endurance was quantified as the decline in force during 15 consecutive isokinetic knee extensions (measured as ratio of mean peak torque of last 3 and first 3 extensions). MCSAs of thigh muscles (141 +/- 28 vs. 167 +/- 47 cm2, P < 0.05) and knee extensors (62 +/- 13 vs. 75 +/- 13 cm2; P < 0.05) were both significantly smaller in patients than in control subjects. These differences persisted after normalization for body size. Isometric strength was less, but not significantly so, in patients (126 +/- 39 vs. 135 +/- 43 Nm; P = NS), but muscle endurance was markedly impaired (endurance ratio 0.67 +/- 0.14 vs. 0.83 +/- 0.11; P < 0.05). A strong correlation was found between isometric strength (r = 0.76) and MCSA of knee extensors, but only a weak correlation between dynamic endurance and MCSA was seen. We conclude that muscle size is smaller in CHF patients but that maximal force generated per area of muscle is not impaired.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1999

Peak muscle perfusion and oxygen uptake in humans: importance of precise estimates of muscle mass.

The knee extensor exercise model was specifically developed to enable in vivo estimates of peak muscle blood flow and O(2) uptake in humans. The original finding, using thermodilution measurements to measure blood flow in relation to muscle mass [P. Andersen and B. Saltin. J. Physiol. (Lond.) 366: 233-249, 1985], was questioned, however, as the measurements were two- to threefold higher than those previously obtained with the (133)Xe clearance and the plethysmography technique. As thermodilution measurements have now been confirmed by other methods and independent research groups, we aimed to address the impact of muscle mass estimates on the peak values of muscle perfusion and O(2) uptake. In the present study, knee extensor volume was determined from multiple measurements with computer tomography along the full length of the muscle. In nine healthy humans, quadriceps muscle volume was 2.36 +/- 0.17 (range 1. 31-3.27) liters, corresponding to 2.48 +/- 0.18 (range 1.37-3.43) kg. Anthropometry overestimated the muscle volume by approximately 21-46%, depending on whether quadriceps muscle length was estimated from the patella to either the pubic bone, inguinal ligament, or spina iliaca anterior superior. One-legged, dynamic knee extensor exercise up to peak effort of 67 +/- 7 (range 55-100) W rendered peak values for leg blood flow (thermodilution) of 5.99 +/- 0.66 (range 4.15-9.52) l/min and leg O(2) uptake of 856 +/- 109 (range 590-1,521) ml/min. Muscle perfusion and O(2) uptake reached peak values of 246 +/- 24 (range 149-373) and 35.2 +/- 3.7 (range 22.6-59. 6) ml. min(-1). 100 g muscle(-1), respectively. These peak values are approximately 19-33% larger than those attained by applying anthropometric muscle mass estimates. In conclusion, the present findings emphasize that peak perfusion and O(2) uptake in human skeletal muscle may be up to approximately 30% higher than previous anthropometric-based estimates that use equivalent techniques for blood flow measurements.

Adult↗

PubMed1995

Sex-specific differentiation of a male-specific abdominal muscle, the Muscle of Lawrence, is abnormal in hydroxyurea-treated and in fruitless male flies.

A prominent sex-specific abdominal muscle in male Drosophila is the Muscle of Lawrence (MOL), which is induced by male-specific innervation. We have examined MOL development in wild-type males, in males fed hydroxyurea to ablate the muscle precursors and in fruitless mutants, in which the MOL muscle develops aberrantly. One striking feature of MOLs in wild-type males was the presence of additional muscle nuclei compared with neighboring muscles or MOL-homologues in females. We tested whether muscle length and the sex-specific expression of a reporter gene depended critically on the number of nuclei present within a MOL fiber. MOL fibers developing from a reduced myoblast pool in hydroxyurea-affected hemisegments were recognizable by their attachment points and still contained more nuclei than did neighboring medial fibers, suggesting that these MOL fibers were able to actively recruit myoblasts nearly as well as wild-type MOLs. However, many of the hydroxyurea-affected MOL fibers were incapable of the normal male-specific expression of a muscle-specific reporter gene. We suggest that early events in MOL development, such as finding the correct muscle attachment points, are relatively insensitive to the number of MOL nuclei compared with later events, such as the sex-specific expression of a reporter gene. In fruitless mutant males, MOL-position fibers are smaller and had substantially fewer nuclei compared to wild-type MOLs. Since the number and distribution of muscle precursors was the same in fruitless mutant and wild-type animals, we propose that one fru+ function is to direct the male-specific recruitment of myoblasts into MOL-myotubes. However, fruitless+ must have more than one role in MOL fiber development, since simple reduction in the number of muscle nuclei, as demonstrated by the hydroxyurea ablations, is insufficient to account for all of the MOL muscle phenotypes in fruitless mutant males.

Abdominal Muscles↗

PubMed2006

In situ muscle power differs without varying in vitro mechanical properties in two insect leg muscles innervated by the same motor neuron.

The mechanical behavior of muscle during locomotion is often predicted by its anatomy, kinematics, activation pattern and contractile properties. The neuromuscular design of the cockroach leg provides a model system to examine these assumptions, because a single motor neuron innervates two extensor muscles operating at a single joint. Comparisons of the in situ measurements under in vivo running conditions of muscle 178 to a previously examined muscle (179) demonstrate that the same inputs (e.g. neural signal and kinematics) can result in different mechanical outputs. The same neural signal and kinematics, as determined during running, can result in different mechanical functions, even when the two anatomically similar muscles possess the same contraction kinetics, force-velocity properties and tetanic force-length properties. Although active shortening greatly depressed force under in vivo-like strain and stimulation conditions, force depression was similarly proportional to strain, similarly inversely proportional to stimulation level, and similarly independent of initial length and shortening velocity between the two muscles. Lastly, passive pre-stretch enhanced force similarly between the two muscles. The forces generated by the two muscles when stimulated with their in vivo pattern at lengths equal to or shorter than rest length differed, however. Overall, differences between the two muscles in their submaximal force-length relationships can account for up to 75% of the difference between the two muscles in peak force generated at short lengths observed during oscillatory contractions. Despite the fact that these muscles act at the same joint, are stimulated by the same motor neuron with an identical pattern, and possess many of the same in vitro mechanical properties, the mechanical outputs of two leg extensor muscles can be vastly different.

Analysis of Variance↗

PubMed1985

Dynamic and static stretch responses in muscle spindle receptors in fatigued muscle.

Dynamic and static stretch responses in muscle spindles were investigated in fatigued muscle to determine if acute adaptations do occur in receptor discharge as has been shown after contractions of short duration. Fatigue to 60-50% maximum tetanic tension was induced in the isolated gastrocnemius muscle in 16 cats by sustained, 7 X threshold electrical stimulation (100 Hz) of the cut L7 ventral root and S1 ventral root. Group Ia and II afferent fiber responses to slow ramp stretches (5 mm X s-1) and vibration (100 Hz) applied to the Achilles tendon were monitored before and immediately after muscle tetany to fatigue. Changes in firing characteristics were similar when results from faster (25-30 mm X s-1) ramp stretches were contrasted. During muscle fatigue, decreases in response latency to displacement and increases in resting discharge, mean frequency during stretch, and frequency of firing to vibration were predominant in both afferent fiber types. Static responses were generally lower, indicating a decrease in position sensitivity. Resting muscle force and passive peak muscle stiffness were consistently higher following contraction. The sum effects of these proprioceptive afferent and mechanical muscle responses would be to increase muscle stiffness and thus resist yield in muscle length to perturbations at lower muscle forces. The magnitude of these adaptations in proprioceptive discharge appears dependent on intrafusal muscle fiber activation.

Adaptation, Physiological↗

PubMed2006

Muscle dissatisfaction and muscle-enhancing substance use: a population-based twin study in young adult men.

In the population-based Finn Twin 16 study, proportions of genetic and environmental factors contributing to muscle dissatisfaction and muscle-enhancing substance use were assessed in 319 pairs of twin brothers: 141 monozygotic (MZ) and 178 dizygotic (DZ) pairs. In addition there were 86 twin individuals from pairs in which only one co-twin responded. Of all respondents, 30% experienced high muscle dissatisfaction. The corresponding proportion of muscle-enhancing substance use was 10%. The subjects were similar in age (23.8 years, 95% confidence interval [CI] 23.76-23.84), body mass index (23.7, 95% CI 23.5-23.9), and waist circumference (84.5 cm, 95% CI 83.7-85.2), independent of their muscle dissatisfaction or muscle-enhancing substance use status and independent of their zygosity. The MZ polychoric correlation for muscle dissatisfaction was .39 (95% CI .17-.58) and .27 for DZ pairs (95% CI .07-.46). The MZ tetrachoric correlation for muscle-enhancing substance use was .65 (95% CI .28-.87) and .56 for DZ pairs (95% CI .26-.78). The AE model, where additive genetic factors (A) accounted for 42% (95% CI .23-.59) and unique environmental factors (E) 58% (95% CI .41-.77) of the liability, provided the best fit for muscle dissatisfaction. The CE model, where common environmental factors (C) accounted for 60% (95% CI .37-.77) and unique environmental factors (E) 40% (95% CI .23-.63) of the liability, provided the best fit for muscle-enhancing substance use. Both genetic and unique (nonfamilial) environmental factors are involved in muscle dissatisfaction in the population. Nongenetic factors (both familial and nonfamilial) appear to best explain the use of muscle-enhancing substances.

Adult↗

PubMed2002

Developmental changes of cardiac and slow skeletal muscle troponin T expression in chicken cardiac and skeletal muscles.

Numerous troponin T (TnT) isoforms are produced by alternative splicing from three genes characteristic of cardiac, fast skeletal, and slow skeletal muscles. Apart from the developmental transition of fast skeletal muscle TnT isoforms, switching of TnT expression during muscle development is poorly understood. In this study, we investigated precisely and comprehensively developmental changes in chicken cardiac and slow skeletal muscle TnT isoforms by two-dimensional gel electrophoresis and immunoblotting with specific antisera. Four major isoforms composed of two each of higher and lower molecular weights were found in cardiac TnT (cTnT). Expression of cTnT changed from high- to low-molecular-weight isoforms during cardiac muscle development. On the other hand, such a transition was not found and only high-molecular-weight isoforms were expressed in the early stages of chicken skeletal muscle development. Two major and three minor isoforms of slow skeletal muscle TnT (sTnT), three of which were newly found in this study, were expressed in chicken skeletal muscles. The major sTnT isoforms were commonly detected throughout development in slow and mixed skeletal muscles, and at developmental stages until hatching-out in fast skeletal muscles. The expression of minor sTnT isoforms varied from muscle to muscle and during development.

Animals↗

PubMed2006

Measurement of muscle thickness as quantitative muscle evaluation for adults with severe cerebral palsy.

BACKGROUND AND PURPOSE: The muscle strength of people with severe cerebral palsy (CP) is difficult to quantify because of cognitive and selective motor control problems. However, if muscle strength is related to muscle atrophy caused by activity limitation, quantitative morphological analysis such as analysis of muscle thickness (MTH), measured by ultrasound imaging, may be used to examine the muscle condition in daily use. The primary purpose of this investigation was to clarify the difference in MTH of several muscles by the motor functions used in daily activity in adults with CP with different levels of severity of involvement. The secondary purpose was to examine whether MTH is associated with age, body characteristics, and muscle spasticity. SUBJECTS: Data were collected from a convenience sample of 25 adults with severe CP. METHODS: The MTH of the biceps brachii (BB), quadriceps femoris (QF), triceps surae (TS), and longissimus (LO) muscles was measured with an ultrasound imaging device. The severity of the condition was classified with the Gross Motor Function Classification System (GMFCS), and functional status in sitting and standing was evaluated with a questionnaire administered to the staff assisting in the care of the subjects. Muscle spasticity was assessed with the Modified Ashworth Scale (MAS). RESULTS: The MTH of the QF, LO, and TS showed significant differences according to the GMFCS level, and the MTH of the QF and LO differed significantly depending on functional status during activities of daily living. Age and body mass index showed no significant correlation with the MTH of any muscle. Body weight was correlated with the MTH of the BB and LO. The girth of the extremity was correlated only with the MTH of the BB. There was no relationship between MTH and MAS scores. DISCUSSION AND CONCLUSION: These results suggest that the MTH of the QF and LO differed significantly depending on the subjects' motor function during daily activity. The measurement of MTH may be an alternative method of quantitative muscle evaluation for people with severe CP for whom direct measurement of muscle strength is difficult.

Activities of Daily Living↗

PubMed1996

Effects of Synovex-S and recombinant bovine growth hormone (Somavubove) on growth responses of steers: II. Muscle morphology and proximate composition of muscles.

Twenty crossbred beef steers (initial BW 182 +/- 1.8 kg) were used in a 2 x 2 factorial to determine the effects of implantation with Synovex-S (SYN; 20 mg 17-beta estradiol benzoate + 200 mg progesterone, ear implant) and administration of recombinant bovine growth hormone (Somavubove SbV, .1 mg.kgBW-1.d-1, i.m.) on the morphology of six muscles (longissimus, psoas major, supraspinatus, triceps brachii, semitendinosus, rectus femoris) of growing steers. Implantation with SYN decreased the percentage distribution of FOG fibers and increased FG fibers in the supraspinatus and rectus femoris muscles (P < .05). Steers treated with SYN had a larger area of SO and FG fibers in the psoas major muscle (P < .05). The administration of SbV decreased the percentage distribution of FOG fibers and increased FG fibers in the rectus femoris muscle (P < .05). Steers administered SbV had larger SO, FOG, and FG fibers in the psoas major muscle and SO fibers in the supraspinatus and semitendinosus muscles (P < .05). The combined administration of SYN and SbV had minimal, if any, effect on the percentage distribution of fiber types (P > .05) but increased (P < .05) the fiber areas of all muscles (18.5 to 54.8%) except the rectus femoris (P > .05). Proximate composition of the muscles was generally not affected (P > .05) by any of the treatments. The only observations were decreases in fat content for psoas major and rectus femoris muscles as a result of the combined administration of SYN and SbV. These results indicate that both growth-promoting agents, SYN and SbV, have potential to increase muscle fiber size, but muscles respond differently to the administrations of SYN and SbV. However, when SYN and SbV are administered in combination, the combined effects result in an additive increase in muscle fiber hypertrophic response.

Animals↗

PubMed2007

Effect of age, muscle type, and insulin-like growth factor-II genotype on muscle proteolytic and lipolytic enzyme activities in boars.

Recently, a paternally expressed quantitative trait nucleotide (QTN) in the regulatory sequence of the IGF-II gene with effects on muscle growth and fat deposition was discovered in the pig. This QTN is also known as the IGF-II intron3 G3072A mutation. The aim of the current study was to determine the effects of age, muscle type, and IGF-II genotype (Apat, mutant allele vs. Gpat, wild-type allele) on muscle proteolytic and lipolytic enzyme activities. At approximately 4, 8, 16, and 26 wk of age, boars (n = 6 to 15 per genotype x age group) were slaughtered and mu- and m-calpain (CALP), calpastatin (CAST), cathepsins (CATH) B+L and H, acid lipase, and phospholipase activities were measured in Longissimus thoracis et lumborum, Semimembranosus, and Triceps brachii muscle samples taken soon after slaughter. Activities of CATH B+L and H, mu- and m-CALP, and acid lipase were not affected by the IGF-II genotype. Activity of CAST was greater (P < 0.005) and m-CALP:CAST was less (P < 0.05) in Apat animals. Because CAST activity and m-CALP:CAST are known to be related to protein degradation, satellite cell fusion, or both, it is likely that differences in proteolytic enzyme activities are involved in the greater percentage of muscle mass in Apat animals. Age and muscle type influenced proteolytic and lipolytic enzyme activities (P < 0.05), except for mu- and m-CALP (no effect of muscle) and acid lipase (no effect of age). The same pattern in mu-CALP, CAST, and m-CALP:CAST with age was found during growth for the 3 muscles, although clear differences (P < 0.05) between muscles existed. In general, and in agreement with previous reports, greater enzyme activities were found in the more oxidative Triceps brachii muscle compared with the other 2 muscles. A remarkable increase (P < 0.05) from 16 to 26 wk of age in mu-CALP, CAST, mu-CALP:CAST, and CATH H and a large decrease (P < 0.05) in acid phospholipase and m-CALP:CAST was found. For m-CALP and CATH B+L, a gradual decrease (P < 0.05) was found with age. Although age effects on enzyme activities could only partly be interpreted biologically in relation to the muscle growth rate, this study showed that proteolytic and lipolytic enzyme activities change during growth.

Aging↗

PubMed2002

A case of an accessory palmaris longus muscle and a duplicate palmaris longus muscle with special reference to their nerve supply--morphologic significance of a common innervation trunk.

During a dissection of the forearm and hand, a duplicate palmaris longus muscle with an accessory palmaris longus muscle was observed on the right side of a 73-year-old Japanese male cadaver. Duplications of the palmaris longus muscle have been reported by many authors. Humphry (1872) suggested the presence of radial, intermediate, and ulnar sectors in the superficial layers of the forearm flexor muscular angulus, based on a comparison of fore- and hind limbs and comparative anatomical theory. The palmaris longus muscle usually differentiates from the intermediate sector but differentiation from the other two sectors may also be possible. Some authors have asserted that a common innervation trunk is critical for determining an ontogenetic relation between the muscles (Fuchino, 1960; Honma, 1980; Yamada, 1986). We examined the nerve supply in addition to scrutinize these anomalous palmaris longus muscles. In our case, the ramification of the innervating nerves was specific. The branches to the second palmaris longus muscle and the flexor carpi radialis arose as a common trunk from the median nerve. The branches to the first palmaris longus muscle and the accessory palmaris longus muscle originated as another common trunk from the median nerve. From these observations, we speculated that the second palmaris longus muscle has differentiated from the flexor carpi radialis, while the accessory palmaris longus muscle has differentiated from the first palmaris longus muscle, based on Humphry's suggestion.

Aged↗

PubMed1988

[Analysis of the composition of skeletal muscle fibers in skaters' muscles].

Muscle fibers composition was investigated in vastus lateralis muscles of 103 skaters. In the total population of skaters muscle fibers composition was as follows: muscle fibers, type I--in 54 +/- 2%, muscle fibers, type II A--in 35 +/- 1% and muscle fibers, type II B--in 11 +/- 1%. 13 +/- 8% muscle fibers, type I; 1.56 +/- 6% muscle fibers, type II A and 31 +/- 7% muscle fibers, type II B were observed in the muscles of sprinters, while the muscles of long-distance skaters contained 60 +/- 4%, 33 +/- 4% and 7 +/- 2% muscle fibers, respectively.

Adenosine Triphosphatases↗

PubMed1988

Localization of proprioceptive neurons innervating the muscle spindles of pig extraocular muscles studied by horseradish peroxidase labelling.

Each muscle of the extraocular muscles, containing abundant muscle spindles, was exposed to horseradish peroxidase (HRP) on 8 young pigs (2-month-old, 20-30 kg in body weight, both sexes). The results obtained are follows: The HRP-labelled neurons innervating the superior rectus muscle were always found in a crescent ventro-medio-dorsal fashion in the most medial position of the contralateral oculomotor nucleus. The HRP-labelled cells for the medial rectus muscle appeared close to the superior rectus group in the ipsilateral nucleus. The labelled cells for the inferior rectus muscle appeared in the ventrolateral position of the ipsilateral nucleus and those for the inferior oblique muscle in the area between the medial rectus and inferior rectus muscle groups. The labelled cells for the superior oblique muscle were found in the contralateral trochlear nucleus and those for the lateral rectus muscle bilaterally in the abducens nuclei, predominantly on the ipsilateral side and poorly on the contralateral side. The HRP-labelled cells were composed of large (alpha) and small (gamma) multipolar cells and of bipolar, oval or round (proprioceptive) cells, all intermingled together within the nucleus. The bipolar cells have been also identified in the 3 nuclei by means of Nissl staining technique. On this basis, they should be considered as the proprioceptive neurons. In the shrew-moles, the cell bodies of the proprioceptive neurons innervating the snout muscle spindles have been found close to the ipsilateral glossopharyngeal ganglion and those of the somatic sensory neurons in the ipsilateral trigeminal ganglion. In the pigs, no HRP-labelled cells were found in the trigeminal mesencephalic tract nucleus, but the HRP-labelled cells were found in the ipsilateral trigeminal and the superior cervical sympathetic ganglia. From the results, it could be emphasized that the proprioceptive neurons innervating the pig extraocular muscle spindles are located within the nuclei of the IIIrd, IVth and VIth cranial nerves.

Animals↗

PubMed1979

Cytochemical differentiation of tonic (slow) and phasic (fast) muscle units in the ocular muscles of a fresh-water carp, Catla catla (Ham.).

1. Functional morphology of the ocular muscles with special reference to their topography, innervation and action have been studied in a fresh-water carp Catla catla. An attempt has also been made to differentiate tonic (slow) and phasic (fast) muscle units in the various ocular muscles by their SDH activities and their lipid contents. 2. Catla catla has large eyes (2 cm in diameter) in a fish measuring 30 cms. There are four recti (inferior, superior, anterior and posterior) and two obliquii (superior and inferior) muscles for the synchronized rotation of the eye ball within the orbit. Anterior and posterior myodomes are well developed. The former accommodates two obliquii muscles, while the latter gives space for the posterior and anterior recti. 3. In this fish, all the ocular muscles are composite in nature being made up of tonic (slow) and phasic (fast) muscle units. The former is made up of red fibers whereas the latter have only white fibers. In the tonic muscle units lipid is more concentrated. 4. The superior and the inferior obliquii muscles rotate the eye ball on its antero-posterior axis. The upward and downward movements of the eye balls are achieved by the superior and the inferior recti. The anterior and posterior recti move the eye ball in the antero-lateral and postero-lateral directions. 5. The superior obliquii contains about 41% of the tonic and 59% of phasic muscle units. The inferior oblique is made up of 25% of tonic and 75% of the phasic muscle units. 6. The Anterior rectus contains greater percentage of tonic muscle fibers (48%) than the superior rectus (40%), the Interior rectus (34%) and the posterior rectus (35%).

Animals↗

PubMed1993

[Correlations between feet posture and muscle fiber size in mammals--comparison of the anterior tibial muscle fiber among plantigrade type, digitigrade type and unguligrade type].

The size (micron2) of red muscle fibers (Type 1), white muscle fibers (type 2) and intermediate muscle fibers (type 3) was quantitatively determined in cross-sectional areas of the venter of the anterior tibial muscle in the plantigrade type, digitigrade type and unguligrade type using 122 individuals of 15 species in 5 orders, and correlations between the type of locomotion and muscle fiber size were analyzed from a comparative anatomical viewpoint. Regardless of species, red muscle fibers with slow contraction were small in diameter, intermediate muscle fibers (which are believed to have characteristics of both types 1 and 2) were intermediate in diameter, and white muscle fibers with fast contraction were large in diameter. Muscle fiber size (types 1 through 3) was largest in the orangutan, followed by the brown bear, rat, crab-eating monkey and human, in that order, in the plantigrade type. The size was intermediate in the goat, pig and horse in the unguligrade type, and white-handed gibbon, chimpanzee and rabbit in the plantigrade type. The size was relatively small in the cat, dog, Japanese raccoon dog and Japanese for in the digitigrade type within the same species, muscle fiber size increased in proportion to the increase in body weight. However, there was no correlation between body size and muscle fiber size among different species. The above results suggest that muscle fiber size in the mammalian leg is regulated by anatomical morphology, i.e., plantigrade, digitigrade and unguligrade types, and shows individual adaptive variation.

Animals↗

PubMed1989

Muscle receptors: content of some of the extrinsic and intrinsic muscles of the larynx in the bonnet monkey (Macaca radiata).

The number of muscle receptors and in particular the muscle spindle content of some of the intrinsic and extrinsic laryngeal muscles was evaluated, using bonnet monkeys (Macaca radiata). The technique of Barker and Ip [J. Physiol. (Lond) 169:73-74, 1963] was used to stain the muscle receptors. The results indicate that the intrinsic laryngeal muscles were devoid of muscle spindles. The extrinsic laryngeal muscles that were examined contain muscle spindles, though their density is less than that reported in the spindle-rich muscles like the rotators of the head and some of the intrinsic muscles of the hand (Cooper in: Structure and Function of Muscle, Vol. I, G.H. Bourne, ed, Academic Press, New York and London, 1960).

Animals↗

PubMed1993

Factors affecting muscle fiber transformation in cross-reinnervated muscle.

Nerves of two fast muscles [peroneus longus (PL) and extensor digitorum longus (EDL)], having different type 2 muscle fiber compositions, were used to cross-reinnervate the slow soleus muscle in the rat. Contraction characteristics, histochemical muscle fiber type compositions and myosin heavy chain (MHC) isoform compositions were determined for the reinnervated muscles. Shortening velocity increased in soleus muscles crossreinnervated with EDL nerve [X-SOL(EDL)] but not in muscles cross-reinnervated with PL nerve [X-SOL(PL)]. Type 2A MHC isoform content was increased in X-SOL(EDL) but not in X-SOL(PL), where MHC isoform composition remained similar to normal soleus. The complement of type 1 (slow) muscle fibers was reduced and that of type 2 (fast) fibers increased in both types of X-SOL muscle, but this change was significantly greater in X-SOL(EDL); the majority of the type 2 fibers in X-SOL muscles were of type 2A. Results show that "the type 2 composition" of the reinnervating motoneuron pool is an important factor in determining the transformation of a target slow muscle after cross-reinnervation.

Animals↗