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PubMed2003

Postnatal suppression of myomesin, muscle creatine kinase and the M-line in rat extraocular muscle.

The M-line and its associated creatine kinase (CK) M-isoform (CK-M) are ubiquitous features of skeletal and cardiac muscle. The M-line maintains myosin myofilaments in register, links the contractile apparatus to the cytoskeleton for external force transfer and localizes CK-based energy storage and transfer to the site of highest ATP demand. We establish here that the muscle group responsible for movements of the eye, extraocular muscle (EOM), is divergent from other striated muscles in lacking both an M-line and its associated CK-M. Although an M-line forms during myogenesis, both in vivo and in vitro, it is actively repressed after birth. Transcripts of the major M-line structural proteins, myomesin 1 and myomesin 2, follow the same pattern of postnatal downregulation, while the embryonic heart-specific EH-myomesin 1 transcript is expressed early and retained in adult eye muscle. By immunocytochemistry, myomesin protein is absent from adult EOM sarcomeres. M-line suppression does not occur in organotypic co-culture with oculomotor motoneurons, suggesting that the mechanism for suppression may lie in muscle group-specific activation or workload patterns experienced only in vivo. The M-line is, however, still lost in dark-reared rats, despite the developmental delay this paradigm produces in the visuomotor system and EOMs. EOM was low in all CK isoform transcripts except for the sarcomeric mitochondrial (Ckmt2) isoform. Total CK enzyme activity of EOM was one-third that of hindlimb muscle. These findings are singularly unique among fast-twitch skeletal muscles. Since EOM exhibits isoform diversity for other sarcomeric proteins, the M-line/CK-M divergence probably represents a key physiological adaptation for the unique energetics and functional demands placed on this muscle group in voluntary and reflexive eye movements.

Adaptation, Physiological↗

PubMed1997

Temporal and spatial expression of distinct troponin T genes in embryonic/larval tail striated muscle and adult body wall smooth muscle of ascidian.

During development of the ascidian Halocynthia roretzi, the tadpole larva hatched from the tailbud embryo metamorphoses to the adult with a body wall muscle. Although the adult body wall muscle is morphologically nonsarcomeric smooth muscle, it contains a troponin complex consisting of three subunits (T, I, and C) as do vertebrate striated muscles. Different from vertebrate troponins, however, the smooth muscle troponin promotes actin-myosin interaction in the presence of high concentration of Ca2+, and this promoting property is attributable to troponin T. To address whether the embryonic/larval tail striated muscle and the adult smooth muscle utilize identical or different regulatory machinery, we cloned troponin T cDNAs from each cDNA library. The embryonic and the adult troponin Ts were encoded by distinct genes and shared only < 60% identity with each other. These isoforms were specifically expressed in the embryonic/larval tail striated muscle and the adult smooth muscle, respectively. These results may imply that these isoforms regulate actin-myosin interaction in different manners. The adult troponin T under forced expression in mouse fibroblasts was unexpectedly located in the nuclei. However, a truncated protein with a deletion including a cluster of basic amino acids colocalized with tropomyosin on actin filaments. Thus, complex formation with troponin I and C immediately after the synthesis is likely to be essential for the protein to properly localize on the thin filaments.

Amino Acid Sequence↗

PubMed2002

Ultrastructural abnormalities of muscle spindles in the rat masseter muscle with malocclusion-induced damage.

Human temporomandibular disorders due to disturbed occlusal mechanics are characterized by sensory, motor and autonomic symptoms, possibly related to muscle overwork and fatigue. Our previous study in rats with experimentally-induced malocclusion due to unilateral molar cusp amputation showed that the ipsilateral masseter muscles undergo morphological and biochemical changes consistent with muscle hypercontraction and ischemia. In the present study, the masseter muscle spindles of the same malocclusion-bearing rats were examined by electron microscopy. Sham-operated rats were used as controls. In the treated rats, clear-cut alterations of the muscle spindles were observed 26 days after surgery, when the extrafusal muscle showed the more severe damage. The fusal alterations affected predominantly capsular cells, intrafusal muscle fibers and sensory nerve endings. These results suggest that in the malocclusion-bearing rats, an abnormal reflex regulation of the motor activity of the masticatory muscles may take place. They also allow us to hypothesize that muscle spindle alterations might be involved in the pathogenesis of human temporomandibular disorders.

Animals↗

PubMed2005

Early quadriceps strength loss after total knee arthroplasty. The contributions of muscle atrophy and failure of voluntary muscle activation.

BACKGROUND: While total knee arthroplasty reduces pain and provides a functional range of motion of the knee, quadriceps weakness and reduced functional capacity typically are still present one year after surgery. The purpose of the present investigation was to determine the role of failure of voluntary muscle activation and muscle atrophy in the early loss of quadriceps strength after surgery. METHODS: Twenty patients with unilateral knee osteoarthritis were tested an average of ten days before and twenty-seven days after primary total knee arthroplasty. Quadriceps strength and voluntary muscle activation were measured with use of a burst-superimposition technique in which a supramaximal burst of electrical stimulation is superimposed on a maximum voluntary isometric contraction. Maximal quadriceps cross-sectional area was assessed with use of magnetic resonance imaging. RESULTS: Postoperatively, quadriceps strength was decreased by 62%, voluntary activation was decreased by 17%, and maximal cross-sectional area was decreased by 10% in comparison with the preoperative values; these differences were significant (p < 0.01). Collectively, failure of voluntary muscle activation and atrophy explained 85% of the loss of quadriceps strength (p < 0.001). Multiple linear regression analysis revealed that failure of voluntary activation contributed nearly twice as much as atrophy did to the loss of quadriceps strength. The severity of knee pain with muscle contraction did not change significantly compared with the preoperative level (p = 0.31). Changes in knee pain during strength-testing did not account for a significant amount of the change in voluntary activation (p = 0.14). CONCLUSIONS: Patients who are managed with total knee arthroplasty have profound impairment of quadriceps strength one month after surgery. This impairment is predominantly due to failure of voluntary muscle activation, and it is also influenced, to a lesser degree, by muscle atrophy. Knee pain with muscle contraction played a surprisingly small role in the reduction of muscle activation.

Aged↗

PubMed2000

Effects of muscle type, castration, age, and compensatory growth rate on androgen receptor mRNA expression in bovine skeletal muscle.

The effect of testosterone on sexual dimorphism is evident by differential growth of forelimb and neck muscles in bulls and steers. Divergent hormone sensitivites may account for the differential growth rates of individual muscles. Therefore, the objective of this study was to compare androgen receptor (AR) expression in three different muscles of bulls and steers at various ages and growth rates. Thirty Montbéliard bulls and 30 steers were assigned to four slaughter age groups. Four or five animals of each sex were slaughtered at 4 and 8 mo of age. Animals in the remaining two slaughter groups (12 and 16 mo) were divided into groups of either restricted (R) or ad libitum (AL) access to feed. Five animals of each sex and diet were slaughtered at the end of the restricted intake period at 12 mo of age. To simulate compensatory growth, the remaining animals (R and AL) were allowed ad libitum access to feed until slaughter at 16 mo of age. Total RNA was extracted from samples of semitendinosus (ST), triceps brachii (TB), and splenius (SP) muscles. Androgen receptor mRNA was quantified in 200-ng total RNA preparations using an internally standardized reverse transcription (RT) PCR assay. Data were analyzed using 18S ribosomal RNA concentrations as a covariable. Steers had higher AR mRNA levels per RNA unit than bulls (P < .01). Androgen receptor mRNA levels differed between muscles (P < .05), with lowest expression in the SP. The pattern of AR expression differed (P < .05) for each muscle with increasing age. Between 4 and 12 mo of age, AR mRNA levels increased (P < .05) in SP but remained unchanged in the ST and TB. Feeding regimen had no effect on muscle AR expression, but steers exhibiting compensatory growth had higher AR mRNA levels than AL steers (P < .01) or bulls (P < .01). Our results show that AR expression is muscle-specific and may be modulated by circulating testicular hormones. These data suggest that the regulation of AR expression may be linked to allometric muscle growth patterns in cattle and compensatory gain in steers.

Aging↗

PubMedDate not supplied

The histochemistry of the posterior cricoarytenoid (PCA) muscle in the dog, compared with the diaphragm, the sternothyroid and the sternomastoid muscle.

The canine posterior cricoarytenoid (PCA) muscle was compared histochemically with pieces of the diaphragm (Dia), an infrahyoid muscle (the sternothyroid, ST), and with a reference skeletal muscle (the sternomastoid, SM) taken from the same animal. The muscle fibre type composition in the PCA, Dia and ST differed very little and showed a slight type II preponderance. In the SM there was a strong type II preponderance. A subgrouping of the type II muscle fibres could not be carried out in any of the muscles. The oxidative activity was greater in the PCA than in the other three muscles and greater in type I than in type II fibres for all muscles except the Dia. In the Dia, some type I fibres had a larger cross-sectional area and showed a greater oxidative activity and contained less glycogen than the rest of the type I fibres in the muscle. These fibres seemed to represent a separate subgroup of type I fibres possibly serving quiet respiration.

Adenosine Triphosphatases↗

PubMed2006

Beef extract supplementation increases leg muscle mass and modifies skeletal muscle fiber types in rats.

The objective of this research was to investigate the effects of beef extract on fat metabolism, muscle mass and muscle fiber types in rats. We also investigated the synergetic effect of endurance exercise. Twenty-four male rats weighing about 270 g were assigned to two diets containing 0 or 6% beef extract (BE). Half the rats fed each diet were subjected to compulsory exercise (CE) for 30 min every other day. After 4 weeks feeding, the blood was collected and various organs were dissected. The muscle fiber type of the soleus and extensor digitorum longus (EDL) muscles were evaluated by histochemical and electrophoretical analyses. Rats supplemented with BE showed a decrease in fat content in liver and abdomen and an increase in the activity of carnitine palmitoyl transferase II in liver. BE as well as exercise increased the relative weights of both soleus and EDL. BE alone and BE plus CE did not affect the distribution of muscle fiber types in soleus. BE without exercise decreased in type IIb of EDL from 54% to 44% with compensatory increase in type IIa from 41% to 49% and type I from 5% to 7% compared with the nonsupplemented, nonexercised control group. No synergetic effect on a fast to slow fiber conversion due to the combination of BE and CE was detected. Thus, BE supplement increased muscle mass and slow type fiber in EDL. The effects of BE supplement on muscle characteristics were similar to those of exercise. beef extract, fat metabolism, muscle fiber type, muscle mass, L-carnitine

Abdomen↗

PubMed1975

[New muscle formation following transplantation of muscle treated with trypan blue].

The sources and mechanism of muscle formation de novo were investigated under the transplantation of skeletal muscle fibers treated in the 1% water solution of Trypan Blue for 48 hrs after Levander under skin and in omentum in rabbits and rats. In some cases the pieces of Trypan Blue stained muscles were placed in the diffusion chambers. Besides, 3H-thymidine autoradiography was used. It was established that after the above described treatment the muscles appeared morphologically as necrotized. They do not develop in the diffusion chambers in which cells do not penetrate. Under the transplantation of such muscles under skin and in omentum, they are phagocytized and disintegrate and in the close neighbourhood myoblasts arise which transform into muscle tubules and differentiated cross-striated muscle fibers. If prior to the transplantation the rats--recipients were labeled by 3H-thymidine, the muscle fibers formed de novo with the labeled nuclei, i. e. from the recipient cells in omentum where there are no muscles, apparently from polyblasts. Under the definite experimental conditions, myoblasts appear to arise from cells of non-myogenic origin by means of induction.

Animals↗

PubMedDate not supplied

[Effect of the graded muscle contraction on the H reflex and long latency reflexes of the thenar and hypothenar muscles to a fixed threshold stimulus].

INTRODUCTION: To determine the percentage of appearance of the H reflex and long latency reflexes (LLRs) in the thenar and hypothenar muscles of normal subjects to a fixed threshold mixed nerve electrical stimulus and variable degrees of muscle contraction. METHODS: Fifteen subjects aged 21 to 32 years of age without any prior history of central or peripheral neurological diseases volunteered for the study. The stimulation was a constant currrent given at the wrist with the cathode positioned proximally; started at 1 mA and it was gradually increased mA by mA until the M response appeared with the subject relaxed. The intensity of the stimulation was thereafter kept constant. The contraction was an abducting movement of the thumb in the case of the thenar muscle and abduction of the digiti minimi in the case of the hypothenar muscle and was sustained throughout the study. The reflexes were elicited with a repetition rate of 3 Hz, the stimulus was a square pulse of 0.5 ms. We used a low frequency pass filter of 10 Hz and a high frequency pass filter of 10 kHz. The sweep speed was set a 10 ms per division. The responses were averaged 200 times and then smoothed. RESULTS: The mean intensity of the stimulus that evoked the H response, for all subjects, was 7.5 2.8 mA. The mean latency of the H reflex elicited with stimulation of the median nerve was 26 ms 2.03 ms (std. error 0.28, maximum 28.2, minimum 22.0). The mean latency of the H reflex elicited with stimulation of the ulnar nerve was 25.1 ms 1.64 ms (std. error 0.230, maximum 28, minimum 22.3). The difference between the percentage of responses attained under a relaxed condition and with any kind of muscle contraction was highly significant statistically using the Chi square method (p < 0.001). When we compared the percentage of the H responses obtained with slight, moderate, strong contraction, and contraction against resistance, between them, we did no find a significant difference. The LLRs appeared only in the trials with strong contraction. CONCLUSIONS: The H reflexes and the LLRs of the thenar and hypothenar muscle were not obtained with threshold stimulation when these muscles were relaxed. With any degree of muscle contraction the H reflex in these muscles could be obtained in 94 percent of the trials. Maximal contraction and contraction against resistance were the best conditions to elicit long latency responses.

Adult↗

PubMed1975

[The structure of muscle spindles in the intercostal muscles and rectus abdominis of the human fetus].

The structure and innervation of muscle fibres were studied in external intercostal muscles and the streight muscle of the abdomen in 24--26-week human fetuses. The diameter of most spindles was shown to be within the range of 50--70 mkm, while in the streight muscle of the abdomen it could reach 100 mkm. In the external intercostal muscles the spindles, as a rule, were longer (300-500 mkm) than in the streight muscle of the abdomen (100--300 mkm) which was likely due to special functioning of the spindles in rhythmically working muscles. According to sensory innervation all the spindles may be divided into 3 main types: simple, intermediate and complex. In the external intercostal muscles there occur 3 types of spindles, while in the streight muscle of the abdomen there are spindles of a complex type.

Humans↗

PubMed1990

[Muscle contraction headache and posture--with special reference to ischemic contraction of the posterior neck muscles].

Cause of muscle contraction headache (MCH) results from sustained contraction of scalp and posterior neck muscles. Recently, we published an effect of posture on the etiology of MCH. According to our data, head bending posture seems to be one of the main causes of sustained contraction of the posterior neck muscles. Wolff presented a hypothesis of ischemic contraction of these muscles as a cause of pain. However, about the blood flow of scalp or posterior neck muscles, only two reports were published so far. These two papers failed to demonstrate a reduction of blood flow in MCH patients, and neglected the effect of posture. The purpose of this report is to examine a change of blood flow of posterior neck muscles with the change of posture. A total of 40 patients with MCH were studied using laser doppler blood flow meter. Needle shaped probe with a diameter of 0.55 mm was inserted 15 mm into the posterior neck muscle. The angle between orbito-meatal line and horizontal plane were measured using a light helmet with goniometer. Surface EMG of the posterior neck muscles was recorded at the same time. In the case of controls who do not experience headache, the amplitude of EMG increases slightly with the bending posture (40 microV with OM line 20 degrees upward from the horizontal plane, 46 microV with OM line horizontal, and 52 microV when 30 degrees downward). In reverse to the increase of the EMG activity, blood flow of the neck muscles decreases (12 ml/100 g/min with OM line 20 degrees upward, 10.8 with OM line horizontal, 7.6 at 10 degrees down, 4.6 at 20 degrees down, and 4.1 at 30 degrees down).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1990

[Ultrastructure of the muscle spindles in the extraocular muscles of pigs].

To define the morphological properties of muscle spindles relative to the accurate control of eyeball movement, muscle spindles were investigated in 6 extraocular muscles of three white pigs by an electron microscope. The muscle spindles were composed mainly of a thin outer capsule, nuclear bag and chain fibers. The bag fibers seem to be slow fibers and the chain fibers to be fast fibers in the external fashion, in so far as the former has a greater myofibril density than the latter. The intrafusal muscle fibers were innervated by three categories of nerve terminals; annulospiral and flower spray sensory terminals and gamma motor terminals. The annulospiral terminal was coiled sparsely on the bag fiber and densely on the chain fiber. The cross terminals were found in the pairing muscle fibers. We frequently observed that the satellite cells were controlled by the sensory terminals. It was also frequently observed that the muscle spindles were composed of only one intrafusal bag muscle fiber. It was suggested that the extraocular muscle spindles of the pig remained a primordial profile in the structure.

Animals↗

PubMed1989

[Muscle action potential and masticatory rhythm of anterior temporal and masseter muscles in children and adults].

For the investigation of the functional change of the masticatory muscles along with growth and development, electromyographic evaluation was carried out. The subjects were 6 children (5 males and 1 female) with full deciduous dentition (Hellman's dental age IIA) aged 4.5 +/- 0.2 years and 6 adults (4 males and 2 females) with full permanent dentition aged 27.7 +/- 3.8 years. EMG signals were recorded bilaterally by means of bipolar silver surface electrodes from the anterior temporal and masseter muscles when the subjects were chewing chewing gum or performing maximum clenches in intercuspal position. The cumulative power values from 62.5 to 1000 Hz in the EMG power spectrum during chewing or clenching were calculated as the muscle action potential. The ratio of the action potential of each muscle to the total action potential of four muscles were analyzed. Masticatory rhythm during chewing was analyzed by means of the time parameter (duration, interval and cycle) and their coefficients of variation. The results were as follows: 1. In children the temporal muscles predominated in chewing and clenching, whereas in adults there were three types with Temporal muscles predominating, Masseter muscles predominating and both muscles sharing equally. 2. No statistically significant differences between children and adults were observed in the duration, interval and cycle. 3. In adults the coefficients of variation of the duration, interval and cycle were smaller and the masticatory rhythm was more stable than in children.

Action Potentials↗

PubMed1988

Diversity of vinculin/meta-vinculin in human tissues and cultivated cells. Expression of muscle specific variants of vinculin in human aorta smooth muscle cells.

Microheterogeneity of different vinculin and meta-vinculin isoforms in adult human tissues and cultured cells was studied by two-dimensional gel electrophoresis and immunoblotting technique. Four isoforms of vinculin (alpha, alpha', beta, and gamma) and two isoforms of meta-vinculin (alpha and beta) were resolved. alpha-, alpha'-, and beta-isoforms of vinculin were found in all cell types and tissue samples analyzed in the present study. gamma-Isoform of vinculin and both alpha- and beta-isoforms of meta-vinculin were found in smooth (aorta wall and myometrium) and cardiac muscle, rather than in skeletal muscle, liver, foreskin fibroblasts, and macrophages. In the primary culture of human aorta smooth muscle cells, the fractional content of gamma-isoform of vinculin and meta-vinculin was dramatically reduced, and, by the onset of intensive cell division, the proteins could hardly be detected. Subcultured human aorta smooth muscle cells did not contain gamma-vinculin and meta-vinculin. We analyzed the microheterogeneity of vinculin and meta-vinculin in three smooth muscle layers of human aorta wall--media, muscular-elastic (adjacent to media) intima, and subendothelial (juxtaluminal) intima. It was shown that in media the fractional content of gamma-isoform of vinculin was 45% and meta-vinculin, 42%; in muscular-elastic intima the fractional content of gamma-vinculin was 42% and meta-vinculin, 36%. However, in subendothelial intima, the share of these proteins was significantly lower than in adjacent muscular-elastic intima and media. Isoactin pattern that is characteristic of smooth muscle was identical in all aortic layers, thus proving the smooth muscle origin of subendothelial intima cells. These findings demonstrate that human aortic smooth muscle cells in vivo and in vitro undergo coordinated differential expression of smooth muscle specific variants of vinculin, i.e. gamma-vinculin and meta-vinculin.

Adult↗

PubMed1983

Experimental study of denervated rat muscle. Part II: The effects of electrical stimulation on the denervated rat muscles.

Electrical stimulation has been widely employed for the treatment of peripheral nerve lesion, however, its effects are not well known. Effects of electrical stimulation on denervated muscles were studied by measuring the weight of anterior crural muscles and the diameter of muscle fibers of the extensor digitorum longus muscle of the rat. The muscle fibers were classified by myofibrillar ATPase reaction. The denervated muscle showed loss of weight, a marked decrease in diameter of type 1 fibers and a small increase in diameter of type 2 fibers. Electrical stimulation suppressed weight loss of the denervated muscles. Electrical stimulation with high frequency cycle, like phasic motoneuron discharges, significantly suppressed the increase in diameter of type 2 muscle fibers. Electrical stimulation with low frequency cycle, like tonic motoneuron discharge, significantly suppressed the decrease in diameter of type 1 muscle fibers.

Adenosine Triphosphatases↗

PubMed1983

[Nature of the changes in water-soluble enzyme activity in the exposure of muscles to harmful agents. III. A study of creatine kinase extractability from intact and altered muscles].

Binding of creatine kinase (CrK) in intact and thermally altered (15 minutes at 37 and 38 degrees C) skeletal muscles of frogs (Rana temporaria L.) was studied according to CrK extractability from muscles. The CrK activity in actomyosin isolated from muscles and its changes in thermally altered actomyosin were detected. Solutions of KCl (0.075, 0.15, 0.3 and 0.6 M) and of NaF (0.15 M) extract additional amounts of CrK from intact and altered muscles. Inhibiting effects of KCl, NaF and K2HPO4 on CrK in muscle extract were found. The latter exerts the most pronounced inhibiting effect, which prevents it from being used for CrK extraction purposes. Among the structural components of muscle that bind CrK actomyosin was detected. The actomyosin isolated from muscles revealed CrK activity. CrK in actomyosin gel is much more stable to thermal effect than that in a water extract of muscle. Such a thermostabity of CrK within the system of the whole muscle cell may apparently result from its being bound to actomyosin.

Actomyosin↗

PubMed1983

Postnatal growth and differentiation of muscle fibres in the mouse. II. A histochemical and morphometrical investigation of dystrophic muscle.

Postnatal development of three hind legs muscles, the soleus, plantaris, and gastrocnemius, of dystrophic mice (ReJ 129) was investigated with histochemical and morphometric methods. The results were compared with normal postnatal development. Especially during the second week postnatally, there was severe fibre necrosis with no apparent preference for any particular fibre type. This period of necrosis was shortly followed by a wave or regeneration during the third week that could not, however, compensate for the loss of fibres. In dystrophic animals of 4-5 months of age, the number of fibres was reduced by 40-70%. Cross sectional areas of dystrophic muscles rarely, if ever, exceeded values for normal animals 14 days of age, while body weights were also drastically reduced. Growth and differentiation of the nonaffected fibres proceeded almost normally during the first month. During the second month, the "slow' fibres in the soleus muscle, and the "fast-oxidative-glycolytic' fibres in the plantaris muscle were hypertrophied, while, incidentally, some "fast-glycolytic' fibres showed hypertrophy; but in this case the average size of the fibre type was not increased. After two months, a general fibre atrophy was observed. The fate of the regenerated fibres was difficult to trace, especially in muscles older than one month. It is assumed that a number of them were capable of developing into "adult' fibre types histochemically. During the course of the disease the percentage of "intermediate' fibres increased markedly, whereas nearly all "fast-glycolytic' fibres disappeared. Because of these shifts in fibre profiles, the plantaris and the gastrocnemius muscles obtained a rather "juvenile' and "oxidative' aspect. Changes in the histochemical character of the soleus muscle were less spectacular. In dystrophic muscles, no new fibre types were found, compared with normal muscles. Rather, fibre types were present at the wrong moment, or occurred in quantities unusual for the age concerned.

Animals↗

PubMed1980

[Synaptoarchitectonic structure of muscles as a synchronizing apparatus for muscle contraction].

Synaptoarchitecture is a new notion, refering to the spatial distribution of motor and plates, to the shape of these synapses and to the last ramifications of motor were fibers. In muscles of the rats limbs, endplates are forming a small strip almost perpendicularly to the main direction of muscle fibers. But in sphincters and in orbicular muscles end plates are randomly distributed. The spatial distributions of end plates in muscles of the limbs build up a synchronizer for simultaneous contraction of all fibers in a given muscle. However in some few muscles of the rat, as are the m. sartorius, m. gracilis and mm. glutei, there are many strips, corresponding to the composite structure of these muscles. A composite structure is one which fibers are not only attached to a tendon, but also to other fibers in the midst of the muscle, without any tendon. It is possible to synchronize even a composite structure, if all synapses are properly located, the end plates being all at the same distance from the farthest insertion. In some rodents, lagomorphs and carnivores almost all muscles are composite. Consequently they are all of the disperse type. There is a bunivoque correspondence between the composite structure and the disperse type of innvervation. The shape of motor end plates is changeable under various pathological and physiological circumstances. Beside the common form, there are "myoid" synapses, as may be encountered in myasthenia gravis, in intensive corticotherapy and in the sphincter ani externus. Myoid synapses are of several sorts: elongated, multipartite and minute synapses. For explanation of these various shapes a hypothesis is put forward, concerning structural changes in the postsynaptic membrane. Finally nervous fibers are so located, as to permit the follow up of the pertinent motor endplate, dislocated by muscular contraction.

Animals↗