Myotendon junctions in the rectus abdominis muscles of bull frogs were examined by the fixation combination of tannic acid and glutaraldehyde using electron microscopy. The features observed on myotendon junctions were the following: (1) There were many deep invaginations of muscle cell membrane at the end of the muscle fibers. Terminal thin filaments of myofibrils were attached to the electron-dense layer lining under the muscle cell membrane on the lateral walls of invaginations. (2) The basement membrane covering the muscle cell membrane was thicker in the invaginations than on the other sites of muscle fibers. (3) Collagen fibers in the invaginations gradually tapered off toward the bottom of the invaginations. But it was not seen that the collagen fibers were attached to both the basement membrane and cell membrane of muscle cells. (4) On the observations using the tannic acid-glutaraldehyde fixation, it was clearly seen that the microfibrils extend from the outer leaflets of the cell membrane to the collagen fibers in invaginations via the basement membrane. It was concluded that the myofibrils might be fastened to the collagen fibers of the tendon by the intermediates of the microfibrils.
ABSTRACT. Histological examination of the skeletal muscle of the slow loris, which displays slow movement and locomotion among the prosimians, revealed a muscle fiber composition which differed from the general condition in mammals. Three types of muscle fiber cells were therefore analyzed quantitatively in order to elucidate their specificity. The skeletal muscle of the limbs of the slow loris was predominantly composed of red muscle fibers (type I) showing persistent tonic contraction.
Histochemical examinations of muscle fiber types by Sudan black B staining were made on m. biceps brachii of male and female white-handed gibbon (Hylobates lar). Three types of muscle fibers could be discriminated in terms of the reaction to the pigment and the cellular diameter : red muscle fiber (type I) with a positive reaction and a small diameter ; white muscle fiber (type II) with a weak reaction and a large diameter ; intermediate muscle fiber (type III) with an intermediate reaction and diameter.Of 4648 muscle fiber cells, in average of male and female, scanned in the cross-section, red muscle fibers accounted for 44.1%, white muscle fibers 28.3%, and intermediate muscle fibers 27.6%, respectively.White muscle fibers were clearly localized in the external layers of both heads of m. biceps brachii.In contrast, red muscle fibers were more evenly distributed throughout the muscle though moderately localized in the regions adjacent to the sulcus bicipitalis medialis. Intermediate muscle fibers showed no specific localization at all. These results suggest that m. biceps brachii of the gibbon, an acrobatic armswinger, is inclined to be a red muscle that is fatigue-resisting rather than power-generating.
In myotome muscle fibers composing the trunk of the lamprey (Lamperrajapomba), parietal muscle fibers and central muscle fibers, which are histochemically and functionally different from each other, formed single compartments which then formed multiple units. Parietal muscle fibers arranged like a chain in the lateralis, were histochemically identified as red muscle fibers, and classified as slow contracting fibers (Type 1). In contrast, central muscle fibers were present in the medialis surrounded by parietal muscle fibers and histochemically were fast contracting white muscle fibers (Type 2). These observations of the architecture of muscle fibers and muscle fiber types suggest that red muscle fibers (parietal muscle fibers) forming the lateralis of the lamprey are involved in trunk architecture because of their continuous tonic contraction, and white muscle fibers (central muscle fibers) located in the medialis function act as a propelling force used in swimming.
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