Skeletal Muscle Bundles Research Articles

The ultrastructure of the striated muscle of the tail of Cercaria chackai, nadakal et al., 1969.

The electron microscopic study of the tail of Cercaria chackai reveals that it contains four sets of striated muscle bundles located central to the nonstriated circular and longitudinal muscles. The striated muscle consists of longitudinally oriented lamellar myofibres. Each myofibre contains a single "U" shaped myofibril. The banding pattern is analogous to that of vertebrate striated muscle. The sarcolemma is a simple surface membrane. There are no transverse tubular extensions of sarcolemma. The sarcoplasmic reticulum (SR) is very well developed with cisternae, tubules, and vesicles. SR cisternae form dyadic couplings with the sarcolemma. There is a set of flattened tubules of SR origin traversing the myofibril exactly at the Z region. These tubules are unique to the striated muscle of the cercarian tail and may have functional significance. A diagrammatic reconstruction of the myofibre is presented.

Tissue specificities of Thelohania duorara, Agmasoma penaei, and Pleistophora sp., microsporidian parasites of pink shrimp, Penaeus duorarum

The pathology of pink shrimp, Penaeus duorarum, infected with the microsporidians Thelohania duorara, Agmasoma penaei, and Pleistophora sp. was described. Infections of T. duorara were widespread in most tissues; spores were located throughout the hemocoel, at the periphery of all striated muscle bundles, and in muscle and connective tissue surrounding the digestive tract. A. penaei infections invaded only dorsal abdominal muscles, muscles adjacent to blood vessels, and ovaries. Infected muscles and ovaries were eventually completely destroyed. Masses of A. penaei spores were often engulfed by hemocytes. Pleistophora sp. infected the interior of all striated muscles. Infected muscles were never completely destroyed but were often atrophied.

Relation between adenosinetriphosphate activity and sarcomere length in stretched glycerol-extracted frog skeletal muscle.

A now familiar feature of myofibrillar structure is the interdigitating array of thick and thin filaments first described by Hanson and Huxley.' Based on this structural feature, a model of muscular contraction has been proposed' which is briefly as follows. Contraction takes place by sliding of thin filaments (I filaments) toward the center of each sarcomere through interaction with thick filaments (A filaments) at projections on the latter termed bridges. Adenosinetriphosphate (ATP) is hydrolyzed at the bridges, and the interaction of thin filaments at these sites accelerates the rate of hydrolysis. The thick filaments are composed of myosin and the thin filaments, at least partially, of actin. Huxley3, 4 has summarized a number of lines of evidence which support this model of the contractile mechanism. Experiments on isolated contractile proteins of skeletal muscle indicate that actin greatly enhances the magnesium-activated adenosine triphosphatase (ATPase) activity of myosin which has a pH optimum at pH 7.3.5 We thought it would be of interest, in relation to the model of contraction proposed by Huxley, to examine the relationship between extent of overlap of thick and thin myofilaments and the rate of Mg++ activated ATP hydrolysis at pH 7.3. Glycerol-extracted skeletal muscle bundles were used, following the method of preparation introduced by SzentGy6rgyi.6 These bundles contract in the presence of ATP, and the amount of tension developed is approximately that developed by the intact muscle on excitation.6 ATPase activity was assayed in bundles of approximately rest length and in ones stretched to various lengths beyond rest length. Sarcomere lemngths in unfixed and uncontracted bundles were estimated by phase microscopy. The amount of myofilament overlap was gauged by electron microscopic examination of sections taken at random points along the length of representative bundles included in the

Rhabdomyosarcoma of the Testis: Report of Two Cases

One of the rarest varieties of intrascrotal neoplasm is a tumor composed of striated muscle. Only a few cases have been published and most of these appear as isolated reports in the older foreign literature. In many cases, the tumor was closely connected with the testicle, but it was difficult to determine whether it arose from the testis or from the adjacent tissue. Rokitansky in 1849 described a paratesticular tumor in an eighteen-year-old boy. The growth, which was composed entirely of skeletal muscle, he interpreted as having arisen from the gubernaculum of Hunter. Senftleben in 1858 described the presence of striated muscle bundles in a well differentiated teratoma of the testis. Neumann in 1886 reported a pure rhabdomyoma in a boy three and one-half years of age. The tumor was attached to the lower pole of the testis and was composed of striated muscle fibers and large muscle cells without striations. The testis and epididymis were unchanged. Like Rokitansky, Neumann thought that the tumor arose from the gubernaculum. Kocher in 1887 collected six cases of mixed tumors of the testis containing striated muscle.