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H RUSKA

Publications and source records attributed to H RUSKA.

At least 37 records · Page 2Linked to original sources
PubMed1958

Neuromuscular junctions in flight and tymbal muscles of the cicada.

The tymbal muscle fiber in the cicada closely resembles the indirect flight muscle fiber in its structural detail. We agree with other authors that the tymbal muscle is a modified indirect flight muscle. The peripheral nerve branches to the tymbal and flight muscle fibers are similar to those in the wasp leg. The axon is loosely mantled by irregular turns of the mesaxon, enclosing cytoplasm. The nerve is therefore a tunicated nerve. The neuromuscular junction in the high frequency muscle fibers shows direct apposition of plasma membranes of axon and muscle fiber, large numbers of mitochondria and synaptic vesicles in the axon, and concentrations of mitochondria, aposynaptic granules, and endoplasmic reticulum in the postsynaptic area of the muscle fiber. Of special interest is the multitude of intracellular, opposing membranes in the postsynaptic area. They form laminated stacks and whorls, vesicles, cysternae, and tubules. They occasionally show continuity with the plasma membrane, the outer nuclear envelope, and the circumfibrillar endoplasmic reticulum. The membrane system in this area is designated "rete synapticum." It is believed to add to the electrical capacity of the neuromuscular junction, to serve in transmission of potentials, and possibly is the site of the oscillating mechanism in high-frequency muscle fibers.

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PubMed1958

Electron microscopy of peripheral nerves and neuromuscular junctions in the wasp leg.

The peripheral nerve branch innervating the femoral muscles of the common yellow jacket (Vespula carolina) has been found to possess a thick lemnoblast basement membrane and a complex mesaxon. The term "tunicated nerve" is proposed to designate the type of peripheral nerve in which one or several axons are loosely mantled by meandering, cytoplasm-enclosing membranes of the lemnoblast. The peripheral axon courses longitudinally in a groove in the muscle fiber between the plasma membrane of the muscle fiber and a cap formed by lemnoblast and tracheoblast. The junction is characterized by apposition of plasma membranes of axon and muscle fiber, abundant mitochondria, and synaptic vesicles in the axon, and aggregates of "aposynaptic granules" plus mitochondria and endoplasmic reticulum on the muscle side of the synapse. Unlike the vertebrate striated muscle fiber, no complex infolding of the synapsing plasma membrane of the muscle fiber occurs. The "connecting tissue" of the insect is formed by tracheoblasts, their basement membranes, and the basement membranes of other cells. Further mechanical support is given by the ramifying tracheoles. The physiologic roles of the specialized structures are considered.

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PubMed1957

Architecture and nerve supply of mammalian smooth muscle tissue.

Smooth muscle tissue from mouse urinary bladder, uterus, and gall bladder has been studied by means of the electron microscope. The smooth muscle cells are distinctly and completely separated from each other by a cytolemma comparable to the sarcolemma of striated muscle. The tissue is thus cellular and not syncytial. With this evidence, supported by electron microscopy of other tissues, we question the existence of true syncytia in animal tissues. Individual cell membranes necessary for the electrophysiologic events exist in smooth muscle, and its nerve and conduction in a tissue such as uterus or bladder can occur at the cellular level as well as at the tissue area level. The smooth muscle cell contains myofilaments, nucleus, endoplasmic reticulum, mitochondria, Golgi complex, centrosome, and pinocytotic vesicles. These structures are described in some detail, and their probable interrelations and functions are discussed. The autonomic nerves innervating smooth muscle cells are composed of axons and lemnoblasts. The axon is suspended by the mesaxon formed by the infolded plasma membrane of the lemnoblast. The respective plasma membranes separate axon and lemnoblast from each other and from surrounding muscle cells. The axons of autonomic nerves never penetrate the plasma membrane of the muscle cell, but pass or intrude into muscle cell pockets, forming a contact between axonal plasma membrane and smooth muscle plasma membrane. The lemnoblast shows well developed endoplasmic reticulum with Palade granules, mitochondria, and a long, elliptical nucleus. The axon contains neurofilaments, mitochondria, and synaptic vesicles; the quantity of the latter two being significantly greater in the periphery of lemnoblasts and near axon-muscle contact regions. We regard the contact regions as the synapses between the autonomic nerves and the smooth muscle cells.

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PubMed1957

The fine structure of capillaries and small arteries.

Details of capillary endothelia of the mammalian heart are described and compared with capillaries of other organs and tissues. Continuous invagination and pinching off of the plasma membrane to form small vesicles which move across the cytoplasm are suggested as constituting a means of active and selective transmission through capillary walls (12). This might be designated as cytopempsis (transmission by cell). The fine structure of the different layers in the walls of small heart arteries is demonstrated. Endothelial protrusions extend through windows of the elestica interna to make direct contact with smooth muscle plasma membranes. The elastica interna appears to vary greatly in both thickness and density, and probably restricts filtration, diffusion, and osmosis to such an extent that windows and the transport mechanisms described (cytopempsis) are necessary for the functional integrity of the smooth muscle layer. The contractile material consists of very fine, poorly oriented filaments.

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PubMed1957

The base of the proximal convoluted tubule cells of rat kidney.

The three dimensional arrangement of the compartments on the base of proximal convoluted tubule cells of rat kidney is described. An extracellular basal labyrinth is found to be enclosed by these compartments. The compartments with their mitochondria and the basal labyrinth are regarded as forming a functional unit. It is supposed that this basal unit serves for excretion of reabsorbed fluid from the cell into the labyrinth and for the development of hydrostatic pressure in the labyrinth to overcome the capillary pressure and to pass the reabsorbed fluid into the blood stream.

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PubMed1957

Electron microscope study of mammalian cardiac muscle cells.

The cellular theory of heart muscle is supported by a detailed description of the intercalary discs. The discs are adjacent plasma membranes separated by an interspace while the sarcolemma appears as plasma membrane, interspace plus basement membrane of the interstitium. The nucleus of the cell is closely associated with the entire cell by way of the endoplasmic reticulum. Transversely it connects the outer nuclear membrane at the level of the Z and M bands with the contractile material and the sarcolemma. Longitudinally it connects the outer nuclear membrane with the plasmalemma at the intercalated discs. The description of the spiral attachment of the endoplasmic reticulum on the outer nuclear membrane supplements earlier observations on the helicoidal structure of the heart muscle cell. Plasma membranes and endoplasmic reticulum are considered to be carriers of membrane potentials and to conduct excitation.

Animals↗
PubMed1956

Electron microscopic and histochemical observations of muscle degeneration after tourniquet.

As an experimental model for the different forms of muscle degeneration, injury caused by 2 hours' ischemia has been studied from 20 minutes to 16 hours after release of the tourniquet. Discoid degeneration developed in stretched fibers by dissolution of the I bands (Z substances and actin). The discs represented the Q bands (A-H-A). In fibers which passively maintained contraction lengths during degeneration, the Z substances were dissolved, but the continuity of the fibrils was preserved, since the filaments are continuous over all sarcomeres under these conditions. Mitochondria and the tubules of the endoplasmic reticulum swelled, ruptured, and disintegrated. Granular degeneration developed in fibers where mitochondria were abundant. Unstretched degenerating fibers with few mitochondria gave a homogeneous or hyaline appearance. The different forms of degeneration therefore were dependent on the status of stretch and the fiber type. The extent of degeneration was not a function of time after ischemia, there being both nearly normal and severely damaged fibers at 20 minutes and 16 hours after the release of tourniquets. When degeneration occurred, however, the basic alterations were the same in all fibers; there was mitochondrial and reticular swelling, dissolution of the Z substances, and finally disintegration of the contractile material. Some damage developed in the sarcolemmas and capillaries. The mitochondrial disintegration was not linked with inactivation of the succinic dehydrogenase system.

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PubMed1956

Comparative cytophysiology of striated muscle with special reference to the role of the endoplasmic reticulum.

1. The structure and distribution of the components of striated muscle cells vary with the species and with the specialization of muscle fiber function. 2. There appear to be two, easily distinguishable, general categories of striated muscle structure. A. High frequency muscle (represented by flight muscle of higher insects and hummingbird, and cicada tympanal muscle) is characterized by widely spaced, non-branching fibrils of large diameter and short period, little endoplasmic reticulum, and large quantities of large mitochondria (low fibril-sarcoplasm ratio). This structure is correlated with heavy tracheolization or vascularization, high oxidative activity, and dark color as compared with other muscles of the same species. B. Low frequency muscle is characterized, in general, by high fibril-sarcoplasm ratio, relatively long period, few mitochondria increasing with activity and decreasing with absolute power of the fiber. Oxidative capacity and color are proportional to the quantity of mitochondria. These fibers are further differentiated into (a) fibrillar arrangement of contractile material which permits a regular pattern of interfibrillar and segmental reticulum, and (b) afibrillar arrangement of contractile material leading to an unsystematic distribution of reticulum. 3. The endoplasmic reticulum appears as a complex coordination system in the muscle fiber. Peripherally, it links the Z and M lines of the fibrils to the sarcolemma and between the fibrils it links the cross-bands, forming the Grundmembran of earlier authors. By longitudinal linkage, it connects with the sarcolemma at the muscle extremity to form a digital arrangement into which the tendon fibrils are spliced. The extent of its development and its position have a definite relationship to the degree and site of fiber shortening. At present the reticulum is the only structure that one can consider to be an internal conducting system. It may distribute the excitation transversely from fibril to fibril, and lengthwise saltatorially to the symmetry centers of the sarcomeres. 4. The nucleus is the mediating element between the cytoplasmic phases within and without the tubular system of the endoplasmic reticulum. A possible mechanism which correlates nucleus, adenylic acid system, ion exchange, and reticulum with the initiation of contraction is postulated.

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