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Neuromuscular Physiology
Published in Michael H. Stone, Timothy J. Suchomel, W. Guy Hornsby, John P. Wagle, Aaron J. Cunanan, Strength and Conditioning in Sports, 2023
Michael H. Stone, Timothy J. Suchomel, W. Guy Hornsby, John P. Wagle, Aaron J. Cunanan
Differentiation of smooth muscle and striated muscle can be accomplished by a variety of methods, particularly microscopic appearance. For example, smooth muscle fibers are mononucleated and their sarcomeres (the functional units of muscle) are arranged at oblique angles. Resulting from the orientation of its sarcomeres, smooth muscle appears to be relatively indistinctive (smooth), as viewed through a light microscope. Striated muscle fibers contain protein arrays (myofibrils) in parallel to each other and thus form striations (stripes). Cardiac muscle fibers can be easily identified from skeletal muscle by appearance. For example, unlike skeletal muscle fibers, cardiac muscle fibers have a distinct end. The ends are termed intercalated discs. So, one cardiac muscle fiber consists of the substance between two intercalated discs. The intercalated discs are somewhat thicker than the striations but are usually darker and distinctive. Under a light microscope, intercalated disks appear as relatively dark lines running from one side of the fiber to the other. Cardiac muscle fibers contain only one or occasionally two nuclei and there are differences in function, such as an intrinsic ability to contract. (A detailed discussion dealing with smooth and cardiac muscle is not within the scope of this book.)
Striated MusclesSkeletal and Cardiac Muscles
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
Cardiac muscle is striated, but the pattern is not as ordered as in skeletal muscle. The striations are similar to those of skeletal muscle cells, being made up of sarcomeres (between Z lines) containing thick myosin filaments (in the A band) and thin actin filaments (in the I band), which are attached to the Z lines. Compared with skeletal muscle, cardiac muscle cells are shorter and thicker and form branching networks with intercalated discs between the ends of adjacent fibres that contain low-electrical-resistance gap junctions. Cardiac muscle functions as a syncytium due to the presence of low-resistance connections between adjacent cells, and when an action potential is generated, the atria or the ventricles contract together. The mechanical connections that prevent the cells from pulling apart include the desmosomes and fascia adherens.
The heart
Published in Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella, Essentials of Human Physiology and Pathophysiology for Pharmacy and Allied Health, 2019
Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella
There are also important differences between skeletal muscle and cardiac muscle. Skeletal muscle cells are elongated and run the length of the entire muscle. Furthermore, there is no electrical communication between these cells. Cardiac muscle cells, on the other hand, are considerably shorter than skeletal muscle fibers, and they branch and interconnect with each other. Intercellular junctions found where adjoining cells meet end-to-end are referred to as intercalated discs. There are two types of cell-to-cell junctions within these discs. Desmosomes hold the muscle cells together and provide the structural support needed when the heart beats and exerts a mechanical stress that would tend to pull the cells apart. Gap junctions are areas of very low electrical resistance (1/400 the resistance of the outside membrane) that allow free diffusion of ions. It is through the gap junctions that the electrical impulse, or heartbeat, spreads rapidly from one cell to another and forms the myocardium into a syncytium, where the initiation of a heartbeat in one region of the heart results in the stimulation and contraction of all the cardiac muscle cells at essentially the same time. The heart is composed of two syncytiums: the atrial syncytium and the ventricular syncytium. In each case, but particularly in the ventricles, the simultaneous stimulation of all the muscle cells results in a more powerful contraction, facilitating the pumping of the blood.
Neutrophil extracellular traps promote cancer-associated inflammation and myocardial stress
Published in OncoImmunology, 2022
J. Cedervall, M. Herre, A. Dragomir, F. Rabelo-Melo, A. Svensson, C. Thålin, A. Rosell, V. Hjalmar, H. Wallén, H. Lindman, G. Pejler, E. Hagström, M. Hultström, A. Larsson, AK. Olsson
While no apparent histological alteration and no fibrosis was observed with light microscopy (data not shown), analysis by electron microscopy revealed several signs of inflammation and tissue damage in hearts from tumor-bearing mice (Fig. S3), including general blood stasis and platelet aggregation in the capillaries of PyMT+ mice (Fig. S3A). Endothelial cells had mitochondria with swollen cristae (Fig. S3B), an indicator of oxidative stress. Cardiomyocytes displayed focally broken cell membranes and the desmosomal gaps of the intercalated discs, connecting neighboring cardiomyocytes in the myocard,33 were widened and distorted (Fig. S3C and D). These alterations were not detected in myocardium from PyMT+ mice treated with DNase I. Interstingly, we detected fibrils of about 11 nm in diameter and “beads on a string” appearance in a PyMT+ mouse capillary lumen, closely resembling previously published TEM pictures of NETs (Fig. S3E).
Epithelial maturity influences EPEC-induced desmosomal alterations
Published in Gut Microbes, 2019
Jennifer Lising Roxas, Gayatri Vedantam, V.K. Viswanathan
We recently reported that enteropathogenic Escherichia coli (EPEC) perturbs desmosomes.16 EPEC effector protein EspH, via its Rho GTPase inhibitory function, induces keratin IF retraction and desmosomal disruption. Beyond EPEC pathogenesis, our studies provide insights on how desmosomes are maintained, particularly in the intestines, and expand our knowledge of the role of Rho GTPases in desmosomal assembly and stability. Impaired Rho GTPase signaling has also been implicated in desmosomal disorders of the heart and the skin.17–19 In the murine heart, inhibition of Rho-kinase, a downstream signaling effector of Rho GTPases, during early cardiac development resulted in junctional abnormalities including less dense desmosomes, widened intercellular gaps at the intercalated discs and translocation of plakoglobin to the nucleus.19 In keratinocytes, Rho GTPase inhibition plays a critical role in the pathophysiology of pemphigus vulgaris and pemphigus foliaceus. Similar to our findings, locking RhoA in the active state via the use of cytotoxic necrotizing factor abolished keratin retraction and the DSG3 loss associated with pemphigus.18
Immunization with plasmids encoding M2 acetylcholine muscarinic receptor epitopes impairs cardiac function in mice and induces autophagy in the myocardium
Published in Autoimmunity, 2018
Karla Consort Ribeiro, Roberto Perez Campelo, Daniela del Rosário Flores Rodrigues, Elisabete C. Mattos, Izaira Trincani Brandão, Célio Lopes da Silva, Eliete Bouskela, Camila Guerra Martinez, Eleonora Kurtenbach
Intercalated disc splitting emerged as a novel structural alteration observed in the myocardium of M2R epitope-immunized mice. The intercalated disc functions as a prominent junctional complex that mechanically and electrically couples cardiomyocytes to each other. A report describing the occurrence of intercalated disc disruption in the myocardia of murine desmoglein-2-mutant mice that develop DCM concomitantly showed the appearance of multiple autophagic vacuoles, swollen mitochondria with disrupted cristae and abnormal Z-disc structure [47]. Accordingly, a biopsy study of cardiac tissue taken from 19 patients with end-stage HF due to idiopathic DCM reported intercalated disc splitting as part of autophagic cell death associated with major defects in the ubiquitin/proteasome cascade [48]. Consistent with these observations, we postulated that altered myocardium sarcomeres, detachment of intercalated discs and vacuolization present in DM2R-il3 mice (Supplementary Figure 2) may be associated with an autophagic process and account for the observed cell uncoupling.