ENTRIES A–Z
Philip Winn in Dictionary of Biological Psychology, 2003
Cardiac muscle is essentially skeletal muscle but with certain specific differences to do with the electrical and MEMBRANE properties of individual cells. Cardiac muscles cells have INTERCALATED DISCS (which normal skeletal muscle cells do not have) that provide the opportunity for direct electrical coupling of cells. Action potentials arriving at one site in the heart can be communicated across all cells very quickly, ensuring uniformity of action in generating heartbeats. In addition, cardiac cells can generate their own action potentials without input, being in possession of PACEMAKER CELLS with oscillatory properties (see OSCILLATION). The entire mass of cardiac muscle can be referred to as the MYOCARDIUM, which gives rise to terms such as myocardial and myocardiac: terms such as this simply refer to the musculature of the heart. Smooth muscle is not striated, the myosin and actin containing myofibrils not being organized in the same way as in skeletal muscle. It lacks the contractile power of skeletal muscle but can maintain contraction over great lengths, allowing it to develop peristaltic movements (see PERISTALSIS) to move blood through vessels or gut contents through the digestive tract.
The heart
Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella in Essentials of Human Physiology and Pathophysiology for Pharmacy and Allied Health, 2019
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.
The transport and exchange systems: respiratory and cardiovascular
Nick Draper, Helen Marshall in Exercise Physiology, 2014
The muscle of the heart, known as cardiac muscle or myocardium, is similar to skeletal muscle in that they are both striated and contract by the sliding filament mechanism. Here, the similarity ends. Cardiac muscle fibres are short, branched and contain a single centrally located nucleus. The fibres are arranged in a network to facilitate co-ordinated contraction, and act as a single unit in terms of both structure and function. The plasma membranes of adjacent fibres interlock to form intercalated discs, an identifying feature of cardiac muscle. At an intercalated disc, desmosomes structurally join fibres together preventing separation during contraction, whereas gap junctions allow action potentials to spread across fibres and transfer the force of contraction. The myocardium, therefore, behaves as a single coordinated unit.
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.
Bridging the gap: Super-resolution microscopy of epithelial cell junctions
Published in Tissue Barriers, 2018
Emily I. Bartle, Tejeshwar C. Rao, Tara M. Urner, Alexa L. Mattheyses
Super-resolution studies of the intercalated disc in murine cardiomyocytes are also of interest when considering desmosome structure. AC associated defects in desmosomal proteins, including Pkp2, can result in disruption of the intercalated disc. dSTORM revealed a nanoscale retraction of the microtubule plus end from N-cadherin in Pkp2 deficient mice, suggesting a mechanism for AC that relies on Pkp2 integrity.104 Related work found that, like disruption of Pkp2, truncation of Cx43 dissociated the microtubule plus end from the junction site and resulted in mislocalization of NaV1.5, the sodium channel protein integral to cardiac function.105 The use of dSTORM in these studies linked electrical coupling, cell adhesion, and excitability in the heart through a common mechanism of microtubule attachment.
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
No histopathological alterations or fibrosis were detected by routine light microscopy. However, electron microscopy revealed pathological changes in the endothelial cells and cardiomyocytes in hearts from mice with mammary carcinoma. Platelet aggregates and blood stasis were observed in the capillaries of PyMT+ mice. This is in agreement with previously published data from our group showing impaired perfusion of the myocardium in PyMT+ mice.19 Mitochondria with swollen cristae, an indicator of oxidative stress, were observed in endothelial cells of PyMT+ mice but not in healthy control mice. The intercalated disc (ID), a highly organized type of cell-cell connection along and between neighboring cardiomyocytes, were widened and distorted in PyMT+ mice. The ID is composed of desmosomes, adherens junctions and gap junctions and is essential for synchronous electrical and mechanical coupling between cardiomyocytes and, consequently, for proper myocardial function.33 Based on previous studies connecting disturbances of the ID to cardiomyopathies and remodeling of the myocardium,58,59 it can be surmised that this plays a role in the alterations in the myocardium indicated by the other analyses. PyMT+ mice treated with DNase I had focally slightly widened intercalated discs, but otherwise no differences from healthy mice, indicating a role for NETs in these histological alterations.
Related Knowledge Centers
- Actin
- Cell Junction
- Desmosome
- Gap Junction
- Intermediate Filament
- Multinucleate
- Sarcomere
- Cardiac Muscle
- Fascia Adherens
- Cardiac Action Potential