Myofiber
Pritam S. Sahota, Robert H. Spaet, Philip Bentley, Zbigniew W. Wojcinski in The Illustrated Dictionary of Toxicologic Pathology and Safety Science, 2019
is a single skeletal muscle cell, also referred to as a myocyte. These cells contain multiple nuclei and can be very long within the muscle fascicle. Myofibers contain contractile components made up of actin and myosin myofilaments. On mammalian tissue sections, skeletal muscle myofibers are distinguished based on histochemical or immunohistochemical characteristics. Skeletal muscle fibers are classified into type I, type IIA, type IIB, and type IIX (or IID). The type IIB fibers described in earlier studies have been reclassified as type IIX and the type IIB fiber does not exist in human muscles. There is little information on existence of fiber type IIX in nonhuman primates. Hybrid fibers have also been described in various muscles (types I and IIA; types IIA and IIX; types IIX and IIB). Type I and II fibers can be distinguished using myofibrillar ATPase histochemistry by varying pH or by immunohistochemistry using antimyosin heavy chain antibodies. Type I fibers or oxidative fibers have more lipid droplets, contain more myoglobin and more mitochondria, and therefore stain more deeply with succinate dehydrogenase, NADH dehydrogenase, or cytochrome c oxidase, enzymes that are part of the respiratory chain. Phosphorylase and phosphofructokinase involved in the breakdown of glycogen stain predominantly type II fibers.
Introduction: Background Material
Nassir H. Sabah in Neuromuscular Fundamentals, 2020
An important subset of living cells is excitable cells, which, when stimulated by an adequate stimulus of appropriate strength, undergo specific changes in the ionic permeabilities of their cell membranes. These permeability changes cause variations in the voltage across the cell membranes of excitable cells, which can result in a characteristic electric signal known as the action potential (AP) or nerve impulse (Chapter 3). The most important excitable animal cells are:(i) sensory cells, or receptors, which respond directly to environmental stimuli such as light, touch, taste, and smell,(ii) nerve cells, or neurons, whose primary function is the processing and transmission of information, and(iii) muscle cells, whose primary function is the development of a mechanical force of contraction. Neurons are discussed in Chapter 7, muscle cells and their receptors in Chapter 9. Neurons are the core of the nervous system (Section 1.3).They have a wide variety of sizes and shapes that serve their particular functions (Section 7.1).The number of neurons in the brain is estimated at 86 billion, with less than 1 billion in the brainstem (Section 1.3) and the spinal cord.Typically, a neuron has four distinct regions that are specialized in terms of function (Figure 1.4):The cell body, also referred to as the perikaryon or soma (plural somas or somata), and which contains the nucleus.The dendritic tree, or dendrites, which are a branched, tree-like structure that extends for up to about a few mms from the cell body.The dendrites are only diagrammatically illustrated in Figure 1.4.They are generally much more elaborate (Figure 7.1).The axon, which is a relatively long process that extends from the cell body and which can vary in length from a fraction of a millimeter to about one meter in an adult human.
Energy Demand of Muscle Machines
Peter W. Hochachka in Muscles as Molecular and Metabolic Machines, 2019
The fundamental structure of muscle is well described in many biochemistry and physiology texts and reviews, and therefore in the next sections we will present only a relatively brief discussion of this topic. Although we feel that readers already familiar with this section may skip it completely, we consider that knowledge of the basic structural data is essential to our later arguments. For many years, it has been known that all vertebrate skeletal muscles display a striated appearance when examined under the light microscope. Such muscles consist of cells, each of which is surrounded by an electrically excitable membrane called the sarcolemma. A muscle cell contains many parallel myofibrils, each about 1 μm in diameter. Electron microscopy of many different kinds of skeletal muscles reveals a common functional unit, called the sarcomere, repeating every 2.3 μm (23,000 Å) along the fibril axis. A dark Å band and a light I band alternate regularly. The central region of the A band, termed the H zone, is less dense than the rest of the band. A dark M line is found in the middle of the H zone. The I band is bisected by a very dense narrow Z line, a kind of proteinaceous coupling of adjacent sarcomeres (Figure 4–1). Electron micrographs of cross-sections of myofibrils show that there are two kinds of interacting protein filaments. The thick filaments have diameters of about 150 Å, whereas the thin filaments have diameters of about 70 Å. The thick filaments primarily consist of myosin. Thin filaments contain actin, tropomyosin, and troponin. Alpha-actinin is present in the Z line, whereas an M-protein is located in the M line.
The hidden role of the Sigma1 receptor in muscle cells
Published in Journal of Receptors and Signal Transduction, 2020
Michał Skrzycki, Beata Kaźmierczak
This review describes the very specific role of Sigma1 receptor in different types of muscle cells. Sigma1 receptor is a transmembrane protein residing in such structures like MAM. It has chaperoning activity supporting function of many proteins, particularly ion channels, including Ca2+ channels. This latter function is of particular meaning for muscle cells, due to their calcium-based/regulated metabolism. Here we discuss new reports pointing to participation of Sigma1 receptor in muscle specific processes like contraction, EC-coupling, calcium currents and in diseases like left ventricular hypertrophy, transverse aortic stenosis and hypertension-induced heart dysfunction.
Electrical stimulation as a biomimicry tool for regulating muscle cell behavior
Published in Organogenesis, 2013
Samad Ahadian, Serge Ostrovidov, Vahid Hosseini, Hirokazu Kaji, Murugan Ramalingam, Hojae Bae, Ali Khademhosseini
There is a growing need to understand muscle cell behaviors and to engineer muscle tissues to replace defective tissues in the body. Despite a long history of the clinical use of electric fields for muscle tissues in vivo, electrical stimulation (ES) has recently gained significant attention as a powerful tool for regulating muscle cell behaviors in vitro. ES aims to mimic the electrical environment of electroactive muscle cells (e.g., cardiac or skeletal muscle cells) by helping to regulate cell-cell and cell-extracellular matrix (ECM) interactions. As a result, it can be used to enhance the alignment and differentiation of skeletal or cardiac muscle cells and to aid in engineering of functional muscle tissues. Additionally, ES can be used to control and monitor force generation and electrophysiological activity of muscle tissues for bio-actuation and drug-screening applications in a simple, high-throughput, and reproducible manner. In this review paper, we briefly describe the importance of ES in regulating muscle cell behaviors in vitro, as well as the major challenges and prospective potential associated with ES in the context of muscle tissue engineering.
Vaginal leiomyoma presenting as a lateral vaginal wall mass
Published in Southern African Journal of Gynaecological Oncology, 2017
Elize Isabella Wethmar, Arnold D Mouton, Greta Dreyer
Leiomyomas are classified as benign mesenchymal neoplasms and consist of smooth muscle cells with variable amounts of fibrous stroma. The tumours occur most frequently in the uterus, affecting 20–30% of women of reproductive age but vaginal leiomyomas are rare with only around 300 cases reported since the first case was described in 1733. These tumours are thought to arise from Müllerian smooth muscle cells in the sub-epithelium of the vagina. Vaginal leiomyomas are usually situated in the anterior vaginal wall. This article reports a case of primary leiomyoma arising from the left lateral vaginal wall, which presented with vaginal discharge and a lateral vaginal wall mass.