Neuromuscular Physiology
Michael H. Stone, Timothy J. Suchomel, W. Guy Hornsby, John P. Wagle, Aaron J. Cunanan in Strength and Conditioning in Sports, 2023
Several proteins make up the Z-disc including spectrin, vimentin, synemin, desmin, and α-actinin. Actin myofilaments are attached to both sides of the Z-discs by α-actinin (127). Desmin, vimentin, and synemin form a structural scaffolding that wraps around the actin myofibrils and the Z-disc. The central part of α-actinin consists of four tandem spectrin-like repeats each of which comprises a triple α-helix anti-parallel bundle. The specialized ends of the dimer allow α-actinin to crosslink with actin myofilaments. Together these proteins serve to hold the actin myofibrils in position at rest and during stretch or contraction. Additionally, Z-disc proteins are connected to the cytoskeletal proteins in the sarcolemma and basement membrane and ultimately to the endomysium connective tissue surrounding the muscle fiber (see Table 1.2).
The locomotor system
C. Simon Herrington in Muir's Textbook of Pathology, 2020
The largest tissue within the body, muscle, accounting for 40% of an average male's weight, is highly organized to contract, produce movement or stability, and do work. Skeletal muscle consists of long multinucleated syncytia formed by the fusion of columns of single cells. The cytoplasm contains bundles of myosin and actin filaments forming contractile myofibrils. The individual subunit is the sarcomere and these are arranged end to end to form muscle fibres. The parallel alignment of actin and myosin bundles gives a characteristic band-like appearance on light microscopy and alternating dark (A, anisotropic) and light (I, isotropic) bands are seen on electron microscopy. A variety of other proteins including α-actinin and dystrophin are found within muscle cells. The individual muscle fibre is surrounded by the endomysium. Fibres are bound into fascicles by the perimysium, whereas the muscle itself is sheathed by the epimysium.
Effects of introducing gap constraints in the masticatory system: A finite element study
J. Belinha, R.M. Natal Jorge, J.C. Reis Campos, Mário A.P. Vaz, João Manuel, R.S. Tavares in Biodental Engineering V, 2019
The jaw muscles present in our model are the lateral pterygoid, digastric, masseter, temporalis and medial pterygoid. Muscles are composed by two entities, one representing the fibrous part and the other the tendon. Hill’s muscle model was employed to represent the fibers and an inextensible wire to represent the tendons, because they undergo very small deformation and may, for this reason, be ignored. In total, eight truss elements represent the following muscles (on each side): Anterior and posterior temporalis, superficial and deep masseter, superior and inferior lateral pterygoid, medial pterygoid and digastric. Muscle fibers are composed by myofibrils. In the case of striated muscles, the myofibrils are arranged into contractile units called sarcomeres. Forces produced by this type of muscle are influenced by the length of their sarcomeres (force-length relationship) and their contraction velocities (force-velocity relationship). Additionally, the muscle exhibits a passive elastic force when stretched. In our model, the characteristic curves of the muscle are taken from van Ruijven & Weijs (1990).
Biologics in refractory idiopathic inflammatory myositis (IIM): What experience in juvenile vs adult myositis tells us about the use of biologics in pediatric IIM
Published in Modern Rheumatology, 2021
Anjali Patwardhan, Charles H. Spencer
Historically, IIM was recognized as antibody driven-complements mediated microangiopathy that involved skin, internal organs, and muscles. It was believed that B cells play a crucial role. Pieces of evidence supported the autoimmune etiology of IIM, suggesting the role of B cells. Evidence was found of immune-mediated muscle damage, presence of myositis-specific and associated autoantibodies (MAS, MSA), infiltration of muscles with immune cells in myofibrils, and the overexpression of major histocompatibility complex (MHC, class I and II) on these myofibrils and other muscle components [1]. However, since 2005 it has been recognized that inappropriate stimulation of the innate immune system (interferons and interferon-regulated proteins) followed by dysregulation of the adaptive immune response through dendritic cells is also crucial to IIM etiopathology, especially in DM and JDM [2,3].
Ultrastructural changes of extraocular muscles in strabismus patients
Published in Ultrastructural Pathology, 2019
Yahya Al-Falki, Mubarak Al-Shraim, Nasser A. Alsabaani, Refaat A. Eid, Khaled Radad
The six EOMs differ from other skeletal muscles in the body with two unique fiber systems. One resembles usual skeletal muscles fibers “fibrillenstructur” which consist of small and well-organized myofibrils surrounded by abundant sarcoplasm, a large number of mitochondria and peripherally located nuclei. The second unique fibers “felderstructur” contain large and partially fused myofibrils embedded in scanty sarcoplasm, few numbers of mitochondria and centrally located nuclei.11,12 Similar to other findings5,12, light microscopic examination of EOMs in our study showed tightly aligned and normally arranged muscle fibers with clear striations. By TEM, EOMs appeared consisting of skeletal muscle fibers with intact basal membrane and sarcolemma, large and tightly aligned myofibrils with well-arranged sarcomeres, Z line and H zone, and normally distributed mitochondria.
The therapeutic potential of a calorie-restricted ketogenic diet for the management of Leber hereditary optic neuropathy
Published in Nutritional Neuroscience, 2019
Mithu Storoni, Matthieu P. Robert, Gordon T. Plant
A ketogenic diet (in the form of a modified Atkins diet protocol) has recently been used in the setting of progressive external ophthalmoplegia (PEO) with mitochondrial myopathy.80 The diet caused progressive muscle damage in all five patients in the study, but healthy control subjects were unaffected. Patients started to experience muscle pain after only a few days on the diet and had rising levels of creatine kinase and myoglobin in serum. The pain began in the lower extremities, and gradually ascended to the arms and neck. Although most muscle fibres appeared normal on histological examination, some myofibrils showed signs of acute degeneration. Histological examination of these degenerating fibres revealed enlarged, subsarcolemmal mitochondria with paracrystalline inclusions, suggesting they were ragged-red-fibres (RRFs). According to the muscle transcriptomic analysis, the diet had upregulated beta-oxidation and fatty acid transport pathways in healthy controls and not in PEO patients. Aside from muscle, no other tissue or organ was adversely affected in the study. It is possible that mitochondria within affected RRFs may have relied extensively on glycolysis and were unable to use ketones or fatty acids as fuel, owing to a significant compromise in respiratory chain function. Of note, a ketogenic diet did not have a similar effect on a Deletor mice model of progressive late-onset mitochondrial myopathy, in a previous study.81