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).
Functional Anatomy
James Crossley in Functional Exercise and Rehabilitation, 2021
Skeletal muscle is composed of many individual muscle fibers wrapped together in bundles. Connective tissue known as fascia covers each of these bundles. The outer layer that covers the whole muscle is called the epimysium. The epimysium runs into tendon of the muscle that attaches and transmits force to the bone. Muscles attach to bone proximally (origin) and distally (insertion). Origin – muscle attachment that is generally more proximal and moves the leastInsertion – muscle attachment that is generally more distal and moves the most Under the epimysium we see bundles of muscle fibers known as the fascicles, wrapped in fascia called the perimysium. Each muscle fiber is wrapped in a connective tissue called the endomysium. Each muscle fiber forms the building blocks of muscle called myofibrils.
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.
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
Pompe disease: An Indian series diagnosed on muscle biopsy by ultrastructural characterization
Published in Ultrastructural Pathology, 2018
Aanchal Kakkar, Mehar C. Sharma, Aruna Nambirajan, Sheffali Gulati, Rohit Bhatia, Vaishali Suri, Chitra Sarkar
The pathogenetic mechanism in PD is the intralysosomal accumulation of glycogen, accompanied by defects in autophagy.1 More than 450 mutations have been reported in the GAA gene, leading to deficient GAA enzyme activity. The lack of GAA enzymatic activity results in reduced breakdown of glycogen, which accumulates within lysosomes, leading to their swelling and subsequent rupture with spill of glycogen into the cytoplasm, which in turn promotes autophagy.3 The resultant cellular damage causes displacement of myofibrils, cumulating in muscle weakness. The identification of pools of autophagic vacuoles and debris within skeletal muscle on electron microscopic examination has confirmed that autophagy plays an important role in the pathogenesis of PD25,26; our findings on ultrastructural examination support this as well.