title: Ultrastructural features of the myotendinous junction of the sternomastoid muscle in Wistar rats: from newborn to aging.
abstract: The myotendinous junction (MTJ) is a major area for transmitting force from the skeletal muscle system and acts in joint position and stabilization. This study aimed to use transmission electron microscopy to describe the ultrastructural features of the MTJ of the sternomastoid muscle in Wistar rats from newborn to formation during adulthood and possible changes with aging. Ultrastructural features of the MTJ from the newborn group revealed pattern during development with interactions between muscle cells and extracellular matrix elements with thin folds in the sarcolemma and high cellular activity evidenced through numerous oval mitochondria groupings. The adult group had classical morphological features of the MTJ, with folds in the sarcolemma forming long projections called "finger-like processes" and sarcoplasmic invaginations. Sarcomeres were aligned in series, showing mitochondria near the Z line in groupings between collagen fiber bundles. The old group had altered "finger-like processes," thickened in both levels of sarcoplasmic invaginations and in central connections with the lateral junctions. We conclude that the MTJ undergoes intense activity from newborn to its formation during adulthood. With increasing age, changes to the MTJ were observed in the shapes of the invaginations and "finger-like processes" due to hypoactivity, potentially compromising force transmission and joint stability.
authors.affiliation: Department of Anatomy, Institute of Biomedical Sciences-ICB III, University of São Paulo, São Paulo, Brazil.
authors.forename: Adriano
authors.initials: A
authors.lastname: Polican Ciena
authors.forename: Sonia Regina
authors.initials: SR
authors.lastname: Yokomizo De Almeida
authors.forename: Cristina
authors.initials: C
authors.lastname: De Sousa Bolina
authors.forename: Regina
authors.initials: R
authors.lastname: De Sousa Bolina-Matos
authors.forename: Rose Eli
authors.initials: RE
authors.lastname: Grassi Rici
authors.forename: Marcelo Cavenaghi
authors.initials: MC
authors.lastname: Pereira Da Silva
authors.forename: Maria Angélica
authors.initials: MA
authors.lastname: Miglino
authors.forename: Ii-sei
authors.initials: IS
authors.lastname: Watanabe
mesh_terms: D000375:Aging; D000818:Animals; D000831:Animals, Newborn; D005109:Extracellular Matrix / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D032342:Muscle Cells / Q000648:ultrastructure; D009132:Muscles / Q000648:ultrastructure*; D009334:Neck Muscles / Q000648:ultrastructure*; D051381:Rats; D017208:Rats, Wistar; D012508:Sarcolemma; D013710:Tendons / Q000648:ultrastructure*