The sarcomeres is the basic structural unit of striated muscle, and under microscopy appear as alternating dark and light bands. Within the sarcoplasm there are also lipid droplets, glycogen, and myoglobin. The sarcoplasmic reticulum is a continuous membrane that is analogous to the endoplasmic reticulum of other cells. The important organelles are the Golgi apparatus, mitochondria, and the sarcoplasmic reticulum. It contains a cellular matrix and organelles, and is exclusive of the nuclei. Within the muscle fibre is the sarcoplasm which is similar to the cytoplasm of other cells. There are also satellite cells on the surface of the muscle which are thought to be stem cells. It has a good capillary supply.Įach muscle fibre has numerous nuclei, and these are generally found at the periphery of the fibre just under the sarcolemma. The endomysium consists of the basement membrane, reticular layer, and the close layer or matrix and collagen fibres. The principal components are collagen, laminin, fibronectin, and other specific glycoproteins. The basement membrane consists of several protein and carbohydrate components produced by the muscle fibre and fibroblasts. The basement membrane merges with the reticular layer and the extracellular matrix. The basement membrane has an inner layer called the lamina rara or lucida, and an outer denser layer called the lamina densa. External to the sarcolemma is the basement membrane. Blood vessels are also found within connective tissue.Īt the cellular level, muscle fibres are surrounded by the sarcolemma which is the plasma membrane. Epimysium loosely surrounds the whole muscle to allow for length changes. The fibres are arranged into fascicles, which are visible to the naked eye. The endomysium surrounds individual fibres and is delicate. Muscle fibres are surrounded by connective tissue which binds the contractile units together. Oblique orientation is seen in pennate, bipennate, multipennate, and other more complex fibre arrangements. Muscle fibres are arranged in either a parallel or oblique direction along the long axis of the muscle. Sarcomeres are seen in both cardiac and skeletal muscle. Muscle fibres contain numerous tubular myofibrils, which in turn are composed of repeating sections of sarcomeres. Muscle fibres are a syncytium of many cells fused together with multiple nuclei to form single long "cells". Muscle fibres are covered by the endomysium. Bundles of muscle fibres, called fascicles, are covered by the perimysium. The hierarchical structure of skeletal muscle. Calcium is dissociated from troponin and a conformational change occurs in tropomyosin preventing further cross-bridge attachment.With muscle relaxation there is active transport of calcium into the longitudinal tubules of the sarcoplasmic reticulum.Through costameres, the majority of force production is transmitted laterally to surrounding myofibrils.With interaction of contractile proteins muscle contraction occurs along with force production.ATP is hydrolysed providing the energy for the sarcomeres to shorten or to resist stretch by pulling the thin filaments arrays into the thick filament arrays.Calcium binds to the thin filaments and causes a conformational change allowing interaction between thick and thin filaments.Calcium is released from the sarcoplasmic reticulum.The electrical potentials pass along the muscle surface and into the fibres via the transverse tubules.Electrical potentials are generated in the muscle membranes.
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