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An in-depth analysis of muscle tissues, their functions, and structures. It covers the concepts of muscle fibers, sarcoplasm, sarcolemma, myofilaments, myoepithelial cells, pericytes, myofibroblasts, functional and structural classification of muscle, and the organization of skeletal muscle. Additionally, it discusses the conducting system for contractile activity in skeletal muscle and the interaction of myofilaments in muscle cell contraction.
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Histology - 2 nd^ stage
the size and shape of internal organs. This tissue is characterized by aggregates of specialized, elongated cells arranged in parallel array that have the primary role of contraction.
Specializations, unique terms are used for certain structures in muscle cells.
1. Individual muscle cells are called muscle fibers or myocytes 2. The cytoplasm of muscle fibers is called sarcoplasm. 3. The muscle fiber plasma membrane is called the sarcolemma. 4. The smooth endoplasmic reticulum is called the sarcoplasmic reticulum, while mitochondria called **sarcosomes.
➢ Functional classification : is based on the type of neural control divided in to two types: Voluntary Involuntary ➢ Structural classification: is based on the presence or absence of cross striations divided in to two types: Striated No striated (smooth) ➢ Combined functional and structural classification divided in to three types: Skeletal muscle Cardiac muscle
Histology - 2 nd^ stage
Smooth (visceral) muscle. Skeletal muscle tissues: contains bundles of very long, multinucleated cells with cross- striations. Their contraction is quick, forceful, and usually under voluntary control. Organization of a Skeletal Muscle
1. Epimysium is the sheath of dense connective tissue that surrounds a collection of fascicles that constitutes the muscle. The major vascular and nerve supply of the muscle penetrates the epimysium. 2. Perimysium is a thicker connective tissue layer that surrounds a group of fibers to form a bundle or fascicle. Fascicles are functional units of muscle fibers that tend to work together to perform a specific function. Larger blood vessels and nerves travel in the perimysium. 3. Endomysium is the delicate layer of reticular fibers that immediately surrounds individual muscle fibers .Only small-diameter blood vessels and the finest neuronal.
Myofibrils and Myofilaments (Actin and Myosin Filaments) A muscle fiber is filled with longitudinally arrayed structural subunits called myofibrils Myofibrils consist of an end-to end repetitive arrangement of sarcomeres. The A and I banding pattern in sarcomeres is due mainly to the regular arrangement of thick and thin myofilaments, composed of myosin and F-actin, respectively, organized within each myofibril in a symmetric pattern containing thousands of each filament type. Organization within Muscle Fibers
Histology - 2 nd^ stage
The conducting system for contractile in skeletal muscle (Sarcoplasmic Reticulum &Transverse Tubule System) In skeletal muscle fibers the smooth ER, or (sarcoplasmic reticulum), is specialized for Ca2+^ sequestration, and cause uniform contraction of all myofibrils, the sarcolemma is folded into a system of transverse or T tubules it is long fingerlike invaginations of the cell membrane penetrate deeply into the sarcoplasm and encircle every myofibril near the aligned A- and I-band boundaries of sarcomeres. Adjacent to each side of every T tubule are expanded terminal cisterns of the sarcoplasmic reticulum. The complex of a T tubule with two closely associated small cisterns of sarcoplasmic reticulum on each side is known as a triad. After depolarization of the sarcoplasmic reticulum membrane, calcium ions concentrated within these cisternae are released through Ca2+^ channels in the membrane into cytoplasm surrounding the thick and thin filaments. Ca2+ binds troponin and allows bridging between actin and myosin molecules. When the membrane depolarization ends, the sarcoplasmic reticulum pumps Ca2+ back into the cisternae, ending contractile activity.
Histology - 2 nd^ stage
types of myofilaments are associated with cell contraction
1. Thin filaments are composed primarily of the protein actin. Each thin filament of fibrous actin ( F-actin ) is a polymer formed from globular actin molecules ( G-actin ). 2. Thick filaments are composed of the protein myosin consists of tail and head (contain binding site for actin and for ATP, ATPase). this myofilament consist of two types: A. Tropomyosin is protein of double helix of two polypeptides. B. Troponin complex consists of a three globular subunits. Troponin-C (TnC) It binds Ca2+ Troponin-T (TnT) , binds to tropomyosin Troponin-I (TnI) , thus inhibiting actin–myosin interaction
Smooth muscle tissues: is specialized for slow, steady contraction and is controlled by a variety of involuntary mechanisms (also called visceral muscle) are elongated, tapering, and nonstriated cells, form the walls of most hollow organs with the exception of the heart.
Histology - 2 nd^ stage
roots of large vessels where they join the heart.
Structure of cardiac muscle fibers