Muscle Tissue PDF

Muscle tissue Ema Bexheti What is muscle tissue ? Muscle tissue is specialized for movement. Their main function is to generate force through contraction. Which this movement is generated by the interaction of the proteins actin and myosin. It effects movement of the limbs and body pa...

Muscle tissue Ema Bexheti What is muscle tissue ? Muscle tissue is specialized for movement. Their main function is to generate force through contraction. Which this movement is generated by the interaction of the proteins actin and myosin. It effects movement of the limbs and body parts (skeletal muscle muscle) Changes dimensions of internal organs like smooth muscle. Moves blood through the chambers of the heart in cardiovascular system (cardiac muscles) Functional appearance of sarcomere Classification of Muscle Tissue Striated muscle (showing Non-Striation muscle ( do striation) not show striation) Skeletal Muscle  Smooth Muscle Visceral muscle Cardiac Muscle Striated Muscle Skeletal Muscle Basic building blocks is striated muscle fiber The striation is caused by the arrangement of contractile subunits, myofibril, composed mainly of actin and myosin. Cardiac Muscle Consists of cardiomyocytes which have internal structure similar to the striated skeletal muscle. Innervation provided by its own conduction system (regulated by autonomic nerves) Skeletal muscle tissue Basic unit of skeletal muscle is formed by myoblast during embryogenesis. The contractile myofilaments fill the cytoplasm of syncytium (originates by the fusion of man unicellular precursors of skeletal muscle fibers. Each syncytium consists of tens to hundred of nuclei. They create larger units called sarcomere, and so bunch of sarcomeres form myofibrils. The cytoplasm of the muscular fiber is called sarcoplasm and the mitochondria are called sarcosomes Sarcolemma refers to three layers of the muscle fiber surface. Muscle fibers can be divided into red and white and according to the amount of glycogen. Skeletal muscle contraction is controlled by free will EPIMYSIUM Cardiac muscle tissue Composed of Cardiac myocytes. These cells are stretched in the longitudinal axis with a centrally located nucleus, with one two and exceptionally more cellular processes at the terminal segments of the cells which connect to adjacent cardiomyocytes forming a network. Cardiac muscle cell work continuously and without fatigue throughout our lives; therefore they perfectly adapt to aerobic metabolism. Smooth muscle tissue They don’t show transverse striation and is made of smaller spindle shaped cells connected to each other and stretched to an average length of 20-50 micrometer. Each cell is surrounded by a basal lamina and a network of reticular fibers, loose collagenous connective tissue with a number vessels and nerves is present between the cells. The nucleus of the smooth muscle is elongated. The contraction of smooth muscle tissue is involuntary. Forms the walls of vessels and internal organs, but also found in the skin. Innervated by autonomic nerves. Longitudinal and Transverse Sections of Skeletal (Striated) Muscles: Tongue Each skeletal muscle fiber (9, transverse section; 11, longitudinal section) is multinucleated. The nuclei (1, 6) are situated peripherally and below the sarcolemma of each muscle fiber. (The sarcolemma is not visible in the figure.) Also, each skeletal muscle fiber shows cross-striations (3) that are visible as alternating dark A bands (3a) and light I bands (3b). With higher magnification and transmission electron microscopy, additional details of the cross-striations are visible (see Figs. 8.5 and 8.6). Skeletal muscle fibers are aggregated into bundles or fascicles (15), surrounded by fibers of connective tissue (5) sheath around each muscle fascicle (15) called the perimysium (12). From each perimysium (12), thin partitions of connective tissue extend into each muscle fascicle (15) and invest individual muscle fibers (9, 11) with a connective tissue layer called the endomysium (4, 7). Small blood vessels (8) and capillaries (2, 14) are present in the connective tissue (5) around each muscle fiber (9, 11). The skeletal muscle fibers that were sectioned longitudinally (11) show light and dark cross-striations (3a, 3b). The muscle fibers that were sectioned transversely (9) exhibit cross sections of myofibrils (13) and peripheral nuclei (6). Skeletal Muscle Fibers (Longitudinal Section) Skeletal Muscles, Nerves, and Motor Endplates A group of skeletal muscle fibers (6, 7) have been teased apart and stained to illustrate nerve terminations or myoneural junctions on individual muscle fibers. The characteristic cross-striations (2, 8) are visible in each muscle fiber (6, 7). The dark-stained, stringlike structures between the separated muscle fibers (6, 7) 303 are the myelinated motor nerves (3) and their branches, the axons (1, 5, 10). The motor nerve (3) courses within the muscle, branches, and distributes its axons (1, 5, 10) to the individual muscle fibers (6, 7). The axons (1, 5, 10) terminate on individual muscle fibers as specialized junctional regions called motor endplates (4, 9). The small, dark, round structures seen in each motor endplate (4, 9) are the terminal expansion of the axons (1, 5, 10). Some axons (1) are also seen without motor endplates as a result of tissue preparation. Cardiac Muscle in Longitudinal Section The cross-striations (1) are similar in both the skeletal and cardiac muscle types but are less prominent in cardiac muscle fibers. The branching cardiac fibers (9) are in contrast to the individual, elongated fibers of the skeletal muscle. The characteristic intercalated discs (5, 7) of cardiac muscle fibers and their irregular structure are more prominent at higher magnification. The intercalated discs (5, 7) appear as either straight bands (5) or staggered (7) across individual fibers. The large, oval nuclei (3), usually one per cell, are centrally located in cardiac fibers, in contrast to the multiple flattened and peripheral nuclei in 311 skeletal muscle fibers. Surrounding the nucleus of a cardiac muscle fiber is a prominent perinuclear sarcoplasm (2, 10) that is devoid of cross-striations and myofibrils. The connective tissue fibrocytes (6, 8) and the fine connective tissue fibers of endomysium (4) surround the cardiac muscle fibers. Capillaries with erythrocytes (11) are normally seen in the endomysium (4, 6, 8). Smooth Muscle: Wall of Small Intestine (Transverse and Longitudinal Section) A photomicrograph of the small intestine illustrates its muscular outer wall. The smooth muscle fibers are arranged in two layers: an inner circular layer (7) and an outer longitudinal layer (8). In the inner circular layer (7), a single nucleus (1) is visible in the center of the cytoplasm (2) of different fibers. In the outer longitudinal layer (8), cut in transverse section, the cytoplasm (5) appears empty, and single nuclei (6) of individual muscle fibers are visible if the plane of section passes through them. Located between the two smooth muscle layers is a group of autonomic neurons of the myenteric nerve plexus (3). Small blood vessels (4) are seen between individual muscle fibers and muscle layers.