Muscles Histology PDF

Assessment muscles Histology of muscles: 288228 1. Histological structure and localisation of smooth muscle tissue Are small elongated spindle shaped cells with finley tapered ends. These cells do not have a striated appearance because they do not contain muscle sarcomeres. Instead, arrays of acti...

Assessment muscles Histology of muscles: 288228 1. Histological structure and localisation of smooth muscle tissue Are small elongated spindle shaped cells with finley tapered ends. These cells do not have a striated appearance because they do not contain muscle sarcomeres. Instead, arrays of actin filaments, connected to dense bodies, surround myosin filaments in a less well- organized fashion. They are specialized for slow, prolonged contractions. Contraction of smooth muscle is triggered by a variety of impulses, including mechanical (passive stretching), electrical (depolarization at nerve endings), and chemical (hormones acting by a second messenger) stimuli. Smooth muscle cells in different organs have different functions. The contractile function of vascular smooth muscle regulates the luminal diameter of the small arteries - arterioles. Thereby contributing significantly to setting the level of blood pressure. In the digestive tract, smooth muscle contracts in a rithmic peristaltic fashion, rhythmically forcing foodstuffs through the digestive tract as the result of phasic contraction. SMooth muscle are also found in urinary tract Of all the muscle types, smooth muscle cells have the greatest capacity for regeneration.They can divide and increase in number. Numerous cells called pericytes, which lie along the small blood vessels can divide and generate new smooth muscle cells. Smooth muscle cells can also hypertrophy 2. Histological structure and localisation of skeletal muscle tissue Skeletal muscle fibers are the largest cells in the body, with a single cell stretching from one end of the muscle to the other. SKeletal muscle fibers contain thousands of nuclei, which are required to maintain a cell of this size. These muscle fibers are single, multinucleated cells. The nuclei are found at the cell periphery, and there is approximately one nucleus every 3μm along the fiber length. Multinucleated skeletal muscle fibers are formed by the fusion of many mononucleated cells (myoblasts) together during development, and growth. The structural and functional subunit of the muscle fiber is the myofibril. It is composed of precisely aligned myofilaments: Myosin- containing thick filaments and actin- containing thin filaments. In longitudinal sections, muscle fibers have a stripes appearance. These strips result from the arrangement of repeating units called sarcomeres in series along the fiber. In skeletal muscle, sarcomeres are about 2.5μm long. A fiber, 30 cm long, contains 120 thousand sarcomeres arranged end to end. Sarcomeres are the smallest contractile unit of started muscle. The arrangement of thick and thin filaments gives rise to the density differences that produce the cross- stations of the myofibril. The light-staining isotropic I band contains mainly thin filaments attached to both sides of the Z line, and the dark-staining anisotropic A band contains mainly thick filaments. The actomyosin cross-bridge cycle represents a series of coupled biochemical and mechanical events between myosin heads and actin molecules that lead to muscle contraction. Muscle fiber (myofibers) are terminally differentiated and do not undergo mitosis. But satellite cells, which are skeletal muscle stem cells, can repair damaged muscle fibers. These cells lie under the basal lamina of the muscle fibers. When the muscle is damaged, they are stimulated to divide to generate new myoblasts, which fuse and repair the damaged muscle fiber 3. Histological structure and localisation of cardiac muscle tissue Cardiac muscle is striated and has the same type and arrangement of contractile filaments as skeletal muscle. Cardiac muscle cells (cardiac myocytes) are short cylindrical cells with a centrally positioned single nucleus. They are attached to each other by intercalated discs to form a cardiac muscle fiber. The intercalated discs represent highly specialized cell- to cell- adhesion junctions. Resting sarcomere length in cardiac muscle (about 2.2 μm) is slightly shorter than in skeletal muscle. Cardiomyocytes are much smaller (about 80-100μm long and about 15 μm in diameter) than skeletal muscle fibers. Specialized cardiac conducting muscle cells exhibit a spontaneous rhythmic contraction. They generate and rapidly transmit action potentials to various parts of the myocardium Cardiac muscle cells can hypertrophy (grow larger) or hypotrophy (grow smaller) as a result of changing demands on the heart, but the cells are terminally differentiated and cannot divide. The heart does not appear to contain large numbers of “stem” cells similar to the satellite cells of skeletal muscle, and therefore only has a limited ability to regenerate when damaged. Heart muscle damaged by a heart attack heals by forming scar tissue. 4. Regeneration capacity of different types of muscle tissue 5. Composition of connective tissue layers that held muscle fibers together Connective tissue in skeletal muscle: - Endomysium- Surrounds individual fibers - Perimysium- Surrounds a group of fibers to form a fascicle - Epimysium- Surrounds the entire muscle and is dense connective tissue Connective tissue in tendon: - Epitendineum- Tendons are surrounded by a connective tissue capsule - Peritendineum- Divide fascicles by connective tissue - Endotendineum- Are groups of fibers surrounded by fibroblasts and very little connective tissue 6. Structure of red and white muscle fibers Red muscle fibers Type I “red” muscle, is dense with capillaries and is rich in mitochondria and myoglobin, giving the muscle tissue its characteristic red color Fibers specialized for aerobic metabolism develop a high myoglobin concentration. Slow twitch fibers contract for long periods of time but with little force. Have relatively more sarcoplasm. White muscle fibers Type II, “white” muscle, fast twitch that is least dense in mitochondria and myoglobin muscle. Fast twitch fibers contract quickly and powerfully but fatigue very rapidly sustains only short, anaerobic bursts of activity before muscle contraction becomes painful. In small animals this is a major fast muscle type, explaining the pale color of their flesh. 7. Histological structure of fascia A fascia is a layer of dense regular connective tissue containing closely packed bundles of collagen fibers oriented in a wavy pattern parallel to the direction of pull. A fascia is a structure of connective tissue that surrounds muscle, groups of muscle, blood vessels, and nerves, binding some structures together. Fasciae are flexible structures which make it able to resist great unidirectional tension forces. 8. Histological structure of tendon sheath Tendon is cord- like structures that attach muscle to bone. They consist of parallel bundles of collagen fibers and are made of dense regular connective tissue. Situated between these bundles are rows of fibroblasts called tendinocytes. It contains very few blood vessels 9. Histological structure of synovial bursa Synovial bursa- saclike cavity, lined with synovial membrane that secretes a viscous lubricating synovial (bursal) fluid, interposed between tendons and bony prominences or at other points of friction between moving structures.