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muscles - 47 Muscles Effectors How Animals Get Things Done...

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47 Effectors: How Animals Get Things Done Brain Legs Eat giraffe ! Run ! The musculoskeletal system Muscles and skeletons: the musculoskeletal system . Muscles and skeletons are the effectors that produce movement. Muscles Three types of vertebrate muscle: Skeletal : voluntary movement, breathing Cardiac : beating of heart Smooth : involuntary, movement of internal organs There are Three Kinds of Muscle
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47.1 How Do Muscles Contract? Skeletal muscle (“striated”) : •Cells are called muscle fibers. •They are extremely large, multinucleated cells. •Form by fusion of embryonic myoblasts. •One muscle consists of many muscle fibers bundled together by connective tissue. The Structure of Skeletal Muscle (Part 1) Bundle of muscle fibers Connective tissue Plasma membrane (sarcolemma) Myofibrils Nucleus Muscle Tendons Mitochondria Single muscle fiber (cell) human skeletal muscle - low power The Structure of Skeletal Muscle (Part 1)
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The Structure of Skeletal Muscle (Part 2) Single sarcomere A band H zone Titin M band Myosin filament Actin filament Z line Z line I band M band Single myofibril show animation: Animation-47-01.swf How Do Muscles Contract? Each muscle fiber has several myofibrils : bundles of actin and myosin filaments. Contractile proteins: Actin : thin filaments Myosin : thick filaments How Do Muscles Contract? Each myofibril consists of repeating units: sarcomeres. Sarcomere : overlapping actin and myosin filaments. Bundles of myosin filaments are held in place by the protein titin , the largest protein in the body.
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Myofibrils; bands of actin and myosin together appear darkest. Transmission-EM How Do Muscles Contract? The sliding filament mechanism of muscle contraction: •Myosin heads can bind specific sites on actin molecules to form cross bridges. Myosin changes conformation, causes actin filament to slide 5–10 nm. Sliding Filaments
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Actin and Myosin Filaments Overlap to Form Myofibrils Actin monomer Single sarcomere Myosin filament Actin filament Myosin molecule Linear polypeptide chain Globular head Troponin Tropomyosin 47.1 How Do Muscles Contract? Muscle cells are excitable : the plasma membrane can conduct action potentials . Acetylcholine is released by the motor neuron at the neuromuscular junction and opens ion channels in the motor end plate.
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