Muscle structure and function Bone CLICKER You manufacture your body weight s supply in ATP Structure fiber myofibril contractile element fiber one giant long cell many nuclei per cell Myofibril is the contractile structure Thin filaments Actin Thick filaments Myosin has ATP ase activity Contraction ATP is required Sarcomere functional unit of striated muscle Sarcomere contracts filaments do not change length degree of overlap changes sarcomere is shorter SLIDE A band length of myosin overlaps actin H zone area with myosin and no actin I band area with actin and no myosin The A band stays the same through contractions and relaxation Myosin head group has ATP ase activity Myosin is not just a contractile molecule it is also an enzyme that breaks down ATP which releases energy Detail Cross bridges myosin head groups Myosin head group attaches to actin Sliding filament model Actin and myosin are bound ATP binds to myosin and causes a dissociation i e actin and myosin become unbound ATP hydrolyzed to ADP P note that P still attached Myosin re attaches with ADP and P P is released When this happens energy is released this stimulates the power stroke conformation change Where does ADP go after this Mitochondria The role of Calcium Actin has two associated proteins Tropomyosin and Troponin Steps Myosin binding site on Actin is blocked by tropomyosin calcium binds to Troponin conformational change of Troponin pushes tropomyosin away allows myosin to bind Calcium What is its role The presence of calcium allows myosin to attach to actin Actin has two proteins associated with it 1 Tropomyosin and 2 Troponin Myosin head group attachment site on actin is blocked by Tropomyosin Problem Calcium binds to troponin which changes its shape which pushes away the Tropomyosin Myosin head attachment site is now free to bind Calcium cont is released by Endoplasmic Reticulum ER is a reservoir of Calcium transverse tubule signals ER to release calcium Smooth muscle occurs in stomach intestine blood vessel uterus doesn t contract to change muscle length gives shape to hollow organs must stay contracted for long periods of time no striations are criss crossed are individual spindle shaped cells have individual nuclei slower muscle contractions Cardiac Muscle has actin and myosin individual cells w own nucleus and membrane branched fibers interrupted by intercalated discs highly oxidative Slow Twitch vs Fast Twitch muscle Slow Twitch muscle fiber High mitochondria and high myoglobin content Rich in oxidative enzymes Can burn fats for energy is endurance muscle More capillaries than fast twitch Has fewer nerves per muscle cell than fast twitch Fast Twitch muscle fiber Moderate mitochondrial content Low myoglobin content High glycolytic enzyme capacity Reaches peak tension faster than slow twitch Has more nerves per muscle cell than slow twitch Greater force generation fast powerful bursts Innervation Slow twitch Small cell body 10 180 fibers are innervated Fast twitch Large cell body 300 800 fibers are innervated However force generated by each fiber type is the same CLICKER Which is true of slow twitch muscle a It generates less force than fast twitch muscle b It can generate more ATP than fast twitch muscle Bone is an organ has blood vessels connective tissue cartilage nerve marrow Not just a support structure it is a storage site for calcium The bone as a regulatory organ Osteoclasts release enzymes that break down bone this helps regulate calcium and phosphorus levels in the blood caffeine affects calcium in bones soft drinks upset calcium phosphorus ratio in blood body responds by leaching calcium from bone Osteoporosis lower bone density caused by inadequate calcium in diet Osteoporosis can be prevented by weight bearing exercise and adequate calcium in diet
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