Muscle Contraction ANSC 3700 Muscle Foods Nerve Impulse Nerves are composed of the Nerve fiber Myelin sheath Motor end plate Nerve Impulse Membrane potential Pumps pump Na+ out of nerve fiber K+ into nerve fiber Permeability of K+ is 50-100X greater than Na+ Negative potential exists just inside membrane Positive potential exists just outside membrane Nerve impulse Action potential initiated by: Sudden increase in membrane permeability to Na+ An excess of positive charges enter the cell Only lasts a few milliseconds Sodium/potassium pumps re-establish the equilibrium Muscle Innervation The nerve impulse travels to nerve motor endplate Acetylcholine is released Because nerve is embedded in the sarcolemma? The sarcolemma is depolarized. Muscle communication Sarcolemma All of the sarcolemma is depolarized ? including the T-tubules This carries the nerve impulse into the center of the muscle fiber Triad The junction of the T-tubule and SR Nerve impulse is transferred to SR Sarcoplasmic reticulum Releases calcium to initiate contraction Contraction Muscle contraction: Ca++ binds to the troponin complex causing a conformation change. The conformation change shifts the tropomyosin into the grooves of the actin filament uncovering binding sites. Contraction cycle - Biochemistry Myosin heads bind to actin forming the actomyosin complex. Myosin head ?bends?, sliding the actin filament. Binding of a new ATP molecule releases the myosin Myosin itself will hydrolize the ATP to ADP + Pi Contraction Sliding the actin filaments moves the Z disks toward the center of the sarcomere. Contraction In 1 sarcomere, each Z disk moves toward the center, shortening the sarcomere. A sarcomere that is fully contracted will have the myosin filaments touching the Z disk. Contraction During contraction: I band and H zone get smaller A band stays the same width Fully contracted: No I band No H zone Contraction Resting state to resting state Contraction Relaxation Energy requirements ATP is used for returning muscle to its resting state in 3 ways: Release myosin head from the thin filament Na/K pump in nerve fiber and sarcolemma Ca pump in the sarcoplasmic reticulum Generation of energy for contraction Glycolysis Aerobic Anaerobic TCA cycle Aerobic Oxidative phosphorylation Muscle fiber types Metabolism type Contraction speed Muscle fiber types Type I Red Type IIA & IIX Intermediate Type IIB White
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