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Skeletal Muscle Contraction Notes Review Epimysium (outer covering of muscle) Perimysium (covering fascicle) Fascicle (bundle of muscle fibers) Endomysium (covers each muscle fiber) Myofibril (bundle in each muscle cell – made of actin & myosin) H - zone A band sarcomere Which band is the thin filament? ACTIN Which band is the thick filament? MYOSIN Z - line I band More Interesting Muscle Facts Your muscles are what percentage of your body weight? 40% - 50% What percentage of muscle is made of water? • SKELETAL MUSCLE CONTRACTION • 8 Steps • STEP I • an action potential travels along a neuron to a synapse at a muscle fiber • STEP II • ACETYLCHOLINE (a neurotransmitter) is released from the neuron • STEP III • Acetylcholine binds to muscle cell membrane • STEP IV • sodium ions diffuse into the muscle fiber, starting an action potential • STEP V • Calcium ions are released from the sarcoplamic reticulum and bind to actin • STEP VI • myosin attaches to actin forming CROSS - BRIDGES • STEP VII • myosin pulls the actin causing it to slide over the myosin • STEP VIII • ATP attaches to myosin and supplies the energy for the myosin to pull the actin