Figure 39-4

 _________ and_______filaments slide over each other______________the muscle length  Always requires ________ ions and ___

 Double chain of ______ proteins  Makes up ____ filament  Attached to end walls of sarcomeres called _____  Makes up __ band of sarcomere  Has ______ binding site which is blocked by ____________ and ____________ in relaxed muscle

 Makes up _______ filament  Has myosin ________ which bind to _______  Make up ___ bands in a sarcomere

 “Joining” of motor ______ and ___________  _______________-motor neurons release _________________ that diffuse across synapse to receptors on muscle fiber membrane  Always ______________  Motor unit- _______branched motor ________ synapsing with ______ muscle _______

1. An __________________travels down a motor neuron 2. The skeletal muscle _________ is activated at the ____________________ junction 3. An _____________________travels down the muscle __________________________ 4. The action potential enters _____________ 5. An action potential stimulates the ____________________________________

6. ______________________are released into the muscle cell ____________________ 7. _____________ ions bind to _____________ 8. ___________________ exposes ___________ binding sites on _________ 9. Myosin _______ bind to ________ 10. Myosin heads __________ 11. _______ filaments are pulled toward sarcomere center, and muscle fiber ________

 When action potential is over, ________ goes back to _______________________________  Calcium is removed from _____________  Troponin and tropomyosin ________ myosin binding sites  Muscle ____________

1 - Calcium released from sarcoplasmic reticulum 2 - Myosin head energized via myosin-ATPase activity which converts the bound ATP to ADP + Pi 3 - Calcium binds to troponin 4 - Tropomyosin translocates to uncover the cross-bridge binding sites 5 - The energized myosin binding sites approach the binding sites 6 - The first myosin head binds to actin 7 - The bound myosin head releases ADP + Pi, flips and the muscle shortens 8 - The second myosin head binds to actin 9 - The first myosin head binds ATP to allow the actin and myosin to unbind 10 - The second myosin head releases its ADP + Pi, flips & the muscle shortens further 11 - The second myosin head binds to ATP to allow the actin and myosin to unbind 12 - The second myosin head unbinds from the actin, flips back and is ready for the next cycle 13 - The cross-bridge cycle is terminated by the loss of calcium from the troponin 14 - Tropomyosin translocates to cover the cross-bridge binding sites 15 - The calcium returns to the sarcoplasmic reticulum, the muscle relaxes & returns to the resting state

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