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Unit 6-Lecture 2.ppt - Overview From Start to Finish Basic...

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Overview: From Start to Finish Basic Structures Nerve ending Neurotransmitter Muscle membrane Stored Ca 2+ ATP Muscle proteins
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Neuromuscular Junction (NMJ) or Synapse NMJ = myoneural junction end of axon nears the surface of a muscle fiber at its motor end plate region (remain separated by synaptic cleft or gap)
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Structures of NMJ Region Synaptic end bulbs are swellings of axon terminals End bulbs contain synaptic vesicles filled with acetylcholine (ACh) Motor end plate membrane contains 30 million ACh receptors.
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How Does Contraction Begin? 1. Nerve impulse reaches an axon terminal & synaptic vesicles release acetylcholine (ACh) 2. ACh diffuses to receptors on the sarcolemma & Na + channels open and Na + rushes into the cell 3. A muscle action potential spreads over sarcolemma and down into the transverse tubules 4. SR releases Ca 2+ into the sarcoplasm 5. Ca 2+ binds to troponin & causes troponin- tropomyosin complex to move & reveal myosin binding sites on actin--the contraction cycle begins
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Contraction Cycle Repeating sequence of events that cause the thick & thin filaments to move past each other. 4 steps to contraction cycle ATP hydrolysis attachment of myosin to actin to form crossbridges power stroke detachment of myosin from actin
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