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    Please can anyone run me through the steps of muscle contraction from when Ca2+ binds to troponin?

    I'm mainly confused about the cross bridge/ATP/ADP and Pi stuff...

    Thanks!
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    (Original post by white_o)
    Please can anyone run me through the steps of muscle contraction from when Ca2+ binds to troponin?

    I'm mainly confused about the cross bridge/ATP/ADP and Pi stuff...

    Thanks!
    Hi there,

    I'm also revising this topic and I've written it out into nice little stages to help me remember.

    Step 1: An action potential from a motor neurone stimulates a muscle cell, it depolarises the sarcolemma. Depolarisation spreads down the T-Tubules to the sarcoplasmic reticulum.

    Step 2: This causes the sarcoplasmic reticulum to release stored Ca2+ into the sarcoplasm

    Step 3: Calcium ions bind to troponin C, causing it to change shape. This pulls the attached tropomyosin out of the actin-myosin binding site on the actin filament.

    Step 4: This exposes the binding site, which allows the myosin head to bind.

    Step 5: The bond formed when a myosin head binds to an actin filament is called an actin-myosin cross bridge.

    Step 6: Calcium ions activate the enzyme ATPase, which breaks down ATP (into ADP + Pi ) to provide the energy needed for muscle contraction

    Step 7: The energy released from ATP moves the myosin head, which pulls the actin filament along in a kind of rowing action.

    Step 8: ATP also provides the energy to break the action-myosin cross bridge, so the myosin head detaches from the actin filament after it's moved.

    Step 9: The myosin head then reattached to a different binding site further along the actin filament. A new actin-myosin cross bridge is formed and the cycle is repeated.

    Step 10: Many actin-myosin cross bridges form and break very rapdily, pulling the actin filament along, which shortens the sarcomere, causing the muscle to contract.

    It's a long process but once you read it over a few times it makes sense
 
 
 
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