question about repolarization and depolarization of the sarcolemma in a sliding filament mechanism?

I need to know if it’s Na+ ions moving in or out of a muscle fiber that cause depolarization or repolarization, OR if it’s K+ ions moving in or out of a muscle fiber that cause depolarization or repolarization in the sarcolemma in a sliding filament mechanism. This question is for my human anatomy test, can anybody please help me? It’s driving me nuts!

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2 comments

  • muscle contraction is dependent on calcium ions, but first sodium must enter the cell. sodium enters as a little potasium exits and this causes initial depolarization. after this calcium enters the cell. it then stimulates the sarcoplasmic reticulum to release more calcium (calcium dependent calcium release). this flood of calcium will cause the muscle to contract. the functional unit of contraction, the sarcomere, consists of troponin. when calcium binds to troponin c it will jump to the fillament and cause contraction. when its time for relaxation ATP will bind this troponin and it will let go
    do not get the initial sodium/potassium gate confused with the sodium-potassium-atpase pumt. this moves sodium out and potassium in after the action potential

  • with each ATP molecule 3 sodium ions are moved out and two potassium ions are moved in the muscle fiber.

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