Term
| In a skeletal muscle fiber what is the functional unit of contraction? |
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Definition
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Term
| How does a sarcomere shorten? |
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Definition
| Myocin heads and thick myofilaments form cross bridges with actin molecules and thin myofilaments |
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Term
| What initiates the formation of a cross bridge? |
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Definition
| Calcium ions (released from the sarcoplasmic reticulum) bind to triponin |
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Term
| How does the calcium ion binding affect troponin? |
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Definition
| Troponin changes shape, and tropomyocin moves away from the myocin binding site on actin allowing myocin head to bind and form a cross bridge |
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Term
| What activates the myocin head before a cross bridge cycle begins? |
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Definition
| ATP binds to myocin head and is hydrolyzed to ADP and inorganic phosphate, the energy liberated from the hydrolysis of ATP activates the myocin head, forcing it into cocked position |
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Term
| STEP 1: Cross Bridge Formation |
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Definition
| Activated myocin head binds to actin, inorganic phosphate is released and bond between myocin and actin becomes stronger |
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Term
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Definition
| ADP is released and the myocin head pivots sliding the thin filament to the center of the sarcomere |
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Term
| STEP 3: Cross Bridge Detachment |
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Definition
| An ATP binds to the myocin head and the bond between the myocin head and actin weakens and the myocin head detaches |
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Term
| STEP 4: Reactivation of Myocin Head |
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Definition
| ATP is hydrolized to ADP + inorganic phosphate, the energy released activates the myocin head returning it to cocked position |
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Term
| What will happen as long as the actin binding sites remain exposed? |
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Definition
| The cross bridge cycle will repeat |
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Term
| As the thin myofilaments are pulled toward each other what is the effect on the muscle? |
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Definition
| This causes the sarcomere to shorten and the whole muscle to contract |
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Term
| What causes the cycle to end? |
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Definition
| Calcium ions being actively transported into the sarcoplasmic reticulum |
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Term
| When the calcium is removed, what happens to troponin? |
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Definition
| Troponin returns to original shape allowing tropomyocin to glide over and cover the myocin binding site on actin |
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