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Questions and Answers
What role does acetylcholine play in muscle activation?
What role does acetylcholine play in muscle activation?
Which step in the sliding filament theory involves the swinging forward of the myosin head?
Which step in the sliding filament theory involves the swinging forward of the myosin head?
What prevents myosin from binding to actin in a resting sarcomere?
What prevents myosin from binding to actin in a resting sarcomere?
What is the primary factor regulating the position of troponin and tropomyosin?
What is the primary factor regulating the position of troponin and tropomyosin?
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What happens during cross-bridge detachment?
What happens during cross-bridge detachment?
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Which type of motor unit allows for greater control over actions?
Which type of motor unit allows for greater control over actions?
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How long can stored ATP in muscles last during intense activity?
How long can stored ATP in muscles last during intense activity?
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What is true about creatine phosphate in muscle energy production?
What is true about creatine phosphate in muscle energy production?
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Study Notes
Muscle Contraction - Mechanism
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Resting State:
- Myosin head is in an energized position, with ATP and a phosphate group (P) bound.
- It is not attached to actin due to tropomyosin blocking the binding site.
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Activation:
- Motor neuron releases acetylcholine.
- Acetylcholine binds to ligand-gated channels on the muscle membrane, triggering an action potential.
- Action potential travels through T-tubules, causing release of calcium ions (Ca++) from the sarcoplasmic reticulum.
- Ca++ binds to troponin, moving tropomyosin away from the actin binding site.
Muscle Contraction - Sliding Filament Theory
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Step 1: Cross-bridge Attachment:
- Myosin binds to actin because tropomyosin has moved.
- Myosin head is still in the back position, with ADP and P bound.
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Step 2: Power Stroke:
- Myosin head swings forward, releasing ADP and P.
- This move is called a power stroke, and it pulls the actin filament towards the center of the sarcomere.
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Step 3: Cross-bridge Detachment:
- ATP binds to the myosin head, causing it to detach from actin.
- Head is now in the forward position.
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Step 4: Myosin Reactivation:
- ATP is hydrolyzed back to ADP and P, causing the myosin head to return to its energized, back position.
- It is now ready to bind with actin again.
Muscle Contraction - Regulation
- Calcium ions (Ca++) determine the position of troponin and tropomyosin.
- This is why muscle contraction is regulated by the release and reuptake of calcium.
- Ca++ is stored in the sarcoplasmic reticulum and is released in response to action potentials carried by T-tubules.
Muscle Contraction - Strength
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Motor Unit:
- A motor neuron and all the muscle fibers it innervates.
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Small Motor Units (4-10 fibers):
- Use less energy, allowing finer control.
- Found in areas requiring precision like eye muscles.
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Large Motor Units (50-100 fibers):
- Generate more strength.
- Found in large muscles like the legs.
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Muscle Tone:
- Some motor neurons are always active, maintaining body position and posture.
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Involuntary:
- This constant activity is involuntary and not consciously controlled.
Energy Production in Muscles
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Stored Energy:
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ATP:
- Enough stored for about 6 seconds of muscle activity.
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Creatine Phosphate:
- Transfers phosphate to ADP to make ATP.
- Enough stored for about 10 seconds.
- 10 times more creatine phosphate can be stored than ATP.
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ATP:
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Anaerobic Respiration:
- Without oxygen.
- Glucose is broken down to produce ATP and lactic acid.
- Lactic acid buildup is a cause of muscle fatigue.
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Description
Test your understanding of the muscle contraction process, focusing on the mechanisms and the sliding filament theory. This quiz covers topics such as the activation of muscle fibers, cross-bridge attachment, and the power stroke involved in contraction.
