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Questions and Answers
What initiates the muscle action potential during skeletal muscle contraction?
What initiates the muscle action potential during skeletal muscle contraction?
- Conformation change of the myosin heads
- Binding of acetylcholine to troponin
- Release of calcium ions from the sarcoplasmic reticulum
- Net entry of sodium ions through the ACh receptor-channel (correct)
Which receptor is directly altered by the action potential in the t-tubule?
Which receptor is directly altered by the action potential in the t-tubule?
- Ryanodine receptor (RyR)
- Troponin
- Dihydropyridine (DHP) receptor (correct)
- ACh receptor-channel
What role does calcium ion (Ca2+) play in skeletal muscle contraction?
What role does calcium ion (Ca2+) play in skeletal muscle contraction?
- Facilitates actin-myosin binding by binding to troponin (correct)
- Causes muscle fiber relaxation
- Inhibits actin-myosin binding
- Promotes the release of acetylcholine at the neuromuscular junction
What is the sequence of events that occurs after calcium (Ca2+) is released into the cytoplasm?
What is the sequence of events that occurs after calcium (Ca2+) is released into the cytoplasm?
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Which of the following describes the outcome of actin-myosin binding during the contraction cycle?
Which of the following describes the outcome of actin-myosin binding during the contraction cycle?
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Study Notes
Overview of Skeletal Muscle Contraction
- Neuromuscular Junction: The process begins when the axon terminal of a somatic motor neuron releases acetylcholine (ACh).
- Sodium Ion Entry: ACh binds to receptors, leading to the net entry of sodium ions (Na+), which creates a muscle action potential.
- T-Tubule Action Potential: The generated action potential travels along t-tubules, inducing a change in the dihydropyridine (DHP) receptor's conformation.
- Calcium Release Mechanism: The altered DHP receptor triggers the opening of ryanodine receptor (RyR) calcium release channels in the sarcoplasmic reticulum.
- Calcium's Role: Calcium ions (Ca2+) are released into the cytoplasm and bind to troponin, which is essential for muscle contraction.
- Actin-Myosin Interaction: Once Ca2+ binds to troponin, it facilitates the binding of actin and myosin, enabling the contraction process.
- Power Stroke: The myosin heads perform a power stroke, a pivotal movement that pulls the actin filament inward.
- Sarcomere Shortening: Actin filaments slide towards the center of the sarcomere, resulting in muscle contraction.
- Cyclic Process: The entire mechanism is cyclic, allowing the muscle to contract repeatedly as long as Ca2+ remains elevated and ATP is available.
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