Multiple Choice
In skeletal muscle physiology, the cell membrane of a muscle fiber is called the:
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15. Cytoskeleton and Cell Movement
Muscle Contractions
Multiple Choice
In skeletal muscle, what event directly initiates an action potential in the muscle fiber (sarcolemma)?
A
Increased binding of troponin to actin, which opens voltage-gated Na channels in the sarcolemma
B
ATP binding to myosin heads, causing a conformational change that triggers a sarcolemmal action potential
C
Binding of acetylcholine to nicotinic receptors at the motor end plate, opening ligand-gated cation channels and depolarizing the sarcolemma to threshold
D
Release of Ca from the sarcoplasmic reticulum through ryanodine receptors, which directly generates the sarcolemmal action potential
Verified step by step guidance1
Understand that the initiation of an action potential in the muscle fiber's sarcolemma is triggered by a specific event at the neuromuscular junction.
Recognize that acetylcholine (ACh) is the neurotransmitter released from the motor neuron into the synaptic cleft, which then binds to receptors on the muscle fiber.
Identify that the receptors on the muscle fiber at the motor end plate are nicotinic acetylcholine receptors, which are ligand-gated cation channels.
Explain that when acetylcholine binds to these nicotinic receptors, it causes the channels to open, allowing Na\(\textsuperscript{+}\) ions to flow into the muscle fiber, leading to depolarization of the sarcolemma.
Note that this depolarization, if it reaches threshold, triggers the opening of voltage-gated Na\(\textsuperscript{+}\) channels, generating an action potential that propagates along the sarcolemma.
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