MUSCLE
SKELETAL MUSCLE
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Calcium Ion Enters the Pre-synaptic Terminal
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Acetylcholine Enters the Synaptic Cleft
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Sodium Ion Enters the Sarcolemma
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Calcium Ion Enters the Sarcoplasm (Cytoplasm).
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Detailed explanation-1: -Upon entering a presynaptic terminal, an action potential opens Ca2+ channels, and transiently increases the local Ca2+ concentration at the presynaptic active zone. Ca2+ then triggers neurotransmitter release within a few hundred microseconds by activating synaptotagmins Ca2+.
Detailed explanation-2: -When the presynaptic membrane is depolarized, voltage-gated Ca2+ channels open and allow Ca2+ to enter the cell. The calcium entry causes synaptic vesicles to fuse with the membrane and release neurotransmitter molecules into the synaptic cleft.
Detailed explanation-3: -Influx of calcium ions into the presynaptic nerve terminal causes vesicles (loaded with neurotransmitters) migrate toward the presynaptic membrane. Then, the vesicle and membrane fuse, and neurotransmitter is released into the synaptic cleft by exocytosis.