Question
Release of synaptic transmitter by this process which is shown in this image would be blocked most effectively by preventing ?
A. Propagation of the action potential into the nerve terminal membrane
B. Depolarization of the nerve terminal membrane
C. Flow of Na+ into the nerve terminal membrane
D. Flow of Ca2+ into the nerve terminal membrane
Show Answer
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Correct Answer » D
Explanation
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The process of vesicular transport as shown in the picture represents Exocytosis.
- Exocytosis – Process by which a cell transports secretory products through the cytoplasm to the plasma membrane.
- Secretory products are packaged into transport vesicles (membrane-bound spheres).
- Simple terms, “Extrusion of cell-bound vesicles” / “Expulsion of cell contents”
Mechanism:
- The inner membrane of vesicle fuses with outer plasma membrane
- Simultaneously, the cytoplasmic side of vesicle fuses with cytoplasmic side of plasma.
I.e., In exocytosis, the cytoplasmic sides of two membranes fuse
Molecular events:
- Ca2+-dependent process of exocytosis
- Preventing Ca2+ flow into cell would prevent release of transmitter.
- Ca2+ initiates intracellular events leading to docking of vesicle to its binding site on active zone.
- Although, Ca2+ normally enters cell through voltage-operated channels.
- Opened by depolarization of nerve terminal that occurs as action potential propagates along nerve axon.
- Thus, the release of the transmitter will not occur if Ca2+ does not enter the nerve terminal.
Types:
- Secretion from the cell occurs via two pathway,
Constitutive
Non-constitutive
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