Question

When an action potential reaches the axon terminal, what is the proper order of events in which exocytosis of the neurotransmitter takes place?

	A.	Ligand-gated Na+ channels open and Na+ rushes into the axon terminal; Na+ binds with synaptotagmin and together they activate the SNARE/vesicle complex, which docks and allows the neurotransmitter-filled vesicle to be exocytosed.
	B.	Voltage-gated Na+ channels open and Na+ rushes into the axon terminal; Na+ binds with synaptotagmin and together they activate the SNARE/vesicle complex, which docks and allows the neurotransmitter-filled vesicle to be exocytosed.
	C.	Ligand-gated Ca++ channels open and Ca++ rushes into the axon terminal; Ca++ binds with synaptotagmin and together they activate the SNARE/vesicle complex, which docks and allows the neurotransmitter-filled vesicle to be exocytosed.
	D.	Voltage-gated Ca++ channels open and Ca++ rushes into the axon terminal; Ca++ binds with synaptotagmin and together they activate the SNARE/vesicle complex, which docks and allows the neurotransmitter-filled vesicle to be exocytosed.
	E.	Ligand-gated Ca++ channels open and Ca++ rushes into the axon terminal; Ca++ binds with the vesicles and releases the neurotransmitter-filled vesicle

Answer 1

Answer :- (d) voltage gated calcium channel open and calcium rushes into the axon terminal ;calcium binds with synaototagamin and together they activate the SNARE/vesicle complex,which docks and allows the neurotransmitter-filled vesicle to be excytosed.

Explanation:- as soon as the action potential reaches the axon terminal ,voltage gated calcium channel opens. Calcium ions get enter inside the axon terminal. Synaototagamin ,a calcium ion sensor present in the membrane of presynaptic axon terminal senses the increase in calcium concentration in the axon terminal. Synaototagamin binds with calcium ions ,this calcium bound synaototagamin then interacts with SNARE/vesicle protein . This causes docking and fusion of synaptic vesicles to the presynaptic membrane. Exocytosis occurs and neurotransmitter present in the synaptic vesicles come out into the synapses.