Final answer:
Vesicles carry neurotransmitters to the postsynaptic membrane, where they may induce excitatory or inhibitory effects, causing depolarization or hyperpolarization of the postsynaptic neuron.
Step-by-step explanation:
Vesicles in the context of neurobiology are small membrane-bound sacs that transport various substances including neurotransmitters within and to the exterior of cells. In a neuronal synapse, when an action potential reaches the axon terminal, it causes the depolarization of the membrane, which then opens voltage-gated Ca2+ channels allowing calcium ions to enter the cell. This entry of calcium ions triggers synaptic vesicles carrying neurotransmitters to fuse with the presynaptic membrane and release their contents into the synaptic cleft.
The released neurotransmitters then diffuse across the synaptic cleft and can bind to ligand-gated ion channels in the postsynaptic membrane. Depending on the neurotransmitter and the type of receptors on the postsynaptic membrane, the binding can either cause a localized depolarization, making the neuron more likely to fire an action potential (excitatory effect), or hyperpolarization, inhibiting the possibility of an action potential (inhibitory effect). Therefore, the correct answer to the question is that vesicles carry neurotransmitters that will bind to the postsynaptic membrane.