For Each of the Following Sentences, Fill in the Blanks

For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below.Not all words or phrases will be used; each word or phrase should be used only once.
$\begin{array}{lll}\text { acetylcholine receptor } & \text { GABA receptor } & \text { postsynaptic } \\\mathrm{Ca}^{2+} \text { channels } & \mathrm{K}^{+} \text {channels } & \text { presynaptic } \\\text { chemical } & \mathrm{Na}^{+} \text {channels } & \text { synapses } \\\text { electrical } & &\end{array}$

Neurons communicate with each other through specialized sites called __________.Many neurotransmitter receptors are ligand-gated ion channels that open transiently in the __________ cell membrane in response to neurotransmitters released by the __________ cell.Ligand-gated ion channels in nerve cell membranes convert __________ signals into __________ ones.Neurotransmitter release is stimulated by the opening of voltage-gated __________ in the nerve-terminal membrane.