What type of channel protein opens temporarily when a specific neurotransmitter binds to it?

The correct answer is the neurotransmitter-gated ion channel. This type of channel protein is specifically designed to respond to neurotransmitters, which are signaling molecules that transmit messages between nerve cells. When a neurotransmitter binds to the receptor site on the channel, it causes a conformational change in the protein structure, leading the channel to open temporarily. This opening allows ions to flow across the cell membrane, contributing to the change in the membrane potential that can ultimately facilitate signal transmission in the nervous system.

In contrast, voltage-gated ion channels open in response to changes in the membrane potential rather than the binding of neurotransmitters. Mechanically-gated ion channels respond to physical changes in the environment, such as pressure or stretch, while leak ion channels are always open and allow ions to passively flow in and out of the cell, maintaining resting potential but not being triggered by specific neurotransmitter interactions.