Explain the difference between a ligand-gated K+ channel and a voltage-gated K+ channel.

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1. Ligand-gated K+ channels are a type of ion channel that open in response to the binding of a chemical messenger (ligand) such as a neurotransmitter to a specific site on the channel. This binding causes a conformational change in the channel protein, allowing K+ ions to flow across the membrane.
2. Voltage-gated K+ channels, on the other hand, open and close in response to changes in the membrane potential. When the membrane potential reaches a certain threshold, the channel undergoes a conformational change that opens the channel, allowing K+ ions to flow through.
3. The primary function of ligand-gated K+ channels is to mediate the effects of neurotransmitters at synapses, contributing to the postsynaptic potential that can initiate a nerve impulse if strong enough.
4. Voltage-gated K+ channels are crucial in returning the depolarized cell to a resting state after an action potential. They help in repolarizing the cell membrane by allowing K+ to exit the cell, thus bringing the membrane potential back towards the negative equilibrium potential of potassium.
5. Both types of channels are essential for the proper functioning of nerve and muscle cells, but they are activated by different mechanisms and serve different roles in cellular communication and excitability.