Final answer:
Resting neurons are most permeable to potassium ions (K+), playing a key role in establishing the negative resting membrane potential. Voltage-gated ion channels are crucial for action potential generation, with their absence making it impossible.
Step-by-step explanation:
Resting neurons are most permeable to potassium ions (K+) and chloride ions (Cl-). Given the options, the correct answer is 2) K+. In the resting state of a neuron, the cell membrane is more permeable to K+ compared to Na+ (sodium ions) due to a larger number of potassium leak channels. This permeability allows K+ to flow out of the neuron, which contributes to the negative charge of approximately -70 millivolts (resting membrane potential) inside the neuron. While there are also chloride ions present and they do contribute to the membrane potential, it is the movement of K+ out of the cell that most significantly establishes this potential. The selective permeability of ion channels, diffusion of ions, and the activity of the Na+/K+ pump all work together to maintain the resting membrane potential.
Voltage-gated ion channels are vital for the initiation and propagation of action potentials. Action potentials require a rapid, transient increase in membrane permeability to Na+, which is followed by an increase in permeability to K+. Without these channels, there would be no mechanism to rapidly change the permeability of the membrane in response to voltage changes, making it impossible to generate action potentials.