Question

which of the following is true with regard to membrane potential? transient opening of gated na⁺ and k⁺ channels in the plasma membrane is a normal means of activating neurons and muscle cells. na⁺ plays the key role in generating the resting membrane potential. all cells in the body must maintain a constant voltage across the membrane. because the number of ions producing the membrane potential is so small that it does not change ion concentrations in any significant way, changes in extracellular na⁺ will not affect membrane voltage. i dont know yet

Explanation:

1. Analyze each option:

• Option 1: Transient opening of gated \( \text{Na}^+ \) and \( \text{K}^+ \) channels in the plasma membrane is a normal means of activating neurons and muscle cells. This is correct. Neurons and muscle cells generate action potentials (a type of membrane potential change) through the transient opening of voltage - gated \( \text{Na}^+ \) and \( \text{K}^+ \) channels.
• Option 2: \( \text{K}^+ \) (not \( \text{Na}^+ \)) plays the key role in generating the resting membrane potential. The resting membrane potential is mainly due to the diffusion of \( \text{K}^+ \) out of the cell down its concentration gradient.
• Option 3: Not all cells in the body maintain a constant voltage across the membrane. Only excitable cells (like neurons and muscle cells) can generate significant changes in membrane potential, and even they have resting and active (action potential) states.
• Option 4: Changes in extracellular \( \text{Na}^+ \) can affect the membrane voltage, especially the amplitude of the action potential. The Nernst equation and the Goldman - Hodgkin - Katz equation show that ion concentrations (including extracellular \( \text{Na}^+ \)) affect membrane potential.

Answer:

A. Transient opening of gated \( \text{Na}^+ \) and \( \text{K}^+ \) channels in the plasma membrane is a normal means of activating neurons and muscle cells.