In relation to RMP, what should always be compared?

The correct choice emphasizes the fundamental concept of resting membrane potential (RMP), which is the voltage difference across the cell membrane when a cell is not actively transmitting signals. This value arises from the distribution of ions across the membrane, specifically the differences in ion concentrations between the intracellular and extracellular fluids.

In the context of RMP, the resting potential is primarily influenced by the permeability of the cell membrane to specific ions, particularly potassium (K+), sodium (Na+), and chloride (Cl-). The cell membrane is typically more permeable to potassium ions, which leads to a higher concentration of potassium inside the cell compared to the outside. The differences in ion concentrations across the membrane create a gradient that is essential in establishing the resting membrane potential.

Therefore, when examining RMP, it is crucial to compare the ion concentrations as they exist in the intracellular and extracellular fluids. This comparison directly informs understanding of how the RMP is established and maintained, as well as the mechanisms by which electrical signaling occurs in excitable tissues like neurons and muscle cells.