Q.What is meant by the 'resting potential' of a neuron? Describe how the unequal distribution of Na+ and K+ ions across the axonal membrane, maintained by the Na+-K+ pump, gives rise to it.

[!TLDR] Resting potential (~-70 mV, inside negative) is set up by the Na+-K+ pump making the outside Na+-rich and inside K+-rich, with the resting membrane far more permeable to K+. [!ANSWER] Resting potential ≈ -70 mV (inside negative); maintained by the Na+-K+ pump (3 Na+ out : 2 K+ in) plus higher K+ permeability of the resting membrane.

The resting potential is the steady electrical potential difference, about -70 mV, that exists across a neuron's membrane when it is not conducting an impulse, with the inside of the membrane negative relative to the outside. It is maintained by the Na+-K+ pump, a membrane protein that uses ATP to actively transport 3 Na+ ions out of the cell for every 2 K+ ions it brings in, against their concentration gradients. Because of this pump, and because the resting membrane is much more permeable to K+ (which leaks outward through 'leak' channels) than to Na+, the extracellular fluid ends up rich in Na+ and the intracellular fluid rich in K+; the net outward leak of positive K+ ions leaves the inside of the membrane negatively charged relative to the outside, producing the resting potential. [!ANSWER] Resting potential (~-70 mV, inside negative) arises because the Na+-K+ pump keeps Na+ concentrated outside and K+ concentrated inside, and the resting membrane's much higher permeability to K+ lets positive charge leak outward, leaving the inside negative.

Separate the two contributing causes: the active pump (sets up the concentration gradients) and the passive K+ leak (converts that gradient into a voltage).

Do not say Na+ 'leaks out' at rest — at rest it is K+, not Na+, that is chiefly permeable and leaks; Na+ only rushes IN once channels open during a stimulus.