Given the following steps: 1. voltage gated potassium channels close; 2. threshold; 3. undershoot; 4. stimulus channels open; 5. voltage gated sodium channels close, pick the option that places them in the correct sequence starting with a neuron at its rmp.

4, 2, 5, 3, 1

Explanation:

The neuron remains at RMP unless stimulated. The stimulus results in opening of stimulus channels, this causes depolarization. if the extent of depolarization reaches to the level of threshold, the sodium and potassium channels begin opening but potassium channels are slow to open. Hence at first sodium goes out causing further depolarization until it reaches the peak at which the potassium channels open and the sodium channels close. This causes the potassium to rush our causing repolarization i.e. return of the membrane potential to RMP but the potassium channels are slow to close and it leads to hyperpolarization (undershoot) making the membrane potential more negative due to excessive movement of potassium outside the cell. Once the potassium channels close, the leak channels and Na K pump acts to return the potential to RMP.  

Explanation:

conservation of mass

mass before something happens = mass afterwards