In a resting state, sodium (Na^+) is at a higher concentration outside the cell and potassium (K^+) is more concentrated inside the cell. During an action potential, the sodium levels inside the cell.
Multiple Choice:
A. decrease
B. increase
C. increase only if potassium levels remain the same
D. stay the same

B. increase

Explanation: During an action potential, the potassium level inside the cell decreases, and the sodium level inside the cell increases. Thats is to say there is an outflow of potassium and an inflow of sodium ions.

Action potential usually occurs when an electrical signal disrupts the balance of Na+ and K+ within a cell membrane, briefly depolarizing the concentrations of each.

B - increases (deplolarization.)

Explanation:

the influx of sodium ion into the cell increases the positive charge of the axoplasm, cause charges reversal of   the   axon  membrane and it is called  depolarization.

Th influx of sodium ion is due combination of three factors

1, to the opening of voltage gated  sodium channels,

2. increase in chemical gradient for sodium ions, and

3. high concentration of sodium ions outside compare to the axoplasm.

The combined effects of  2 and 3 above is called electrochemical gradients; and this pull sodium ions with the psotive  charges  through the voltage gated sodium channels into the axoplasm.

Few  gated channels were open initially however as the intensity of the stimulus increases, more gated channels of sodium opens, with many Na+ diffused in.And if the voltage generated due to deoplarization is up to the threshold levels,Action potential occurs.

i thinking chemical change

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.