The word hyponatremia derives from the words hypo ("under" or "less") and natrium ("sodium"). The word natrium is the basis for the abbreviation Na for sodium. Hyponatremia is a rare condition, but has become of more concern with the rise in amateur runners participating in marathons. Since they run slower, they spend longer on the course and have more opportunity to drink water and sweat out additional sodium. Marathon runners are encouraged to stop at water stations along the course to stay hydrated. However, occasionally a runner drinks too much water and suffers from hyponatremia, or "water intoxication". While water itself is not toxic, drinking too much can upset ion balance in the extracellular space. Based on what you know about ions and nerve signaling, the levels of which important ion are most likely to be disrupted in hyponatremia?
A. Potassium
B. Hydrogen
C. Oxygen
D. Sodium
E. Calcium

The correct answer is option D. "Sodium".

Explanation:

Hyponatremia is a condition that rises from a low concentration of sodium in the blood. Therefore, people that suffers from hyponatremia is suffering from the effects that low levels of sodium have in nerve signaling, particularly after the brain is swelling in what is known as cerebral edema. The worst cases of hyponatremia can lead to permanent brain damage or they even can have fatal consequences.

D

Explanation:

Definitely sodium balance . Sodium is an extracellular ions whose influx and outflux across the  neuronal membranes(with intracellular  K+ )ensures propagation and transmission of action potential along the axon.

it is also an important water balance in the Nephron to maintain osmotic potential   of the body

Therefore when hyponatremia sets in,with large loss of sodium in the urine due to ex-osmosis,  and sweating,  from too much water intake,nervous transmission is disrupted. Thus fatigue, seizure, lethargy, nervousness, headache, loss of muscular control, spasm  set in

regulation of gene expression. gene expression can be regulated by various cellular processes with the aim to control the amount and nature of the expressed genes. these regulatory proteins bind to dna and send signals that indirectly control the rate of gene expression

explanation: