Hyponatremia is a condition in which the sodium in the blood is too low. Uncontrolled spasms, which are sudden, involuntary contractions of muscles, are among the symptoms of hyponatremia. Why do they occur? A.
Sodium is needed to generate an action potential.
B.
Sodium makes up most of the myelin sheath.
C.
Sodium is the signaling molecule that transmits impulses across a synapse.
D.
Sodium controls voluntary movement, and potassium controls involuntary movement.
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Option A. Sodium is needed to generate an action potential.

Explanation:

Action potentials are generated by the special types of the voltage-gated channels which are embedded in the plasma membrane of the cell.

These channels are shut when the membrane potential is near zero and the voltage-gated channels open only when the membrane potential is more than the threshold voltage.

When the channels are open then they allow the flow of sodium ions which ultimately changes the electrochemical gradient which rises the membrane potential. This rise in membrane potential generates the action potential.

a. decomposes use carbon from dead organisms as fuel for cellular respiration, returning carbon dioxide back into the atmosphere.