Question

select the correct answer.
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.

Explanation:

• Option A: Action potentials (nerve impulses) rely on sodium ion (Na⁺) influx. Low sodium (hyponatremia) disrupts action potential generation, causing muscle spasms (since muscles rely on nerve signals).
• Option B: Myelin sheaths are mainly lipids (like cholesterol) and proteins, not sodium. Eliminate B.
• Option C: Neurotransmitters (e.g., acetylcholine) transmit impulses across synapses, not sodium. Eliminate C.
• Option D: Sodium and potassium are involved in ion gradients for action potentials, not direct "control" of voluntary/involuntary movement (the nervous system’s motor neurons and brain regions control this). Eliminate D.

Answer:

A. Sodium is needed to generate an action potential.