The primary problem in hyperkalemia is that

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BlackTom AI · Accepted Answer

Delving into the question about the primary problem in hyperkalemia, we need to evaluate how elevated potassium levels affect neuronal excitability step by step.
Option 1: 'neurons are harder to excite because their resting potential is hyperpolarized and neurons respond too quickly to smaller graded potentials.' This is inconsistent with hyperkalemia. Elevated extracellular potassium depolarizes the neuron (makes the resting potential less negative), not hyperpolarizes it. Therefore this statement mischaracterizes the core effect and is false.
Option 2: 'neurons are harder to excite because their resting potential is hyperpolarized.' As noted, hyperkalemia does not cause hyperpolarization; it causes depolarization. So this option relies on an incorrect premise about the resting potential and is not correct.
Option 3: 'neurons are easier to excite because their resting potential is closer to threshold and neurons respond too quickly to smaller graded potentials.' This captures two established consequences of hyperkalemia: depolarization brings the resting potential closer to the threshold for action potential initiation, and the heightened extracellular potassium can enhance responsiveness to small stimuli, making neurons more excitable. This option aligns with the physiological effect of elevated K+ on excitable membranes, and is therefore correct.
Option 4: 'neurons are easier to excite because their resting potential is closer to threshold.' While this statement is partially true (closer to threshold does increase excitability), it omits the related aspect described in hyperkalemia about the rapid responsiveness to small graded potentials. The missing second component makes this incomplete and not fully accurate as a standalone explanation.
Option 5: 'neurons respond too quickly to smaller graded potentials.' This isolates the second part of the correct explanation but fails to mention the underlying cause—the depolarized resting potential due to hyperkalemia. On its own, it is an incomplete characterization and thus not correct as a stand-alone answer.
In summary, option 3 correctly identifies both the depolarization bringing the resting potential closer to threshold and the enhanced responsiveness to small stimuli, whereas the other options present either incorrect premises (hyperpolarization) or incomplete/partial explanations that do not fully capture the primary problem in hyperkalemia.

The primary problem in hyperkalemia is that

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