So, with low potassium in the blood, the membrane potential can hyperpolarize, or become more negative.

因此，血中低钾时，膜电位会超极化或者说变得更负。

So, with too much potassium outside the cell, the membrane potential can become more positive, to the point of even causing contraction.

所以，当太多的钾离子聚集在细胞外，细胞膜电位会变得更高，甚至达到可以引起收缩的值。

Instead, as their channels let sodium ions trickle in, they cause the membrane potential to slowly and inevitably drift toward its threshold.

相反，当它们的通道让钠离子滴入时，它们会导致膜电位缓慢且不可避免地向阈值漂移。

Then, when some stimulus causes the sodium channels open up, the sodium ions flood back in, which raises the membrane potential until it reaches its threshold.

然后，当一些刺激导致钠通道打开时，钠离子会涌入，这会提高膜电位，直到达到阈值。

This concentration gradient is extremely important for setting the resting membrane potential of excitable cell membranes, which is needed for normal contraction of smooth, cardiac, and skeletal muscle.

电化学梯度在可兴奋细胞膜静息电位的形成中十分重要，而平滑肌，心肌还有骨骼肌的收缩都需要可兴奋细胞膜的参与。

The second type are voltage-gated channels, which are mostly found in muscle and nerve cells and are primarily controlled by changes in the electrical membrane potential.

第二种是电压门控离子通道，大多分布在肌肉和神经细胞中，主要由膜电位的改变来调控。

That process started by depolarizing the cell — that is, pushing the cell's membrane potential from negative toward positive, past a threshold that triggered voltage-gated ion channels to open.

这个过程是从细胞去极化开始的——也就是说，将细胞膜电位从负极推高到正极，超过了触发电压门控离子通道打开的阈值。

But eventually, the resting membrane potential gets so high that it's above the threshold potential, meaning that once the muscle depolarizes and contracts, it can't repolarize to allow another contraction.

但最终，静息电位变得太高，以至于超过阈值点位，这意味着一旦肌肉去极化收缩，就不能复极化以进行下一次收缩了。

This is because the value of membrane potential at the onset of an action potential DETERMINES the number of voltage-gated sodium channels activated during depolarization.

这是因为，动作电位开始时的膜电位值决定了去极化过程中激活的电压门控钠通道的数量。

The exact mechanism here, though, is unclear, but it might be due to an ion channel dysfunction that leads to an unexpected change in the membrane potential during or right after repolarization.

尽管这里确切的机制还不清楚，但它可能是由于一个离子通道的功能障碍导致了复极化期间或之后细胞膜电位发生意料之外的变化。

As potassium levels INcrease in the EXTRAcellular space, the MAGNITUDE of potassium gradient across the cell membrane is REDUCED, and so is the ABSOLUTE value of the resting membrane potential.

随着细胞外钾离子浓度增加，跨细胞膜上钾离子梯度减小，静息膜电位的绝对值也减小。