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Essay

Use the answer code below to answer this section.
$\begin{array}{lr}\text { 1. Two permeability changes that occur at the }\\\text { peak of an action potential }&\text { increased } \mathrm{P}_{\mathrm{Na}+}\_\_\_\\\text { 2. Ion movement responsible for the rising }&\text { decreased } \mathrm{P}_{\mathrm{Na+}} \text { and }\\\text { phase of the action potential }&\text { increased } \mathrm{P}_{\mathrm{K}+}\_\_\_\\\text { 3. Ion movement responsible for the falling }\\\text { phase of the action potential }&\mathrm{Na} \text { influx }\_\_\_\\\text { 4. Permeability change that occurs at threshold }&\mathrm{K}^{+} \text {efflux }\_\_\_\end{array}$