Question 1
What stops the rising phase of the action potential?
◦ The sodium activation gate closes.
◦ The Na
+ activation gate opens.
◦ The Na
+ inactivation gate opens.
◦ The K
+ gate closes.
◦ The Na
+ inactivation gate closes.
Question 2
During the relative refractory period, an initial threshold-level depolarization is usually not sufficient to initiate an action potential. Why?
◦ Only some Na
+ channels have returned to their resting position.
◦ The statement is incorrect; a threshold-level depolarization always triggers an action potential.
◦ Only K
+ channels are still open, so Na
+ entry is offset by K
+ loss.
◦ Only a few K
+ channels have returned to their resting position.
◦ Some Na
+ channels have returned to their resting position and K
+ channels are still open, so Na
+ entry is offset by K
+ loss.