403
Na
+
Na
+
Na
+
Na
+
Na
+
Potassium
channel
Sodium
channel
1
Resting state:
All gated Na
+
and K
+
channels are closed.
2
Depolarization:
Na
+
channels open.
3
Repolarization:
Na
+
channels are
inactivating, and K
+
channels open.
4
Hyperpolarization:
Some K
+
channels
remain open, and Na
+
channels reset.
Voltage-gated Na
+
channels
have two gates and alternate
between three different states.
Voltage-gated K
+
channels
have
one gate and two states.
The key players
The events
Each step corresponds to one part of
the AP graph.
Closed
at the
resting state, so no
Na
+
enters the cell
through them
Opened
by
depolarization,
allowing Na
+
to
enter the cell
Closed
at the
resting state, so no
K
+
exits the cell
through them
Opened
by
depolarization, after
a delay, allowing K
+
to exit the cell
Inactivated—
channels
automatically
blocked by
inactivation gates
soon after they open
Outside
cell
Inside
cell
Outside
cell
Inside
cell
Activation
gates
Activation
gate
Inactivation
gate
Inactivation
gate
K
+
K
+
K
+
Na
+
K
+
Na
+
K
+
K
+
403
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