Phases of the action potential Flashcards
What are the 7 parts of the phases of the action potential?
depolarization repolarization hyperpolarization threshold all-or-none phenomenon absolute refractory period relative refractory period
a stimulus (at or above threshold) causes the activation gate of the voltage-gated Na+ channels to open, Na+ flows in due to its electrochemical gradient and the cell becomes more positive (less negative)
depolarization
What does depolarization establish?
a positive feedback loop
sodium flowing into the cell causes more voltage-gated Na+ channels to open
positive feedback loop
In depolarization what causes the activation gate of the voltage-gated Na+ channels to open?
a stimulus at or above threshold
In depolarization why does Na+ flow into the cell?
due to the electrochemical gradient
What happens to the cell when Na+ flows in due to its electrochemical gradient in depolarization?
the cell becomes more positive (less negative)
Depolarization establishes a positive feedback, which causes?
sodium flwoing into the cell causes more voltage-gated Na+ channels to open
In depolarization where is the density of voltage gated Na+ channels the greatest?
on the axon hillock
When the voltage gets clost to +30mV, the Na+ inactivation gates start to close and voltage gated K+ channels open, K+ moves out of the cell with its electrochemical gradient
repolarization
In repolarization when do the Na+ inactivation gates strat to close and voltage-gated K+ channels open?
when the voltage gets close to +30mV
Where does K+ move with repolarization?
K+ moves out of the cell with its electrochemical gradient
The K+ channels stay open for a short time resulting in the cell becoming slightly more negative than the resulting membrane potential.
hyperpolarization
In hyperpolaization what do the K+ channels staying open for a short time result in?
the cell becomes more negative than the resting membrane potential
the minimum change in voltage that will result in an action potential usually a depolaization of 15 to 30 mV
threshold
if threshold is met an action potential will occur, smaller stimuli will not generate an action potential
all-or-none phenomenon
voltage-gated sodium channels are inactivated due to the closing of the inactivation gate, the neuron can not respond to a stimulus no matter how strong
absolute refractory period
During absolute refractory period why are voltage-gated sodium channels inactivated?
due to the closing of the inactivation gate
if the stimulus is greater than the previous stimulus (suprathreshold) sodium gates will reopen, this must follow the absolute refractory period.
relative refractory period
In relative refractory period why will sodium gates reopen?
if the stimulus is greater than the previous stimulus (suprathreshold)
What must relative refractory period follow?
absolute refractory period
