Action Potential Flashcards
What is an action potential?
an increased voltage beyond a set point, generating a nervous impulse
What is depolarisation and why does it occur?
an increase in voltage, which occurs as the membrane becomes more permeable to Na+
How does the action potential move along an axon?
similarly to a mexican wave
What protein channels are voltage dependent?
voltage-gated Na+ channels
How might a stimulus cause depolarisation?
as it may allow voltage-gated Na+ channels to open, allowing Na+ ions to diffuse in, meanwhile K+ ions still diffuse out
What happens if the voltage is raised above the threshold?
More Na+ ions can move into the cell, so voltage increases further
What is the maximum voltage an axon can reach?
+40mV
What happens at +40mV?
more K+ channels are opened, and voltage-gated Na+ channels close. This causes voltage to decrease
What is the hyperpolarisation?
where voltage goes temporarily below the resting potential
What are the different stages in generating an action potential?
resting, depolarisation, repolarisation, hyperpolarisation, resting
Why do action potentials move across an axon like a mexican wave?
as one part reaches +40mV, the voltage is enough to trigger the next part (nodes of Ranvier) of the axon to start depolarisation
What happens if the voltage does not pass -55mV?
nothing, the action potential and impulse are not produced
Why does a depolarisation that does not reach the threshold not cause an action potential?
not enough energy to open voltage gated Na+ channels
What does a bigger stimuli cause?
a greater frequency
Why is the all or nothing principle important?
makes sure animals only respond to large enough stimuli, rather than the animal becoming overwhelmed
