L4 - Action Potentials Flashcards
If a mystery ion with a positive charge has an equilibrium potential of -60mV and membrane potential is -70mV, then the ion will…
have net movement into the cell
If a mystery ion with a positive charge has an equilibrium potential of -60mV and membrane potential is -40mV, then the ion will…
have net movement out of the cell
Does an upward deflection result in a decrease in membrane potential or an increase?
decrease in membrane potential
Does a downward deflection result in a decrease in membrane potential or an increase?
increase in membrane potential
What is hyperpolarization?
when the membrane potential becomes more negative at a particular spot on the neuron’s membrane
What is depolarization?
when the membrane potential becomes more positive
What is repolarization?
when the membrane potential begins to move back towards its resting voltage
What is a graded potential change?
a change in the membrane potential relative to the resting potential
If the membrane of a neuron suddenly became more permeable to Na+, what would happen to membrane potential?
it depolarises
During a triggering event, what happens to the resting potential of a neuron if there is only one Na+ voltage gated ion channel?
the active area will be depolarised by a graded potential and this depolarisation will spread in both directions towards inactive areas of the neuron
however if there is only one Na+ voltage gated ion channel the charge will be lost over the course of the neuron
What is the threshold voltage?
the voltage required to change the shape of the voltage gated sodium ion channel and initiate an action potential
What is required to open the voltage-gated sodium channel?
the threshold voltage
What are the two gates found on the voltage-gated sodium channel and what do they do?
the activation gate opens very fast, and the inactivation gate closes slowly resulting in a period of time when sodium can pass through
the inactivation gate closes at the peak of the action potential
What is the positive feedback cycle of Na+ channels?
triggering event -> depolarisation (decreased potential) -> opening of some voltage-gated Na+ channels -> influx of Na+ (which further decreases membrane potential) -> depolarisation (decreased potential)
How does the voltage-gated potassium channel repolarise the cell membrane?
at threshold voltage the activation gate opens very slowly and once it is completely opened potassium is able to very quickly leave the cell and repolarise the membrane (negative charge)
What is the after-hyperpolarization period caused by?
the slow closing of the voltage gated potassium ion channel
If a person’s ECF K+ concentration increases then neurons will be ____________ to fire an action potential
more likely
If the voltage-gated potassium channels were removed from a neuron, would it be able to repolarise after an action potential?
yes, just more slowly
Ouabain, a specific inhibitor of the Na+-K+-ATPase, is applied to a neuron. The next action potential that fires after ouabain application will appear…
the same as normal because Na+-K+-ATPase does not exchange enough Na+/K+ ions to make a difference
What allows for the conduction of an action potential?
the charge of an active area at peak of action potential spreads out over the cell membrane resulting in the voltage gated sodium channels of inactive areas being activated (reaching their threshold voltage) which results in these areas reaching peak of action potential which continues the cycle
Can a neuron fire off another action potential during an absolute refractory period? Why?
no, because this is the period of time when the voltage gated sodium channels are open or resetting back to their original conformation
Can a neuron fire off another action potential during a relative refractory period? Why?
yes, but it is relatively difficult because we are further away from threshold voltage (as a result of hyperpolarization), therefore harder to create an action potential (bigger stimulus is required)
Why is the absolute refractory period important in the physiology of firing off action potentials?
prevents backward current flow and the re-excitement of previous active areas which have been returned to RMP
What determines the conduction velocity of a neuron?
the diameter of the axon (larger = faster) and whether it is myelinated or not
What is the name of the gaps between two layers of myelination on an axon?
nodes of Ranvier
Is the movement of ions that causes an action potential active or passive?
passive
Why is an action potential faster in axons of larger diameter?
this is because there is less resistance to current flow
How does myelination allow an action potential to move more quickly?
myelin insulates the axon, prevents ion leak and allows the action potential to jump from node to node all the way down the axon (avoids having to activate voltage gated sodium ion channels all the way down the neuron)
What is the name for the movement of an action potential down a myelinated axon?
saltatory conduction
What is the point of having different conduction velocities in different neurons?
so that action potentials can reach their target at the same time
