Physio-Action Potentials Flashcards
What does the membrane potential do as electrical stimulus continually increases?
The membrane potential will increase until it reaches the action potential, once the threshold is reached it doesn’t matter how strong the stimulus is.
What cells can produce action potentials?
Cardiac muscle, skeletal muscle, neurons and some smooth muscle.
In what cells do action potentials travel the quickest? The slowest?
Quickest to slowest = Neuron .5 ms, Skeletal muscle 1-2 ms, Cardiac muscle .5 s
Why would cardiac muscle have a slow action potential?
So contraction is long enough to eject blood from the ventricles.
What happens to sodium conductance and potassium conductance in an action potential?
Na floods and returns to resting level, then K floods and needs Na/K ATP pump to get things back to resting level.
What determines the resting potential of a membrane? What maintains the resting potential?
Non-gated Na and K channels. Na/K ATP pump
What are the unique features of the Na Voltage gated channel and K voltages gated channel?
Na VGC has two gates: one closed gate that opens rapidly upon membrane depolarization and one open gate that closes slowly upon membrane depolarization. K VGC has one closed gate that opens very slowly upon depolarization.
What causes depolarization of the membrane in an action potential?
Inward Na current. Opening of the Na VGC increases conductance/permeability and the driving force is already large. This makes for a huge inward Na+ current that floods the cell with positive Na, depolarizing the membrane
Why does the action potential peak?
The second Na VGC gate begins to close. This causes conductance to decrease at the same time the driving force is decreasing due to depolarization, this decreases current.
What causes the K+ to enter the cell in an action potential?
The driving force is increased because of depolarization and thus current increases. K+ now wants to get out of the cell.
How does the cell hyper polarize?
K+ continually leaves through the K+ VGC and Na VGCs are all closed.
What causes hyper polarization after an action potential to halt?
As K+ leaves the cell the driving force become less for K+, conductance decreases and current decreases.
When is the channel ready to produce another action potential?
When the Na VGC is reset with the top channel closed and the bottom channel open.
How is sodium conductance controlled in a cell?
Resting potential has the top gate closed. Depolarization causes the top gate to open and increase sodium conductance. This makes sodium come into the cell and cause more depolarization and more channels opening. The gate then closes and depolarization stops.
How is K+ conductance controlled?
Depolarization increases K+ conductance, K+ leaves the cell and causes hyper polarization which causes the channel to close. Its like hosing the action potential down with cold water.
How does an action potential propagate down an axon?
Depolarization of the membrane causes Na+ to flood the cell. Na+ will flooding will cause the K+ VGC to open and K+ will leave the cell behind the action potential, causing depolarization of the membrane. In front of the action potential, Na+ is attracted to - charged molecules sitting near the membrane across from the + charged molecules out side of the cell. This causes the - charge to become neutral, the EC + to leave, membrane to depolarize, Na+ VCGs to open and start another action potential.
Why do myelinated axons produce faster conduction of signals?
It reduces the amount of extracellular fluid in contact with the axon. This increases the distance a single action potential can travel. Less current leaves the axon after the action potential
Where does the most current leave from a myelinated axon?
Nodes of Ranvier…these are what cause saltatory conduction
Where do sodium and potassium VGCs tend to reside?
Na+ VCG at the nodes and K+ VGC underneath the myelin. Non-gated K+ channels also reside under the myelin and help restore membrane potential before the next node.
