Action Potentials Flashcards
What are the four phases of an action potential?
Rising phase
Overshoot phase
Falling phase
Undershoot phase
What are the three functional components of the voltage gate sodium channel?
Volatage sensor
Ball and chain gating mechanism
Pore
What happens when depolarization reaches threshold?
Opening of voltage gated sodium channels and sodium influx
What happens to sodium channels shortly after activation?
The “ball and chain” binds within the inner mouth of the pore and inactivates the channel
What is the purpose of delayed rectifier voltage gated K channels?
They open in response to depolarization, but slower than sodium channels.
Allow potassium efflux and a larger K conductance
Responsible for hyperpolarization
What happens once the membrane potential becomes negative again?
Delayed-rectifier channels close
resting state of membrane is restored
membrane potential returns to normal resting level
What is responsible for the absolute refractory period?
The inactivation of voltage gated sodium channels
What is responsible for the relative refractory period?
Activation of voltage-gated K channels and hyperpolarization
What two toxins block sodium channels?
Tetrodotoxin
Saxitoxin
What types of drugs affect sodium channels?
Local Anesthetics
Some antiarrhythmics
Some antiepileptic drugs
What is frequency coding?
Allows action potential frequency to vary with amplitude of depolarization from graded potentials
Where does the capacitance current flow and what is its function?
“Ahead” of the action potential
it is responsible for depolarizing the next segment along the axon
What determines how far the capacitance current spreads in unmyelinated axons?
The length constant
How does myelination affect membrane resistance and capacitance?
Increases membrane resistance
Decreased capacitance
Where are sodium channels located in myelinated axons?
Nodes of Ranvier
