Action Potentials Flashcards
Does the inner surface of the cell membrane have a negative or positive potential with respect to the outer surface?
Negative
What is depolarization?
Membrane potential becomes less negative
What is hyperpolarization?
Where membrane potential becomes more negative
What 2 things does direction of change of potentional (hyper or depolarization) depend on?
Direction of ion movement and charge carried by ion
What drives passive movement through ion channels?
Electrochemical gradient
What is movement of sodium in response to?
Opening of cell membrane sodium-selective channels (sodium conductance)
What is the symbol for G? How can you rearrange Ohm’s law to fit it in?
G. V=1/G
What is Ohm’s law?
V=IR
In what direction does Sodium flow?
Inwardly
In what direction does Potassium flow?
Outwardly
What is the membrane potential for sodium ions?
+60mV
What is the membrane potential for potassium ions?
-100mV
What is the membrane potential for most neurones?
-70-80mV
What is the definition of an action potential?
Brief electrical signal in which the polarity of the nerve cell membrane is reversed.
In action potentials, what happens once depolarization reaches a critical value (threshold value)?
Voltage-gated sodium channels open very rapidly along the neurone, causing rapid depolarization (upstroke)
What causes the downstroke in action potentials?
Voltage gated potassium channels are opened, leading to rapid repolarisation
Why does undershoot occur?
Voltage gated potassium channels are still open
Do action potentials propagate along nerve cell axons with constant or varying magnitude and velocity?
constant (allowing signalling over long distances)
What was discovered in the Hodgkin-Katz experiment?
Sodium ions cause upstroke, potassium ions cause downstroke
What activates voltage-activated Na+ and K+ channels?
membrane depolarization
Is activation of sodium channels self limiting (negative feedback) or self reinforcing (positive feedback)?
self reinforcing (positive feedback)
Is activation of potassium channels self limiting (negative feedback) or self reinforcing (positive feedback)?
self limiting (negative feedback)
During maintained depolarization, what do voltage-activated sodium channels enter?
non-conducting, inactivated state
What is required for the channel to enter the closed state?
repolarization
