MP+AP Flashcards
What is the typical range of a resting membrane potential?
-5 to -100mV
How is resting mebrane potential measured?
Measured electrophysiologically by comparing the cell potential to a reference (external)
Net movement of charges =
electrical current (I)
All currents in a cell are carried by…
ions
What are the conditions for a cell to have a membrane potential?
- must be permeable to ions
- there must be a concentration gradient for an ion
What ion determines RMP for a neuron?
K+
The concentration gradient for a neuron (K+) favours diffusion ______ the cell.
out of
The electrical potential is when…
the concentration force drawing the K+ out of the cell balanced by electrical force holding it in.
What does the Nernst equation quantify?
The equilibrium potential for an ion
What is the Nernst equation? What are the variables?
R = thermydynamic gas constant (8.314 J/mol*K)
Z = valence of the ion
F = Faraday’s constant (9.65x104 C/mol)
Modification of the Nernst equation allows the calculation of RMP based on concentration and permeabilities of all relevant ions, giving what equation?
Goldman-Hodgkin-Katz equation (aka the constant field equation)
What are the characteristics and functions of the Na+/K+ ATPase pump?
Moves 3Na+out and 2K+ in
Electrogenic
Hyperpolarizes the cell
Requires an ATP molecule for each cycle, RMP requires energy for maintenance
Who developed the voltage clamp technique to address the question of hor depolarization precisely affects the permeability of ions?
Hodgkin and Huxley
The apparatus involved in the voltage clamp technique was used on what kind of axon and what did it manipulate?
A giant squid axon, the size of the axon allowed researchrs to plave electrodes in the axon and manipulate voltage and current.
When Hodgkin and Huxley manipulated the salinity of the extracellular solution by decreasing the [Na+], what was observed? What did this suggest?
They found that the peak of the action potential for smaller. This suggested that the flow of Na+ ions is incolved in the peak of the action potential.
When Hodgkin and Huxley manipulated the voltage to meausure the current, what did they find?
When the hyperpolarized the cell they saw virtually no current, only a capacitive transient. When they depolarized the cell they saw large inward and outward currents.
What were Hodgkin and Huxley’s major findings about the permeability of ions and the action potential?
Action potentials do indeed change the permeability of certain ions. As the action potential rised, so does the permeability of Na+ ions. This same relationship is seen with K+ ions; however, the increase is of a lower magnitude and the increase is delayed and persists longer than that of Na+
What two toxins can block voltage gated Na+ channels?
Tetrodotoxin (TTX) and saxitoxin (STX)
During RMP, Na+ and K+ are open/closed.
open/closed - however K+ is moving through leak channels.
Does K+ or Na+ have higher permeability during RMP?
K+
During depolarization what is the movement of Na+ and K+ ions?
During repolarization, what is the movement of ions?
The Na+ channel is inactivates (“ball and chain”) blocking any Na+ movement, K+channel opens allowing K+ to rush out of the cell.
Define absolute refractory period.
Cell is incapable of generating a new AP
Define relative refractory period.
More difficult to generate a new AP
TImmediately following an action potential, why is the threshold for initiation higher than usual?
The relative refractory period.
During which type of refractory period is there no Na+ conductance?
Absolute
Do individual action potentials travel along the axon?
No, an AP at one location will lead to the depolarization at adjecent areas of the axon. (Propagation)
