Membrane Potentials Flashcards
Have gates controlled by change in membrane potential
voltage gated channels
have gates controlled by the binding of a ligand such as a neurotransmitter
ligand-gated channels
the potential difference generated across a membrane when an ion diffuses down its concentration gradient
diffusion potential
the magnitude of a diffusion potential depends on what?
the size of the concentration gradient
what is the driving force of diffusion potential?
concentration gradient
what is diffusion potential measured in?
millivolts
Movement of an ion across the membrane is determined by what?
both by the concentration gradient and by the electrical potential difference across the membrane
estimates the equilibrium potential for a given ion
the nernst equation
what is the approximate concentration of Na+ in the ECF?
140 mM
what is the approximate concentration of Na+ in the ICF?
14 mM
what is the approximate concentration of K+ in the ECF?
4 mM
what is the approximate concentration of K+ in the ICF?
120 mM
what is the equilibrium potential for Na+?
+65 mV
what is the equilibrium potential for K+?
-95 mV
the driving force for net diffusion of ions must account for what?
both the concentration gradient and the electrical potential across the membrane
How do you calculate the net driving force?
[membrane potential (mV)]- [equilibrium potential for a given ion (mV)]
If the driving force is negative [membrane potential is more negative than the equilibrium potential for a given ion] what will happen?
cation will enter the cell, anion will leave the cell
if the driving force is positive, what will happen?
cation will leave the cell, anion will enter the cell
the activation gate of the Na+ channel in nerve is opened by what?
depolarization
What happens to the inactivation gate of the Na+ channel in depolarization?
it is closed
At rest, the nerve membrane is far more permeable to…?
K+ than to Na+
Makes the membrane potential less negative (the cell interior becomes less negative aka more positive)
Depolarization
makes the membrane potential more negative
hyperpolarization
the flow of positive charge into the cell
inward current
inward current causes what?
depolarization
the flow of positive charge out of the cell
outward current
outward current causes what?
hyperpolarization
membrane potential at which the action potential is inevitable
threshold
portion of the action potential where the membrane is positive
overshoot
portion of the action potential where the membrane is actually more negative than at rest of hyperpolarized
undershoot
period during which another action potential cannot be elicited
absolute refractory period
period during which another action potential can only be generated with a stronger stimulus because the threshold has raised
relative refractory period
at rest, the activation gate is?
closed
at rest the inactivation gate is?
open
at the peak of the action potential, the slow inactivation gate will?
close
when the membrane potential has repolarized back to its resting level, the activation gate will be? and the inactivation gate will be?
the activation gate will be closed and the inactivation gate will be open
What affect does depolarization have on K+ channels?
slowly opens K+ channels and increases K+ conductance
What is repolarization caused from?
an outward K+ current
When the serum/blood K+ concentration increases, what happens to the K+ equilibrium potential and the resting membrane potential?
they become less negative
What happens to the inactivation gates on Na+ channels with hyperkalemia?
they are closed
a reduction in the serum/blood potassium concentration will do what to the cell membrane?
hyperpolarize it
the process that occurs when the cell membrane is held at a depolarized level such that the threshold potential is passed without firing an action potential
accommodation
if depolarization occurs slowly enough, the Na+ channels do what?
The Na+ channels close and remain closed
In accommodation, The upstroke of the AP will not be able to occur because?
there are not enough Na+ channels available to carry inward current
What effect does lidocaine have on action potentials?
Lidocaine will block voltage-gated Na+ channels and therefore the inward current of Na+ and the upstroke of the AP will not occur
the speed at which action potentials are conducted along a nerve or muscle fiber
conduction velocity
What two factors affect time constant?
membrane resistance and membrane capacitance
How does a high membrane resistance (Rm) affect time constant?
it will increase it; current does not readily flow 1
the ability of the cell membrane to store charge
membrane capacitance
what affect does a high membrane capacitance (Cm) have on the time constant?
it will increase it because injected current must first discharge the membrane capacitor before it can depolarize it
What are the cable properties?
Time constant and length constant
The length constant indicates what?
how far a depolarizing current will spread along a nerve
When will the length constant be longest?
when the diameter of the nerve is large (Ri is low and Rm is high)
What effect does increased nerve diameter have on internal resistance?
decreases internal resistance
What effect does myelination have on membrane resistance?
increases it
What effect does myelination have on nerve capacitance?
decreases it
Periodic breaks at regular intervals along the length of the myelin sheath covering an axon
Nodes of Ranvier
Is the membrane resistance high or low at nodes of ranvier?
low
the AP will seem to leap along the axon from node to node
saltatory conduction
Where are action potentials generated in myelinated nerves?
at the nodes of ranvier
Loss of the myelin sheath around nerves causes what?
a decrease in membrane resistance
What effect does a decrease in membrane resistance have on an AP?
current “leaks out” across the membrane during conduction of local currents
What are the signs and symptoms of MS?
weakness of the LEs, numbness, paresthesia, blurred vision, and pain with eye movements
