7. Membrane Potentials Flashcards
What is resting membrane potential primarily due to?
The permiability of the plasma membrane to potassium ions.
Do voltage gated sodium channels open quickly or slowly?
Quickly
What is the equation to determine the “driving force” of an ion?
Resting membrane potential - Equalibrium constant of a given ion = Driving force
What is the equilibrium potential for Potassium?
-91 mV
If a driving force is positive, what is the direction of movement for an ion?
Out of the cell
What is the equilibrium potential for Calcium?
+123 mV
What is the equilibrium potential for Chloride?
-66.4 mV
What is the function of voltage gated sodium channels?
Depolarization phase of an action potential
What is a main contributor to causing the hyperpolarization period?
Voltage gated potassium channels stay open a bit too long.
What two forces act on ions to help develop membrane potential, and what determines those forces?
Chemical Gradients: Concentration of a given ion in vs out of the cell
Electrostatic Forces: Like repels like, and opposites attract. (A negative ion is less likely to cross over to the side of the membrane with more negative ions, but more likely to cross over to the side with more positive ions)
What do we mean when we say that action potentials are non-decremental?
The signal does not change relative to distance in the axon
What is the function of a voltage gated potassium channel?
Repolarization phase of an action potential
(positive potassium leaves the cell)
What is equilibrium potential for a given ion?
The membrane potential when electrical and chemical forces on that ion are equal, and no further movement of that ion occurs.
What do you see in patients with intermittantly low blood potassium?
Paralysis due to a larger gap between resting membrane potential and threshold.
Repolarization occurs more quickly
(Hypokalemic Periodic Paralysis / HypoPP)
What goes into the cell, and what goes out of the cell, via Na/K ATPase
3 Na Out
2 K In
If a driving force is negative, what is the direction of movement for an ion?
Into the cell
What state are voltage gated sodium channels in during repolarization?
Their activation gates are open, but their inactivation gates are closed
What makes up the absolute refractory period?
Depolarization
(Overshoot)
Repolarization
What two things are happening relating to voltage gated ion channels to make it harder to generate an action potential during the relative refractory period?
Voltage gated Potassium channels are still open, or too much potassium has left the cell.
Not all voltage gated sodium channels are reset and ready to open.
Why can you not cause sodium channels to open during the absolute refractory period?
Because they are either already open, or the inactivation gates are closed, and have not yet reset.
What is a graded potential?
A stimulus that does not reach the threshold to become an action potential
Do voltage gated potassium channels open quickly or slowly?
Open slowly
What is the accepted resting membrane potential for cardiac and skeletal muscle cells?
-80 to -90 mV
What type of cell has an unusual repolarization graph?
What is a consequence of this fact?
Cardiac Ventricle cells - their repolarization curve is very broad, and they have a long absolute refractory period.
What is the Nernst Equation?
Equilibrium constant of a given ion = (61.5/valence)(log [out]/[in])
Where [out] is the extracellular concentration of a given ion
Where [in] is the intracellular concentration of a given ion
In terms of potassium movement, what is happening when a neuron is at its resting membrane potential?
Potassium movement out of the cell is roughly equal to potsassium movement into the cell
What phase makes up the relative refractory period?
Hyperpolarization
What is the accepted resting membrane potential for smooth muscle?
-60 mV
In terms of the Nernst Equation, if the concentration of an ion is greater inside the cell, will the log come out as positive or negative?
Negative
Log [x]out/[x]in
The denominator is larger, requiring the log to be negative.
What is the accepted resting membrane potential for Neurons?
-60 to -70 mV
For voltage gated sodium channels
What blocks out sodium ions after the initial opening?
Inactivation gates
Is it easier to depolarize a cell with a higher or lower resting membrane potential?
Higher
The higher the resting membrane potential, the closer it is to threshold, and the less is required to depolarize it.
What is the resting membrane potential for Sodium?
+61.5 mV
