Section 6 Flashcards
The electrical potential difference between the inside and outside of the cell
Membrane potential or membrane voltage
Movement of an ionic current through the membrane
Ionic charge
Requires displacement of a positive charge off the cell membrane; no ion movement through the membrane
Capacitative charge
What are the two forces pushing ions through the plasma membrane?
- Diffusion force
2. Electromotive force
Particles that fit or carry a given charge pass through these channels freely; depends on size and/or concentration gradient
Open or intermittently opened channel
Changes in the membrane potential open and close the channel, important for action potential propagation/conduction
Voltage gated channel
Ligands attaching to protein open the channel; responsible for graded potentials
Ligand gated channels
Responsible for facilitated diffusion (carries specific molecules with its concentration gradient) and active transport
Membrane carrier protein channel
Membrane protein uses ATP energy to move specific molecules against their concentration gradient; oxygen dependent
Active transport
The plasma membrane is [hydrophilic/hydrophobic] on the outside and [hydrophilic/hydrophobic] on the inside.
Hydrophilic; hydrophobic
The net result of the separation of + and - charges is more [+/-] on the inside of the cell and more [+/-] on the outside of the cell.
-; +
Term used to describe the baseline voltage level of membrane polarization that exists in a cell at rest
Resting membrane potential
What is the average resting potential for motoneurons?
-70 mV
What is the average resting potential for muscle cells?
-90 mV
Name the four factors that cause the resting membrane potential
- Maintained charge separation by a semipermeable ion selective cell membrane
- K+ efflux - while leaving an organic anion (A-) inside the cell
- Cl- influx - while leaving Na+ outside the cell
- The Na+/K+ pump which prevents ions from distributing at equilibrium, thus maintaining charge separation
Rank the relative permeability of the membrane to charged particles from least to greatest.
A- < Na+ < Cl- < K+
The unequal membrane permeability and ion concentration allows more ____ diffusion out of the cell than ____ into the cell; this leads to the 2nd major cause of the resting membrane potential, ___ efflux leaving A- inside the cell.
K+; Na+; K+
True or False:
In a resting cell there is a higher concentration of K+ outside the cell and a higher concentration of Na+ inside the cell.
False; K+ is higher inside the cell and Na+ is higher outside the cell
What ions make the inside of the cell negatively charged?
A- left in the cell and Cl- moving in the cell (nerve cell only)
What ions make the outside of the cell positively charged?
K+ moves out and Na+ left out
True or False:
Na+ left behind because resting membrane’s permeability to Na+ is relatively low.
True
In a resting cell, the electromotive force tends to draw K+ [into/out of] the cell [against/with] its concentration gradient
Into; against
In a resting cell, the electromotive force tends to draw Na+ [into/out of] the cell [against/with] its concentration gradient
Into; with
Since Na+ slowly leak into the cell over time, the Na+/ K+ pump actively pumps out _____ and pumps in _____
3 Na+ ions; 2 K+ ions
The force that pushes an ion at the cell membrane from a region of greater concentration to a region of lesser concentration
Diffusion force
The force that repels ions that have the same charge and attracts ions with opposite charges
Electromotive force (EMF)
If an ion moves down its concentration gradient, would K+, Na+, and Cl- move into or out of the cell?
- K+ = out of
- Na+ = into
- Cl- = into
If an ion moves with its EMF, would K+, Na+, and Cl- move into or out of the cell?
- K+ = into
- Na+ = into
- Cl- = out of
When diffusion force and EMF action on the ion(s) are not equal, it results in
Ion movement
The membrane potential/voltage at which the diffusion force is equal to the EMF is defined as ______.
Equilibrium potential
No outward movement of K+ ions occurs when membrane potential = ____mV
-96
No inward movement of Na+ ions occurs when membrane potential = ____mV
+66
No inward movement of Cl- ions occurs when membrane potential = ____mV
-90
K+ efflux causes the membrane potential to become more [positive/negative] with respect to the outside.
Negative
Na+ influx causes the membrane potential to become more [positive/negative] with respect to the outside.
Positive
Cl- influx causes the membrane potential to become more [positive/negative] with respect to the outside.
Negative
The algebraic difference between the membrane potential and the ion’s equilibrium potential
(Driving Force = Em - Eion)
Driving Force
Greater driving force = [greater/lesser] push on an ion
Greater
True or False:
The polarity of the driving force is relative only to the ion in question.
True
In a resting membrane, what is the net driving force for K+? Is it being driven in or out of the cell?
+6 mV; net outward force
[-90mV - (-96mV) = +6mV]
In a resting membrane, what is the net driving force for Na+? Is it being driven in or out of the cell?
-156 mV; net large inward force
[-90mV - (+66mV) = -156mV]
In a resting membrane, what is the net driving force for Cl- in a muscle cell? Is it being driven in or out of the cell?
0mV; no movement
[-90mV - (-90mV) = 0mV]
In a resting membrane, what is the net driving force for Cl- in a nerve cell? Is it being driven in or out of the cell?
+20mV; net inward force
[-70mV - (-90mV) = +20mV]
With ionic current, whether an ion moves thru a membrane depends on 2 things
- Driving force
2. Membrane permeability
What ion has the greatest driving force at the resting membrane potential?
Na+
During the upstroke of the action potential, the driving forces on both K+ and Cl- [increased/decreased] compared to resting condition.
Increased
During the upstroke of the action potential, the driving forces on Na+ [increased/decreased] compared to resting condition.
Decreased
During the upstroke of an action potential, what is the net driving force for K+ in a muscle cell? Is it being driven in or out of the cell?
+136mV; (increased) net outward force
[+40mV - (-96mV) = +136mV]
During the upstroke of an action potential, what is the net driving force for Na+ in a muscle cell? Is it being driven in or out of the cell?
-26mV; (decreased) net inward force
[+40mV - (+66mV) = -26mV]
During the upstroke of an action potential, what is the net driving force for Cl- in a muscle cell? Is it being driven in or out of the cell?
+130mV; (increased) net inward force
[+40mV - (-90mV) = +130mV]
At the peak of an action potential, what is the net driving force for K+ in a muscle cell? Is it being driven in or out of the cell?
+151mV; large net outward force
[+55mV - (-96mV) = +151mV]
At the peak of an action potential, what is the net driving force for Na+ in a muscle cell? Is it being driven in or out of the cell?
-11mV; small inward force
[+55mV - (+66mV) = -11mV]
At the peak of an action potential, what is the net driving force for Cl- in a muscle cell? Is it being driven in or out of the cell?
+145mV; large net inward force
[+55mV - (-90mV) = +145mV]
During the downstroke of the action potential, the driving forces on both K+ and Cl- [increased/decreased]compared to the +55mV at the peak of the action potential.
Decreased
During the downstroke of the action potential, the driving forces on Na+ [increased/decreased]compared to the +55mV at the peak of the action potential.
Increased
Charge movement without ionic current flow through the membrane; initially depolarizes inactive membrane
Capacitive current
Name the 4 steps of capacitive current.
- Na+ current moves from active to inactive region of membrane inside cell
- Positive charge displaces or neutralizes negative charge
- Positive charge repelled off outside membrane
- Positive charge outside of cell is replaced with a negative charge (capacitive current)
