L3 - Membrane Potential Flashcards
What is the input zone of a nerve cell?
dendrites/cell body
What is the trigger zone of a nerve cell?
axon hillock
What is the conducting zone of a nerve cell?
axon
What is the output zone of a nerve cell?
axon terminals
Which cations are more concentrated in extracellular fluid?
calcium and sodium
What is the equilibrium potential of K+?
-90 mV
What is the equilibrium potential of Na+?
+60 mV
What is the equilibrium potential of Cl-?
-63 mV
What is the equilibrium potential of Ca2+?
+137 mV
What is the resting membrane potential?
membrane potential of non-excitable cells at “rest”
What allows for»_space;90% of resting membrane potential?
passive diffusion of K+ and Na+ down their concentration gradients
What allows for «10% of resting membrane potential?
Na+/K+ pump (active transport)
as this pump maintains Na+ and K+ gradients it has indirect effect to maintain RMP
How many Na+ and K+ ions does the Na+/K+ pump exchange?
three Na+ out and two K+ in
What causes a membrane potential?
near the cell membrane separated charges are responsible for creating a membrane potential (most of the fluid in the cell is electrically neutral)
Are cells more permeable to Na+ or K+? Are potassium ions able to leave quicker than sodium ions enter?
cells are more permeable to potassium
therefore potassium ions are leaving quicker than sodium ions are entering
Why is the equilibrium potential of K+ negative?
this is because a negative charge is required to keep K+ ions from leaking out into the extracellular fluid
K+ ions are at much higher concentrations inside the cell in comparison to outside the cell and are, therefore, driven to leak out into the extracellular fluid as a result of diffusion
Why is the equilibrium potential of Na+ positive?
this is because a positive charge is required to keep Na+ ions from entering into the cell
Na+ ions are at much higher concentrations outside the cell in comparison to inside the cell and are, therefore, driven to enter the cell as a result of diffusion
What will ultimately determine the value of the resting membrane potential?
determined by which occurs at a higher rate: Na+ influx, or K+ efflux
K+ efflux > Na+ influx because there are more K+ leak channels than Na+ leak channels in the membrane
thus resting membrane potential sits around -70mV, closer to the equilibrium potential for K+
In the living body, is Na+ in the ECF and ICF in equilibrium or is it not in equilibrium?
is not in equilibrium
Resting cell membranes are most permeable to…
K+
What are the methods by which Na+ and K+ enter and leave the cell?
Na+ leak channels, K+ leak channels and Na+/K+ pumps
What happens to the resting membrane potential of a cell if the extracellular K+ concentration increases?
it becomes more positive
What happens to the resting membrane potential of a cell if the K+ leak channels are blocked?
it becomes more positive because only sodium ions are going to be moving into the cell
What happens to the membrane potential of a cell that suddenly becomes more permeable to Na+?
it becomes more positive
What is the Nernst potential of an ion?
the potential level across the cell membrane that exactly opposes net diffusion of the ion through the membrane
What determines that magnitude of the Nernst potential and what is the formula for this equation?
determined by the ratio of the concentrations of that specific ion on the two sides of the membrane
E = V(in) - V(out) = RT/zF x In[C]out/[C]in
