Lecture 4 Flashcards
Define resting membrane potential
Difference in potential energy between two sides of cell membrane resulting from chemical and electrical gradients
Define chemical energy in terms of the RMP
Different concentrations of ions on each side of the cell, creating chemical gradients
Define electrical energy in terms of the RMP
Different amounts of negative charges on each side of the cell, creating electrical gradient
What is the typical RMP range for neurons, muscle cells, and glial cells?
-60 to -90 mV
What is the typical RMP range for non-excitable cells (e.g. epithelial cell and red blood cells)?
-8 to -60 mV
How is resting membrane potential established?
Ion pumps and exchangers
How are ion pumps powered?
ATP
How are ion exchangers powered?
Ion concentration gradients
Is K+ more abundant inside or outside a cell?
Inside
Is Na+ more abundant inside or outside a cell?
Outside
Is Ca2+ more abundant inside or outside a cell?
Outside (extremely low inside)
Is Cl- more abundant inside or outside a cell?
Variable
Are anions larger or smaller inside the cell?
Larger (e.g. DNA, RNA, proteins)
Are anions larger or smaller outside the cell?
Smaller (e.g. Cl- and bicarbonate HCO3-)
In seawater animals, how do ion concentrations differ? (3)
Double ion concentrations
K+ more abundant inside
Na+ more abundant outside
Define chemical potential energy
Potential energy produced by ion concentration differences across cell membrane
Define electrical potential energy
Potential energy produced by charge concentration differences across cell membrane
Define electrochemical potential energy
Chemical + electrical potential energies
What happens at E_ion?
No net movement of ion (i.e. inward = outward flow)
What does the Nernst equation describe?
Membrane voltage at which ion is at equilibrium
Ions with higher conductances…
are better at “pulling” RMP towards their E_ion
What ion typically determines RMP?
K+
At low levels of K+_out, what happens to V_m?
Does not decrease linearly with K+_out because the driving force for Na+ increases as V_m increases in difference from E_Na
What happens when i_ion is negative?
Ion flows into cell since V_m is lower than E_ion (increases V_m)
What happens when i_ion is positive?
Ion flows out of cell since V_m is higher than E_ion (decreases V_m)
What is membrane voltage determined by?
Equibilbrium potentials of all ions that can transverse membrane and their conductance at that point in time
What are the two assumptions of the Goldman, Hodgkin, and Katz (constant field) equation?
- Cl- is at equilibrium
2. At rest, i_K = i_Na
Define permeability
Ease at which ions can pass through an open channel
Define conductance
Permeability + availability of ions
What is the Mullins and Noda modification of the GHK/constant field equation?
i_Na:i_K ratio = 3:2
