Lecture 10 Ions and Membrane Potentials Flashcards
Diffusion of Ions
through Ion channels down an electrochemical gradient electrical potential (measure in millivolts) is electrical force on an ion
Electrical potential difference between ICF and ECF is due to
imbalance of + and - charges across the membrane
membrane potential
Resting membrane potential is
-70mV (negative inside)
Membrane potential
results from?
results from the unequal distribution of permeable ions (K+ and Na+) between the ICF and ECF, and resulting movements of these ions across the membrane
Potential difference
potential difference across the membrane of an unstimulated nerve or muscle cells
what forms the concentration gradients
the Na+/K+ pump actively transports Na+ out and K+ in
forming concentration gradients of Na+ and K+ ions
The resting cell membrane is
permeable to K+ due to the presence of K+ leak channels in the membrane
How does K+ move
K+ diffuses out of the cell down its concentration gradient
What makes the ICF more negative?
what does this cause?
Movement of K+ out of the cell makes the ICF more negative. The resulting negative electrical potential inside the cell creates an electrical gradient that acts in the opposite direction as the concentration gradient.
Equilibrium potential for K+
at some point the concentration gradient and electrical gradient for K+ will exactly counterbalance each other. This point is the equilibrium potential for K+
Ek = -90mV
Diffusion of K+ outward
tends to move the membrane potential toward Ek
since the resting membrane is most permeable to K+, the RMP is close to Ek
Resting Membrane
is slightly permeable to Na+ so some Na+ diffuses inward
this makes the RMP slightly less negative than Ek
Equilibrium potential of an ion
is the potential difference at which the electrical force exactly balances the chemical force (concentration gradient) on the ion
The EP of an ion can be calculated using the Nernst equation
Nernst Equation
Eion=60/z * log(cout/cin)
Eion is the equilibrium potential of the ion in millivolts (mV)
Z is the charge on the ion (1+ for K+ and Na+)
Cout and Cin are concentrations of the ion in the ECF and ICF
log is the base 10 logarithm
ENa
+60mV
What determines the membrane potential
the concentration gradients of permeable ions, primarily Na+ and K. Formed by the Na+/K+ pump
The relative permeability of the membrane to these ions (K+ vs Na+) due to specific ion channels
What has the largest influence on RMP
what does it create
K+ has the greatest influence on RMP because the resting membrane is most permeable to K+
K+tends to move out of the cell which creates a negative potential inside the cell
Main factors of the RMP
RMP is close to Ek, but is slightly less negative because of some inward Na+ leakage
RMP is very sensitive to changes in K+ in the ICF or ECF
RMP is only slightly affected by Na+ because the resting membrane is not very permeable to Na+
The membrane potential results from
the unequal distribution of permeable ions (K+ and Na+) between the ICF and ECF and the resulting movements of these ions across the membrane
what forms the gradients and what happens once the gradients are in place
The Na+/K+ pump forms concentration gradients of K+ and Na+ between the ICF and ECF. Once these gradients are in place the membrane potential depends on the relative permeability of the membrane to K+ and Na+ which is determined by specific ion channels.
What will permeable ions do
Ions that are permeable will diffuse across the membrane down their electrochemical gradients, which moves the membrane potential toward the equilibrium potential of the most permeable ion(s).
What is dominant is a resting cell
K+ leak channels are dominant so RMP is close to Ek
How does the membrane potential change
the membrane potential can change very rapidly in response to changes in permeability of the membrane to Na+, K+, or other ions. Changes in permeability to these ions result from opening or closing of different ion channels.
