Chapter 2 Resting potential Flashcards
simply a device that separates positive and negative
charges
battery
The separation of charges
is due to two major things. Please enumerate
First is that there is an imbalance of various ions on the inside compared to the outside
of the cell.
Inside, more K
Outside, more Na
Second is that the cell membrane is semipermeable
simply means that
the membrane has pores or channels that allow only certain molecules to pass while preventing
others from crossing from one side to the other.
Semipermeable
The semipermeable membranes of all cells
allow _____ ions to pass through easily
K+ ions
The semipermeable membranes of all cells
allow K+ ions to pass through easily, but act as barriers for the passage of
Na+, Cl-, and Ca++ ions.
law of diffusion
that all molecules move
from a region of higher concentration to a region of lower concentration, and will continue to do
so until the concentrations become equal throughout.
In other words, there are
two opposing forces acting on K+ ions;
the concentration force driving K+
electrical force driving K
In other words, the net movement of K+ across the membrane will cease when
the two
opposing forces acting on K+ are equal
ccurs when the
concentration force tending to drive K+ from left to right is exactly balanced by the electrical force
tending to attract K+ from the right back into the left compartment.
equilibrium
This electrical force, or
electrical potential, that counterbalances the concentration force is called the
equilibrium potential for that ion.
the greater the
concentration difference for the permeable ion, K+ in this case, the more _____ the left
compartment has to be to counteract the concentration force
more negative
is a statement of the equilibrium condition for a single ion species
across a membrane that is permeable only to that ionic species.
Nernst Equation
Nernst equation tell you
what electrical force (electrical potential E in equation below) has to act on that ion in
order to exactly balance the concentration force acting on the same ion.
The E in the Nernst equation is referred to as the
equilibrium
potential for the ion
is the potential at which equilibrium is attained
equilibrium
potential for the ion
Cell membranes are impermeable to large organic anions existing inside the
cell, such as
aspartate, isothionate, and other amino acids as well as proteins
All Cells have a Resting Potential Determined Largely by
Potassium
Nernst Equation is
58/z log (ion ouside/ ion inside)
in squit, K+ concentration in the interstitial
(extracellular) fluid is
20 mM
squid : K+ concentration inside the cell
400 mM.
The actual resting potential of the squid giant axon can be accurately measured and is only
about
-70 mV.
is the electrical state of the cell (the voltage across its
membrane) when it is not active and thus not generating action potentials.
resting membrane potential
The reason that the actual resting potential of the cell is not equal to Ek is that
both Na+ and
Cl- play a small role in determining the electrical state of the cell (the cell’s resting potential).
The membrane is not absolutely impermeable to Na+.
force/s that drive Na into the cell
concentration
and electrical forces
[Na]o
450 mM
[Na]i
50 mM
ENa
+55 mv
Ek,
-70 mV
Based on
concentrations of Cl-, the Nernst equation tells us that the equilibrium potential for Cl-
-67 mV
The Concentration Gradients of All Ions Should Run Down but the cell has a means to combat this problem which is
it has sodium-potassium pumps.
The pump is open to the intracellular fluids and ____ are bound to protein
3 Na+ are bound to the protein.
The pump has ATPase activity and the binding of Na+ causes the
hydrolysis of ATP to ADP+Pi.
Inorganic Pi binds to the pump leads to
changing its configuration. The change in shape then allows
the release of Na+ into the extracellular space.
also allows the protein to bind 2 K+.
binding of K+ to N-K pump causes
de-phosphorylation of the protein, which then causes the protein to
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assume its original shape, which then transfers the K+ across the membrane and releases it into the
intracellular fluid.
Na-K pump also known as
Na-K
ATPase
utilizes the energy stored in ATP to actively transport Na+ out of the cell and K+ into
the cell (note that this transport is active because it occurs against concentration gradients-that is,
the protein transports Na+ and K+ ions from regions where they have low concentrations to
regions were they have high concentrations).
Na-K
ATPase
In its normal operation, the pump
transports ________ for each ATP molecule utilized.
2K+ ions into the cell and 3 Na+ ions out of the cell
Thus, the Na-K pump itself is actually separating charges because it pumps more positive Na+
charges out of the cell than it pumps K+ into the cell. In such cases the operation of the pump is
said to be
electrogenic
do not establish the resting potential, but rather their
purpose is to maintain the concentration gradients so that neurons can retain their resting
potentials even though they continuously lose K+ and continuously gain Na+.
Na-K pump
this drug inhibits the activity of this Na-K pump
ouabain
and digitalis
The Resting Potential is given by this equation
Goldman-Hodgkin-Katz Equation
thi ion has the greatest permeability, it receives the greatest weight and thus makes the largest
contribution to RMP
K+
is much less permeable and contributes only slightly to the resting potential.
Na+
The calculation of the resting potential can be made from the
Goldman-Hodgkin-Katz
(GHK) equation
The membrane potential computed from the GHK equation is
-70.18 mV
electrical state of the cell when it is not receiving inputs from other cells (when it is at rest).
resting potential
large change in membrane potential
action potential
when the membrane potential,
indicated by the symbol Vm, is more positive than the resting potential
cell is considered to be depolarized
when the membrane potential, Vm, is more negative than the resting potential
hyperpolarized
is the difference between the concentration and electrical
forces.
net strength
`The resting potential exists because of
oncentration differences of Na+, K+, and Cl- across
the semi-permeable membrane.
The major determinant of the resting potential
K+
Although K+ is considered the primary ion underlying the resting membrane potential, the
actual resting potential will not equal EK because
Na+ continuously leaks
into the cell
The exact magnitude of the resting membrane potential thus depends on the weighted
contributions of the several ions moving across the membrane, expressed formally by the
the
Goldman-Hodgkin-Katz equation.
required to maintain (note maintain, not generate) RMP
Na+ - K+ exchange pump
