Membrane Potential Flashcards
muscle (cardiac skeletal)
-80 to -90 mv
smooth muscle
-60 mv
neurons
-60 to -70 mv
astroglia
-80 to -90 mv
erythrocytes
-9 mv
types of gated channels
- voltage-gated
- ligand-gated
- signal-gated
- mechanically-gated
electrochemical forces
- diffusion forces
- electrostatic forces
equilibrium potentil (Eion)
- membrane potential when electrical and chemical forces are equal
- no further movement occurs
equlibrium potential for Na+
+66 mv
equalibrium potential for K+
-91 mv
Nernst equation
Potassium (K+)
In: 150 mM
Out: 5 mM
E: -91 mv
Sodium (Na+)
In: 15 mM
Out: 150 mM
E: 61.5 mv
Calcium (Ca2+)
In: 0.0002
Out: 2
E: +123 mv
Chloride (Cl-)
In: 10 mM
Out: 120 mM
E: -66.4 mv
effect of increased extracellular K+ concentration
more positive RMP = easier to depolarize
effect of decreased extracellular K+
more negative RMP = more difficult to depolarize cell (cell is hyperpolarized and further from threshold)
insulin (effect on K+)
[Na-K-ATPase]
enhanced cell uptake
beta-catecholamines (effect on K+)
[Na-K-ATPase via + cAMP]
enhanced cell uptake
alpha-catecholamines (effect on K+)
[opposite of beta]
impaired cell uptake
acidosis (effect on K+)
[Donnan effect; inhibition of Na-K-ATPase]
impaired cell uptake
alkalosis (effect on K+)
enhanced cell uptake
[“k is lo”]
external potassium balance (effect on K+)
loose correlation
[ratio vs. total body K+ until severe states]
cell damage (effect on K+)
impaired cell uptake
[release of intracellular contents]
hyperosmolality (effect on K+)
enhanced cell efflux
[due to conctraction of ICF volume and increased K+]
strenuous exercise (effect on K+)
enhanced cell efflux
[+ alpha-catecholamines]
main contributor to resting m embrane potential
K+ diffusion potential
minimal contribution to the RMP due to low permeability at rest (~5 mv positive)
Na+ diffusion
minimal direct contribution to the RMP (~4 mv) with indirect contribution to maintain ion concentration gradients
Na+-K+ ATP pump
- permit mosty unregulated passage of ions (open always)
- why K+ is more likely to passively leave the cell than Na+
- main component in permeability of K+ to the plasma membrane
K+ leak channels
are channels involved in membrane potential active or passive?
passive
deviation from 0 mv
polarization
when membrane potential becomes less negative
depolarization
when membrane potential becomes more negaive
hyperpolarization
when membrane potential is returning towards resting membrane potential
repolarization
A. Resting - phase 4
B. Depolarization - phase 0
D. Repolarization - phase 3
E Hyperpolarization - refractor period)
key players in action potential
- Na+ ions
- K+ ions
- voltage-gated Na+ channels
- voltage-gated K+ channels
- K+ leak channels
* Ca2+ in certain cell types, such as cardiac
identify the phases of opening for the activation & inactivation gates
- resting: activation closed, inactivation open
- activation: activation open during depolarizaton
- inactivation: inactivation gate closed rapidly after activation phase
when can the inactivation gate be opened?
when membrane potential returns to near resting
2 things that contribute to repolarization
- potassium leaks out via K+ “leak” channels
- voltage-gated K+ channels slowly open to assist leak channels to increase membrane permeability to K+
(voltage gated Na+-channels are closed)
what contributes to hyperpolarization/refractory period?
voltage-gated K+ close slowly and stay open too long causing too much K+ to leave (more difficult to stimulate subsequent AP)
types of refractory periods
- absolute refractory period
- relative refractory period
- phase when Na+ channels are either open OR inactivation gate is closed/cannot reopen
- no other AP can be generated
absolute refractory period
- phase when inactivation gate is now open and activation gate is closed
- K+ permeablity fairly high and overshootsK+ leaving cell so membrane becomes slightly more negative than RMP
- not all voltage-gated Na+-channels are in same state at same time yet varying the potential response
- AP may be initiated but requires stronger stimulus
relative refractory period
events of membrane permeability
A. Na+ permeability increased rapidly
B. K+ permeability increases slowly
C. Na+ permeability decreases rapidly
D. K+ permeability decreases slowly
