Membrane Potential Flashcards
thin layer that encloses intracellular contents, is a mechanical barrier, controls movement of waste, and maintains different concentrations
plasma membrane
Why are cells from muscle and nervous tissue excitable?
because they produce electrical signals when excited,
What’s membrane potential?
separation of opposite charges across the membrane in ECF and ICF. Slight excess of negative charges
What’s resting membrane potential?
potential that exists when an excitable cell is at rest and not responding to an electrical stimulus, is stable, negative, and influenced by leaky K+
What is resting membrane potential in neurons, skeletal muscle, and cardiac?
-60 to -70, -85 to -95, -80 to -90
What are two types of gradients?
electrical - produced by unequal charged particles
chemical - produced by unequal distribution of ions
What 3 factors contribute to resting membrane potential?
Ionic concentration gradient, caused by K+ and Na+ diffusion. Selective membrane permeability, and sodium potassium pump.
What happens to resting membrane potential when NA/K+ pump inhibited?
depolarization
How is K+/Na+ diffusion different than K+ leaky channels?
K+ and Na+ channels are ion specific whereas the K+ leaky channels usually permit K+ but sometimes Na+ can sneak through
Small water filled passageways, formed from proteins, highly selective, and let ions transport passively
channels
Membrane proteins that can undergo reversible changes in shape to expose specific binding sites, bind with and transfer substances unable to cross plasma membrane
transporter - example is Na+ K+ pump
Potential that exists when concentration gradient for given ions counterbalances for no net movement
equilibrim potential
Nerst Equation
Equilibrim potential for a given ion with differing concentrations across a membrane
What’s equilibrium potential of K+?
-90
What’s equilibrium potential for Na+
+60
True or false: If concentration out is greater than concentration in than the log will be positive
True
Ion Movements based on Driving force
Cations:
If VDF is (+), then the ion is moving OUTof the cell.
If VDF is (-), then the ion is moving INTO the cell.
If VDF = 0, then there is NO net movement of the ion
Anions:
If VDF is (+), then the ion is moving INTO the cell.
If VDF is (-), then the ion is moving OUT of the cell.
If VDF = 0, then there is NO net movement of the ion.
When membrane potential becomes less polarized inside and less negative than resting
Depolarization
When membrane returns to resting potential after being depolarized
Repolarization
When membrane becomes more polarized inside becomes more negative than at resting potential
Hyperpolarization
Local changes in membrane potential that signal over short distances, usually produced from triggering event, can initiate AP
Graded potential
Brief, quick changes in membrane potential that signal over long distances, reverses membrane potential so inside cell is more positive
Action potential
What is different between voltage gated sodium channels and potassium channels?
Sodium channels have activation and inactivation gates leading to 3 conformations of closed open, and inactive. Whereas potassium channels are only closed or open
8 ion fluxes during action potential?
- Resting - Na+ and K+ voltage are closed and Na+ inactivation gate is open
- Threshold potential - Na+ activation gates open which leads to 3. Rapid depolarization.
- End of depolarization - Na+ inactivation gates close, K+ activation gates open which leads to 5. Repolarization - K+ efflux
- Resting membrane potential Nat+ activation closed and inactivation gates open
- Hyperpolarization - K+ activation gates close
- Resting potential - K+ activation gates close so cell can go back to RMP
AP cannot be initiated to ensure one way propagation of AP in neurons to limit frequency this is due to…
Refractory period
What are the two types of refractory periods?
- Absolute - activated patch of membrane where AP cannot initiate no matter the strength
- Relative - when another AP can be triggered with a greater than normal stimulus
What are 5 steps of AP in cardiac contractile cells?
- Rapid depolarization - activates voltage Na+ channels for fast influx
- Brief repolarization - Na+ channels close and K+ open
- Plateau - closure of K+, activates slow L Ca2+ channels which cause slow calcium influx and low K+ efflux
- Repolarization - inactivation of Ca2+ channels, activation of K+ channels
- Resting potential K+ channels close and leaky ones stay open
These cells initiate cardiac contraction, possess intrinsic automaticity, and are composed of conduction tissue
pacemaker cells
How does pacemaker self induce an action potential?
- Influx of sodium through funny channels, decreased K+ efflux, and activation of T type calcium channels causing influx
- Self induced AP
- Rising phase - activated L - type calcium channels causing influx
- Falling phase - activate K+ channels and closure of L-type channels causing efflux
What does conduction velocity depend on?
depends on size of inward current during AP upstroke, correlates with dV/dT, does not depend on AP duration
How does autonomic nervous system affect heart rate?
Sympathetic causes increases depolarization and SA node depolarizes more frequently. Parasympathetic decreases depolarization and increases threshold potential
Properties of nerve and muscle APs
