Action Potentials Flashcards
Which ion channel has the greatest influence on resting membrane potential?
Potassium (K+) leak channels
What are electrochemical forces made of?
Diffusion and Electrical forces
Equilibrium potential
membrane potential when electrical and chemical forces are equal and there is no movement
DOES NOT EQUAL RESTING MEMBRANE POTENTIAL
Driving force
predicts the movement of ions (efflux or influx)
What channels influence resting membrane potentials but less than K+ leak channels?
NA+/K+ ATPase channels
Resting membrane potential is primarily caused by what?
From membrane permeability to K+ (very permeable to K+)
Ratio of Na+ to K+ pumped
3NA+ OUT and 2K+ IN (PUMP K IN)
Normal resting potential of skeletal/cardiac muscle?
-80 to -90 mV (about -85 mV average)
Normal resting potential of smooth muscle?
-60 mV
Normal resting potential for neurons?
-60 to -70 mV (about -65 mV average)
How do you calculate driving force?
Resting potential minus equilibrium potential of ion.
Positive value = Eflux
Negative value = Influx
Eq potential of K+
-91 mV (potassium Pit)
Eq potential of Na+
+61.5 mV (sodium shuttle)
Eq potential of Ca+?
+123 (Calcium denim)
Eq potential of chlorine?
-61.5 mV (Chlorine Cheshire)
When calculating the driving force of Na+ in skeletal muscle, you find the force to be negative indicating Influx. However, no influx occurs. Why?
The membrane is mostly impermeable to Na+!!
Goldman Eq
accounts for different ion concentrations all at once… permiability
Permiability of K+?
80-85%
Permiability of Cl-?
10-12%
Permiability of Na+?
1-2%
Permiability of Ca++?
1%
Cardiac glycoside drugs target what part of the membrane?
Na+/K+ ATP Pumps
minimal direct contribution to resting potential
4mV negative contribution
Indirectly contributes to maintain ion concentration gradients
An increase of potassium (Hyperkalemia) outside of the cell causes what?
Depolarize…. resting membrane potential moves to the right and is more positive. Cell depolarizes and repolarizes more quickly with shorter refractory.
A decrease of potassium (hypokalemia) outside of the cell causes what?
Hyperpolarization, resting membrane potential becomes more negative and moves to the left on the graph.
What is the threshold for action potentials?
-55 mV
Polarization
deviation from 0 mV
All-or-none
the signal travels everywhere with the same intensity of threshold is met
Propagation or self-reinforcing signal
Dissipation of signals… stronger near site of stimulus then decreases… ONLY OCCURS IF THRESHOLD IS NOT MET
Action potential graph: Phase 4, Phase 3, Phase 0
Resting = Phase 4 Depolarize = Phase 0 Repolarize = Phase 3 Hyperpolarize = refractory
Describe what happens to voltage-gated Na+ ion channels when stimulated
- Resting: activation gate closed, inactivation gate open
- Activation: activation gate opens (these gates close at some point near threshold)
- Inactivation: inactivation gate closes quickly and does not re-open until membrane potential is nearly back to resting
Which channels open slowly during activation?
Voltage-gated K+ channels slowly open and increase the permeability of K+. This allows the membrane to repolarize quickly.
What causes hyperpolarization?
Voltage-gated K+ ion channels stay open a little too long which leads to hyperpolarization (absolute refractory period)
Relative refractory period occurs when __?
Na+ channels have reset but K+ channels are still open. Another action potential can occur doing this time.
How are hypERkalemic attacks managed?
Mild exerise, administer potassium-wasting diuretics, glucose consumption
