02 | RMP and AP Flashcards
Define: RMP
difference in electrical charge between the inside and outside of a cell (written: inside relative to outside)
Factors that affect RMP
- E(K)
- E(Na)
- g(K)
- g(Na)
- Na/K ATPase
3 requirements for stable Vm
- Electrical balance
- Osmotic balance
- No net flow of ions
E(Ca) =
+150 mV
Amount of current generated depends on…
driving force
Formula: driving force
= Vm - E(ion)
Define: conductance
How easily electrical charge moves across the membrane
Conductance depends on…
- If channel is opened or closed
2. Channel density
Define: permeability
How easily the particle mass moves across the membrane
What is Nernst equation used to calculate?
Equilibrium potential of the ion
What does the Goldman equation calculate?
Membrane potential
What is the limitation to the Goldman equation?
Only applies to steady state (aka Vm not changing) (aka no depolarization/hyperpolarization)
Na/K ATPase contributes __ mV to the Vm
-6 mV
How many Na and K ions are moved per cycle of Na/K ATPase?
3 Na out, 2 K in (net negative)
Define: AP
Explosive change in electrical activity (sudden change in Vm)
5 things that can induce AP
- Electrical change
- Chemical
- Mechanical
- Light
- Temperature
What are the 4 types of currents involved in an AP?
- Capacitive current
- Leak current
- Early inward current (Na)
- Late outward current (K)
What is capacitive current?
The spike in current when membrane potential initially changes. This is because the membrane acts like a capacitor. The current can be ignored during analysis.
What is leak current? Which ion is responsible for it?
Current that is always present due to flow of K ions.
What did ion manipulation find out about AP current?
- Na replaced with choline — no driving force for Na
- Only outwards current was observed
- ∴ Na must be responsible for the inward current
What is the unit for current?
mA/cm^2
What does TTX block?
v-gated Na channels
What does TEA block?
v-gated K channels and K leak channels
Magnitude of early inward current depends on…
Vm (because this determines the driving force for Na)
Define: reversal potential
The Vm at which the ion’s flow changes direction
What does “delayed rectifier” mean?
Delayed = does not change right away
Rectifier = current increases during depolarization, but hot hyperpolarization (“rectifies” Vm back to resting)
Define: inactivation (in terms of current flow)
The fall of Na current
Absolute refractory period is due to…
inactivation of Na channels
Effects of Ca
- Enhance depolarization
- Inhibit depolarization
- Hypercalcemia
How does Ca inhibit depolarization?
open Ca-activated K channels
Ca-induced AP usually found in…
- cardiac muscle
- invertebrate neurons
- mammalian cerebellar Purkinje cells
Na is usually used to depolarize the soma, while Ca is used to depolarize ___
dendrites
Why does hypercalcemia result in decreased excitability?
Ca-induced Na channel block
Summation usually occurs at…
axon hillock
Common examples of graded potentials (rather than AP)
- Light hitting eye
- Sound wave in ear
- Pressure on skin
(things where magnitude matters)
