Membrane Resting Potential and Action Potential Flashcards
Why is there no energy required in simple diffusion?
Because of the concentration gradient
T/F Sodium and Potassium are moved with the concentration gradient in active transport
False, they are moved against the concentration gradient
What is the resting membrane potential?
-90 mv
Describe what would happen if the membrane was only permeable to K+
K+ would diffuse down its concentration gradient until the electrical potential across the membrane counters the K+ diffusion (concentration difference = electrical difference)
What is the electrical potential that counters net diffusion of K+?
Equilibrium or Nernst Potential for K+
Define Nernst Potential
The electrical diffusion potential across a membrane that EXACTLY opposes the net diffusion of a particular ion through the membrane
What is the Nernst equation?
EMF = +/- 61 log (concentration inside/ concentration outside)
What determines if the 61 is positive or negative in the Nernst equation?
The sign is positive if the ion diffusing is negative and it is negative if the ion is positive
What is the electrical potential that counters net diffusion of K+?
-94 mv
If thee membrane was only permeable to K+ what would the membrane potential be?
-94 mv
How are the molecules kept inside and outside of the cell?
with unequal concentrations
Describe the extracellular fluid
High in Na+, Ca 2+ and Cl-, positively charged
Describe the intracellular fluid
high in K+, Mg 2+, proteins, negatively charged
Describe what would happen if the membrane was only permeable to Na+
Na+ would diffuse down its concentration gradient until a potential across the membrane (diffusion potential) counters the Na+ diffusion
What would the electrical potential that counters the net diffusion of Na+ be?
+61 mv
What is the Goldman (Goldman Hodgkin-Katz) equation?
EMF = -61 log (CNa+i PNa+ +Ck+i PK +CClo/ CNa+ o + PK+ CCli PCL-)
What does the membrane potential to several different ions depend on?
Concentration of respective ions on the inside and outside of the membrane
Permeability of membrane to each ion
Polarity of the electrical charge of ions positive or negative
Why is Vm so close to Ek?
Because the membrane is much more permeable to K+ than Na+
Which ion are leak channels more permeable to?
They are more permeable to K+ than Na+
What is the resting membrane potential for large nerve fibers (motorneurons) and small neurons
Large nerve fibers: -90 mv
Small neurons: -70 mv
What does the resting membrane potential of nerves depend on?
- Diffusion of potassium and sodium ions
- Permeability of ions through leak channels (P to K+»_space; P to Na+ (100 times)
- Na+/ K+ pump (creates more negativity inside (transports 3 Na+ to outside vs 2 K+ to inside))
What is the take home message about membrane potential?
The resting membrane potential is closer to the equilibrium potential for the ion with the highest permeability (K+)
What are synonyms for Action Potential?
Spike, impulse or firing
Define an AP
A very rapid change in the membrane potential from “-“ to “+” values and return back to initial resting potential level
T/F the amplitude of an AP never changes
true
What are the two functions of Action Potentials?
1.Transmitting nerve signals
2.Rapid transmission over distance
What does speed of transmission depend on?
fiber size and whether it is myelinated (bigger size = faster transmission)
What are the 5 sequences of events for a nerve action potential?
- Resting stage
- Depolarization
- Repolarization
- Afterpotential
- Back to resting stage
What is the Vm aat the resting stage?
-90 mv
What causes depolarization?
A sudden opening of Na+ channels, Na+ ions flow to inside the cell
How long does the depolarization phase last?
0.1 ms
What is the Vm in the repolarization phase?
+35 mv to -90 mv
In what phase do Na+ channels begin to close and the K+ channels begin to slowly open?
Repolarization
Why do the Na+ channels close and the K+ channels start to open?
to re-establish negative resting potential
What is the Vm in the afterpotential?
<-90 mv
Name synonyms for afterpotential
Hyperpolarization, undershoot
What causes the afterpotential?
The K+ channels remain open for a few milliseconds after repolarization of the membrane is completed, excess K+ flows out of the membrane
What causes the Vm to go back to resting stage?
The closing of the K+ channels
What two protein channels cause the different staves of the action potential?
Voltage-gated Na+ channels
Voltage-gated K+ channels
What type of diffusion are volatge gated channels?
Simple diffusion
What are the two gates in a voltage gated sodium channel and where are they located?
Activation gate: exterior side of membrane
Inactivation gate: Interior side of membrane
What are the three states of the voltage-gated sodium channels and which gates are open and closed?
Resting state: Activation closed & inactivation opens
Activated state: Both are open
Inactivated state: Activation open & inactivation closed
T/F, during the resting state there is entering of Na+ ions
False
What triggers the opening of the activation gate?
The shifting of membrane potential towards + values
What is the opening threshold in the activated (depolarization) state?
-70 mv and -50 mv
T/F the permeability to Na+ increases to 500 to 5000 times in the activated state
True
Which stage of the action potential are the activated and inactivated states associated with?
Activated = depolarization
Inactivated = repolarization
When is the inactivation gate activated?
When the membrane potential increases above 0 mv (overshoot)
What is the refractory period?
When the inactivation gates do not re-open until the membrane returns to resting potential
T/F there is more than one gate in the voltage-gated potassium channel
False, there is only one gate
What are the two states in the voltage-gated potassium channel and what is the state of each gate?
Resting state: Gate closed
Slow activation state: Gate open
What is another word for the slow activation state?
Repolarization
What is overshoot?
When the K+ channels are activated when the membrane potential increases above 0
Describe what occurs during the afterpotential
K+ channels remain open for a few ms after repolarization, excess K+ flow out of cell
What is the resting membrane potential?
-90 mv
What are mirror neurons referred to as?
Empathy neurons
What is the threshold of initiation?
The level of membrane potential at which the positive-feedback cycle is created (point of no retunr)
When does the threshold of initiation occur?
When the number of sodium ions entering the nerve becomes greater than the number of potassium ions leaving the nerve
What are the three factors that can cause the initial increase in membrane potential?
Electrical stimulation, mechanic stimulation, chemical stimulation
Explain the “all-or-none” principle
AP= signal either occurs fully or not at all
T/F the frequency of firing (# of APs) is dependent on the intensity of the stimulus?
True
Can an action potential occur if the membrane is still depolarized from the preceding AP? why or why not?
Np because Na+ channels are inactivated and the membrane needs to return to near original or resting potential to allow inactivation gates to reopen
In which period can a new AP occur?
The relative refractory period
What is myelin produced as an extension of?
Glial cells
What are the glial cells in the PNS and CNS?
Schwann cells (PNS)
Oligodendrocytes un the (CNS)
What insulates the nerve fibers?
Myeline sheath
What interrupts the myelin sheath once every 1-3 mm?
Nodes of Ranvier
What is saltatory conduction?
Where APs can only occur at the nodes of Ranvier
What are the speeds of the AP in an unmyelinated and myelinated axon
unmyelinated: 0.25 m/s
myelinated: 100 m/s
What is Multiple Sclerosis?
An immune-mediated inflamatory disease that causes the demyelination of the CNS
What are 3 symptoms of MS
Muscle weakness, loss of sensation and death
