Membrane Resting Potential and Action Potential

Question 1

Why is there no energy required in simple diffusion?

Answer 1

Because of the concentration gradient

Question 2

T/F Sodium and Potassium are moved with the concentration gradient in active transport

Answer 2

False, they are moved against the concentration gradient

Question 3

What is the resting membrane potential?

Answer 3

-90 mv

Question 4

Describe what would happen if the membrane was only permeable to K+

Answer 4

K+ would diffuse down its concentration gradient until the electrical potential across the membrane counters the K+ diffusion (concentration difference = electrical difference)

Question 5

What is the electrical potential that counters net diffusion of K+?

Answer 5

Equilibrium or Nernst Potential for K+

Question 6

Define Nernst Potential

Answer 6

The electrical diffusion potential across a membrane that EXACTLY opposes the net diffusion of a particular ion through the membrane

Question 7

What is the Nernst equation?

Answer 7

EMF = +/- 61 log (concentration inside/ concentration outside)

Question 8

What determines if the 61 is positive or negative in the Nernst equation?

Answer 8

The sign is positive if the ion diffusing is negative and it is negative if the ion is positive

Question 9

What is the electrical potential that counters net diffusion of K+?

Answer 9

-94 mv

Question 10

If thee membrane was only permeable to K+ what would the membrane potential be?

Answer 10

-94 mv

Question 11

How are the molecules kept inside and outside of the cell?

Answer 11

with unequal concentrations

Question 12

Describe the extracellular fluid

Answer 12

High in Na+, Ca 2+ and Cl-, positively charged

Question 13

Describe the intracellular fluid

Answer 13

high in K+, Mg 2+, proteins, negatively charged

Question 14

Describe what would happen if the membrane was only permeable to Na+

Answer 14

Na+ would diffuse down its concentration gradient until a potential across the membrane (diffusion potential) counters the Na+ diffusion

Question 15

What would the electrical potential that counters the net diffusion of Na+ be?

Answer 15

+61 mv

Question 16

What is the Goldman (Goldman Hodgkin-Katz) equation?

Answer 16

EMF = -61 log (CNa+i PNa+ +Ck+i PK +CClo/ CNa+ o + PK+ CCli PCL-)

Question 17

What does the membrane potential to several different ions depend on?

Answer 17

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

Question 18

Why is Vm so close to Ek?

Answer 18

Because the membrane is much more permeable to K+ than Na+

Question 19

Which ion are leak channels more permeable to?

Answer 19

They are more permeable to K+ than Na+

Question 20

What is the resting membrane potential for large nerve fibers (motorneurons) and small neurons

Answer 20

Large nerve fibers: -90 mv
Small neurons: -70 mv

Question 21

What does the resting membrane potential of nerves depend on?

Answer 21

1. Diffusion of potassium and sodium ions
2. Permeability of ions through leak channels (P to K+&raquo_space; P to Na+ (100 times)
3. Na+/ K+ pump (creates more negativity inside (transports 3 Na+ to outside vs 2 K+ to inside))

Question 22

What is the take home message about membrane potential?

Answer 22

The resting membrane potential is closer to the equilibrium potential for the ion with the highest permeability (K+)

Question 23

What are synonyms for Action Potential?

Answer 23

Spike, impulse or firing

Question 24

Define an AP

Answer 24

A very rapid change in the membrane potential from “-“ to “+” values and return back to initial resting potential level

Question 25

T/F the amplitude of an AP never changes

Answer 25

true

Question 26

What are the two functions of Action Potentials?

Answer 26

1.Transmitting nerve signals 2.Rapid transmission over distance

Question 27

What does speed of transmission depend on?

Answer 27

fiber size and whether it is myelinated (bigger size = faster transmission)

Question 28

What are the 5 sequences of events for a nerve action potential?

Answer 28

1. Resting stage 2. Depolarization 3. Repolarization 4. Afterpotential 5. Back to resting stage

Question 29

What is the Vm aat the resting stage?

Answer 29

-90 mv

Question 30

What causes depolarization?

Answer 30

A sudden opening of Na+ channels, Na+ ions flow to inside the cell

Question 31

How long does the depolarization phase last?

Answer 31

0.1 ms

Question 32

What is the Vm in the repolarization phase?

Answer 32

+35 mv to -90 mv

Question 33

In what phase do Na+ channels begin to close and the K+ channels begin to slowly open?

Answer 33

Repolarization

Question 34

Why do the Na+ channels close and the K+ channels start to open?

Answer 34

to re-establish negative resting potential

Question 35

What is the Vm in the afterpotential?

Answer 35

<-90 mv

Question 36

Name synonyms for afterpotential

Answer 36

Hyperpolarization, undershoot

Question 37

What causes the afterpotential?

Answer 37

The K+ channels remain open for a few milliseconds after repolarization of the membrane is completed, excess K+ flows out of the membrane

Question 38

What causes the Vm to go back to resting stage?

Answer 38

The closing of the K+ channels

Question 39

What two protein channels cause the different staves of the action potential?

Answer 39

Voltage-gated Na+ channels Voltage-gated K+ channels

Question 40

What type of diffusion are volatge gated channels?

Answer 40

Simple diffusion

Question 41

What are the two gates in a voltage gated sodium channel and where are they located?

Answer 41

Activation gate: exterior side of membrane Inactivation gate: Interior side of membrane

Question 42

What are the three states of the voltage-gated sodium channels and which gates are open and closed?

Answer 42

Resting state: Activation closed & inactivation opens Activated state: Both are open Inactivated state: Activation open & inactivation closed

Question 43

T/F, during the resting state there is entering of Na+ ions

Answer 43

False

Question 44

What triggers the opening of the activation gate?

Answer 44

The shifting of membrane potential towards + values

Question 45

What is the opening threshold in the activated (depolarization) state?

Answer 45

-70 mv and -50 mv

Question 46

T/F the permeability to Na+ increases to 500 to 5000 times in the activated state

Answer 46

True

Question 47

Which stage of the action potential are the activated and inactivated states associated with?

Answer 47

Activated = depolarization Inactivated = repolarization

Question 48

When is the inactivation gate activated?

Answer 48

When the membrane potential increases above 0 mv (overshoot)

Question 49

What is the refractory period?

Answer 49

When the inactivation gates do not re-open until the membrane returns to resting potential

Question 50

T/F there is more than one gate in the voltage-gated potassium channel

Answer 50

False, there is only one gate

Question 51

What are the two states in the voltage-gated potassium channel and what is the state of each gate?

Answer 51

Resting state: Gate closed Slow activation state: Gate open

Question 52

What is another word for the slow activation state?

Answer 52

Repolarization

Question 53

What is overshoot?

Answer 53

When the K+ channels are activated when the membrane potential increases above 0

Question 54

Describe what occurs during the afterpotential

Answer 54

K+ channels remain open for a few ms after repolarization, excess K+ flow out of cell

Question 55

What is the resting membrane potential?

Answer 55

-90 mv

Question 56

What are mirror neurons referred to as?

Answer 56

Empathy neurons

Question 57

What is the threshold of initiation?

Answer 57

The level of membrane potential at which the positive-feedback cycle is created (point of no retunr)

Question 58

When does the threshold of initiation occur?

Answer 58

When the number of sodium ions entering the nerve becomes greater than the number of potassium ions leaving the nerve

Question 59

What are the three factors that can cause the initial increase in membrane potential?

Answer 59

Electrical stimulation, mechanic stimulation, chemical stimulation

Question 60

Explain the "all-or-none" principle

Answer 60

AP= signal either occurs fully or not at all

Question 61

T/F the frequency of firing (# of APs) is dependent on the intensity of the stimulus?

Answer 61

True

Question 62

Can an action potential occur if the membrane is still depolarized from the preceding AP? why or why not?

Answer 62

Np because Na+ channels are inactivated and the membrane needs to return to near original or resting potential to allow inactivation gates to reopen

Question 63

In which period can a new AP occur?

Answer 63

The relative refractory period

Question 64

What is myelin produced as an extension of?

Answer 64

Glial cells

Question 65

What are the glial cells in the PNS and CNS?

Answer 65

Schwann cells (PNS) Oligodendrocytes un the (CNS)

Question 66

What insulates the nerve fibers?

Answer 66

Myeline sheath

Question 67

What interrupts the myelin sheath once every 1-3 mm?

Answer 67

Nodes of Ranvier

Question 68

What is saltatory conduction?

Answer 68

Where APs can only occur at the nodes of Ranvier

Question 69

What are the speeds of the AP in an unmyelinated and myelinated axon

Answer 69

unmyelinated: 0.25 m/s myelinated: 100 m/s

Question 70

What is Multiple Sclerosis?

Answer 70

An immune-mediated inflamatory disease that causes the demyelination of the CNS

Question 71

What are 3 symptoms of MS

Answer 71

Muscle weakness, loss of sensation and death