Lecture 2 Resting Membrane Potential

Question 1

What is the Goldman-Hodgkin-Katz equation used for?

Answer 1

It is a calculation of the cell’s conductance mechanisms at rest; used to determine the resting membrane potential (V)

Question 2

Which channels are the sole determinants of action potential properties?

Answer 2

Voltage-gated Na+ and voltage-gated K+ channels

Question 3

What are the characteristics of the action potential?

Answer 3

• “all-or-none” principle: either it happens or it does not
• uniform amplitude (due to voltage-gated Na+ channels) and duration (due to voltage-gated K+ channel activation kinetics)
• activation threshold: critical Vm (minimum voltage) required to activate VG Na+ channel sensor
• regenerative: depolarizing wave activates adjacent membrane, VG K+ channel repolarizes membrane to basal state
• rapid, non-decremental propagation: VG Na+ and VG K+ activation kinetics are extremely rapid

Question 4

Describe voltage-gated Na+ channel inactivation via the “ball and chain” model

Answer 4

A negatively charged “ball” in the N-terminus moves into the inner mouth of the pore and blocks Na+ flow.
The ball requires hyperpolarization to be removed. Inactivated VG Na+ channels cannot be reactivated - the absolute refractory period.

Question 5

What are the Na+ and K+ Nernst potentials (E) in the cell membrane?

Answer 5

E(Na)= +61mV, E(K)= -94 mV

Question 6

Describe the K+ Leak Channels

Answer 6

• Belong to the Tandem 2-pore K+ channel family
• Have mild sequence homology to voltage-gated K+ channels, but only in the pore region
• leak channel that has been cloned and is called the Tandem 2-pore K channel

Question 7

What is the Potassium Nernst Potential Equation?

Answer 7

EK = -RT/ZF ln(Ki/Ko)
R= ideal gas constant
T= temperature (K)
Z = valence charge
F= Faraday constant

RT/ZF = =26mV and ln = 2.3 *log

EK = -61mVlog(Ki/Ko)
EK= -94mV

Question 8

What is the Sodium Equilibrium Potential (ENa) or the Na+ Nernst Potential Equation?

Answer 8

ENa = -RT/ZTln(Nai/Nao)

R= ideal gas constant
T= temperature (K)
Z = valence charge
F= Faraday constant

RT/ZF = =26mV and ln = 2.3 *log

ENa = 61mVlog (Nai/Nao)

Question 9

The resting membrane potential of the cell is between what and what.

Answer 9

RMP (Vm) = -90 to 70mV

Question 10

Thinking of the Goldman-Hodgkin-Katz Equation, the RMP is closest to the equilibrium potential for the what?

Answer 10

Ion with the highest permeability

Question 11

What is the resting membrane potential range for skeletal muscle?

Answer 11

-85mV to 94mV

Question 12

What is the resting membrane potential range for cardiac muscle?

Answer 12

~-85mV

Question 13

What is the resting membrane potential range for smooth muscle?

Answer 13

-50mV to -60mV

Question 14

What is the resting membrane potential range for neurons?

Answer 14

-60mV to -70mV

Question 15

What is the resting membrane potential range for Erythrocytes?

Answer 15

-8mV to -12mV

Question 16

What is the resting membrane potential range for Photoreceptors?

Answer 16

-40mV (dark) to -70mV (light)

Question 17

What are the net driving forces of K+ and Na+?

Answer 17

K+ = 20mV
Na+ = 135mV

Question 18

What happens when the K+ permeability increases?

Answer 18

Vm goes towards hyperpolarizing potentials

Question 19

What happens when the Na+ permeability increases?

Answer 19

Vm foes toward depolarizing potentials

Question 20

In dealing with the action potential, depolarization means what?

Answer 20

Vm is towards the ENa

Question 21

In dealing with the action potential, overshoot means what?

Answer 21

Vm greater than 0mV

Question 22

In dealing with the action potential, hyperpolarization means what?

Answer 22

Vm is towards the EK

Question 23

In dealing with the action potential, the excitability/inhibition threshold means what?

Answer 23

Vm is required to initiate action potential

Question 24

In dealing with the action potential, repolarization means what?

Answer 24

Vm is towards the EK

Returns towards rest

Question 25

What do refractory periods limit?

Answer 25

Refractory periods limit the maximum frequency of Action Potentials

Question 26

What kind of refractory period occurs when an action potential cannot be evoked by any intensity of stimulation?

Answer 26

Absolute Refractory Period

Question 27

What kind of refractory period occurs when an action potential needs supra-maximal stimulus in order to be evoked?

Answer 27

Relative Refractory Period

Question 28

What happens in the Ball and Chain Model of Voltage Na+ Channel Inactivation?

Answer 28

1. A negative charged ball in the N-terminus moves into the inner mouth of the pore and blocks Na+ flow.
2. The ball requires hyperpolarization to be removed. An inactivated voltage gated Na+ channel cannot be reactivated because its in the absolute refractory period.

Question 29

What does it mean when an action potential wave depolarizes in an orthodromic fashion?

Answer 29

It depolarizes toward the synaptic terminal, which is the correct direction.

Question 30

What does it mean when an action potential wave depolarized in an antidromic fashion?

Answer 30

It depolarizes toward the cell body, which is in the opposite or incorrect direction.