1.3.1 Resting Potential Generation

Question 1

What does conductance (g) refer to?

Answer 1

The ability of the ions to cross the cell membrane

Question 2

At any instant of time, how does the magnitude of electrical force compare b/t ions?

Answer 2

All ions experience the same magnitude of force. The directionality will vary depending on the charge of the ion.

Question 3

What are three factors that influence the conductance of an ion?

Answer 3

of open ion channels

of leak channels

Ion [] (especially important in hypo- and hyperkalemia)

Question 4

What is the chemical potential (Nernst potential) of sodium? potassium?

Answer 4

Na+: +60 mV

K+: = -80 to -90 mV

Question 5

What changes during an action potential?

Answer 5

Fractional K-conductance and Fractional Na-conductance

Question 6

What effect do positive currents have on V (membrane potential)?

Answer 6

Make V more negative

Question 7

How does the range of membrane potential compare to E_Na and E_k?

Answer 7

V cannot be more negative than E_k and or more positive than E_Na

Question 8

What allows sodium to move across the cell membrane during resting membrane potential?

Answer 8

Leak channels

Question 9

Answer 9

Question 10

How do flux and current differ? Describe the directionality of current and flux for the movement of anions and cations

Answer 10

Flux: the direction of movement of the ion

Current: refers to the movement of positive charges

For anions, Flux and Current in opposite directions

Cations: Flux and current in the same direction

Question 11

What is the equation for the conductance of potassium?

Answer 11

g_k x K_o , this helps explain how potassium conductance during hyper- and hypokalemia

Question 12

What are some other names for a positive current?

Answer 12

Outward current

Repolarizing current

Hyperpolarizing current

Question 13

Compare how the conductance of urea and potassium are effected by extracellular concentration changes?

(May be easiest to draw it out and note differences)

Answer 13

Question 14

Answer 14

Question 15

Answer 15

E. The membrane potential is negative

Question 16

Describe the same scenario except this time sodium is made permeable.

Answer 16

Since Na+ is high outside of the cell, it will flow in the opposite direction thus moving into the cell. The same forces will be at play just working in opposite directions.

Question 17

What does the resting membrane potential of nerve, cardiac and skeletal muscle(-70 to -80 mV) tell you about the conductances of sodium and potassium?

Answer 17

g_K >>>> g_Na

Question 18

Be able to interpret the meanings of this graph

Answer 18

This slide again illustrates (more quantitatively than previously) relationships between membrane potential, fractional conductances and electrochemical potentials for a membrane permeable only to potassium and sodium. The situation for a membrane potential of -30 mV is emphasized when EK is -90 mV and ENa is +60 mV. Note that the absolute value of the sodium electrochemical energy is greater than that for potassium electrical energy but the potassium fractional conductance is greater than the sodium fractional conductance.

Question 19

A negative current will make the membrane potential more?

Answer 19

POSITIVE!

Question 20

What will the effect of a negative current be on V?

Answer 20

Negative current will make V more positive

Question 21

What always happens to V when G_ion is increased?

Answer 21

V will always move closer to that ion’s Nernst potential, E_ion

Question 22

Describe the nature of chemical force and its effect of ions.

Answer 22

Each ion has its own chemical force driving its movement

Question 23

Answer 23

A. Chloride influx exceeds chloride efflux

Question 24

What are the equations for fractional conduction (fg) of potassium and sodium?

Answer 24

Question 25

How many gates does a Na+ ion gated channel have and what are their names? Which one remains open during the resting membrane potential?

Answer 25

2; the activation and inactivation gate

The inactivation gate remains open while a cell is at its resting membrane potential. Despite this gate being open, so sodium can’t pass through this channel b/c the other gate is closed. (A “somewhat decent but probably terrible” analogy would be a bird trying to fly through a glass window b/c the curtains are open.)

Question 26

What creates the charge seperation across the cell membrane?

Answer 26

Differences in movement of ions

Question 27

The resting potential will be closest the Nernst potential of which ion?

Answer 27

The ion with the highest conductance

Question 28

What happens when V = E_ion?

Answer 28

When V = E_ion, there is no electrochemical force. This results in no movement of ions (current)

Question 29

Answer 29

B. the ion’s current

Question 30

Answer 30

Question 31

Answer 31

B. -60 mV

Question 32

Answer 32

C. -52 mV

Question 33

Answer 33

B. membrane potential would be positive to the potassium Nernst potential

Question 34

What determines the sign of a current?

Answer 34

The sign of (V - E_ion) determines the sign of current b/c conductance can only be positive or zero.

Question 35

How does increasing or decreasing fg_ion affect V movement in relation to that ion’s Nernst potential?

Answer 35

Increasing fg_ion = Closer to ion’s Nernst potential

Decreasing fg_ion = Away from ion’s Nernst potential

Question 36

What is the equation for current that includes conductance, membrane potential, and Nernst potential?

Answer 36

I_ion = g_ion x (V - E_ion)

Question 37

Answer 37

D. The potassium electrochemical potential is +40mV

Question 38

When V is negative, what type of force (inward/outward) is exerted on cations? anions?

Answer 38

Cations: inward (attraction)

Anions: outward (repulsion)

Question 39

Currents are always defined in terms of the movement of what type of molecules?

Answer 39

Cations

Question 40

At RMP,

Answer 40

Question 41

What are two forces involved in driving ion movement?

Answer 41

Electrical (membrane potential)

Chemical (due to differences in a single ion concentration of ICF and ECF)

Question 42

What is the equation for Nernst potential (E_ion)?

Answer 42

Question 43

A positive current will make the membrane potential more?

Answer 43

NEGATIVE!!!!

Question 44

The magnitude of an ion’s current depend on what two factors?

Answer 44

Forces driving movement: electical (membrane potential) and chemical (Nernst potential)

Conductance

Question 45

If a cell membrane was made only permeable to potassium (under standard body conditions), describe the movement of potassium ions and how it would effect membrane potential. Also, when would it stop?

Answer 45

Since potassium concentration is high within cells and low outside, the potassium when begin to flow outward due to the chemical force. As the potassium ions flow out of the cell, the membrane potential will steadily become more negative. Since the membrane potential is steadily increasing, the rate of movement of the potassium ions will steadily decrease until both forces equal each other resulting in equilibrium (no net movement).

Question 46

What is true about the currents of sodium and potassium when a cell is at its resting membrane potential?

Answer 46

I_Na + I_K = 0

Question 47

What are the two factors that determine the magnitude of the chemical force?

Answer 47

1. Ratio of Extracellular and Intracellular Ion Concentrations
2. The valence of the ion

Question 48

What is a current?

(I’m pretty sure I’ve seen this question asked on Are You Smarter Than a Fifth Grader?)

Answer 48

Movement of ions across the cell membrane