Nerve, Muscle, Synapse Lecture 2

Question 1

What does E_m represent?

Answer 1

Resting Membrane Potential

Question 2

E_m is set by:

Answer 2

Leak channels

Question 3

What are leak channels?

Answer 3

• Always open
• Allow passive flow of ions into/out of the neuron
• Selective: each ion has its own leak channels through which only they can pass

Question 4

What are the two forces acting on each ion at leak channels that determine direction of movement?

Answer 4

1. Chemical gradient
2. Electrical gradient

Question 5

For every 3 sodium ions pumped out of the cell (Na/K pump), how many potassium ions are pumped into the cell and what is the result?

Answer 5

2 are pumped inside

-Higher concentration of potassium inside the cell

1. Chemical force pushes potassium outside the cell through potassium leak channels
2. Inside of the cell is more negatively charged = electrical force pulls K+ into the cell

Chemical and electrical forces are acting on potassium at the same time

Question 6

What is the equilibrium potential of K+

Answer 6

-90mv

Question 7

What is equilibrium potential?

Answer 7

The membrane potential at which the chemical concentration gradient is balanced

Question 8

What is used to calculate an ion’s equilibrium potential?

Answer 8

Nernst equation

Question 9

Equilibrium potential for K+ is -90mv; the resting membrane potential is -70mv. What is potassium doing at -70mv?

Answer 9

Potassium will be moving OUT of the cell - to try to bring resting membrane potential down to -90mv.

Net movement out of cell taking with it positive charge

Question 10

How many sodium ions are pumped out of the cell by the sodium potassium pump? What is the result?

(Concentration gradient and electrical gradient)

Answer 10

3 sodium ions out (2 potassium in)

Increase in sodium ions outside the cell

1. High concentration sodium out = chemical force pushes sodium into the cell
2. Electrical force pushes sodium into the cell (more positive outside the cell)

Question 11

What is the equilibrium potential for Na+?

Answer 11

+55mV

Question 12

At resting membrane potential (-70mV) what is Na+ doing?

Answer 12

Na+ will move to make the potential equal to +55mV (just as potassium tries to make potential equal to -90mV)

Question 13

Alone, Na+ would force RMP to ______

Alone, K+ would force RMP to _______

Both Na+ and K+ are present in Nerve cells: What happens to E_m?

Hint: RULE: More permeant the ion, the greater it’s ability to force E_m towards its own equilibrium potential

Which ion has greater permeability?

Answer 13

Alone, Na+ would force RMP to +55mV

Alone, K+ would force RMP to -90mV

Both Na+ and K+ are present in Nerve cells: What happens to E_m?

There are more leak channels for potassium therefore, E_m is closer to E_K+

permeability is 50-100x greater to K+ than Na+

Question 14

Ratio of Na+ leak channels to K+ leak channels determines:

Answer 14

The membrane resting potential

Question 15

Activity of the Na+/K+ATPase causes intracellular environment to be ________ charged with respect to the extracellular environment

Answer 15

Activity of the Na+/K+ATPase causes intracellular environment to be negatively charged with respect to the extracellular environment

Question 16

What happens to ensure that the E_m remains constant?

Answer 16

Passive ionic fluxes are balanced so that there is a charge separation

-constant movement of ions

Question 17

The value of resting membrane potential (-70mV) is always closest to the equilibrium potential of the ____________ which is always ____ over ____

Answer 17

The value of resting membrane potential (-70mV) is always closest to the equilibrium potential of the ion with greatest membrane permeability which is always K+ over Na+

Question 18

Outside the nerve cell it is relatively _____ charged with respect to inside the cell

Answer 18

positively

Question 19

At rest, the Na+/K+ pump is _____

Answer 19

active = K+ enters and Na+ leaves

Question 20

At a constant or resting membrane potential, K+ is being pumped in through _____ and is leaving through ______; Na+ is being pumped out through ______ and coming back in through _____

Answer 20

At a constant or resting membrane potential, K+ is being pumped in through Na+K+ pump and is leaving through K+ leak channels; Na+ is being pumped out through Na+/K+ pump and coming back in through Na+ leak channels

Question 21

If many sodium channels open, what happens to the membrane potential?

Answer 21

It goes up (becomes more positive)

Question 22

When a nerve cell is active, many _____-gated Na+ channels open and the membrane potential shoots up close to the Equilibrium potential of ____

Answer 22

When a nerve cell is active, many voltage-gated Na+ channels open and the membrane potential shoots up close to the Equilibrium potential of Na+