Lecture 6: Cell excitability, Cunningham

Question 1

At -94 mV for the inside of a cell, what is implicated for potassium in regards to its net movement?

Answer 1

The concentration force and electrical forces are balanced, and potassium has no net tendency to diffuse

Question 2

At Em=-74 mV for the inside of a cell, what is implicated for the movement of potassium in regards to its net movement?

Answer 2

The electrical force is too weak, and potassium will tend to diffuse out of the cell due to the concentration force being greater than the electrical force

Question 3

Why is the inside of the cell negative?

Answer 3

Due to proteins that perform cellular activities, and proteins are negative

Question 4

What does the 3:2 Na-K pump really mean?

Answer 4

3 sodium ions are pumped out of the cell for every 2 potassium ions that are pumped into the cell

Question 5

Why does sodium’s movement into the cell overshadow the movement of potassium?

Answer 5

1. There is a much larger driving force for sodium (both concentration and electrical gradients facing in).
2. The potassium channels open more slowly than do the sodium channels, so the rise in potassium permeability happens more.

Question 6

The depolarization phase occurs when what happens to sodium?

Answer 6

When sodium becomes the most permeable ion

Question 7

What causes the repolarization phase (has to do with the sodium and potassium permeability)

Answer 7

When the sodium permeability returns to rest, and the potassium permeability peaks

Question 8

The afterhyperpolarization occurs when in regards to sodium and potassium permeability?

Answer 8

When sodium is resting, while the potassium permeability is greater than resting level

Question 9

What’s the equation for driving force? What is a positive driving force?

Answer 9

Nernst potential - membrane potential; positive driving force means the driving force is itself positive

Question 10

“The membrane potential of a cell will always most closely resemble the ___ of the most permeable ion”

Answer 10

Nernst potential

Question 11

What substance from puffer fish can block the selectivity filter in the voltage-gated sodium channels?

Answer 11

Tetrodotoxin

Question 12

How many positive charges need to shift in order to open the voltage-gated sodium channels?

Answer 12

About 6

Question 13

What is the absolute refractory period? When does this period end?

Answer 13

The time when the inactivation gate is closed. This period ends when the membrane potential goes back below threshold

Question 14

What are two big differences between voltage-gated potassium and sodium channels?

Answer 14

For potassium, there is only 1 gate and it is either open or closed; the charges in the conductance pore are arranged to stabilize potassium instead of sodium

Question 15

What drug poison the sodium potassium pump?

Answer 15

Ouabain

Question 16

What does calcium do the voltage-gated channels?

Answer 16

It stabilizes the membrane and increases the threshold

Question 17

What does Tetrodotoxin do to voltage-gated channels??

Answer 17

It blocks sodium channels from the extracellular side

Question 18

What does local anesthetic do to sodium permeability?

Answer 18

It increases the sodium permeability

Question 19

What does batrachtotoxin (from poisonous frogs) do to sodium channels?

Answer 19

Irreversibly opens them

Question 20

What does scorpion toxin do to potassium channels?

Answer 20

It blocks potassium channel opening

Question 21

What does TEA do to potassium channels?

Answer 21

It blocks them, only from the intracellular fluid side of the channel