Module 3: Lecture 3

Question 1

What is the threshold potential?

Answer 1

its the potential that comes after graded potentials that allows for an action potenial to occur

Question 2

What is included in an action potential?

Answer 2

• everything that occurs after the threshold potential has been reached
• big explosive depolarization phase followed by a repolarization phase back down to rest

Question 3

At the peak of an action potential, at the end of the depolairizaiton what is the resting membrane at in mV?

Answer 3

+30

Question 4

How long does an action potential last?

Answer 4

a millisecond

Question 5

What is an action potential?

Answer 5

the rapid change in potential from threshold to peak and the back to the resting potential

Question 6

What is a voltage gated channel?

Answer 6

• gated channel that responds and open when the threshold potential is reached
• when opened it will allow ions to travel down their electrochemical gradient

Question 7

Which gated channels are responsible for action potentials?

Answer 7

voltage channels

Question 8

which voltage channels respond faster, sodium or potassium?

Answer 8

sodium

Question 9

What are the components of the Sodiums voltage-gated channel?

Answer 9

• activation gate (gate)
• inactivation gate (ball in chain)

*Both are triggered by the threshold potential but the inactivation gate moves at a slower rate allowing some ions to pass through before closing

Question 10

What is the mV of the threshold potential?

Answer 10

-50 to -55 mV range

Question 11

What are the 4 steps in the positive- feedback cycle with sodium gated ion channels?

Answer 11

1. Triggering event, Na+ gated channels either mechanically or chemically
2. Depolarization which decreased membranes potential
3. Causes the membrane to reach the threshold potential and open some voltage-gated Na+ channels, allowing more sodium into the cell
4. Influx of Na+

Question 12

True or False
The membrane after all the Na+ voltage-gated channels are open is now 600 times more permeable to Na+ than K+?

Answer 12

True

Question 13

What causes the Na+ to stop and not reach its equilibrium potential of +65?

Answer 13

the inactive gates from the sodium voltage-gated channels

Question 14

When does the inactived ball and chain gate open again?

Answer 14

when the resting membrane is re-achieved at -70mV

• until the cell repolarizes

Question 14

Does the potassium votage-gate open fast or slow when the threshold potential is reached?

Answer 14

slow

Question 15

What repolarizes the cell at peak action potential?

Answer 15

the potassium voltage-gated channels

• as potassium leaves the cell the inside of the cell becomes more negative

Question 16

When does the potassium gates fully open?

Answer 16

at the peak of the action potential

Question 17

True or False
The K+ permeability is increased to about 300 times at peak action potential?

Answer 17

true

Question 18

Which two gradients are acting together to push potassium out of the cell when the cell hits +30?

Answer 18

• chemical gradient
• electrochemical gradient

Question 19

Why is there a hyper polarization period after an action potential?

Answer 19

due to the slow closing of the K+ channels

Question 20

What is the typical rule when thinking about how to find a threshold?

Answer 20

it is about 15 mV less negative than the resting potential

Question 21

What is a sub-threshold potential?

Answer 21

weak depolarization due to gated channels that do not reach the threshold

Question 22

How do we differentiate the magnitude of the stimulus for action potentials? (Light touch and stabbing should have different results)

Answer 22

• the frequency