L6 - The Action Potential

Question 1

What is an AP and how long does it last?

Answer 1

Transient reversal of membrane potential

Few ms (nerve, 2/skeletal, 5)

Few hundred ms (heart, 200)

Cardio - Diff shape and longer

Question 2

Threshold potential

Answer 2

-55mV

Sub threshold - no AP

Larger - same size (intensity = frequency)

Question 3

Sodiums role in the AP

Answer 3

Responsible for rising phase

At rest - Na channels closed

Voltage sensitive - depol = increases open props

Threshold = probs open > probs closed

Positive feedback

Question 4

What causes the spike and plateau?

Answer 4

Calcium channels opening

Question 5

Structure of Na Channel

Answer 5

alpha subunit = channel / large (>2000)

Beta = accessory

4 blocks that come together that are part of a single polypeptide

INACTIVE after 1 ms - ball and chain

Voltage sensor in fourth transmembrane domain

Question 6

Structure of K channel

Answer 6

4 subunits (separate proteins)

Smaller than Na channel

Both have voltage sensor in middle of each subunit

Open slower

Question 7

Feedback loops

Answer 7

+ve on K so essential for inactivation

K - -ve control it so no need for inactivation

Question 8

What is absolute refractory period?

Answer 8

Cannot produce another AP

Question 9

What is relative refractory period?

Answer 9

Less excitable - need larger stimulus

Question 10

What causes the refractory period?

Answer 10

Inactivation of Na and turn on K current