Module 3 Lecture 3 - Action Potentials

Question 1

What are action potentials? How are they different from graded potentials?

Answer 1

Action potentials are brief, rapid changes in membrane potential
* Unlike graded it can reverse membrane potential (can make the inside of a excitable cell more positive than the outside)
* Unlike graded potentials, action potentials are conducted throughout the entire membrane

Conduction is non-decremental meaning its perfect for long distance signals
Graded potentials can generate an action potential with right magnitude

Question 2

What are the stages of the action potential? Describe each stage

Answer 2

1. Triggering event
   - Causes membrane to depolarize from resting potential (-70mV) slowly until threshold potential is reached
   - Threshold potential is at -55mV
2. Explosive Depolarization
   - At threshold depolarization an upward deflection to +30mV
   - At the same time reversal of membrane potential occurs causing the inside of the cell to become more positive
3. Repolarization & Hyperpolarization
   - When the membrane potential is repolarized its often pushed a bit too far to -80mV which is a hyperpolarization.

In this time a bunch of Na+ gates and K+ gates are opening and closing
* Reversion period is known as reversing the potential above 0mV from -70mV
* Action potential A.K.A spike

Question 3

What happens to the membrane during the action potential?

Answer 3

The membranes permeability starts to go through many changes

Question 4

What causes the permeability of the membrane during an action potential?

Answer 4

Movement of ions (K+ and Na+) down their electrochemical gradient
* This movement is responsible for the opening and subsequent closing of K+ and Na+ voltage gated channels which effect permeability during action potential

Question 5

What different amongst the Na+ and K+ voltage gated channels

Answer 5

1. Na+ has two gates (activation and inactivation) while K+ only has one simple gate
2. Na+ channels respond faster to change in membrane voltage

Question 6

How do the Na+ Voltage gated channels open?

Answer 6

At resting potential (-70mV) Voltage gated channels are closed and the Na+ channels have the inactivation gate open but activation closed
* When membrane depolarizes to threshold (triggering event) voltage gated channels of Na+ open activation gate

Inward movement of Na+ ions => greater depolarization of membrane => more voltage gated Na+ channels open

Question 7

What does opening of Na+ voltage gated channels mean for permeability

Answer 7

Membrane at the threshold potential becomes 600 times more permeable to Na+ than K+

Question 8

When the threshold potential is reached there is a flux of Na+ ions into the cell. What are the Na+ voltage channels trying to do?

Answer 8

At the threshold the gated channels are trying to activate the inactivation gate but it takes time which is why we see the peak of the action potential.

Question 9

How long does the closing process of the Na+ voltage gated channels take?

Answer 9

0.5ms delay which gives Na+ to rush into the cell before getting blocked off

Question 10

When do the K+ voltage gated channels begin to open?

Answer 10

They open when the Na+ voltage channels close
* Slowly leaving the cell to counteract Na+ influx

Triggering signal: Initial depolarization to threshold
* This means it has the same signal that Na+ had but its much slower at opening