Action Potentials

Question 1

General: what is an action potential

Answer 1

Quick flips of Na+ and K+ ion concentration inside and outsie axon

Question 2

What structures allow an action potential

Answer 2

• axons
• ion leak channels
• voltage gated channels
• Na/K pumps

Question 3

Theshold Potential

Answer 3

• if enough Na+ enters the axon, and raises membrane potential threshold is reached causing Na+ voltage gated channels to open
• All or nothing response - if threshold not reached then reset to resting potential
  NOTE: thresholds in diff neurons may be diff but all action potentials are the same strength

Question 3

Resting membrane potential

Answer 3

• Na/K pumps regulate an imbalance of Na (outside) and K (inside) concentractions
• Na pumps: 3 Na out/ 2 K in
• Since theres more Na+ out (pos) axon is more negative inside
  –> -70mV

Question 3

Graded Potential/Stimulus

Answer 3

• A neuron recieves a stim causeing Na+ leak channels to open.
• Na+ rushes into the axon
• Note: The number of leak channels opening depends on the stim

Question 3

Depolarization

Answer 3

• Na+ going in makes the inside less negative so the charges equalize
• Positive feedback causes membrane potential to continue to rise - since threshold is positive, and more positive Na+ is entering. we constantly reach threshold and more Na+ comes in through voltage gated channels
  OVERALL: membrane potential becomes positive

Question 4

Repolarization

Answer 4

• At the peak of action potential Na+ voltage gated channels close and K+ voltage gated channels open
• K+ exits axon (negative feedback since it pumps pos ions out of cell, making inside less pos)
  OVERALL: membrane potential becomes negative and Na/K concentrations are flipped

Question 5

Hyperpolarization

Answer 5

• Neg charge in axon closes K+ voltage channels and activates Na/K pumps
• refractory period is entered and axon cant be fired until reset
• all Na out and all K in… flips the Na and K concentrations back to resting membrane potential

Question 6

Propogation of action potentials

Answer 6

SALTATORY CONDUCTION
- self propogating
- myelin sheaths insulates axon so Na+ cant leave and Na+ gets pushed to the next section with a node of ranvier
- Next section is positive enough to reach threshold and open more voltage gated Na+ channels and go through action potential
- only one direction - even though na+ can flow both ways, it only goes one since the side the Na+ came from is in hyperpolarized state alr
- Faster and less energy is lost

Question 7

IPSP and EPSP

Answer 7

• epsp are excitatory (towards threshold)
• ipsp are inhibitory (away from threshold)
• balance determines whether threshold is reached

Question 8

draw and label the process of an action potential

Question 9

Draw and label the graph of an action potential