Action Potential

Question 1

Where does an AP initiate?

Answer 1

in axon hillock

Question 2

After initiation, where does an AP propagate?

Answer 2

AWAY from cell body/soma

Question 3

What type of pumps establish and maintain membrane potential?

Answer 3

ATP dependent

Question 4

Which postsynaptic potentials dictate what happens at the post synaptic membrane potential?

Answer 4

IPSPs and EPSPs

Question 5

What is the Goldman equation?

Answer 5

Em = 58 log (Pk[Ko] + Pna[Nao] + Pcl[Clin] / Pk[Kin] + Pna[Nain] + Pcl[Clo])

Question 6

What causes a change in Vm?

Answer 6

1. by changing internal/external ionic conc.
2. by changing relative permeability of ions across the plasma membrane

Question 7

What conc. has the greatest permeability and influence on Vm?

Answer 7

K+

Question 8

How are ionic permeabilities changed?

Answer 8

1. ligand gated
2. voltage gated
3. nucleotide gated; 2nd messenger systems
4. inward rectifier “leak” channels
5. mechanosensitive gated (stretch)

Question 9

What are examples of ligand gated channels?

Answer 9

(GABA, Glu, 5HT)

Question 10

What are examples of voltage gated channels?

Answer 10

Na+ and K+

Question 11

What are examples of nucleotide gated channels?

Answer 11

cAMP and cGMP

Question 12

What are the 5 types of voltage gated channels?

Answer 12

• Na+
• Ca+
• K+
• Cl-
• H+

Question 13

What types of ion channels play a major role in pH/homeostasis?

Answer 13

proton gated

Question 14

What channel opens after depolarization and re-polarizes the membrane?

Answer 14

K+

Question 15

What happens when Na+ channels open?

Answer 15

• membrane potential depolarizes
• increased flow of ions

Question 16

What happens when K+ channels open?

Answer 16

membrane is repolarized

Question 17

What happens AFTER K+ channels open?

Answer 17

• Na channels change conformation and inactivate
• increased Pna is shut down

Question 18

What are the 3 conformational states following a depolarization?

Answer 18

• open: “a” or “m” gate
• inactive: “i” or “h” gate
• closed

Question 19

When Pk remanis high, what happens to Vm?

Answer 19

becomes transiently more negative than the baseline resting Vm

Question 20

What is the response of K+ relative to Na+ channel during an outward current?

Answer 20

delayed

Question 21

What region has a voltage sensor on it and what is its function?

Answer 21

S4: sense changes in Vm and move in repsonse to the changes

Question 22

Where is ion selectivity located in regards to the molecular structure of the channels?

Answer 22

within the pore itself

Question 23

What is the trend of Pna and Pk in neuronal AP?

Answer 23

• rapid increase in Pna
• slower, more stable increase in Pk

Question 24

Slower activation of what channel contributes to repolarization?

Answer 24

K+

Question 25

What does the activation of K+ channels lead to?

Answer 25

* negative feedback loop * hyperpolarization that decreases probability of activating more channels

Question 26

AP will NOT fire if what?

Answer 26

Vm is under threshold

Question 27

What type of phenomenon is AP?

Answer 27

all or none

Question 28

Na channels can be blocked by what?

Answer 28

TTX and riluzole

Question 29

What are the 2 factors influencing length constant?

Answer 29

membrane and internal resistance

Question 30

What is high membrane resistance?

Answer 30

* very little ions are leaking out * directly proportional to length constant

Question 31

What is low internal resistance?

Answer 31

* less ions within the cell * inversely proportional to length constant

Question 32

What is the length constant?

Answer 32

distance it takes to reach 37% of Vmax

Question 33

What is absolute refractory period?

Answer 33

2nd AP CANNOT fire because Na channels can't be reactivated in open/inactivated state (peak in graph)

Question 34

What is relative refractory period?

Answer 34

* greater depolarization is required for an AP to fire (flatter line in graph) * active K+ channels move membrane away from threshold potential

Question 35

What is the rate limiting event for AP propagation?

Answer 35

time needed to charge the membrane to change Vm

Question 36

What is the formula to charge the membrane?

Answer 36

t= Rm * Cm

Question 37

How does myelination increase the conduction velocity?

Answer 37

by increasing membrane resistance

Question 38

What is the relationship between the myelination of an axon and its conduction velocity?

Answer 38

directly proportional

Question 39

What can affect conduction velocity?

Answer 39

myelination and size of axon

Question 40

What is capacitance?

Answer 40

ability to hold charges on the membrane

Question 41

When does capacitance decrease?

Answer 41

when myelin membrane is added

Question 42

What is saltatory conduction?

Answer 42

* propagation along myelinated axons * AP jumps from one node to the next

Question 43

What happens during saltatory conduction?

Answer 43

1. myelination increases membrane resistance 2. decreases membrane capacitance 3. decreases membrane permeability 4. increase conduction velocity 5. length constant increased

Question 44

How does increasing conduction velocity affect unmyelinated axons?

Answer 44

* slower conduction * local current flow (electrotonic conduction)

Question 45

How does increasing conduction velocity affect myelinated axons?

Answer 45

* faster conduction * saltatory conduction * AP jumps from node to node

Question 46

What is multiple sclerosis?

Answer 46

autoimmune, degenerative disease of axon demyelination

Question 47

What affect does axonal demyelination have on AP conduction velocity?

Answer 47

causes it to decrease

Question 48

What are the key concepts of AP propagation?

Answer 48

1. depolarization attenuates as it moves down the axon 2. peak membrane potential during an AP remains consistently depolarized 3. action propagation takes time to charge membrane 4. myelination increases conduction velocity

Question 49

As depolarization moves down the axon, this is caused by what?

Answer 49

membrane and interaxonal resistance