Electrophysiology Principles 3

Question 1

What underlies the initial portion of an AP?

Answer 1

passive membrane properties

Question 2

TRUE or FALSE: if there are no leak channels, we would have no resistance

Answer 2

FALSE: resistance would be infinite

Question 3

What are the 3 key things to remember about passive membrane properties?

Answer 3

1. membrane properties in the absence of voltage-gated channel activity
2. voltage response across a membrane, when the membrane acts as a capacitor and resistor in parallel
3. the main characteristics are: the input resistance, the length constant (lambda), and the time constant (tao)

Question 4

Which constant determines how long the initial depolarization bump takes to reach threshold?

Answer 4

time constant (tao)

Question 5

TRUE or FALSE: short tao = slow AP (longer time for bump to reach threshold)

Answer 5

FALSE: short tao = fast AP (short time for bump to reach threshold)

Question 6

Where does the maximum voltage change occur when a current is injected?

Answer 6

at the site of current injection

Question 7

The voltage change increases and decreases _________________.

Answer 7

exponentially

Question 8

The voltage change increase exponentially to a ____________ but then ___________ after the current has ended.

Answer 8

plateau, decays

Question 9

What does the exponential change in voltage represent in terms of capacitor and resistor?

Answer 9

shift of current from going to capacitor to going to resistor

Question 10

TRUE or FALSE: change in voltage takes longer than the actual current injection

Answer 10

TRUE

Question 11

In terms of the cell membrane what is capacitance and resistance?

Answer 11

• capacitance = membrane has charge
• resistance = ion channels

Question 12

TRUE or FALSE: more ion channels = more resistance

Answer 12

FALSE: more ion channels = less resistance

Question 13

The cell membrane can be modelled as a capacitor and resistor in _______________.

Answer 13

parallel

Question 14

What is the time constant tao defined as?

Answer 14

the time it takes for the voltage to rise to 1-1/e or 63% of its final value

Question 15

TRUE of FALSE: the time constant is independent of cell or axon size

Answer 15

TRUE

Question 16

What is the specific capacitance per unit area (Cm) in cells?

Answer 16

1 microF/cm^2

Question 17

What is the range of tao?

Answer 17

1 to 20 milliseconds

Question 18

What is the input resistance a measure of?

Answer 18

resistance through the axoplasm and then across the cell membrane

Question 19

What is the length constant lambda defined as?

Answer 19

distance over which the potential falls to 1/e or 37% of the original value

Question 20

TRUE or FALSE: As the membrane resistance increases then lambda decreases

Answer 20

FALSE: membrane resistance INCREASE, lambda INCREASE

Question 21

TRUE or FALSE: As the axoplasm resistance increases then lambda increases

Answer 21

FALSE: axoplasm resistance INCREASE, lambda DECREASE

Question 22

When lambda increases, does that mean the action potential conduction velocity is greater or smaller?

Answer 22

lambda increases, AP travel faster

Question 23

Which property of the action potential does lambda underlie?

Answer 23

conduction velocity

Question 24

Which property of the action potential does tao underlie?

Answer 24

how quickly depolarization occurs to cause AP at threshold

Question 25

What are the 3 main parameters that specify the behaviour of an axon?

Answer 25

1. input resistance
2. length constant lambda
3. time constant tao

Question 26

Does having a high input resistance make it easier or harder to depolarize?

Answer 26

easier

Question 27

How does myelin affect membrane resistance?

Answer 27

increase resistance

(hint: make it easier to depolarize)

Question 28

How does myelin affect capacitance?

Answer 28

decrease capacitance

Question 29

How does myelin affect the time constant?

Answer 29

no effect

Question 30

TRUE or FALSE: an increase in diameter and a decrease in myelin causes an increase in velocity of depolarization

Answer 30

FALSE: increase in both diameter and myelin = increase in velocity of depolarization

Question 31

TRUE or FALSE: internodal regions are myelinated

Answer 31

TRUE

Question 32

Where are Na+ channels found on an axon?

Answer 32

at the nodes (unmyelinated areas)

Question 33

TRUE or FALSE: APs occur at the myelinated regions

Answer 33

FALSE: only occur at the nodes

Question 34

TRUE or FALSE: paranodal regions have more Na+ channels whereas internodal regions have more K+ channels

Answer 34

FALSE:
- paranodal = K+
- internodal = Na+

Question 35

Why do internodal regions have a higher membrane resistance?

Answer 35

fewer leak channels (=more resistance)

(remember: more channels = less resistance)