Electrophysiology Principles 3 Flashcards
What underlies the initial portion of an AP?
passive membrane properties
TRUE or FALSE: if there are no leak channels, we would have no resistance
FALSE: resistance would be infinite
What are the 3 key things to remember about passive membrane properties?
- membrane properties in the absence of voltage-gated channel activity
- voltage response across a membrane, when the membrane acts as a capacitor and resistor in parallel
- the main characteristics are: the input resistance, the length constant (lambda), and the time constant (tao)
Which constant determines how long the initial depolarization bump takes to reach threshold?
time constant (tao)
TRUE or FALSE: short tao = slow AP (longer time for bump to reach threshold)
FALSE: short tao = fast AP (short time for bump to reach threshold)
Where does the maximum voltage change occur when a current is injected?
at the site of current injection
The voltage change increases and decreases _________________.
exponentially
The voltage change increase exponentially to a ____________ but then ___________ after the current has ended.
plateau, decays
What does the exponential change in voltage represent in terms of capacitor and resistor?
shift of current from going to capacitor to going to resistor
TRUE or FALSE: change in voltage takes longer than the actual current injection
TRUE
In terms of the cell membrane what is capacitance and resistance?
- capacitance = membrane has charge
- resistance = ion channels
TRUE or FALSE: more ion channels = more resistance
FALSE: more ion channels = less resistance
The cell membrane can be modelled as a capacitor and resistor in _______________.
parallel
What is the time constant tao defined as?
the time it takes for the voltage to rise to 1-1/e or 63% of its final value
TRUE of FALSE: the time constant is independent of cell or axon size
TRUE
What is the specific capacitance per unit area (Cm) in cells?
1 microF/cm^2
What is the range of tao?
1 to 20 milliseconds
What is the input resistance a measure of?
resistance through the axoplasm and then across the cell membrane
What is the length constant lambda defined as?
distance over which the potential falls to 1/e or 37% of the original value
TRUE or FALSE: As the membrane resistance increases then lambda decreases
FALSE: membrane resistance INCREASE, lambda INCREASE
TRUE or FALSE: As the axoplasm resistance increases then lambda increases
FALSE: axoplasm resistance INCREASE, lambda DECREASE
When lambda increases, does that mean the action potential conduction velocity is greater or smaller?
lambda increases, AP travel faster
Which property of the action potential does lambda underlie?
conduction velocity
Which property of the action potential does tao underlie?
how quickly depolarization occurs to cause AP at threshold
What are the 3 main parameters that specify the behaviour of an axon?
- input resistance
- length constant lambda
- time constant tao
Does having a high input resistance make it easier or harder to depolarize?
easier
How does myelin affect membrane resistance?
increase resistance
(hint: make it easier to depolarize)
How does myelin affect capacitance?
decrease capacitance
How does myelin affect the time constant?
no effect
TRUE or FALSE: an increase in diameter and a decrease in myelin causes an increase in velocity of depolarization
FALSE: increase in both diameter and myelin = increase in velocity of depolarization
TRUE or FALSE: internodal regions are myelinated
TRUE
Where are Na+ channels found on an axon?
at the nodes (unmyelinated areas)
TRUE or FALSE: APs occur at the myelinated regions
FALSE: only occur at the nodes
TRUE or FALSE: paranodal regions have more Na+ channels whereas internodal regions have more K+ channels
FALSE:
- paranodal = K+
- internodal = Na+
Why do internodal regions have a higher membrane resistance?
fewer leak channels (=more resistance)
(remember: more channels = less resistance)
