Flashcards in Lecture 1 - Neuronal Action Potential Deck (54)
Which vertebrate cell has the longest duration?
3. Cardiac Ventricle
- duration is fast, about 200 milliseconds
- heart has long AP to protect it from additional AP'
- thus cannot be activated as quickly
What is the term for the response that does NOT generate an AP because the voltage is not large enough?
Sub threshold response
- decreases in amplitude with distance
- change in membrane potential not sufficient for action potential
What is the length constant?
Distance over which a sub threshold depolarization (local response) will spread & influence the next membrane
- larger length constant = MORE RAPID CONDUCTION
(fires an AP)
When you decrease Rm, what happens to the space constant? What about decreasing Ri?
1. decrease Rm = decrease length constant
2. decrease Ri = INCREASE length constant
What is Rm and Ri?
Rm = membrane resistance
Ri = internal resistance (or Ra)
With a large axonal diameter, is the length constant large or small?
length constant is LARGE since Ri is LOW(internal resistance)
As distance increases from the current source, what happens to the sub threshold voltage?What manner does this decay (graph wise)
DECREASES (decays) with increasing distance from source
- decays EXPONENTIALLY
Larger diameter axons have lower or higher membrane and internal resistance? (rm and Ri)
Large diamter = LOWER resistance than smaller axon
- but since Ri is squared, it decreases more than rm
Large diameter results in _____ conduction
Faster conduction velocity
What determines how easily an axon can conduct an AP?
What determines the space constant?
What occurs once an area of membrane is activated by an action potential?
REVERSAL OF MEMMBRANE POLARITY
(inside becomes more positive than outside)
- originally NEG inside
Local current flow occurs between activated (depolarized) and inactive regions, activating ______ channels to depolarize the next segment of membrane and initiating an AP/
A stimulus is a ____ or ____ response.
All or none
Upstroke of the action potential graph is caused by what? Repolarization is caused by what?
1. Na activation (opening of M channels)
2. delayed increase in K+ conductance and inactivation of Na channels (closing of h gates)
Where is the only place AP's occur?
Nodes of Ranvier
An action potential occurs between the E of what two ions?
Ena and Ek
Repolarization turns off what channel conductance completely?
Describe the gating properties of Na channel at the following stages:
1. resting: M closed, h open
2. Activated: both open, NA INFLUX (h slowly closing)
3. Inactivated: M open, h closed
What is the time required to reset the channel from inactivated state back to resting state?
Recovery from Inactivation
Recovery from inactivation requires what?
Gating kinetics for Na and K both depend on what?
Time and Voltage
What gates due NOT have inactivation gates?
What channels respond RAPIDLY to depolarization?
What occurs during regenerative depolarization?
1. Na+ moves into the cell down its electrical & conc gradient
2. DEPOLARIZE membrane to Ena
3. increase Na permeability
4. causing FURTHER DEPOLARIZATION
What channels close rapidly at depolarized (positive) voltages?
- inactivation is time and voltage dependent
What is the basis for refractory periods?
Voltage-dependent inactivation of Na+ channels
Recovery from inactivation requires what?(to reach resting state)
2. Negative voltages (repolarization)
What channels remain open with maintained depolarization of the membrane? When do these channels completely deactivate?
- no inactivation
- completely deactivate with DEPOLARIZATION