Membrane Depolarization & AP Flashcards
If AP will be propagated by postsynaptic cell depends on?
- Stimulus number
- Stimulus magnitude
- Stimulus nature (EPSP/IPSP)
- Stimulus locale (axon hillock → this is important)
Permeability is the same as?
Conductance
Steps of Nt-stimulated ion current
- Nt causes local increase in Vmem
- Change in Vmem permits flow of ionic current
- Local current flow leads to depolarization of small area of membrane
- Area of depolarization may grow
The area of depolarization will grow IF:
- V-sensitive channels are present
2. Depolarization is of sufficient magnitude
How does flow of current affect depolarization magnitude?
Greater flow of current → greater magnitude of depolarization
How does flow of current affect area of depolarization?
Greater current flow → larger area of depolarization
Length constant provides an indication of?
Area that will be affected
Bigger length constant = ?
Bigger area affected
If 2 cells receive the same stimulus, which will have a larger area of depolarization?
One with longer length constant
Decremental conduction
Not sustained over time → as it gets farther from the stimulation site, it gets smaller
What is (positive) spatial summation of non-propagating depolarization?
Overlapping zones of depol. construnctively reinforce one another → results in greater depolarization in area of overlap
For an AP to be propagated, the zone of depol. must include?
Axon hillock
What is destructive spatial summation?
Overlapping zones of depol. and high Cl- conductance destructively reinforce on another → results in reduced propagation of depolarization
What is temporal summation?
Stimulations close in time build on one another
How long does it take V-sensitive Na channels to deactivate?
What are the two conductance components of AP?
PNa and PK
E(m) is the weighted average of?
E(Na) and E(k)
What is the weighting factor for E(m)?
Relative conductance of Na and K
Magnitude of depolarization at any point depends on?
- Magnitude of depolarization at source (current density)
2. Distance from source
Electrotonic depolarization does not depend on?
Activation of V-sensitive channels
What does electrotonic depolarization do?
Changes distrubtion of charge to change membrane polarization without change in conductance
What is the final site of integration (logic gate of cell)?
Axon hillock
Where is the highest density of Na(V) channels?
Axon hillock
Types of channels at axon hillock?
- Na(V)
- K(V)
- Ca(V)
- K(Ca)
Absolute refractory period
Most Na(V) channels are activated or inactivated → ARP cannot occur
Relative refractory period
Membrane is hyperpolarized → requires stronger than normal stimuli
What prevents AP from moving retrograde?
Refractory period
Length constant depends on?
Ratio of membrane resistance to cytoplasmic resistance
How can cell increase length constant?
- Decrease cytosolic resistance
2. Increase membrane resistance
How can cell decrease cytosolic resistance?
Increase diameter
How can cell increase membrane resistance?
Myelination
Which is more effective, increased axon size or myelination?
Myelination
