Generation & Propagation of Action Potentials Flashcards
What acts as a capacitor in the cell?
Where are the - charges?
Cell membranes
Negative charges on the intracellular ide
What effect does capacitance have on action potential?
Slows the time course because capacitance must first be disipated for depolarization & hyperpolarization.
Rapid
Membrane Time Constant
Time it takes for a 63% change in membrane potential
1-10 milliseconds
Temporal summation and effect of time constant
Longer time constant = action potentials can overlap
Also refers to small stimuli that can only generate an AP if fired closely after each other
Speed of propagation
1/sqrt((rmXri) X Cm)
Length Constant
sqrt(rm/ri)
Name 4 passive membrane properties
- Capacitance
- Membrane time constant
- Speed of propagation
- Length constant
Name 1 organism that relies solely on passive properties for membrane AP
C. elegans
Absolute refractory period
No AP can be generated
Na channels open & become inactivated
Refractory period
Greater stimulus required to generate an AP
K + channels open but overshoot hyperpolization
Role of pore loops
Ion selectivity based on size + hyrdophobicity
Role of S4 membrane
Every 3rd amino acid + charged
AP results in confirmation change, twists ad moves up, opens channel
K channel inactivation method
Ball and chain
Na channel inactivation method
Loop between 3rd and 4th domains stays “plugged in” until membrane is repolarized
Rank activation speed
NA K Ca
- Na
- Ca
- K
Rank Inactivation speed
Na and Ca
Na faster than Ca
Role of CA on AP
Depolaization
Role of K on AP
Repolarization
Delays reaching threshhol
Role of Ca on AP
Delays repolirization
Sometimes see Ca shoulder
What are “A current” channels
Special K channels that prolong the interspike interval
What are Nucleotide gated channels
- Important in pacemaker cells
- Open only in hyperpolarized state
- Encourage depolarization towards threshold
- Cation influx
Name 3 Na channel blockers
Tetrodotoxin
Saxitoxin
Lidocaine
Name 1 K channel blocker
Tetrathyamonium (TEA)
Name 1 Ca channel blocker
Conus toxin
What channel is overactive in pain
Na
What channels are responsible for hyperactivity in epilepsy
Na
- Fail to inactivate, prolonged deolarization, abnormal excitability
Define channelopathies
Genetic disorders in channel functioning
Dysmylinating vs Demylinating disease
Dys = abnormal myelin De = No myelin
Gullian Barre Syndrome
PNS myelin is lost
Multiple sclerosis
CNS myelin is lost
Charcot-Mari-Toot Syndrome
Gap junctions are abnormal, no nutrient transfer to outer layers = death
Proagation is usally uni-directional but what channels can cuse bidirectional propagation?
Na
Effect of diametr on the following Capaciatance Membrane Resistance Speed Internal resistance
Inc. capacitance
Dec. membrane resistance
Inc. speed
Dec. internal resistance (inverse square of diameter)
Benefits of mylination
Less ATP
Decrease capacitance
Increases speed, length constant, membrane resistance
Support neurons of PNS
Schawn cells
Support neurons of the CNS
Glial cells
What cells interact in order to trigger myelination
Glia and axons
What molecule determines the number of “wraps” of myelin
neuroglin
Role of Myelin Associated Protein in myelination
PNS or CNS
Initial glial-axon interaction
PNS & CNS
Po
PNS or CNS
Myelin compaction
PNS
Proteolipid Protein
PNS or CNS
Mylin compaction
CNS
Myelin Basic Protein
PNS or CNS
Myelin compaction
CNS & PNS
