The Action Potential - II Flashcards
(37 cards)
What is Ohm’s Law?
g = I / (Em-Eion)
What is Em-Eion?
The electrochemical driving force action on the ion
With knowledge of Vm, Ena, and Ek, what three things were learned?
- Both conductances are voltage dependent
- Both conductances change over time
- Activation saturates
The coincidence of the initial increase in g-na with the rapid rising phase of the action potential demonstrates what?
A selective increase in gNa is responsible for AP initiation
Increased gNa causes Na to ______ the neuron
Enter
What causes the rate of gNa to fall? (2 reasons)
the electrochemical driving force on Na decreases
gNa inactivates
What does depolarization slowly activate? What happens?
gK, allowing K+ to leave the cell
gK being higher than in resting condition causes….
undershoot
Undershoot causes what to occur?
Voltage dependent gK to turn off, mem. pot return to resting level
Which ion cycle is regenerative?
Na
Inward Na Current –> Depolarization –> Increase in gNa –> Inward Na Current
Which ion cycle is not regenerative?
K
Depolarization –> Increase in gK –> outward K current –> repolarization
What stops the Na positive feedback?
Na+ conductance inactivation
What is passive spread?
Current conduction in the absence of an action potential
How does potential change change over increasing distance.
Exponentially decays
What is lambda?
sqrt((Rm/Ri))
Though there is a decrement of APs spreading along the axon, local depolarization….
is still large enough spread to depolarize adjacent regions of the axon above threshold and generate an AP nextdoor
How long will the AP regeneration process continue?
Until the AP travels the full length of the axon
Is action potential instantaneous?
No. Action potentials occur later at greater distances down the axon.
What is the measurement of the rate of AP transmission?
Conduction Velocity
What causes a nerves conduction velocity to vary?
Size and Myelination of the Nerve
What causes the refractory period?
Transient inactivation of the Na and K channels
What do refractory periods limit?
Number of APs a given cell can produce at a time
Inability to reverse direction of signal
Why can’t APs reverse direction?
Inactivated Na channels left in the APs wake
Axon diameter is ______ related to internal resistace
Inversely
