The Action Potential - II Flashcards
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
Large axons with low resistance will conduct at ____ rates.
Higher
Electrically, what does myelination do for the neuron.
Prevents leakage of current out of the axon
Where are neuron Na/K channels located on an axon?
Node of Ranvier
How do Schwann cells get nutrients to their most wrapped components? What happens when this goes awry?
Gap Junctions
Charcot Marie Tooth
Name the type of conduction seen in myelinated nerves.
Saltatory Conduction
Why are dendrites less likely to develop AP?
Few voltage gated channels.
Highest density of voltage gated channels?
Axon Hillock
How does local anesthesia work?
Temporarily blocking the voltage gated sodium channels of neuronal axons
What do anesthetics bind?
Small lipid soluble molecules bind hydrophobic sites og the transmembrane protein involved in activation.
Normal WBC count?
5-6
What is Guillone Barre? Treatment?
Ab against myelin
Plasmaphoresis, IgG to downreg. Ab production
What is MS? Treatment?
Ab against central myelin, lose function, no repair
Selective Immunosuppressive Drugs may stop progression
A bilateral Babinski sign in an adult means….
Pyramidal Tract Damage
