Action Potential Flashcards
(27 cards)
How do you record resting and action potentials?
Insert an electrode into the cell and one outside the cell. The oscilloscope shows resting potential
What does it mean if you measure outward current?
It means that positive current is going out of the cell.
Describe the shape of an action potential.
- Resting (-70mV)
- Depolarization
- Repolarization
- Hyperpolarization
- Resting state
What is absolute refractory period?
A period where Na gates are inactive; during this period no stimulus will trigger an action potential; limits max firing rate to 1000 Hz
What is relative refractory period?
Period where membrane is trying to go back to resting; only strong stimulus may trigger an action potential
When is action potential triggered?
When membrane depolarizes about 10-20 mV
What technique did Hodgkin, Huxley, and Katz use?
Voltage clamp technique
What is voltage clamp technique?
Allows one to control the membrane potential at any level while measuring the current necessary to maintain that membrane potential
What follows a brief capacitive current? After that?
rapidly rising inward ionic current (Na), followed by a slower delayed outward current(K).
How can we eliminate the early inward current that follows a brief capacitive current?
Replace sodium with choline.
What poisons block voltage-gated Na channels?
TTX, STX, and conotoxins
What poisons blocks voltage-gated K channels?
TEA and 4-aminopyridine
Evidence for Na current
- Equilibrium potential = +55 mV
- Ionic substitution
- Use of TTX
Evidence for K current
- Ionic substitution
- Use of TEA
Describe action of proteins during action potential?
- During rest, only leak K channels open.
- During depolarization, voltage-gated Na channels open
- At overshoot, voltage-gated Na channels close and voltage-gated K channels open
- During repolarization, Na channels close
- During resting, voltage-gated K channels close
After determining ion currents during action potentials, what did Hodgkin and Huxley calculate?
Magnitude and time course of the conductance change for each ion
What are three important phenomena in the voltage-dependent conductance model?
- Both conductance’s are voltage-dependent
- Both conductance’s change over time
- Activation saturates
What happens to the conductance of Na and K when neuron depolarizes?
The conductance increases
Why does the rate of depolarization decrease?
- the driving force for sodium decreases
- sodium channels become inactivated
- potassium channels open
Describe positive feedback loop of ionic currents during action potential
Depolarization causes increase in sodium conductance which causes inward sodium current which causes more depolarization
Describe negative feedback loop of ionic currents during action potential
Depolarization causes an increase in potassium conductance which causes outward potassium current which causes repolarization.
Two functions of refractory period
- Limits the firing frequency
- causes the AP to continue propagating in one direction
How is AP regenerated?
Opening new adjacent sodium channels
What is concentrated at nodes and paranodes of myelinated axons?
Voltage-gated K and Na channels
