Action Potentials Flashcards
What three things affect the magnitude of an action potential?
- Number of channels that open
- Number of ions that move through the channels per unit time
- Duration of open channels
Are action potentials “all-or none?”
Yeah
The AP upstroke and overshoot are dependent on the ___ concentration gradient.
Na+
The AP repolarization and undershoot are dependent on the ___ concentration gradient.
K+
How do voltage-gated ion channels open in response to changes in electric field?
Charged protein domains are oriented in such a way that an electrical field causes a conformational change in the channel to allow ions through.
What are the three conformational states of voltage-gated Na+ ion channels?
- Closed and ready to open
- Open
- Closed and inactivated
What are the two conformational states of voltage-gated K+ ion channels?
Open and closed
Is the Hodgkin cycle a positive or negative feedback loop? Why?
Positive. Na+ influx from voltage-gated channels opening cause surrounding channels to open, propagating the action potential.
Name two differences between sodium and potassium channel gating.
Sodium channels are more sensitive to voltage changes and they open more rapidly.
What is the difference between the absolute refractory period and the relative refractory period?
Absolute refractory period is when Na+ channels are unable to open again, and the relative refractory period is when the Na+ channels can open if a larger-than-normal stimulus is applied (the overshoot is also smaller). The relative refractory period is due to the increased conductance (residual open) K+ channels.
Where are voltage-dependent K+ channels located in a myelinated nerve?
Peri-nodally
What role do voltage-dependent K+ channels play in a myelinated nerve?
None.
What affects the length constant of a nerve?
Indirectly proportional to the square of the longitudinal resistance and directly proportional to transmembrane resistance.
What is the defect in Multiple Sclerosis and how are action potentials affected?
Autoimmune demyelination of nerves exposes voltage-gated K+ channels. The absence of saltatory conduction coupled with K+ ion channels opening cause decreased action potential propagation along the nerve.
