Neuronal Excitability Flashcards
Describe the state of voltage gated Na+ and K+ channels during the absolute refractory period.
- Most Na+ channels are inactivated (closed).
- Most K+ channels are open.
Describe the state of voltage gated Na+ and K+ channels during the relative refractory period.
- Na+ channels are closed and recovering from inactivation.
- Some K+ channels are open.
What is the advantage of the refractory period?
An action potential cannot travel backwards.
Describe saltatory conduction.
- Myelin sheath increases the speed of AP conduction.
- Ions are allowed to flow between Nodes of Ranvier rather than across the whole axon.
How can the conductance (g) of ion channels be measured?
g = 1 / R.
What is ion channel conductance directly proportional to?
The number of open ion channels; permeability.
How do the states of voltage gated ion channels change with depolarisation and repolarisation?
- With depolarisation, all voltage-gated ion channels open.
- With repolarisation, all voltage-gated ion channels close.
Why does hyperpolarisation occur with action potential generation?
Because K+ channel opening is delayed, so remain open for a short while after voltage returns to Em.
Why does Em approach ENa during an action potential?
Because Na permeability increases 1000x.
During an action potential, what is the highest voltage reached?
~+40-mV.
Which equation can be used to calculate equilibrium potential for a particular ion using ion concentrations?
The Nernst equation.
Which equation can be used to calculate the membrane potential using ion permeabilities and concentrations?
The Goldman equation.
