When does an action potential occur?
When membrane potential in a cell rapidly rises and falls
Definition: potential difference
result of an equilibrium between electrical gradient and concentration gradient
What channels initiate action potential in nerve and skeletal muscle?
ligand-gated Na+ channels - opened by neurotransmitters
How does an action potential occur after ligand-gated Na+ channels are opened
if the membane potential becomes positive and the stimulus is enough to meet threshold potential, voltage gated Na+ channels open.
Which ion influxes during an action potential
Na+
When does depolarisation end?
when the positive voltage inactivates the voltage gated Na+ channels
Describe the steps of repolarisation
As the voltage gated Na+ channels close, voltage gated K+ channels open and potassium flows out of the cell. Delayed closure of these potassium channels results in a transient hyperpolarisation
What is the absolute refractory period?
1ms - following depolarisation when sodium channels remain closed and no depolarisation can occur regardless of the stimulus
What is the relative refractory period
2-3ms = whilst the cells are hyperpolarised they may be depolarised but require a larger stimulus
Resting membrane potential in excitable tissues
In excitable tissues the resting membrane potential is -60 to -90mV.
resting potential in SAN
-60
threshold potential in SAN
-40
resting potential ventricular and atrial myocytes
-90
threshold potential for ventricular and atrial myocytes
-70
What ions are used in the cardiac action potential
-depolarisation: rapid sodium influx
-repolarisation: efflux of K+
-plateau: slow influx of calcium
- repolariation: efflux of potassium
