Cardiac action potentials etc Flashcards
What is the pacemaker potential?
slow depolarisation of membrane potential to threshold - occurs in between APs
What are the ionic causes of the pacemaker potential?
reduced K+ efflux
Na+ and K+ influx (funny current)
Transient Ca2+ influx
What happens once threshold is reached?
L-type Ca2+ channels are activated -> Ca2+ influx -> rising phase / depolarisation
What causes the falling phase of the cardiac pacemaker AP?
inactivation of L-type Ca2+ channels and activation of K+ channels -> K+ efflux + decreased Ca2+ conc.
What is the resting membrane potential of atrial and ventricular myocytes?
-90mV
What causes phase 0 of atrial/ventricular AP?
fast Na+ influx
What happens in plateau phase?
phase 2
mainly Ca2+ influx through L-type channels
What happens in the falling phase of atrial/ventricular APs?
K+ efflux
closure of Ca2+ L-type channels
Contraction occurs in which phase of atrial/ventricular AP ?
phase 2
CICR - induces Ca2+ to be released from the SR -> contraction
SA and AV nodes are enervated by which parasympathetic source?
vagus nerve
What is the effect of vagal stimulation on the heart?
slows HR and increases AV nodal delay
What is the parasympathetic neurotransmitter involved in vagal stimulation of the heart and what is it’s receptor?
acetylcholine
muscarinic M2 receptors
What is the competitive inhibitor of acetylcholine and when is it used to increase HR?
atropine
extreme bradycardia
Vagal stimulation has a …tropic effect?
negative chronotropic (decreases contractions)
What is the sympathetic neurotransmitter to the heart and what is its receptor?
noradrenaline
b1-ADR
