Physiology Flashcards
where does excitation of the heart originate from? and what cells?
Sino-atrial node
pacemaker cells
location of SA node
in the right atrium (close to where superior vena cava enteres
what is the pacemaker potential?
occurs in the cells of SA node
the unstable membrane potential
(gradually depolarisation till threshold)
what causes the pacemaker potential?
the decrease in K+ efflux and increase in Na+ influx
what happens once membrane potential reaches threshold?
there is a transient influx of Ca2+ causing depolarisation
where is the AV node located?
at the base of the right atrium
what is the purpose of a delay in the AV node conduction?
to allow all the blood to enter the ventricle before ventricle systole
what are the main phases of action potential in contractile cells?
phase 4- resting membrane potential phase 0- depolarisation phase 1- small repolarisation phase 2- plateau phase phase 3- repolarisation
action potentials in contractile cells phase 4?
resting membrane potential due to K+ efflux
AP in contractile cells phase 0?
depolarisation caused by Na+ influx
AP in contractile cells phase 1?
little repolarisation caused by closure of Na+ channels and opening of K+ channels
K+ efflux is dominant
AP in contractile cells phase 2?
plateau phase caused by Ca+ influx via L-type channels and K+ efflux simultaneous
essential to muscle contraction of heart
AP in contractile cells phase 3?
repolarisation caused by closure of Ca+ channels and K+ efflux
3 types of K+ channels used
what is the purpose of drugs that reduced the plateau phase of the AP?
reduces muscle contraction
what are funny potassium channels?
K+ channels opened by hyperpolarisation
what is a positive chronotropic effect?
an increase the number of AP causing more frequent contraction
what is a positive inotropic effect?
an increase the strength of contraction
what is a positive dromotropic?
an increase in the rate of AP
what nerve dominates the heart under resting conditions?
Vagus nerve (CN X) parasympathetic control on the heart
what does the vagus nerve supply to in the heart?
SA node and AV node
what exactly does vagus nerve stimulation do?
slows heart rate and increases the AV node delay
what happens to the pacemaker potential slope in parasympathetic effects?
it decreases
what do cardiac sympathetic nerves supply?
SA node, AV node and myocardium
what is the neurotransmitter and receptor used in sympathetic response?
noradrenaline acting on B1 adrenoceptors
