electrical systems of the heart Flashcards
what does the term autorhythmicity mean?
when some cardiac muscle cells they get can be self-excitable
- this means they generate an AP which causes heart to contract as a single unit
- this Ap spreads out throughout the myocardium
what are ion channels and pumps made up of?
they are made up of cardiomyocytes
where is calcium stored?
in the cytosol
what does the phrase action potential mean?
it means the transient depolarisation as a result of ion channels
what are the three broad patterns of cardiac AP? how do they differ?
- AV and SV nodes
- Atrial muscle for fast depolarisation
- purkinje fibres and ventricular muscle
they all differ in shape, ionic basis and duration
what are the phases of ventricular action potential?
Phase 0 = depolarisation ; influx of Na+ ions
Phase 1 = partial depolarisation ; Na+ channels close and more K+ efflux
Phase 2 = plateau ; slow K efflux and Ca2+ influx
Phase 3 = Repolarisation; efflux of K+ and closing of Ca2+ channels
Phase 4 = resting membrane potential
what occurs for an SA node action potential?
at around -60mV to the threshold you have slow depolarisation where K+ channels are closed and funny current of Na is coming in
At the threshold the Ca2+ channels open and fast depolarisation occurs until a peak hits at just above 0mV and calcium channels close
then depolarisation occurs where inactivation of Ca2+ channels occur and more K+ efflux to bring back down AP to -60mV
why is a pacemaker used and what does it do?
it will control the heart rhythm
when the heart has an unstable resting membrane potential
pacemaker cells produce an electrical impulse causing contraction
what is cardiac muscle excitation-contraction coupling?
when the AP causes myocyte to contract
- cardiomyocytes have a microfilament for contraction
how can the depolarisation of adjacent cells occur?
the current will flow to the adjacent cells through ‘gap functions’
what is the conduction pathway in the heart?
from the SA node -> to the AV node -> to the bundle of his -> to the bundle branches -> purkinje fibres (cause of ECG rise)
