Flashcards in the heart Deck (61)
where is the sino-atrial node located?
in the crista terminalis of the right atrium
how is electrical activity in the heart activated?
1. action potential is generated
2. at -60mV it leads to opening of HCN channels - allow Na+ ions to move into cell which depolarises from -60mV to -40mV
3. voltage gated Ca2+ channels open and Ca2+ enters inside and results in depolarisation of cell membrane to +20mV
4. at +20mV K+ channels open and K+ move out of the cell - this results in repolarisation
5. hyperpolarisation threshold gets reached and this reopens HCN channels again - this is a cycle
what is the effect of catecholamine on SAN activation?
it has a positive chronotropic effect
it leads to faster repolarisation - reaches threshold faster
heart rate is increased
what is the effect of acetylcholine on SAN activation?
it slows down the opening of HCN channels
this decreases heart rate
how is an action potential propagated from the SAN?
it exits the SAN and spreads to other cells through gap junctions (connexins)
this activates other myocytes (Na+ ions depolarise adjacent cells)
what happens in a myocardial action potential?
1. initial depolarisation past threshold of -70mV leads to Na+ fast gated channels opening - Na+ enters cell and depolarises it to +20mV
2. K+ channels open and K+ leaves cell - drops to -15mV
3. slow voltage gated Ca2+ channels open and Ca2+ move into cell - counteracts loss of K+ and results in plateau
4. Ca2+ channels close - K+ continues to leave and cell repolarises until it reaches resting potential -90mV
what is phase 0 of myocardial action potential and what ions are responsible for it?
what is phase 1 of myocardial action potential and what ions are responsible for it?
inflow of Na+ stops
what is phase 2 of myocardial action potential and what ions are responsible for it?
Ca2+ slow inflow
what is phase 3 of myocardial action potential and what ions are responsible for it?
inflow of Ca2+ stops
what is phase 4 of myocardial action potential and what ions are responsible for it?
what is the length of time for the plateau in the myocardial action potential?
what is the role of the SAN?
it determines heart rate
what is the resting potential of the SAN?
what is the AVN?
it is the only exit of electrical impulse from atria to ventricle
it slows down impulse by 100-200ms and allows atria to contract and ventricles to fill
why does the AVN slow down electrical impulse in the heart?
it allows the atria to contract and the ventricles to fill
what is the role of the His-purkinje system?
it transmits electrical conductions into ventricles
it is much faster than atrial conduction as it has large fibres
what is the effect of sympathetic stimulation on the heart?
increase heart rate - (positive chronotropic)
increase force of contraction - (positive ionotropic)
which neurotransmitter is responsible in sympathetic stimulation of the heart?
adrenaline and noradrenaline
which receptors are involved in sympathetic stimulation of the heart?
type 1 beta adrenoreceptors - these increase adenyl cyclase and increase cAMP
what is the effect of parasympathetic stimulation of the heart?
decrease heart rate (negative chronotropic)
decrease force of contraction (negative ionotropic)
which neurotransmitter is responsible in parasympathetic stimulation of the heart?
which receptors are involved in parasympathetic stimulation of the heart?
M2 receptors - these inhibit adenyl cyclase and decrease cAMP
what are the differences between myocardial and skeletal action potentials?
myocardial = activated by adjacent cells
skeletal = activated by nervous system
myocardial = Ca2+ channels open and maintain plateau phase
skeletal = rapid entry of Na+ and repolarised by K+, there is no plateau
myocyte = 15 times longer than skeletal
what do class I heart drugs affect?
what do class II heart drugs affect?
what do class III heart drugs affect?
K+ channel blocker - prolongs repolarisation
what do class IV heart drugs affect?
Ca2+ channel blocker
what is the total time for heart conduction?