Origin and conduction of cardiac impulse Flashcards
(37 cards)
SAN location?
Upper right atrium close to where the SVC enters the right atrium.
Excitation is the heart occurs in what cells and where are they located?
Specialised Pacemaker cells in the SA node.
SA node do/don’t have a stable resting membrane potential?
They exhibit ____________ pacemaker potential that takes the membrane potential to a threshold to generate an action potential in the SA nodal cells.
Don’t, Spontaneous
Does permeability to K+ remain constant between action potentials in the pacemaker cells?
No
The pacemaker potential (i.e. The slow depolarisation of membrane potential to a threshold) is due to?
- Decrease in K+ efflux superimposed on a
- Slow Na+ influx (the funny current)
Depolarisation is caused by _________?
Activation of voltage gated Ca2+ channels resulting in Ca2+ influx.
Repolarisation is caused by ______?
Activation of K+ channels resulting in K+ efflux.
How does excitation spread from the SA to AV node?
Cell to cell through the atria. Also some internodal pathways between the SAN and AV node.
Gap junctions ______
Allow cell to cell current flow (conduction)
Desomsomes ______?
Stop separation during contraction by binding intermediate filaments, joining the cells together.
AV node is ____?
Small bundle of specialised cardiac cells.
Location of the AV node?
At the base of the right atrium, just above the junction of the atria and ventricles.
How does electrical excitation spread through the ventricular muscle walls?
Through cell-to-cell conduction (using gap junctions)
Action potential for Contractile Cardiac Muscle Cells.
Phase 0?
Depolarisation caused by fast Na+ influx. This rapidly reverses the membrane potential to +30mV
Action potential in contractile cardiac muscle cells.
Phase 1?
Closure of Na+ channels and transient K+ efflux.
Action potential in contractile cardiac muscle cells.
Phase 2?
Plateau phase - membrane potential maintained near the peak of action potential for few hundred milliseconds. It is a unique characteristic of contractile cardiac muscle cells. Plateau phase mainly due to influx of Ca2+ through voltage gated Ca2+ channels.
Action potential in contractile cardiac muscle cells.
Phase 3?
Repolarisation caused by inactivation of Ca2+ channels and activation of K+ channels, resulting in a K+ efflux.
Action potential of contractile cardiac muscle cells.
Phase 4?
Back to normal resting membrane potential.
HR < 60 BPM
Bradycardia
HR > 100BPM
Tachycardia
Sympathetic stimulation ______ heart rate and ______ AV nodal delay and ______ the force of contraction.
Increases, decreases, increases.
Cardiac sympathetic nerves supply?
SA node, AV node and myocardium.
For sympathetic stimulation, neurotransmitter is? Acting through?
Noradrenaline acting through beta1-adrenoceptors.
Positive Chronotrophic Effect?
- Slope of pacemaker potential increases.
- Pacemaker potential reaches threshold quicker.
- Frequency of Action Potentials increases.
