Electrical activity of the heart Flashcards
What does cardiac muscle form ?
A functional syncytium
What is the calcium store in muscle ?
Sarcoplasmic reticulum
What forms the electrical connection in the heart ?
Gap junctions
What are the intercalating disks formed by ?
Desmosome followed by gap junction. Desmosome ensures that cells contract at the same time
What are the cells called with an unstable resting membrane potential ?
Pacemakers
What causes the resting membrane potential in non-pacemaker APs ?
High resting permeability for potassium
What causes the initial depolarisation in non-pacemaker APs ?
Increase in permeability for sodium
What causes the plateau in non-pacemaker APs ?
Increase in permeability for calcium (L - type channels) and decrease in permeability for potassium
What causes the repolarisation in non-pacemaker APs ?
Decrease in permeability for calcium and increase in permeability for potassium
What causes the AP in pacemaker APs ?
Increase in permeability for calcium (L-type receptors)
What causes the pacemaker potential (pre-potential) in pacemaker APs ?
Gradual decrease in permeability for potassium
Early increase for permeability for sodium (Pf channels)
Late increase in calcium in (T-type channels)
What does the pacemaker explain ?
autorhythmicity
What is the function of the SAN ?
Pacemaker - 0.5 metres per second
What is the annulus fibrosus ?
Non- conducting insulator between the atria and the ventricles, Action potential can only pass through the atrioventricular node
What is the atrioventricular node ?
A delay box - 0.05 m/s
What is the function of bundle of his ?
Bundle of his ensures all the ventricle contracts at the same time
What is the function of purkinjie fibres ?
Rapid conducting system, innervate ventricles - ~5m/sec
What is the extracellular effect of an action potential in a single myocyte ?
Evokes a very small extracellular electrical potential
How are large extra-cellular electrical waves created ?
Lots of small extracellular electrical potentials evoked by many cells depolarising and repolarising at the same time can summate to create large extracellular electrical waves
What does the P wave correspond to ?
Atrial depolarisation
What does the QRS complex correspond to ?
Ventricular depolarisation
What does the T wave correspond to ?
Ventricular repolarisation
What are blocks the result of ?
Issues in conducting
What are flutters and fibrillations due to ?
Errors in rhythm
What is characteristic of atrial fibrillation on an ECG ?
No distinguishable P wave
How does a defibrillator work ?
Defibrillator puts all the cells into their refractory state – they are now ready to receive the next action potential
How does hyperkalaemia affect the electrical activity of the heart ?
Fibrillation and heart block - reduces concentration gradient for potassium – cell starts to depolarise, spontaneous firing of action potentials
What is the affect of hypokalaemia on electrical activity of the heart ?
fibrillation & heart block (anomalous) – cells start to hyperpolarise – loads of channels open and the cell depolarises
