Electrical Properties of The Heart Flashcards
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.
Why does cardia muscle have a long action potential?
Long refractory period ensures there is no tetanic contraction. Means Ca2+ entry from outside the cell can regulate contraction.
How does Ca2+ entry from outside the cell regulate contraction?
impaired thermogenesis and energy expenditure.
What are the cells called with an unstable resting membrane potential?
Pacemakers
What causes the wave of electrical activity in the non-pacemaker action potential?
Resting membrane potential?
Initial depolarisation?
Plateau?
Repolarisation?
Resting membrane potential - High resting permeability for potassium
Initial depolarisation - Increase in permeability for sodium
Plateau - Increase in permeability for calcium (L - type channels) and decrease in permeability for potassium.
Repolarisation - Decrease in permeability for calcium and increase in permeability for potassium
What causes the wave of electrical activity in the pacemaker action potential?
Action potential?
Pacemaker potential (or pre-potential)?
Action potential - increase in permeability for calcium (L-type receptors)
Pacemaker potential (pacemaker potential):
- Gradual decrease in permeability for potassium
- Early increase for permeability for sodium (Pf channels)
- Late increase in calcium in (T-type channels)
When do sodium pF channels open?
During repolarisation of the previous action potential
How can drugs affect electrical activity of the heart?
–Ca2+-channel blockers – decrease force of contraction – target L type calcium channels – fewer cross bridges formed – smaller strength of contraction
–Cardiac glycocides – increase force of contraction – More calcium comes in - More cross bridges formed– stronger strength of contraction
How does temperature affect the electrical activity of the heart?
–increases ~10 beats/min/ºC
How does hyperkalemia 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.
What is the affect of hypercalcemia on electrical activity of the heart?
–Increased HR & force of contraction – more calcium comes in when the channels open – increase force of contraction.
What is the effect of hypocalcaemia on electrical activity of the heart?
–Decreased HR & force of contraction
What is the function of the sinoatrial node?
Pacemaker - 0.5 metres per second
Describe the annulus fibrosis
Non- conduciting insulator between the atria and the ventricles. Action potential can only pass through the atroventricular node.
Describe the stages shown
What is the arterioventricular node?
A delay box - 0.05 m/s
What is the function of the bundle of his?
Bundle of his ensures all the ventricle contracts at the same time
What is the name given to the fibres responsible for innervating the ventricular cardiac muscle?
•Purkinje fibres
–rapid conduction system
–~ 5 m/sec
What is the extracellular effect of an action potential in a single myocyte?
eEokes 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 each wave correspond to?
P wave corresponds to atrial depolarisation
QRS complex corresponds to ventricular depolarisation
T wave corresponds to ventricular repolarisation
What are blocks the result of?
Issues in conduction
What are flutters and fibrilations 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
