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 cells contract at the same time
Why does cardiac muscle have a long action potential?
Long refractory period ensures 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?
- High resting permeability for potassium
- Increase in permeability for sodium
- Increase in permeability for calcium (L - type channels), decrease in permeability for potassium
- 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
- increase in permeability for calcium (L-type receptors)
What causes the wave of electrical activity in the Pacemaker potential (or pre-potential)?
Pacemaker potential (pacemaker potential):
- Gradual decrease in permeability for potassium
- Early increase for permeability for sodium (Pf channels)
- Late increase in permeability for calcium (T-type channels)
When do sodium pF channels open?
repolarisation of previous action potential
How can Ca2+ channel blocking 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
How can cardiac glycoside drugs affect electrical activity of the heart?
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 cell depolarises
What is the affect of hypercalcemia on electrical activity of the heart?
Increased HR & force of contraction
more calcium comes in when channels open
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- conducting insulator between atria and ventricles
Action potential can only pass through atrioventricular node
Describe the stages shown
What is the arterioventricular node?
delay box - 0.05 m/s
What is the function of the bundle of his?
ensures whole 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?
Evokes very small extracellular electrical potential
