Electrical Activity of the Heart Flashcards
What acts as a large calcium store?
Sarcoplasmic reticulum
What does calcium bind to?
Troponin
What does cardiac muscle act as?
A massive functional syncytium
How are cells linked together?
- Desmosomes
- Intercalated discs
- Gap junctions
What kind of connection to desmosomes provide?
Physical connection
What kind of connection do gap junctions provide?
Electrical connection
How is the strength of contraction regulated?
Control of the amount of calcium entering the cell
What kind of refractory period do cardiac muscle cells experience?
Very long
Why do you not want tetanic muscle contraction in your heart?
It would mean that your heart would beat once and there would not be another bet causing asystole
What form the intercalated discs?
Gap junctions and desmosomes
How does the action potential in cardiac muscle compare to that in skeletal?
It is much longer
What does the long refractory period of cardiac muscle mean?
It cannot exhibit tetanic contraction
Why can regulation of Ca release be used to vary strength of contraction?
Ca release does not saturate troponin
What do cells which have unstable resting membrane potentials act as?
Pacemaker cells
What is responsible for the resting membrane potential of non-pacemaker action potentials?
High resting PK
What is responsible for the initial depolarisation in non-pacemaker action potentials?
Increase in PNa
What is responsible for the plateau in non-pacemaker action potentials?
Increase in PCa (L-type) and decrease in PK
What is responsible for the repolarisation in non-pacemaker action potentials?
Decrease in PCa and increase in PK
What is responsible for the action potential in pacemaker action potentials?
Increase in PCa (L-type)
What is the pacemaker potential?
Pre-potential
What is the pacemaker potential due to?
- Gradual decrease in PK
- Early increase in PNa
- Late increase in PCa (T-type)
What does pacemaker explain?
Auto rhythmicity and basis of understanding modulation of the activity of the heart
What are modulators of electrical activity? (7)
- Sympathetic and parasympathetic systems
- Drugs
- Temperature
- Hyperkalaemia
- Hypokalaemia
- Hypercalcaemia
- Hypocalcaemia
How do drugs modulate electrical activity?
- Ca channel blockers decrease force of contraction
- Cardiac glycosides increase force of contraction
How does temperature modulate electrical activity?
Increases HR by 10 beats/min/degree
How does hyperkalaemia modulate electrical activity?
Fibrillation and heart block
How does hypokalaemia modulate electrical activity?
Fibrillation ad heart block (anomalous)
How does hypercalcemia modulate heart activity?
Increased HR and force of contraction
How does hypocalcaemia modulate electrical activity?
Decreased HR and force of contraction
What is the only area of the heart which is non-conducting?
Annulus fibrosis
Where are the fastest pacemaker cells found?
Sinoatrial node
How does the sinoatrial node contribute to the special conducting system?
- Pacemaker
- ~0.5m/sec
How does the atrioventricular node contribute to the special conducting system?
- Delay box
- ~0.05m/sec
How do the Purkinje fibres contribute to the special conducting system?
- Rapid conduction system
- ~5m/sec
What does an action potential in a single myocyte evoke?
A very small extracellular (cf transmembrane) electrical potential
How are large extracellular electrical waves evoked?
By lots of small extracellular electrical potentials evoked by many cells depolarising and repolarising at the same time can summate
Where can large extracellular electrical waves by recorded?
At the periphery as and ECG
What do P waves correspond to?
Atrial depolarisation
What do QRS complexes correspond to?
Ventricular depolarisation
What do T waves correspond to?
Ventricular repolarisation
What are the components of the special conducting system?
- Sinoatrial node
- Annulus fibrosus
- Atrioventricular node
- Bundle of His
- Purkinje fibres
