Electrical Activities of the Heart Flashcards
Are cardiac muscles able to exhibit tetanus (Y/N)
No
Why are cardiac muscles not able to exhibit tetanus
Long refractory period and a long action potential which allows a period of relaxation and contraction
What do cardiac muscles form
A functional syncytium
What is a synctium
Cells are electrically connected via gap junctions
Physically connected by desmosomes to form intercalated discs
What is used to regulate contraction
Ca2+
Why is Ca2+ able to regulate contraction
Does not saturate troponin
Non pacemaker resting membrane potential
High resting K+
Non pacemaker initial depolarisation
Increase in Na+
Non pacemaker plateau
Increase in Ca2+
Decrease in K+
Non pacemaker repolarisation
Decrease in Ca2+ and increase in K+
Pacemaker action potential
Increase in Ca2+ (L-type)
Pacemaker pre-potential (3)
Gradual decrease in Pk+
- Early increase in PNa+= PF
- Late increase in PCa2+
What does the pacemaker function explain
autorythmicity
Modulators for electrical activity
Sympathetic & parasympathetic systems Drugs Temperature Calcium Potassium
How does drugs modulate electrical activity
Ca2+ blockers- reduces force of contraction
Cardiac glycocides- increase force of contraction
How does temperature modulate electrical activity
Increases 10 beats/min/C
How does potassium modulate electrical activity
Hyperkalaemia: fibrillation and heart block
How does calcium modulate electrical activity
Hypercalcaemia- High Ca2+ increased HR and force of contraction
Hypocalcaemia- low Ca2+ decreased HR and force of contraction
What does the conducting system consist of
Sinoatrial node Annulus fibrosus Atrioventricular node Bundle of his Purkinje fibres
Function of Sinoatrial node
Pacemaker
Function of Annulus fibrosus
Non-conducting
Function of Atrioventricular node
Delay box (0.05 m/sec)
Function of Purkinje fibres
rapid conduction system (5m/sec)
