Electrical Activity of the Heart Flashcards
Which type of muscle, cardiac or skeletal, can exhibit tetanus?
Skeletal muscle
Which type of muscle, cardiac or skeletal, has the longest refractory period?
Cardiac
What is a syncytium?
A large cell formed by lots of cells with multiple nuclei
How does cardiac muscle form a functional syncytium?
The cells are electrically connected by gap junctions and physically connected by desmosomes
What is meant by an intercalated disc?
The alternating gap junctions and desmosomes
What ion can regulate contraction?
Calcium
How does calcium entry from outside of the cell regulate contraction
Calcium release does not fully saturate the troponin, so regulation of calcium release can vary the strength of contraction
What causes the initial depolarisation in a non-pacemaker cell?
An increase in PNa+
What causes the plateau in potential in a non-pacemaker cell?
An increase in PCa2+(L-type) and a decrease in PK+
What causes the repolarisation of a non-pacemaker cell?
A decrease in PCa2+ and an increase in PK+
What causes the action potential in pacemaker cells?
An increase in PCa2+ (L-type)
What causes the pacemaker potential in pacemaker cells?
Gradual increase in PK+, an early increase in Pf and a late increase in PCa2+ (T-type)
What is meant by Pf
Sodium channels that were opened by the previous repolarisation
How do Calcium channel blockers effect electrical activity?
They decrease the force of contraction
How d cardiac glycosides effect electrical activity?
They increase the force of contraction
How does temperature effect electrical activity?
Heart rate increases approx. 10beats/min/ºC
How do hyperkalemia and hypokalemia effect electrical activity?
Both cause fibrillation and heart block
How does hypercalcemia effect electrical activity?
It increases the heart rate and the force of contraction
How does hypocalcemia effect electrical activity?
It decreases heart rate and the force of contraction
What is the function of the sinoatrial node?
It acts as the main pacemaker
How fast does the sinoatrial node conduct?
Approx. 0.5m/s
Does the annulus fibrosus conduct?
No
What is the function of the atrioventricular node?
It acts as a delay box
How fast does the atrioventricular node conduct?
0.05m/s
What is the function of the purkinje fibres?
They are a rapid conduction system
How fast do the purkinje fibres conduct?
5m/s
