electrical function of the heart

Question 1

how is an action potential propagated

Answer 1

from cell to cell via branching of the cells and cell to cell communication through intercalated discs

Question 2

how are action potentials generated

Answer 2

specialised pacemaker cells possess automaticity which means they spontaneously depolarise and generate action potentials.

Question 3

what is the pathway electrical excitation follows in the normal mammalian heart

Answer 3

AP generated in the sinoatrial node
propagated across atria moving from cell to cell to cause near simultaneous atrial contraction
electrical impulse coalesces at the AV node - conduction slows down due to av node being narrow
ensures there is a gap between atrial and ventricular contraction - atrial systole acts as booster pump to optimise ventricular filling.
impulse then passes from AV node into the AV bundle (Bundle of His) - transverses the annulus fibrosis (slowed conduction same as AVN)
impulse then takes 2 paths through interventricular septum - left and right bundle branches.
small offshoot of RBB crosses lumen of right ventricle via septomarginal band to right ventricular free wall.
LBB subdivides into anterior and posterior fascicles to supply thick wall of left ventricle.
left and right BB further divide into the branching Purkinje fibres - fast conduction to ensure ventricles contract as a unit.
contraction starts at apex and finishes at top of ventricle.

Question 4

how does an ectopic pacemaker function

Answer 4

develop automaticity after injury (works by itself)

Question 5

what is the movement of cations during a cardiac action potential

Question 6

how can electrolyte abnormalities affect the movement of cations during a cardiac action potential

Question 7

how is the pacemaker potential generated