conducting system Flashcards
cardiac conduction pathways: explain cardiac conduction pathways
location of SAN
lies just below epicardial surface at boundary between right atrium and superior vena cavae
what marks start of conduction pathway
specialised cells comprising SAN spontaneously depolarising membrane to generate own rhythm (autorhythmicity)
what does the SAN consist of
specialised cluster of autorhythmic cells
when the SAN depolarises where does the wave of excitation spread to and what do these stimulate
internodal fibres (rapid contraction tracts) which stimulate atrial myocardium to contract in atrial bundles
where does the wave of excitation then spread to
AVN
what is the function of the AVN
specialised cells to delay wave of excitation and insulate from superior ventricular myocardium, allowing blood to be propelled from atria into ventricle
what is the function of the bundle of His
rapid conduction cells (slightly insulated) to transport wave of excitation from atria down apex to base of ventricles
what is the function of ventricular fibres (ventricular Purkinje system)
bundle branches which propagate impulse across ventricular myocardium from apex, pushing blood into artery (afterload)
what causes impulse propagation
combination of passive spread of current (local currents) and reach of threshold potential
outcome of wave of depolarisation exceeding threshold
cause an ation potential, but keeps spreading and diminishing
what junction is used to allow impulse propagation and where
gap junctions at intercalated discs
how do gap junctions allow impulse propagation
reduce resistance between cells to allow current to leak
what do connexons (consist of connexins) in gap junctions do
join to form a tube between cells
