Generating Cardiac Rhythm

cgeorge's version from 2016-02-27 10:29


Question Answer
How do cardiac AP'S differ to each other and to other AP'S ?1) Cardiac AP =200ms. Skeletal AP = 1-2ms 2)Ions involved 3) Shape
SAN potential begins at ...mV and reaches ....mV which is threshold for these cells-60mV and reaches -40mv
Key feature of the SAN ccellsThey have no resting membrane potential
Describe the channels involved in the generation of SAN depolarisation1) Na channels are open, K channels closed 2)Transient Ca channels open 3)L type Ca channels open giving rise to AP 4)Opening of K channels, closing of L type channels,allows repol
Intrinsic rate of SAN is ... action potentials/min but resting heart rate is x beats/min100 action potentials/min, 60-70 beats/min
If you stimulate vagus nerve, releases .... to .... receptors on SANAch, Muscarinic
Effects of stimulating the vagus nerve with regards to K channels and pacemaker potential1) Hyperpolarises cell (opens k channels ) 2)Reduces slope of pacemaker potential so takes longer to reach threshold
If you stimulate sympathetic nerves, releases ... which binds to ... receptors on SANNeuradrenaline, binds to beta-adrenergic receptors (B1)on SAN
Effect of stimulating the sympathetic nerve with regards to Na/Ca channels and the pacemaker potential1) Increases conductance of Na/Ca 2) Increases slope of the pacemaker potential
Depolarisation of atrium is complete within ....seconds of SAN firigin0.09s
Pacemaker rate of AVN is ... beats/min40
Heart rate is defined asThe number of ventricular contractions per min
Do ventricular myocytes has a stable resting membrane potential? If so what is itYes, -90mv (nearly equal to Ek), so v permeable to K
Phase 0 of ventricular depolarisation?Inward Na movement via fast voltage gated channels
Phase 1 of ventricular depolNa channel inactivation
Phase 2 of ventricular depolAP plateu by Ca influx via L type channels
Phase 3 of ventricular depolMembrane repol is by opening of K channels. Ca channels inactivate
Phase 4 of ventricular depolNa/K pumps restore conc grads and return Ca to intracellular stores
Absoloute refractory period of ventricular myocytes is what?200ms
Relative refractory period of ventricular myocytes is ?50ms
Absoloute refractory period of skeletal muscle?1ms
Why is summation not possible in the heart?Due to the long refractory period. If summation was possible u would have sustained contraction which is bad as ventricles wouldnt fill

Recent badges