Cardiac Myocytes

Question 1

how does the SAN set the rhythm of the heart?

Answer 1

through spontaneous and regular depolarisations that induce APs causing contraction

Question 2

how can the SAN be influenced?

Answer 2

by transmission from medulla oblongata

allows heart to adapt to different activity levels

Question 3

what are the structural differences of SAN myocytes compared to atrial and ventricular cells?

Answer 3

thinner: more easily and regularly depol by funny current
fewer contractile units
incapable of large, forceful contraction

Question 4

what are the contributions to pacemaker potential?

Answer 4

slow decrease in K+ permeability and slow increase in Ca2+ and Na+ permeability: gradual depol until v.g. Ca2+ channels open, causing rapid + prolonged depol + contraction

leads to depol, initiaties AP which propagates through intercalated discs + gap junctions

Question 5

why can the AP from the SAN spread throughout the whole heart?

Answer 5

whole heart is electrically coupled

Question 6

why are larger cells less likely to be spontaneously depolarised?

Answer 6

a larger influx of +ve charge is needed for depol

Question 7

why do we have funny currents in cells which are not the SAN?

Answer 7

in the case of SAN dysfunction or heart attack, patients have bradycardia, heart does not stop beating, other regions of atria take on pacemaker role

ensures heart can continue pumping blood even if SAN is damaged/defective

Question 8

how does ACh affect the SAN contraction rate?

Answer 8

increases cycle length and decreases rate of depolarisations i.r slows hr