ElphinStar

I think the Ca2+ channels are slower than Na+?

The cardiac AP would have stages; Na+ in (rapidly) where it depolarises, K+ and Cl- out, Ca2+ in and K+ out (delayed), then K+ out (rapid) where it repolarises. SA node AP; Ca2+ in depolarising, K+ out repolarising, Ca2+ in and Na2+ in. So Na+ entry causes depolarisation of cardiac muscle, whereas Ca2+ entry causes it in SA node?

Do you mean that cardiac muscle can depolarize spontaneously, whereas smooth muscle can't?

Another physiology question I am not sure about... True or False: 'In smooth muscle, the amount of actin and myosin is the same as in skeletal muscle but smooth muscle lacks troponin.' I know smooth muscle has no troponin, but not sure whether is has more/less actin and myosin than skeletal muscle? At a guess, I would say skeletal is likely to have more actin and myosin, but not sure. Help will be appreciated

The 'stable RMP' part - I thought ventricular muscle had unstable contraction? I THINK the other part about Ca2+ and K+ is true.. but generally a little lost.

A question from my Body Systems Physiology heart practical... True or False: 'Action potentials in contractile ventricular muscle cells exhibit a different electronic profile, relative to cells of the SA node, due to a stable resting membrane potential, and the opening of voltage gated Ca2+ gates and delayed opening of K+ gates, during the AP.' Any help would be greatly appreciated!