How does the heart work?

[angelo]

How does the heart work? I mean, is every beat mediated by an electrical signal from the brain? If so (or not) , where does the signal originate? What creates it, and what keeps it from stopping? (How could it be so robust?)

[pratistha]

our heart is called myogenic heart because wave of contraction starts from heart itself.there is sinu auricular node at the top of right auricle which is a small island of tissues.it starts the wave.it is also called as pace maker.the wave is picked by atrioventricular node present in between right and left auricle. it is divided in 2 branches witheach having sub branches called purkinje fibres.these help heart do its work

[angelo]

Ok (thanks). So I suppose that the chemical properties of cells in the SA node and their enviroment are generating action potentials in the cells. But what makes them fire so slowly, and in such a rythmic manner?

[sdekivit]

Ok (thanks). So I suppose that the chemical properties of cells in the SA node and their enviroment are generating action potentials in the cells. But what makes them fire so slowly, and in such a rythmic manner?

yes, they have so called If-Ca(2+)-channels which depolarize when e membrane potential of -60 mV is reached, resulting in contraction cycles.

[jnkdna]

hey is auricle and atrium the same?
just wanted to be sure

[opuntia]

No they are not same, auricle is a small conical pouch projecting from the upper anterior part of each atrium of the heart and you know what atrium is.

[Dr.Stein]

The heartbeat is initiated by the pacemaker

[opuntia]

In other words it's the Sinoatrial Node that originates the excitation...isn't it?

[angelo]

yes, they have so called If-Ca(2+)-channels which depolarize when e membrane potential of -60 mV is reached, resulting in contraction cycles.

Ok. So at the time of action potential, the Ca(2+) channels are letting calcium flow into the cell. The refractory period is relatively long. Why is it so long?

[jnkdna]

In other words it's the Sinoatrial Node that originates the excitation...isn't it?

yeah i think it is! i just studied it yesterday!

[sdekivit]

yes, they have so called If-Ca(2+)-channels which depolarize when e membrane potential of -60 mV is reached, resulting in contraction cycles.

Ok. So at the time of action potential, the Ca(2+) channels are letting calcium flow into the cell. The refractory period is relatively long. Why is it so long?

the pacemaker actionpotential is way shorter than the cardiac actionpotential (plateauphase and initiation by Na-influx). The pacemaker actionpotential doesn't rely on Na-ions.

[Dr.Stein]

I like the term "all or none" in this topic