How does the heart work?

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angelo
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How does the heart work?

Post by angelo » Sat Jan 21, 2006 12:31 am

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?)

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Post by pratistha » Sat Jan 21, 2006 3:13 am

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

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Post by angelo » Sat Jan 21, 2006 10:03 pm

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?

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Post by sdekivit » Sun Jan 22, 2006 8:36 am

angelo wrote: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.

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jnkdna
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Post by jnkdna » Sun Jan 22, 2006 11:55 am

hey is auricle and atrium the same?
just wanted to be sure :-D
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opuntia
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Post by opuntia » Sun Jan 22, 2006 12:06 pm

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.
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Post by Dr.Stein » Sun Jan 22, 2006 12:27 pm

The heartbeat is initiated by the pacemaker :)
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opuntia
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Post by opuntia » Sun Jan 22, 2006 12:39 pm

In other words it's the Sinoatrial Node that originates the excitation...isn't it?
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Post by angelo » Sun Jan 22, 2006 2:45 pm

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?

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Post by jnkdna » Sun Jan 22, 2006 9:37 pm

opuntia wrote: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! 8)
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Post by sdekivit » Mon Jan 23, 2006 1:22 pm

angelo wrote:
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.

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Post by Dr.Stein » Tue Jan 24, 2006 7:04 am

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