Heart beat control

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asutoshsahu
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Heart beat control

Post by asutoshsahu » Tue Mar 07, 2006 8:25 am

Hey I have a doubt on the regulation of heart beat.

As I know heart is connected with sympathetic and parasympathetic nerve fibres.

Sympathetic nerves secrete adrenalin / norepinephrin to increase the heart beat and similarly vagus nerves secrete acetylcholin to decrease the heart beat when required.
Heart has S-A node which automatically generate impulse so that heart will beat at 70-80 times/minute.(as per sex)

My question is if Sympathetic nerves are cut will the heart beat at the same rate or will it fluctuate?

As per my opinion the heart will beat at the same rate as they are the regulators but not the stimulators. That means at the time of need the heart can't beat at a faster rate.


Please give comments.

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Post by sdekivit » Tue Mar 07, 2006 9:12 am

the heart will beat slower, but regularly --> the influence of acetylcholine will be greater. But as you pointed correctly, the SA-node fires on its own.

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Post by cardiorrhexis » Wed Mar 08, 2006 2:39 am

If the SA Node is not working, then the AV node kicks in (or node with the next highest chronotropic rate). basically...the node which beats fastest, wins.

No sympathetic nervous system??? I imagine there would not be a heart beat that's compatible with life.

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Post by asutoshsahu » Wed Mar 08, 2006 6:48 am

sdekivit wrote:the heart will beat slower, but regularly --> the influence of acetylcholine will be greater. But as you pointed correctly, the SA-node fires on its own.


That means when by the influence of acetylcholine heart beats slowly then adrenalin is required to bring it to the normal rate.

I am confused, I think after the secretion of acetylchoine is over then the heart beat can automatically come to its original leve.

Does adrenalin and acetylcholine counterbalence each other which results in the rhythmical beating of heart?

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Post by MrMistery » Wed Mar 08, 2006 7:43 pm

No. Adrenaline is released by the sympathetic nervous system only in cases of stress.
If you put a heart in a liquid that contains water, electrolites and glucose you will see it will continue to beat constantly for quite some time...
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Post by Dr.Stein » Thu Mar 09, 2006 5:23 am

Come on, make it straight, adrenaline is released by adrenal medullary cells 8)
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Post by asutoshsahu » Thu Mar 09, 2006 6:53 am

That means in normal conditions heart can beat rhythmically independent of the secretion of hormone either adrenalin or acetylcholine

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Post by Dr.Stein » Thu Mar 09, 2006 7:55 am

Yes, the initiation of the heartbeat is fired by the pacemaker (SA) which will rhythmically by AV. In normal condition, the impulse will be transmitted by neurotransmitter not a hormone.

The hormone, epinephrine/norepinephrine will be secreted in special condition like in physical or mentally stressness, which will act to excite the transmission of the impulse (excitator). That's why the heartbeat is increasing when we got stress.
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Post by asutoshsahu » Thu Mar 09, 2006 9:55 am

Dr.Stein wrote: In normal condition, the impulse will be transmitted by neurotransmitter not a hormone.

That's why the heartbeat is increasing when we got stress.


If we'll cut the sympathetic nerve from the heart or that nerve supply is made defective, then there will be no secretion of epinephrin under stress and no increase in heart beat.

so the heart will be at a constant rate i.e 72/min

Is it correct?

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Post by sdekivit » Thu Mar 09, 2006 1:13 pm

asutoshsahu wrote:
Dr.Stein wrote: In normal condition, the impulse will be transmitted by neurotransmitter not a hormone.

That's why the heartbeat is increasing when we got stress.


If we'll cut the sympathetic nerve from the heart or that nerve supply is made defective, then there will be no secretion of epinephrin under stress and no increase in heart beat.

so the heart will be at a constant rate i.e 72/min

Is it correct?


By blocking all autonomic input (thus symapthetic and parasympathetic), the heart beats 90-100 bpm. This indicates that acetylcholine is contantly produced at rest to maintain the heartrate at 70 bpm.

So when we have the sympathetic nerve cut the parasymathetic inpulses are more than the symapthetic impulses, so initially heart rate will decrease.

--> this results in a lower blood pressure and the feedback system in the medulla decreases parasymathetic impulses to maintain bloodpressure and thusi heartrate.

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