sienna2266
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Hi guys, do parasympathetic neurones secrete acetycholine and smpathetic neurones secrete noradrenaline? How does that work?
Just want to double check bc other sources dont really mention the acetylcholine and noradrenaline
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sienna2266
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Jpw1097
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(Original post by sienna2266)
Hi guys, do parasympathetic neurones secrete acetycholine and smpathetic neurones secrete noradrenaline? How does that work?
Just want to double check bc other sources dont really mention the acetylcholine and noradrenaline
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Yes that's right; parasympathetic fibres release acetylcholine whereas sympathetic fibres release noradrenaline, though there are some exceptions to these rules. I'm surprised that you say other sources don't mention this, as it's a well-known and well-documented fact. Just searching 'noradrenaline sympathetic acetylcholine parasympathetic' in Google should point you to some sources. And what do you mean by 'how does that work'? How does what work exactly?
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macpatgh-Sheldon
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" And what do you mean by 'how does that work'? How does what work exactly?"

Quote from above.

Let me try and help with this:-

Continuing from the description in your excerpts, when noradrenaline is released from sympathetic fibres, it acts on adrenergic beta1 receptors on the SA node neuromyocytes; beta receptors are GPCRs (G Protein Couple Receptors) that link to heterotrimeric [Greek hetero = varying; trimer = has three parts] G proteins.which in turn elevates cAMP (cyclic AMP) levels. This has the effect of increasing the slope of the "resting potential" of the myocytes [which already spontaneously depolarizes due to a sodium leak [unlike in other neurones] which explains the intrinsity {the ability to depolarize spontaneously} of cardiac myocytes] so the potential reaches the threshold level earlier, and therefore beats occur more quickly after each previous one = tachycardia.

The opposite effect (=bradycardia) is brought about by the action of acetylcholine on [parasympathetic] muscarinic receptors (mainly M2 in the heart). The mechanism of this is quite complex and not needed for A level biology, but if you are a medical student and interested to know, please tag me, and I will try to explain it (I might struggle myself!).

M (specialist biology tutor and previous medic)
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