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Comment by krackers | Hacker News Reader

But presumably the nerves between the brain and heart exist for a reason. What functionality do you lose by not reattaching them? Do things like "heart beating faster when nervous" depend on this nerve signaling, or is it done via other chemical signaling.

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Yes, nerves from the brain to the heart can influence heart beat (and other features like heart conduction and blood flow to the heart itself) in response to stress and exercise. Heart transplant recipients lose these features. They make poor marathon runners :)

Heart rate muscle tissue is largely influenced by hormones. The sympathetic system releases noradrenaline to speed up the heart rate, while the parasympathetic system releases acetylcholine to slow it down. But the release of these hormones is controlled by nerves, which are largely severed. So you typically end up with a less "dynamic" heart rate -- resting rate higher and responsiveness to stimuli reduced. These nerve connections can regenerate to some degree but it's individual and rarely close to what they were before.

Reading up on this there is some chemical signaling from the blood, but the brain is not controlling the rate of the new heart

That is actually wild and I wonder about the practical consequences as well.

So you get into a stressful situation or get a flee or flight response, and your heart is not affected by it, or at least the heart rate, but your cardiovascular system may be needed because in that case the rest of your body is, and presumably you may need much more blood to be pumped out to your organs among other things.

It is a cool food for thought.

He's asking about what the nerves do in a normal person

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