Heart transplant. vagus nerve not retransplanted. How is the heart rate kept in check?

Question

Understand that the vagus nerve is not retransplanted after transplant and so Atropine would be useless in symptomatic bradycardia. But what stops the heart from beating faster and faster if there is no parasympathetic innervation to slow it down? Is this something to do with its intrinsic regulation where it does not need signals from the brain to make it beat? Is this the same as "heart brain"? Isn't the heart exposed to unopposed stimulation by sympathetic nerves if the vagus nerve is missing?

Answer 1

I think this will help you out, I agree with your questionable reasoning:

The medulla, located in the brainstem above the spinal cord, is the primary site in the brain for regulating sympathetic and parasympathetic (vagal) outflow to the heart and blood vessels. The nucleus tractus solitarius (NTS) of the medulla receives sensory input from different systemic and central receptors (e.g., baroreceptors and chemoreceptors). The medulla also receives information from other brain regions (e.g., hypothalamus). The hypothalamus and higher centers modify the activity of the medullary centers and are particularly important in stimulating cardiovascular responses to emotion and stress (e.g., exercise, thermal stress). Autonomic outflow from the medulla is divided principally into sympathetic and parasympathetic (vagal) branches. Efferent fibers of these autonomic nerves travel to the heart and blood vessels where they modulate the activity of these target organs.

The heart is innervated by vagal and sympathetic fibers. The right vagus nerve primarily innervates the SA node, whereas the left vagus innervates the AV node; however, there can be significant overlap in the anatomical distribution. Atrial muscle is also innervated by vagal efferents, whereas the ventricular myocardium is only sparsely innervated by vagal efferents. Sympathetic efferent nerves are present throughout the atria (especially in the SA node) and ventricles, including the conduction system of the heart.

Cardiac function is altered by neural activation. Sympathetic stimulation increases heart rate (positive chronotropy), inotropy and conduction velocity (positive dromotropy), whereas parasympathetic stimulation of the heart has opposite effects. Sympathetic and parasympathetic effects on heart function are mediated by beta-adrenoceptors and muscarinic receptors, respectively.

Sympathetic adrenergic nerves travel along arteries and nerves and are found in the adventitia (outer wall of a blood vessel). Varicosities, which are small enlargements along the nerve fibers, are the site of neurotransmitter release. Capillaries receive no innervation. Activation of vascular sympathetic nerves causes vasoconstriction of arteries and veins mediated by alpha-adrenoceptors.

Parasympathetic fibers are found associated with blood vessels in certain organs such as salivary glands, gastrointestinal glands, and in genital erectile tissue. The release of acetylcholine (ACh) from these parasympathetic nerves has a direct vasodilatory action (coupled to nitric oxide formation and guanylyl cyclase activation). ACh release can stimulate the release of kallikrein from glandular tissue that acts upon kininogen to form kinins (e.g., bradykinin). Kinins cause increased capillary permeability and venous constriction, along with arterial vasodilation in specific organs.

Answer 2

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Answer 4

Normally, the heart communicates with the brain via nerve fibers running through the vagus nerve and the spinal column. In a heart transplant, these nerve connections do not reconnect for an extended period of time, if at all; however, the transplanted heart is able to function in its new host through the capacity of its intact, intrinsic nervous system.

The heart's nervous system contains around 40,000 neurons, called sensory neurites, which detect circulating hormones and neurochemicals and sense heart rate and pressure information. Hormonal, chemical, rate and pressure information is translated into neurological impulses by the heart's nervous system and sent from the heart to the brain through several afferent (flowing to the brain) pathways. It is also through these nerve pathways that pain signals and other feeling sensations are sent to the brain. These afferent nerve pathways enter the brain in an area called the medulla, located in the brain stem. The signals have a regulatory role over many of the autonomic nervous system signals that flow out of the brain to the heart, blood vessels and other glands and organs.

Answer 5

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RE:
Heart transplant. vagus nerve not retransplanted. How is the heart rate kept in check?
Understand that the vagus nerve is not retransplanted after transplant and so Atropine would be useless in symptomatic bradycardia. But what stops the heart from beating faster and faster if there is no parasympathetic innervation to slow it down? Is this something to do with its intrinsic...

Answer 6

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Answer 7

Funny! 10!

Answer 8

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Answer 9

So amazed that I found this topic already answered! Its like you read my mind!

Answer 10

Can you give more details?