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Parasympathetic innervation of the heart is partially controlled by the vagus nerve and is shared by the thoracic ganglia. Vagal and spinal ganglionic nerves mediate the lowering of the heart rate. The right vagus branch innervates the sinoatrial node. In healthy people, parasympathetic tone from these sources is well-matched to sympathetic tone.
The only cardiac nerves which do not enter into the formation of the deep part of the cardiac plexus are the superior cardiac nerve of the left sympathetic trunk, and the lower of the two superior cervical cardiac branches from the left vagus nerve, which pass to the superficial part of the plexus.
The vagus nerve plays a crucial role in heart rate regulation by modulating the response of sinoatrial node; vagal tone can be quantified by investigating heart rate modulation induced by vagal tone changes. As a general consideration, increased vagal tone (and thus vagal action) is associated with a diminished and more variable heart rate.
In most cases, vagal tone is not measured directly. Instead the processes affected by the vagus nerve – specifically heart rate and heart rate variability – are measured and used as a surrogate for vagal tone. Increased vagal tone (and thus vagal action) is generally associated with a lower heart rate and increased heart rate variability.
The cardiac nerves are autonomic nerves which supply the heart. [1] They include: Superior cardiac nerve [1] (nervus cardiacus cervicalis superior) Middle cardiac nerve [1] (nervus cardiacus cervicalis medius) Inferior cardiac nerve [1] (nervus cardiacus inferior)
Sympathetic nerves also influence the force of heart contraction. [34] Signals that travel along these nerves arise from two paired cardiovascular centres in the medulla oblongata. The vagus nerve of the parasympathetic nervous system acts to decrease the heart rate, and nerves from the sympathetic trunk act to increase the heart rate. [8]
The two nerves acting on the heart are the vagus nerve, which slows heart rate down by emitting acetylcholine, and the accelerans nerve which speeds it up by emitting noradrenaline. [ 1 ] [ 2 ] This results in an increased blood flow , preparing the body for a sudden increase in activity.
The cardiovascular centre affects changes to the heart rate by sending a nerve impulse to the cardiac pacemaker via two sets of nerves: sympathetic fibres, part of the autonomic nervous system, to make heart rate faster. the vagus nerve, part of the parasympathetic branch of the autonomic nervous system, to lower heart rate.