Editing Heart (section)

===Nerve supply===
[[File:2032 Automatic Innervation.jpg|thumb|Autonomic innervation of the heart]]
The heart receives nerve signals from the [[vagus nerve]] and from nerves arising from the [[sympathetic trunk]]. These nerves act to influence, but not control, the heart rate. [[Sympathetic nervous system|Sympathetic nerves]] also influence the force of heart contraction.{{sfn|Davidson's|2010|p=526}} Signals that travel along these nerves arise from two paired [[cardiovascular centre]]s 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.<ref name="CNX2014"/> These nerves form a network of nerves that lies over the heart called the [[cardiac plexus]].<ref name="CNX2014"/>{{sfn|Gray's Anatomy|2008|p=982}}

The vagus nerve is a long, wandering nerve that emerges from the [[brainstem]] and provides parasympathetic stimulation to a large number of organs in the thorax and abdomen, including the heart.{{sfn|Gray's Anatomy|2008|p=945}} The nerves from the sympathetic trunk emerge through the T1–T4 [[thoracic ganglia]] and travel to both the sinoatrial and atrioventricular nodes, as well as to the atria and ventricles. The ventricles are more richly innervated by sympathetic fibers than parasympathetic fibers. Sympathetic stimulation causes the release of the neurotransmitter [[norepinephrine]] (also known as [[noradrenaline]]) at the [[neuromuscular junction]] of the cardiac nerves{{Citation needed|date=October 2024}}. This shortens the repolarisation period, thus speeding the rate of depolarisation and contraction, which results in an increased heart rate. It opens chemical or ligand-gated sodium and calcium ion channels, allowing an influx of [[cation|positively charged ions]].<ref name="CNX2014"/> Norepinephrine binds to the [[beta-1 adrenergic receptor|beta–1 receptor]].<ref name="CNX2014"/>