Study note
MedicineCardiology

Autonomic control of the heart

THE CONTEXT
Sympathetic and parasympathetic nerves regulate cardiac activity, with changes during rest, stress and disease.

Sympathetic innervation and receptor effects

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Adrenergic nerves from the cervical sympathetic chain supply atrial and ventricular muscle fibres and the electrical conducting system.
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Activation of cardiac β1-adrenoceptors produces positive inotropic and chronotropic effects.
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Activation of β2-adrenoceptors in vascular smooth muscle causes vasodilatation.

Parasympathetic control and physiological responses

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Parasympathetic preganglionic fibres and sensory fibres reach the heart through the vagus nerves.
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Cholinergic nerves supply the atrioventricular and sinoatrial nodes through muscarinic M2 receptors.
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At rest, vagal inhibitory activity predominates and heart rate is slow.
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Exercise, emotional stress and fever increase heart rate through decreased parasympathetic activity and increased sympathetic stimulation.

Changes in disease

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The sympathetic system may be upregulated in heart failure.
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In diabetes mellitus, autonomic neuropathy may damage cardiac nerves, resulting in little variation in heart rate.
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