Carotid Sinus Nerve

nervus sinus carotici

The carotid sinus nerve (Hering's nerve) is a branch of the glossopharyngeal nerve (CN IX) that descends to the carotid bifurcation to innervate the carotid sinus (baroreceptor) and the carotid body (chemoreceptor). The baroreceptors in the carotid sinus wall monitor blood pressure; the chemoreceptors in the carotid body sense oxygen, carbon dioxide, and pH, sending signals that regulate heart rate, blood pressure, and respiratory drive.

Region: Neck

Clinical Relevance

Clinical Notes

Carotid sinus hypersensitivity syndrome occurs when the carotid sinus nerve response is exaggerated, causing sudden bradycardia and hypotension from light pressure at the neck such as a tight collar, shaving, or head turning, leading to syncope. Carotid endarterectomy requires anaesthetising the carotid sinus with local anaesthetic infiltration at the bifurcation to prevent vagal reactions during surgical manipulation. Denervation of the carotid body chemoreceptors occurs after bilateral carotid endarterectomy, impairing the ventilatory response to hypoxia.

Pathology

Common Injuries & Conditions

Carotid Sinus Hypersensitivity

An exaggerated baroreceptor response causing vasovagal syncope on neck pressure or head turning, diagnosed by carotid sinus massage producing asystole greater than 3 seconds or a fall in systolic BP greater than 50 mmHg, managed with pacemaker implantation for the cardioinhibitory type.

Carotid Body Denervation

Loss of carotid body chemoreceptor function after bilateral neck surgery or carotid endarterectomy abolishes the hypoxic ventilatory drive, a potentially dangerous consequence in patients dependent on hypoxic drive such as those with chronic obstructive pulmonary disease.