Carotid sinus
Sinus caroticus
Also known as: carotid bulb, carotid baroreceptor
The carotid sinus is a widening at the origin of the internal carotid artery. Its wall contains stretch-sensitive baroreceptors that monitor arterial pressure and signal through the glossopharyngeal nerve.
Overview
In the carotid sinus the media is thin and the adventitia is rich in sensory nerve endings. These endings fire when the wall is stretched. Their signals travel in the carotid sinus nerve (of Hering), a branch of the glossopharyngeal nerve (CN IX), to the nucleus tractus solitarius in the medulla.
The receptors respond to pressures between about 60 and 180 mmHg and are most sensitive near normal mean arterial pressure. They respond to how fast pressure changes as well as to its level. Over days of sustained high or low pressure they reset to the new level, so they cannot set long-term blood pressure.
Baroreceptors in the aortic arch work in the same way but signal through the vagus nerve. The carotid body is a different structure. It is a small chemoreceptor in the fork of the bifurcation whose glomus cells detect low PaO₂, high PaCO₂ and high H⁺. It is also supplied by CN IX.
- Location
The first part of the internal carotid artery, at the bifurcation of the common carotid (about C3–C4).
Anatomy
- Innervation
Carotid sinus nerve (of Hering), a branch of the glossopharyngeal nerve (CN IX).
Function
- Senses arterial blood pressure and the rate at which it changes.
- Provides the afferent signal for the baroreceptor reflex, which adjusts heart rate and vascular tone.
Clinical significance
Carotid sinus massage
Massaging one carotid sinus increases vagal output and can stop AV nodal re-entrant tachycardia. Listen for a carotid bruit first, and never massage both sides at once.
Carotid sinus hypersensitivity
In older people an exaggerated baroreflex can cause bradycardia or vasodilation, and hence syncope, when the neck is turned or a tight collar is worn.
Carotid body tumour
A carotid body tumour (paraganglioma) splays apart the internal and external carotid arteries on angiography (the "lyre sign").
Test yourself
Afferent signals from the carotid sinus baroreceptors travel in which nerve?
- Vagus nerve (CN X)
- Glossopharyngeal nerve (CN IX)
- Hypoglossal nerve (CN XII)
- Facial nerve (CN VII)
Answer: Glossopharyngeal nerve (CN IX)
The carotid sinus nerve (of Hering) is a branch of the glossopharyngeal nerve. It ends in the nucleus tractus solitarius. Aortic arch baroreceptors signal through the vagus nerve instead.
Compiled from standard anatomy and physiology references — see the Cardiovascular System sources. For education only; not medical advice.