Corpus: Carotid sinus

The carotid sinus is a vascular dilatation at the initial part of the internal carotid artery, which contains important receptors for the regulation of blood pressure.

The vessel wall of the carotid sinus contains baroreceptors that are innervated by the carotid sinus ramus of the glossopharyngeal nerve. The cell bodies of the baroreceptors are located in the ganglion inferius nervi glossopharyngei. They transmit the incoming stimuli to the nucleus tractus solitarii.

Adequate stimulation of the baroreceptors is when the blood pressure exceeds the target value, which results in glossopharyngeal-induced stimulation of the cardioinhibitory neurones of the medulla oblongata. These mediate the reduction in heart rate via an increase in vagal tone

• heart rate (negative chronotropy),
• cardiac output (negative inotropy),
• cardiac excitability (negative bathmotropy) and
• conduction (negative dromotropy).

These physiological reactions reduce blood pressure and are collectively referred to as the carotid sinus reflex or more comprehensively as the baroreceptor reflex.

Arteriosclerotic vascular wall changes or tumours in the area of the carotid sinus can result in hypersensitivity of the baroreceptors (carotid sinus syndrome). As a result, even minor external pressure on the carotid sinus - e.g. the pressure of a shirt collar or tie - can trigger bradycardia or even brief asystole with syncopal symptoms.

As part of the functional diagnostics of the carotid sinus and for the treatment of paroxysmal tachycardia, the pressoreceptor reflex can be iatrogenically provoked by a carotid sinus massage (CSM).

See also: Parasympathetic nervous system