|Arteries of the neck. The carotid sinus is at the origin of the internal carotid artery.|
|Nerve||branch of glossopharyngeal nerve to carotid sinus|
In human anatomy, the carotid sinus is a dilated area in the bifurcation of the common carotid at the level of the superior border of thyroid cartilage. The carotid sinus is sensitive to pressure changes in the arterial blood at this level.
|This section does not cite any references or sources. (February 2009)|
The carotid sinus contains numerous baroreceptors which function as a "sampling area" for many homeostatic mechanisms for maintaining blood pressure. The carotid sinus baroreceptors are innervated by the sinus nerve of Hering, which is a branch of cranial nerve IX (glossopharyngeal nerve). The glossopharyngeal nerve synapses in the nucleus tractus solitarius (NTS) located in the medulla of the brainstem. The NTS indirectly modulates the activity of sympathetic and parasympathetic (vagal) neurons in the medulla and pons through the hypothalamus. These neurons then regulate the autonomic control of the heart and blood vessels. The aortic arch baroreceptors are innervated by the aortic nerve (Nerve of Cyon), which combines with CN X (vagus nerve) and travels to the NTS.
Disease of the carotid sinus 
The carotid sinus often has atherosclerotic plaques because of disturbed hemodynamics (low wall shear stress, flow reversal/recirculation). Since these plaques, if large and unstable, predispose to ischemic strokes and transient ischemic attacks, carotid endarterectomies are frequently done for prophylaxis.
The carotid sinus can be oversensitive to manual stimulation, a condition known as carotid sinus hypersensitivity, carotid sinus syndrome or carotid sinus syncope, in which manual stimulation causes large changes in heart rate and/or blood pressure. This classically presents as a patient who has "fainted" on several occasions while shaving, or in some other way coming into contact with their carotid sinus.
Carotid sinus syndrome is a temporary loss of consciousness that sometimes accompanies convulsive seizures because of the intensity of the carotid sinus reflex when pressure builds in one or both carotid sinuses.
Carotid sinus massage 
Massage of the carotid sinus, carotid sinus massage is used to diagnose carotid sinus syncope and is sometimes useful for differentiating supraventricular tachycardia (SVT) from ventricular tachycardia. Like the valsalva maneuver, it is a therapy for SVT. It is less effective than pharmaceutical management of SVT with verapamil or adenosine though is still the preferred first-line of treatment in a hemodynamically stable patient
Carotid sinus reflex death 
Carotid sinus reflex death is a disputed mechanism of death in which manual stimulation of the carotid sinus allegedly causes strong glossopharyngeal nerve (Vagus nerve is for aortic arch baroreceptors) impulses leading to terminal cardiac arrest. Carotid sinus reflex death has been pointed out as a possible cause of death in cases of strangulation, hanging and Autoerotic Strangulation, but such deductions remain controversial. Studies have also suggested that the carotid sinus reflex can be a contributing factor in other mechanisms of death by reducing blood pressure and heart rate, especially in the elderly or in people suffering from carotid sinus hypersensitivity. A carotid massage can also possibly dislodge a thrombus, or some plaque. This could lead to any number of life threatening effects, including stroke.
See also 
- Glagov S, Zarins C, Giddens DP, Ku DN. Hemodynamics and atherosclerosis. Insights and perspectives gained from studies of human arteries. biod degradable Arch Pathol Lab Med. 1988 Oct;112(10):1018-31. PMID 3052352
- Lim SH, Anantharaman V, Teo WS, Goh PP, Tan AT. Comparison of treatment of supraventricular tachycardia by Valsalva maneuver and carotid sinus massage. Ann Emerg Med. 1998 Jan;31(1):30-5. doi:10.1016/S0196-0644(98)70277-X PMID 9437338
- Ballo P, Bernabo D, Faraguti SA. Heart rate is a predictor of success in the treatment of adults with symptomatic paroxysmal supraventricular tachycardia. Eur Heart J. 2004 Aug;25(15):1310-7. doi:10.1016/j.ehj.2004.05.011 PMID 15288158
- American Heart Association. Tachycardia algorithm. Advanced Cardiac Life Support Provider Manual (2007).
- Passig, K. Carotid sinus reflex death - a theory and its history. URL last accessed February 28, 2006.
Additional Images 
- Anatomy at MUN head/cbv
- lesson5 at The Anatomy Lesson by Wesley Norman (Georgetown University) (livingneck)