In
human anatomy
The human body is the structure of a human being. It is composed of many different types of cells that together create tissues and subsequently organ systems. They ensure homeostasis and the viability of the human body.
It comprises a he ...
, the carotid sinus is a dilated area at the base of the
internal carotid artery
The internal carotid artery (Latin: arteria carotis interna) is an artery in the neck which supplies the anterior circulation of the brain. In human anatomy, the internal and external carotids arise from the common carotid arteries, where these b ...
just superior to the
bifurcation of the internal carotid and
external carotid at the level of the superior border of
thyroid cartilage. The carotid sinus extends from the bifurcation to the "true" internal carotid artery. The carotid sinus is sensitive to pressure changes in the
arterial blood at this level. It is the major
baroreception site in
humans and most
mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
s.
Structure
The carotid sinus is the
reflex
In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus.
Reflexes are found with varying levels of complexity in organisms with a nervous system. A reflex occurs ...
area of the
carotid artery Carotid artery may refer to:
* Common carotid artery, often "carotids" or "carotid", an artery on each side of the neck which divides into the external carotid artery and internal carotid artery
* External carotid artery, an artery on each side of t ...
, consisting of
baroreceptor
Baroreceptors (or archaically, pressoreceptors) are sensors located in the carotid sinus (at the bifurcation of external and internal carotids) and in the aortic arch. They sense the blood pressure and relay the information to the brain, so that a ...
s which monitor blood pressure.
Function
The carotid sinus contains numerous
baroreceptors which function as a "sampling area" for many
homeostatic mechanisms for maintaining
blood pressure
Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressure" r ...
. The carotid sinus baroreceptors are innervated by the
carotid sinus nerve
The carotid branch of the glossopharyngeal nerve (carotid sinus nerve or Hering's nerve) is a small branch of the glossopharyngeal nerve that innervates the carotid sinus and carotid body. It is a branch of the glossopharyngeal nerve that runs down ...
, which is a branch of the
glossopharyngeal nerve (CN IX). The neurons which
innervate
A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system.
A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the e ...
the carotid sinus centrally project to the
solitary nucleus
In the human brainstem, the solitary nucleus, also called nucleus of the solitary tract, nucleus solitarius, and nucleus tractus solitarii, (SN or NTS) is a series of purely sensory
nuclei (clusters of nerve cell bodies) forming a vertical column ...
in the
medulla of the brainstem. The solitary nucleus indirectly modulates the activity of
sympathetic and
parasympathetic
The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of t ...
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, Ludwig nerve), which combines with CN X (
vagus nerve) and travels to the NTS.
Clinical significance
It is a sensitive site of the body because stimulation can drive large-scale
reflex effects throughout the body. This can be used therapeutically in treatment of
resistant hypertension by
baroreflex
The baroreflex or
baroreceptor reflex is one of the body's homeostatic mechanisms that helps to maintain blood pressure at nearly constant levels. The baroreflex provides a rapid negative feedback loop in which an elevated blood pressure causes the ...
activation.
Physical assault at this point, producing massive baroreflex activation can cause
dramatic falls in blood pressure and
cerebral ischemia.
Disease
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
Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressure" r ...
. This classically presents as a patient who has "
fainted" (actually a
presyncope) 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
In human anatomy, the carotid sinus is a dilated area at the base of the internal carotid artery just superior to the bifurcation of the internal carotid and external carotid at the level of the superior border of thyroid cartilage. The carotid ...
when pressure builds in one or both carotid sinuses.
Treatment of resistant hypertension
Stimulation of
baroreceptor
Baroreceptors (or archaically, pressoreceptors) are sensors located in the carotid sinus (at the bifurcation of external and internal carotids) and in the aortic arch. They sense the blood pressure and relay the information to the brain, so that a ...
s at the carotid sinus can be used to treat
resistant hypertension via activation of the
baroreflex
The baroreflex or
baroreceptor reflex is one of the body's homeostatic mechanisms that helps to maintain blood pressure at nearly constant levels. The baroreflex provides a rapid negative feedback loop in which an elevated blood pressure causes the ...
. A pacemaker-like device can be implanted to electrically stimulate the receptors chronically, which is found to lower blood pressure by 15–25 mmHg.
Massage
Massage of the carotid sinus, carotid sinus massage is used to diagnose
carotid sinus syncope
In human anatomy, the carotid sinus is a dilated area at the base of the internal carotid artery just superior to the bifurcation of the internal carotid and external carotid at the level of the superior border of thyroid cartilage. The carotid ...
and is sometimes useful for differentiating
supraventricular tachycardia
Supraventricular tachycardia (SVT) is an umbrella term for fast heart rhythms arising from the upper part of the heart. This is in contrast to the other group of fast heart rhythms – ventricular tachycardia, which start within the lower cham ...
(SVT) from
ventricular tachycardia. Like the
valsalva maneuver
The Valsalva maneuver is performed by a forceful attempt of exhalation against a closed airway, usually done by closing one's mouth and pinching one's nose shut while expelling air out as if blowing up a balloon. Variations of the maneuver can ...
, it is a treatment for acute SVT. It is less effective than pharmaceutical management of SVT with
verapamil or
adenosine
Adenosine ( symbol A) is an organic compound that occurs widely in nature in the form of diverse derivatives. The molecule consists of an adenine attached to a ribose via a β-N9-glycosidic bond. Adenosine is one of the four nucleoside building ...
, but it is still the preferred first line of treatment in a
hemodynamically stable patient.
Carotid sinus reflex death
Carotid sinus reflex death is a potential
etiology
Etiology (pronounced ; alternatively: aetiology or ætiology) is the study of causation or origination. The word is derived from the Greek (''aitiología'') "giving a reason for" (, ''aitía'', "cause"); and ('' -logía''). More completely, e ...
of sudden
death in which manual stimulation of the carotid sinus allegedly causes strong
glossopharyngeal nerve (
Vagus nerve is for
aortic arch baroreceptor
Baroreceptors (or archaically, pressoreceptors) are sensors located in the carotid sinus (at the bifurcation of external and internal carotids) and in the aortic arch. They sense the blood pressure and relay the information to the brain, so that a ...
s) 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. Medical literature examining the use of
carotid sinus massage
In human anatomy, the carotid sinus is a dilated area at the base of the internal carotid artery just superior to the bifurcation of the internal carotid and external carotid at the level of the superior border of thyroid cartilage. The carotid ...
involving brief gentle pressure of the carotid sinus in therapeutic settings as a diagnostic and therapeutic examination tool have reported few potentially fatal complications.
[Darrell L. Ross, Ted Cha]
Sudden Deaths in Custody
/ref> A carotid massage can also possibly dislodge a thrombus, or some plaque. This could lead to any number of life-threatening effects, including stroke
A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...
.
In martial arts and self defense
Stimulation of the carotid sinus via a slap or a strike, to induce (usually temporary, but sometimes lethal) loss of consciousness is a self-defense technique, and is often taught in martial arts
Martial arts are codified systems and traditions of combat practiced for a number of reasons such as self-defense; military and law enforcement applications; combat sport, competition; physical, mental, and spiritual development; entertainment; a ...
such as karate
(; ; Okinawan language, Okinawan pronunciation: ) is a martial arts, martial art developed in the Ryukyu Kingdom. It developed from the Okinawan martial arts, indigenous Ryukyuan martial arts (called , "hand"; ''tii'' in Okinawan) under the ...
.
See also
* Baroreflex
The baroreflex or
baroreceptor reflex is one of the body's homeostatic mechanisms that helps to maintain blood pressure at nearly constant levels. The baroreflex provides a rapid negative feedback loop in which an elevated blood pressure causes the ...
* Carotid body
References
Additional Images
File:Slide12hhh.JPG, Carotid sinus
External links
* ()
{{DEFAULTSORT:Carotid Sinus
Arteries of the head and neck