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 thyroid cartilage is the largest of the nine cartilages that make up the ''laryngeal skeleton'', the cartilage structure in and around the trachea that contains the larynx. It does not completely encircle the larynx (only the cricoid 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
human
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, cultu ...
s 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 ...
s.
Structure
The carotid sinus is the
reflex area of the
carotid artery, 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 ...
s which monitor blood pressure.
Function
The carotid sinus contains numerous
baroreceptors
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 ...
which function as a "sampling area" for many
homeostatic
In biology, homeostasis (British also homoeostasis) (/hɒmɪə(ʊ)ˈsteɪsɪs/) is the state of steady internal, physical, and chemical conditions maintained by living systems. This is the condition of optimal functioning for the organism an ...
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 ...
. The carotid sinus baroreceptors are innervated by the
carotid sinus nerve, which is a branch of the
glossopharyngeal nerve
The glossopharyngeal nerve (), also known as the ninth cranial nerve, cranial nerve IX, or simply CN IX, is a cranial nerve that exits the brainstem from the sides of the upper medulla, just anterior (closer to the nose) to the vagus nerve. ...
(CN IX). The neurons which
innervate 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 neurons in the
medulla and pons through the
hypothalamus
The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamus ...
. These neurons then regulate the
autonomic control of the
heart
The heart is a muscular Organ (biology), organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as ca ...
and
blood vessel
The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide awa ...
s. The
aortic arch
The aortic arch, arch of the aorta, or transverse aortic arch () is the part of the aorta between the ascending and descending aorta. The arch travels backward, so that it ultimately runs to the left of the trachea.
Structure
The aorta begins ...
baroreceptors are innervated by the
aortic nerve (nerve of Cyon, Ludwig nerve), which combines with CN X (
vagus nerve
The vagus nerve, also known as the tenth cranial nerve, cranial nerve X, or simply CN X, is a cranial nerve that interfaces with the parasympathetic control of the heart, lungs, and digestive tract. It comprises two nerves—the left and righ ...
) 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 th ...
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 plaque
An atheroma, or atheromatous plaque, is an abnormal and reversible accumulation of material in the inner layer of an arterial wall.
The material consists of mostly macrophage cells, or debris, containing lipids, calcium and a variable amount ...
s 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 ...
. 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 s ...
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 ...
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 th ...
. 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 and is sometimes useful for differentiating
supraventricular tachycardia (SVT) from
ventricular tachycardia
Ventricular tachycardia (V-tach or VT) is a fast heart rate arising from the lower chambers of the heart. Although a few seconds of VT may not result in permanent problems, longer periods are dangerous; and multiple episodes over a short period ...
. 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 of sudden
death
Death is the irreversible cessation of all biological functions that sustain an organism. For organisms with a brain, death can also be defined as the irreversible cessation of functioning of the whole brain, including brainstem, and brain ...
in which manual stimulation of the carotid sinus allegedly causes strong
glossopharyngeal nerve
The glossopharyngeal nerve (), also known as the ninth cranial nerve, cranial nerve IX, or simply CN IX, is a cranial nerve that exits the brainstem from the sides of the upper medulla, just anterior (closer to the nose) to the vagus nerve. ...
(
Vagus nerve
The vagus nerve, also known as the tenth cranial nerve, cranial nerve X, or simply CN X, is a cranial nerve that interfaces with the parasympathetic control of the heart, lungs, and digestive tract. It comprises two nerves—the left and righ ...
is for
aortic arch
The aortic arch, arch of the aorta, or transverse aortic arch () is the part of the aorta between the ascending and descending aorta. The arch travels backward, so that it ultimately runs to the left of the trachea.
Structure
The aorta begins ...
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 ...
s) impulses leading to terminal
cardiac arrest
Cardiac arrest is when the heart suddenly and unexpectedly stops beating. It is a medical emergency that, without immediate medical intervention, will result in sudden cardiac death within minutes. Cardiopulmonary resuscitation (CPR) and possi ...
. Carotid sinus reflex death has been pointed out as a possible cause of death in cases of
strangulation,
hanging
Hanging is the suspension of a person by a noose or ligature around the neck.Oxford English Dictionary, 2nd ed. Hanging as method of execution is unknown, as method of suicide from 1325. The ''Oxford English Dictionary'' states that 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 s ...
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
A thrombus (plural thrombi), colloquially called a blood clot, is the final product of the blood coagulation step in hemostasis. There are two components to a thrombus: aggregated platelets and red blood cells that form a plug, and a mesh of ...
, or some plaque. This could lead to any number of life-threatening effects, including stroke
A stroke is a disease, medical condition in which poor cerebral circulation, blood flow to the brain causes cell death. There are two main types of stroke: brain ischemia, ischemic, due to lack of blood flow, and intracranial hemorrhage, hemorr ...
.
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
Self-defense (self-defence primarily in Commonwealth English) is a countermeasure that involves defending the health and well-being of oneself from harm. The use of the right of self-defense as a legal justification for the use of force ...
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; competition; physical, mental, and spiritual development; entertainment; and the preser ...
such as karate.
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 th ...
* Carotid body
References
Additional Images
File:Slide12hhh.JPG, Carotid sinus
External links
* ()
{{DEFAULTSORT:Carotid Sinus
Arteries of the head and neck