In
human anatomy, the carotid sinus is a dilated area at the base of the
internal carotid artery just superior to the
bifurcation
Bifurcation or bifurcated may refer to:
Science and technology
* Bifurcation theory, the study of sudden changes in dynamical systems
** Bifurcation, of an incompressible flow, modeled by squeeze mapping the fluid flow
* River bifurcation, the ...
of the internal carotid and
external carotid
The external carotid artery is a major artery of the head and neck. It arises from the common carotid artery when it splits into the external and internal carotid artery. External carotid artery supplies blood to the face and neck.
Structure
Th ...
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
Arterial blood is the oxygenated blood in the circulatory system found in the pulmonary vein, the left chambers of the heart, and in the artery, arteries. It is bright red in color, while venous blood is dark red in color (but looks purple through ...
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
mammals.
Structure
The carotid sinus is the
reflex area of the
carotid artery, consisting of
baroreceptors 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 and ...
mechanisms for maintaining
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
Medulla or Medullary may refer to:
Science
* Medulla oblongata, a part of the brain stem
* Renal medulla, a part of the kidney
* Adrenal medulla, a part of the adrenal gland
* Medulla of ovary, a stroma in the center of the ovary
* Medulla of t ...
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 hypothalamu ...
. These neurons then regulate the
autonomic control of the
heart
The heart is a muscular 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 carbon dioxide to t ...
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 away ...
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
The aortic nerve, is a branch of the vagus nerve. It supplies autonomic afferent nerve fibers to the peripheral baroreceptors and chemoreceptors found in the aortic arch.
Structure
The aortic nerve is an autonomic afferent nerve fiber, and r ...
(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 activation.
Physical assault
An assault is the act of committing physical harm or unwanted physical contact upon a person or, in some specific legal definitions, a threat or attempt to commit such an action. It is both a crime and a tort and, therefore, may result in crim ...
at this point, producing massive baroreflex activation can cause
dramatic falls in blood pressure and
cerebral ischemia
Brain ischemia is a condition in which there is insufficient bloodflow to the brain to meet metabolic demand. This leads to poor oxygen supply or cerebral hypoxia and thus leads to the death of brain tissue or cerebral infarction/ischemic stroke. ...
.
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
Hemodynamics or haemodynamics are the dynamics of blood flow. The circulatory system is controlled by homeostatic mechanisms of autoregulation, just as hydraulic circuits are controlled by control systems. The hemodynamic response continuously m ...
(low
wall shear stress
Shear stress, often denoted by ( Greek: tau), is the component of stress coplanar with a material cross section. It arises from the shear force, the component of force vector parallel to the material cross section. '' Normal stress'', on th ...
, flow reversal/recirculation). Since these plaques, if large and unstable, predispose to
ischemic 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 funct ...
s and
transient ischemic attack
A transient ischemic attack (TIA), commonly known as a mini-stroke, is a minor stroke whose noticeable symptoms usually end in less than an hour. TIA causes the same symptoms associated with strokes, such as weakness or numbness on one side of ...
s,
carotid endarterectomies are frequently done for
prophylaxis
Preventive healthcare, or prophylaxis, consists of measures taken for the purposes of disease prevention.Hugh R. Leavell and E. Gurney Clark as "the science and art of preventing disease, prolonging life, and promoting physical and mental hea ...
.
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
Heart rate (or pulse rate) is the frequency of the heartbeat measured by the number of contractions (beats) of the heart per minute (bpm). The heart rate can vary according to the body's physical needs, including the need to absorb oxygen and excr ...
and/or
blood pressure. This classically presents as a patient who has "
fainted
Syncope, commonly known as fainting, or passing out, is a loss of consciousness and muscle strength characterized by a fast onset, short duration, and spontaneous recovery. It is caused by a decrease in blood flow to the brain, typically from ...
" (actually a
presyncope
Lightheadedness is a common and typically unpleasant sensation of dizziness or a feeling that one may faint. The sensation of lightheadedness can be short-lived, prolonged, or, rarely, recurring. In addition to dizziness, the individual may feel ...
) 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.
Treatment of resistant hypertension
Stimulation of
baroreceptors at the carotid sinus can be used to treat
resistant hypertension via activation of the
baroreflex. 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
Massage is the manipulation of the body's soft tissues. Massage techniques are commonly applied with hands, fingers, elbows, knees, forearms, feet or a device. The purpose of massage is generally for the treatment of body stress or pain. In E ...
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 (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 perio ...
. 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
Verapamil, sold under various trade names, is a calcium channel blocker medication used for the treatment of high blood pressure, angina (chest pain from not enough blood flow to the heart), and supraventricular tachycardia. It may also be ...
or
adenosine, 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 ...
baroreceptors) 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 poss ...
. Carotid sinus reflex death has been pointed out as a possible cause of death in cases of
strangulation
Strangling is compression of the neck that may lead to unconsciousness or death by causing an increasingly hypoxic state in the brain. Fatal strangling typically occurs in cases of violence, accidents, and is one of two main ways that hangin ...
,
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
Controversy is a state of prolonged public dispute or debate, usually concerning a matter of conflicting opinion or point of view. The word was coined from the Latin ''controversia'', as a composite of ''controversus'' – "turned in an opposite d ...
. 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
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
Plaque may refer to:
Commemorations or awards
* Commemorative plaque, a plate or tablet fixed to a wall to mark an event, person, etc.
* Memorial Plaque (medallion), issued to next-of-kin of dead British military personnel after World War I
* Pl ...
. This could lead to any number of life-threatening effects, including stroke.
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 such as karate.
See also
* Baroreflex
* Carotid body
The carotid body is a small cluster of chemoreceptor cells, and supporting sustentacular cells. The carotid body is located in the adventitia, in the bifurcation (fork) of the common carotid artery, which runs along both sides of the neck.
The ...
References
Additional Images
File:Slide12hhh.JPG, Carotid sinus
External links
* ()
{{DEFAULTSORT:Carotid Sinus
Arteries of the head and neck