Cerebral circulation
Encyclopedia
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
through the network of blood vessel
Blood vessel
The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...
s supplying the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
. The arteries
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....
deliver oxygenated blood, glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
and other nutrients to the brain and the vein
Vein
In the circulatory system, veins are blood vessels that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood to the heart...
s carry deoxygenated blood back to the heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
, removing carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
, lactic acid
Lactic acid
Lactic acid, also known as milk acid, is a chemical compound that plays a role in various biochemical processes and was first isolated in 1780 by the Swedish chemist Carl Wilhelm Scheele. Lactic acid is a carboxylic acid with the chemical formula C3H6O3...
, and other metabolic products. Since the brain is very vulnerable to compromises in its blood supply, the cerebral circulatory system has many safeguards. Failure of these safeguards results in cerebrovascular accidents, commonly known as strokes. The amount of blood that the cerebral circulation carries is known as cerebral blood flow
Cerebral blood flow
Cerebral blood flow, or CBF, is the blood supply to the brain in a given time. In an adult, CBF is typically 750 millitres per minute or 15% of the cardiac output. This equates to 50 to 54 millilitres of blood per 100 grams of brain tissue per minute. CBF is tightly regulated to meet the brain's...
. The presence of gravitational fields or accelerations also determine variations in the movement and distribution of blood in the brain, such as when suspended upside-down.
The following description is based on idealized human cerebral circulation. The pattern of circulation and its nomenclature vary between organisms.
Cranial arteries
There are two main pairs of arteries that supply the cerebral arteriesCerebral arteries
Cerebral arteries describe three main pairs of arteries and their branches, which irrigate the cerebrum of the brain. The three main arteries consist of the:*Anterior cerebral artery *Middle cerebral artery...
and the cerebellum
Cerebellum
The cerebellum is a region of the brain that plays an important role in motor control. It may also be involved in some cognitive functions such as attention and language, and in regulating fear and pleasure responses, but its movement-related functions are the most solidly established...
:
- Internal carotid arteriesInternal carotid arteryIn human anatomy, the internal carotid arteries are two major arteries, one on each side of the head and neck. They arise from the common carotid arteries where these bifurcate into the internal and external carotid artery, and they supply the brain....
: These large arteries are the left and right branches of the common carotid arteriesCommon carotid arteryIn human anatomy, the common carotid artery is an artery that supplies the head and neck with oxygenated blood; it divides in the neck to form the external and internal carotid arteries. - Structure :...
in the neck which enter the skull, as opposed to the external carotidExternal carotid arteryIn human anatomy, the external carotid artery is a major artery of the head and neck. It arises from the common carotid artery when it bifurcates into the external and internal carotid artery.-Course:...
branches which supply the facial tissues. The internal carotid artery branches into the anterior cerebral artery and continues to form the middle cerebral arteryMiddle cerebral artery-External links:*... - Vertebral arteriesVertebral arteryThe vertebral arteries are major arteries of the neck. They branch from the subclavian arteries and merge to form the single midline basilar artery in a complex called the vertebrobasilar system, which supplies blood to the posterior part of the circle of Willis and thus significant portions of the...
. These smaller arteries branch from the subclavian arteriesSubclavian arteryIn human anatomy, the subclavian arteries are two major arteries of the upper thorax , below the clavicle . They receive blood from the top of the aorta...
which primarily supply the shoulders, lateral chest and arms. Within the cranium the two vertebral arteries fuse into the basilar arteryBasilar arteryIn human anatomy, the basilar artery is one of the arteries that supplies the brain with oxygen-rich blood.The two vertebral arteries and the basilar artery are sometimes together called the vertebrobasilar system, which supplies blood to the posterior part of circle of Willis and anastomoses with...
, which supplies the midbrain, cerebellum, and usually branches into the posterior cerebral arteryPosterior cerebral artery-External links: - Posterior Cerebral Artery Stroke* at strokecenter.org* at State University of New York Upstate Medical University* at psyweb.com* at neuropat.dote.hu...
.
Both internal carotid arteries
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....
, within and along the floor of the cerebral vault, are interconnected via the anterior communicating artery
Anterior communicating artery
In human anatomy, the anterior communicating artery is a blood vessel of the brain that connects the left and right anterior cerebral arteries....
. Additionally, both internal carotid arteries
Internal carotid artery
In human anatomy, the internal carotid arteries are two major arteries, one on each side of the head and neck. They arise from the common carotid arteries where these bifurcate into the internal and external carotid artery, and they supply the brain....
are interconnected with the basilar artery via bilateral posterior communicating arteries
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....
.
The Circle of Willis
Circle of Willis
The Circle of Willis is a circle of arteries that supply blood to the brain...
, long considered to be an important anatomic vascular formation, provides backup circulation to the brain. In case one of the supply arteries is occluded, the Circle of Willis
Circle of Willis
The Circle of Willis is a circle of arteries that supply blood to the brain...
provides interconnections between the internal carotid arteries
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....
and basilar artery
Basilar artery
In human anatomy, the basilar artery is one of the arteries that supplies the brain with oxygen-rich blood.The two vertebral arteries and the basilar artery are sometimes together called the vertebrobasilar system, which supplies blood to the posterior part of circle of Willis and anastomoses with...
along the floor of the cerebral vault, providing blood to tissues that would otherwise become ischemic.
Cerebral venous drainage
The venous drainage of the cerebrum can be separated into two subdivisions: superficial and deep. The superficial system is composed of dural venous sinusesDural venous sinuses
The dural venous sinuses are venous channels found between layers of dura mater in the brain...
, which have wall composed of dura mater as opposed to a traditional vein. The dural sinuses are, therefore located on the surface of the cerebrum. The most prominent of these sinuses is the Superior sagittal sinus
Superior sagittal sinus
The superior sagittal sinus , within the human head, is an unpaired area along the attached margin of falx cerebri. It allows blood to drain from the lateral aspects of anterior cerebral hemispheres to the confluence of sinuses...
which flows in the sagittal plane under the midline of the cerebral vault, posteriorly and inferiorly to the torcula, forming the Confluence of sinuses
Confluence of sinuses
The confluence of sinuses or torcular herophili is the connecting point of the superior sagittal sinus, straight sinus, and occipital sinus. It is found deep to the occipital protuberance of the skull. Blood arriving at this point then proceeds to drain into the left and right transverse sinuses...
, where the superficial drainage joins with the sinus the primarily drains the deep venous system. From here, two transverse sinuses
Transverse sinuses
The transverse sinuses , within the human head, are two areas beneath the brain which allow blood to drain from the back of the head. They run laterally in a groove along the interior surface of the occipital bone...
bifurcate and travel laterally and inferiorly in an S-shaped curve that form the sigmoid sinuses which go on to form the two jugular vein
Jugular vein
The jugular veins are veins that bring deoxygenated blood from the head back to the heart via the superior vena cava.-Internal and external:There are two sets of jugular veins: external and internal....
s. In the neck, the jugular vein
Jugular vein
The jugular veins are veins that bring deoxygenated blood from the head back to the heart via the superior vena cava.-Internal and external:There are two sets of jugular veins: external and internal....
s parallel the upward course of the carotid arteries and drain blood into the superior vena cava
Superior vena cava
The superior vena cava is truly superior, a large diameter, yet short, vein that carries deoxygenated blood from the upper half of the body to the heart's right atrium...
. The deep venous drainage is primarily composed of traditional veins inside the deep structures of the brain, which join behind the midbrain to form the Vein of Galen
Vein of Galen
The great cerebral vein is one of the large blood vessels in the skull draining the cerebrum . It is also known as the "vein of Galen" , named for its discoverer, the Greek physician Galen. However, it is not the only vein with this eponym....
. This vein merges with the Inferior sagittal sinus
Inferior sagittal sinus
The inferior sagittal sinus , within the human head, is an area beneath the brain which allows blood to drain outwards posteriorly from the center of the head. It drains to the straight sinus , which connects to the transverse sinuses...
to form the Straight sinus
Straight sinus
The straight sinus , within the human head, is an unpaired area beneath the brain which allows blood to drain from the inferior center of the head outwards posteriorly...
which then joins the superficial venous system mentioned above at the Confluence of sinuses
Confluence of sinuses
The confluence of sinuses or torcular herophili is the connecting point of the superior sagittal sinus, straight sinus, and occipital sinus. It is found deep to the occipital protuberance of the skull. Blood arriving at this point then proceeds to drain into the left and right transverse sinuses...
.