Artery: Circle of Willis
Schematic representation of the circle of Willis, arteries of the brain and brain stem. The brain stem (or brainstem) is the lower part of the Brain, adjoining and structurally continuous with the Spinal cord.
The brain and arteries at base of the brain. The brain is the center of the Nervous system in animals All Vertebrates and the majority of Invertebrates have a brain Circle of Willis is formed near center. The temporal pole of the cerebrum and a portion of the cerebellar hemisphere have been removed on the right side. The temporal lobes are parts of the cerebrum that are involved in speech, Memory, and Hearing. The telencephalon (tɛlɛnˈsɛfəlɒn cerebrum, or forebrain is the most Anterior or especially in humans most Dorsal region of the The cerebellum ( Latin: "little brain" is a region of the Brain that plays an important role in the integration of sensory perception Inferior aspect (viewed from below).
Latin	circulus arteriosus cerebri
Gray's	subject #147 574
MeSH	Circle+of+Willis

The circle of Willis (also called the cerebral arterial circle or arterial circle of Willis) is a circle of arteries that supply blood to the brain. Latin ( lingua Latīna, laˈtiːna is an Italic language, historically spoken in Latium and Ancient Rome. Medical Subject Headings ( MeSH) is a huge Controlled vocabulary (or metadata system for the purpose of indexing journal articles and books Arteries are Blood vessels that carry blood away from the Heart. The brain is the center of the Nervous system in animals All Vertebrates and the majority of Invertebrates have a brain It is named after Thomas Willis (1621-1673), an English physician. Thomas Willis ( 27 January 1621 &ndash 11 November 1675) was an English doctor who played an important part in the history of England is a Country which is part of the United Kingdom. Its inhabitants account for more than 83% of the total UK population whilst its mainland A physician, medical practitioner or medical doctor who practices Medicine, and is concerned with maintaining or restoring human Health ^[1]

Components

• Anterior cerebral artery (left and right)
• Anterior communicating artery
• Internal carotid artery (left and right)
• Posterior cerebral artery (left and right)
• Posterior communicating artery (left and right)

The basilar artery and middle cerebral arteries, though they supply the brain, are not considered part of the circle. In Human anatomy, each anterior cerebral artery supplies Oxygen to most medial portions of Frontal lobes and Superior medial parietal lobes In Human anatomy, the anterior communicating artery is a Blood vessel of the Brain that connects the left and right anterior cerebral arteries In Human anatomy, the internal carotid artery is a major Artery of the head and neck that helps supply blood to the Brain. In Human anatomy, the posterior cerebral artery is the Blood vessel that supplies oxygenated Blood to the posterior aspect of the brain ( Occipital In Human anatomy, the posterior communicating artery is a one of a pair of right-sided and left-sided Blood vessels in the Circle of Willis. In Human anatomy, the basilar artery is one of the arteries that supplies the Brain with oxygen-rich blood The middle cerebral artery (MCA is one of the three major paired arteries that supplies Blood to the Brain. ^[2]

Physiologic significance

The arrangement of the brain's arteries into the Circle of Willis creates redundancies in the cerebral circulation. If one part of the circle becomes blocked or narrowed (stenosed) or one of the arteries supplying the circle is blocked or narrowed, blood flow from the other blood vessels can often preserve the cerebral perfusion well enough to avoid the symptoms of ischemia. A stenosis ( Plural: stenoses; from Ancient Greek στένωσις "narrowing" is an abnormal narrowing in a Blood vessel The blood vessels are part of the Circulatory system and function to transport Blood throughout the body In Medicine, ischemia ( Greek ισχαιμία, isch- is restriction hema or haema is Blood) is a restriction ^[3]

Anatomic variation

Considerable anatomic variation exists in the circle of Willis. Based on a study of 1413 brains, the "textbook version" of the circle is only seen in 34. 5% of cases. ^[4] In one common variation the proximal part of the posterior cerebral artery is narrow and its ipsilateral posterior communicating artery is large, so the internal carotid artery supplies the posterior cerebrum. In Human anatomy, the posterior cerebral artery is the Blood vessel that supplies oxygenated Blood to the posterior aspect of the brain ( Occipital In Human anatomy, the posterior communicating artery is a one of a pair of right-sided and left-sided Blood vessels in the Circle of Willis. In Human anatomy, the internal carotid artery is a major Artery of the head and neck that helps supply blood to the Brain. In another variation the anterior communicating artery is a large vessel, such that a single internal carotid supplies both anterior cerebral arteries.

Subclavian steal and the Circle of Willis

The redundancies that the Circle of Willis introduce can also lead to reduced cerebral perfusion. ^[5][6] In subclavian steal syndrome, which results from a proximal stenosis (narrowing) of the subclavian artery (a vessel that is supplied by the same vessel (the Aorta) that eventually feeds the circle of Willis via the Common carotid artery), blood is "stolen" from the circle of Willis to preserve blood flow to the upper limb. In medicine subclavian steal syndrome (SSS also subclavian steal phenomenon and subclavian steal steno-occlusive disease, is a constellation of signs In fields of Anatomy, anatomical terms of location are descriptive terms to help identify relative positions or directions within a species A stenosis ( Plural: stenoses; from Ancient Greek στένωσις "narrowing" is an abnormal narrowing in a Blood vessel In Human anatomy, the subclavian artery is a major Artery of the upper Thorax that mainly supplies blood to the head and arms In 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 In Human anatomy, the upper limb (also upper extremity) refers to what in common English is known as the arm, that is the region of the shoulder

Origin of arteries

Cerebral angiogram showing a anterior/posterior projection of the vertebrobasilar and posterior cerebral circulation, i. The vertebral arteries are branches of the subclavian arteries. In Human anatomy, the basilar artery is one of the arteries that supplies the Brain with oxygen-rich blood In Human anatomy, the posterior cerebral artery is the Blood vessel that supplies oxygenated Blood to the posterior aspect of the brain ( Occipital e. the posterior aspect of the circle of Willis and one of its feeding vessels.

The left and right internal carotid arteries arise from the right and left common carotid arteries. In 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

The posterior communicating artery is given off as a branch of the internal carotid artery just before it divides into its terminal branches - the anterior and middle cerebral arteries. The anterior cerebral artery forms the anterolateral portion of the Circle of Willis, while the middle cerebral artery does not contribute to the Circle.

The right and left posterior cerebral arteries arise from the basilar artery, which is formed by the left and right vertebral arteries. In Human anatomy, the posterior cerebral artery is the Blood vessel that supplies oxygenated Blood to the posterior aspect of the brain ( Occipital In Human anatomy, the basilar artery is one of the arteries that supplies the Brain with oxygen-rich blood The vertebral arteries are branches of the subclavian arteries. The vertebral arteries arise from the subclavian arteries. The vertebral arteries are branches of the subclavian arteries. In Human anatomy, the subclavian artery is a major Artery of the upper Thorax that mainly supplies blood to the head and arms

The anterior communicating artery connects the two anterior cerebral arteries and could be said to arise from either the left or right side. In Human anatomy, the anterior communicating artery is a Blood vessel of the Brain that connects the left and right anterior cerebral arteries

All arteries involved give off cortical and central branches. The central branches supply the interior of the Circle of Willis, more specifically, the Interpeduncular fossa. The cortical branches are named for the area they supply. Since they do not directly affect the Circle of Willis, they are not dealt with here.

References