Circle of Willis - wikipedia Circle of Willis Circle of Willis Schematic representation of the circle of Willis, arteries of the brain and brain stem. Blood flows up to the brain through the vertebral arteries and through the internal carotid arteries. The arteries of the base of the brain. Basilar artery labeled below center. The temporal pole of the cerebrum and the cerebellar hemisphere have been removed on the right side. Inferior aspect ( viewed from below ). Details Identifiers Latin Circulus arteriosus cerebri Circulus Willisi MeSH D002941 TA A12. 2.07. 080 FMA 50454 Anatomical terminology ( edit on Wikidata ) The circle of Willis ( also called Willis ' circle, loop of Willis, cerebral arterial circle, and Willis polygon ) is a circulatory anastomosis that supplies blood to the brain and surrounding structures. It is named after Thomas Willis ( 1621 -- 1675 ), an English physician. Contents 1 Structure 1.1 Origin of arteries 1.2 Variation 2 Function 3 Clinical significance 3.1 Aneurysms 3.2 Subclavian steal syndrome 4 Additional images 5 References 6 See also Structure The circle of Willis is a part of the cerebral circulation and is composed of the following arteries : 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 middle cerebral arteries, supplying the brain, are not considered part of the circle. Origin of arteries The left and right internal carotid arteries arise from the left and right common carotid arteries. 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. The vertebral arteries arise from the subclavian arteries. The anterior communicating artery connects the two anterior cerebral arteries and could be said to arise from either the left or right side. 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. Variation Considerable anatomic variation exists in the circle of Willis. Based on a study of 1413 brains, the classic anatomy of the circle is only seen in 34.5 % of cases. 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 another variation the anterior communicating artery is a large vessel, such that a single internal carotid supplies both anterior cerebral arteries. Function The arrangement of the brain 's arteries into the circle of Willis creates redundancy ( analogous to engineered redundancy ) for collateral circulation 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. Clinical significance Aneurysms Circle of Willis with the most common locations of ruptured aneurysms marked Main article : Subarachnoid haemorrhage Subclavian steal syndrome The redundancies that the circle of Willis introduce can also lead to reduced cerebral perfusion. In subclavian steal syndrome, blood is `` stolen '' from the circle of Willis to preserve blood flow to the upper limb. Subclavian steal syndrome results from a proximal stenosis ( narrowing ) of the subclavian artery, an artery supplied by the aorta which is also the same blood vessel that eventually feeds the circle of Willis via the vertebral artery. Additional images Fetal ultrasound image at the level of circle of Willis, showing PCA, MCA and ACA Cerebral angiogram showing an anterior / posterior projection of the vertebro basilar and posterior cerebral circulation, the posterior aspect of the circle of Willis and one of its feeding vessels. An anterior view of major cerebral and cerebellar arteries. Circle of Willis Circle of Willis References Jump up ^ Uston, Cagatay ( February 20, 2004 ). `` Dr. Thomas Willis ' Famous Eponym : The Circle of Willis '' ( PDF ). Turkish Journal of Medical Sciences. 34 : 271 -- 274. Retrieved 16 July 2010. Jump up ^ Purves, Dale ; George J. Augustine ; David Fitzpatrick ; William C. Hall ; Anthony - Samuel LaMantia ; James O. McNamara ; Leonard E. White ( 2008 ). Neuroscience, 4th Ed. Sinauer Associates. pp. 834 -- 5. ISBN 978 - 0 - 87893 - 697 - 7. Archived from the original on 2007 - 12 - 07. Jump up ^ Bergman RA, Afifi AK, Miyauchi R, Circle of Willis. Illustrated Encyclopedia of Human Anatomic Variation, URL : http://www.anatomyatlases.org/AnatomicVariants/Cardiovascular/Text/Arteries/CircleofWillis.shtml. Accessed on November 6, 2005. Jump up ^ Boorder, Michiel J. ; Van Der Grond, J ; Van Dongen, AJ ; Klijn, CJ ; Jaap Kappelle, L ; Van Rijk, PP ; Hendrikse, J ( 2006 ). `` Spect measurements of regional cerebral perfusion and carbon dioxide reactivity : Correlation with cerebral collaterals in internal carotid artery occlusive disease ''. J Neurol. 253 ( 10 ) : 1285 -- 1291. doi : 10.1007 / s00415 - 006 - 0192 - 1. PMID 17063318. Jump up ^ Klingelhöfer, J ; Conrad, B ; Benecke, R ; Frank, B ( 1988 ). `` Transcranial Doppler ultrasonography of carotid - basilar collateral circulation in subclavian steal ''. Stroke : A Journal of Cerebral Circulation. 19 ( 8 ) : 1036 -- 42. doi : 10.1161 / 01. STR. 19.8. 1036. PMID 3041649. Jump up ^ Lord, RS ; Adar, R ; Stein, RL ( 1969 ). `` Contribution of the circle of Willis to the subclavian steal syndrome ''. Circulation. 40 ( 6 ) : 871 -- 8. doi : 10.1161 / 01. CIR. 40.6. 871. PMID 5377222. See also This article uses anatomical terminology ; for an overview, see Anatomical terminology. Wikimedia Commons has media related to Circle of Willis. Cerebral circulation Leptomeningeal collateral circulation Arteries of the head and neck CC EC sup. thyroid superior laryngeal sternocleidomastoid branch infrahyoid branch cricothyroid branch glandular branches asc. pharyngeal posterior meningeal pharyngeal branches inferior tympanic lingual suprahyoid dorsal lingual deep lingual sublingual facial cervical branches ( ascending palatine, tonsillar, submental, glandular ) facial branches ( inferior labial superior labial / nasal septum lateral nasal angular ) occipital sternocleidomastoid meningeal occipital auricular descending post. auricular stylomastoid stapedial auricular occipital Parotid sup. temporal transverse facial middle temporal ( zygomatico - orbital ) anterior auricular frontal parietal maxillary 1st part / mandibular anterior tympanic deep auricular middle meningeal ( superior tympanic, petrosal ) accessory meningeal inferior alveolar 2nd part / pterygoid to muscles of mastication ( deep temporal, pterygoid, masseteric ) buccal 3rd part / pterygopalatine posterior superior alveolar infraorbital ( anterior superior alveolar ) descending palatine ( greater palatine, lesser palatine ) artery of the pterygoid canal sphenopalatine ( posterior septal branches, posterior lateral nasal ) pharyngeal IC cervical carotid sinus petrous Vidian caroticotympanic cavernous / ophthalmic orbital group : anterior ethmoidal posterior ethmoidal lacrimal ( lateral palpebral ) medial palpebral terminal ( supraorbital, supratrochlear, dorsal nasal ) ocular group : central retinal ciliary ( short posterior, long posterior, anterior ) Circulus arteriosus major hypophysial ( superior, inferior ) brain Circle of Willis ACA ( anterior communicating, Recurrent artery of Heubner, Orbitofrontal artery ) MCA ( anterolateral central, Prefrontal artery, Superior terminal branch, Inferior terminal branch, Anterior temporal branch ) posterior communicating anterior choroidal SC vertebral artery meningeal spinal ( posterior, anterior ) basilar : pontine labyrinthine cerebellar ( AICA, SCA, PICA ) cerebral ( PCA ) thyrocervical trunk inferior thyroid inferior laryngeal tracheal esophageal ascending cervical pharyngeal glandular branches transverse cervical superficial branch deep branch / dorsal scapular scapular anastomosis suprascapular acromial branch scapular anastomosis costocervical trunk deep cervical Supreme Intercostal artery Retrieved from `` https://en.wikipedia.org/w/index.php?title=Circle_of_Willis&oldid=825331720 '' Categories : Arteries of the head and neck Hidden categories : Pages with unresolved properties Talk Contents About Wikipedia Català Čeština Dansk Deutsch Español فارسی Français Hrvatski Italiano עברית Latina Nederlands 日本 語 Norsk Plattdüütsch Polski Português Русский Српски / srpski Suomi Svenska Українська اردو 中文 16 more Edit links This page was last edited on 12 February 2018, at 20 : 12. Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia ® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. About Wikipedia

Question: an important function of the circle of willis is to
Answer: supplies blood to the brain and surrounding structures; supplies blood to the brain and surrounding structures; supplies blood to the brain and surrounding structures; supplies blood to the brain and surrounding structures