circle of Willis


Also found in: Dictionary, Thesaurus, Legal, Financial, Encyclopedia, Wikipedia.

circle

 [ser´k'l]
a round figure, structure, or part.
Berry's c's charts with circles on them for testing stereoscopic vision.
cerebral arterial circle circle of Willis.
Minsky's circle a device for the graphic recording of eye lesions.
sensory circle a body area within which it is impossible to distinguish separately the impressions arising from two sites of stimulation.
circle of Willis the anastomotic loop of blood vessels near the base of the brain. Called also cerebral arterial circle.

ce·re·bral ar·te·ri·al cir·cle

[TA]
the roughly pentagonally shaped circle of vessels on the ventral aspect of the brain in the area of the optic chiasm, hypothalamus, and interpeduncular fossa; formed, sequentially and in an anterior to posterior direction, by the anterior communicating artery and by the two anterior cerebral, the two internal carotid, the two posterior communicating, and proximal segments of the two posterior cerebral arteries.

circle of Willis

Etymology: Thomas Willis, English physician, 1621-1675
a vascular network at the base of the brain formed by the interconnection of the middle cerebral, anterior cerebral, posterior cerebral, basilar, anterior communicating, and posterior communicating arteries.
enlarge picture
Circle of Willis

circle of Willis

Imaging
A large network of interconnecting blood vessels that appear as a circle at the base of the brain.

circle of Willis

circulus arteriosus cerebri Anatomy A conduit of anastomosed arteries that encircle the optic chiasm and hypophysial region at the base of the brain, consisting of parts of each internal carotid, anterior, middle, and posterior cerebral arteries, and anterior and posterior communicating arteries. See Berry aneurysm.

cir·cle of Wil·lis

(sĭr'kĕl wil'is)
A ring of arteries at the base of the brain formed by anastomoses of the internal carotid arteries and the basilar artery.
Enlarge picture
CIRCLE OF WILLIS: Inferior view of brain

circle of Willis

An arterial anastomosis that encircles the optic chiasm and hypophysis, from which the principal arteries supplying the brain are derived. It receives blood from the two internal carotid arteries and the basilar artery formed by union of the two vertebral arteries. See: illustration
See also: Willis, Thomas

Willis,

Thomas, English physician, 1621-1675.
accessorius willisii - nerve that arises by two sets of roots: cranial, emerging from the side of the medulla, and spinal, emerging from the ventrolateral part of the first five cervical segments of the spinal cord. Synonym(s): accessory nerve
chordae willisii - Synonym(s): Willis cords
circle of Willis - an anastomotic circle of arteries at the base of the brain. Synonym(s): arterial circle of cerebrum
Willis centrum nervosum - the largest and highest group of prevertebral sympathetic ganglia, located on the superior part of the abdominal aorta. Synonym(s): celiac ganglia
Willis cords - several fibrous cords crossing the superior sagittal sinus. Synonym(s): chordae willisii
Willis pancreas - a portion of the head of the pancreas formed by the superior mesenteric artery and abdominal aorta. Synonym(s): uncinate process of pancreas
Willis paracusis - the apparent increase in auditory acuity of a deaf person to conversation in noisy surroundings due to a companion's unconscious voice raising. Synonym(s): false paracusis
Willis pouch - obsolete term for lesser omentum.

circle of Willis

; CofW arteries (anterior communicating, anterior cerebral [×2], internal carotid [×2], posterior communicating [×2] and posterior cerebral [×2] arteries) that circle the base of the brain, supplying oxygenated blood to all brain areas; cerebrovascular accident involving one or more CofW arteries induces widespread brain infarction and marked body-wide effects

circle of Willis 

An arterial ring surrounding the optic chiasma and hypothalamus. It is formed anteriorly by the anterior cerebral arteries which are linked by the anterior communicating artery; posteriorly, by the division of the basilar artery into the posterior cerebral arteries and, laterally the latter are united by the posterior communicating arteries to the internal carotid arteries. An aneurysm in one part of the circle of Willis may compress the optic chiasma, resulting in a visual field loss. As the terminal branches of the internal carotid arteries are called the middle cerebral arteries, the circle of Willis is sometimes considered to be formed laterally by the latter (Fig. C11). See internal carotid artery; preretinal haemorrhage; heteronymous hemianopia.
Fig. C11 Diagram showing the circle of Willis and the optic chiasmaenlarge picture
Fig. C11 Diagram showing the circle of Willis and the optic chiasma

circle

a round figure, structure or part.

circle block
see ring block.
ciliary arterial circle
formed from the anterior ciliary arteries; lies within the ciliary muscle.
iridial arterial circle
formed from the posterior long ciliary arteries and supplying blood to the iris.
iridial vascular circle
a ring of vessels formed by the anterior ciliary arteries; provide fine branches to the iris and ciliary body.
circle of safety
circle system
see breathing circuit.
circle test
walking a horse in a small circle, first one direction then the other, is used in a neurological examination to detect ataxia and abnormalities in proprioception.
circle of Willis
anastomotic loop of vessels near the base of the brain. See cerebral arterial circle.