318 Neuroanatomy: Draw It to Know It
Know-It Points
The Circle of Willis
■ Two main arterial systems exist: an anterior-lying
internal carotid artery system and a posterior-lying
vertebral-basilar arterial system.
■ Th e middle cerebral arteries originate from the
internal carotid arteries and extend laterally.
■ Th e anterior cerebral arteries branch anteriorly from
the internal carotid arteries.
■ Th e two vertebral arteries join to form the basilar
artery.
■ Th e basilar artery ascends the brainstem and
bifurcates, superiorly, into the posterolaterally
directed posterior cerebral arteries.Leptomeningeal Cerebral Arteries
■ Th e anterior cerebral artery supplies the medial one
third of the mid/upper cerebrum.
■ Th e middle cerebral artery supplies the lateral two
thirds of the cerebrum.
■ Th e posterior cerebral artery supplies the posterior
portion of the mid/lower cerebrum.
■ Th e superfi cial portion of the anterior choroidal
artery supplies the medial temporal lobe.Deep Cerebral Arteries ( Advanced )
■ Th e perforating branches of the middle cerebral
artery supply the anterior-superior-lateral basal
ganglia region.
■ Th e perforating branches of the anterior cerebral
artery supply the anterior-inferior-medial basal
ganglia region.
■ Th e perforating branches of the internal carotid
artery supply the genu of the internal capsule and the
area that immediately surrounds it.
■ Th e perforating branches of the anterior choroidal
artery supply the posterior-inferior-medial basal
g a n g l i a r e g i o n.Arterial Borderzones
■ Infarcts in the borderzones in between the superfi cial,
leptomeningeal arteries and the deep, perforating
arteries are called “end-zone infarcts.”
■ Infarcts in the borderzones in between the superfi cial,
leptomeningeal arteries are called “watershed infarcts.”
■ Th e somatotopic organization of the homunculus,
from inferolateral to superomedial, is as follows: the
tongue, face, hand, arm, and hip; and hanging over
the medial face of the hemisphere are the leg and
foot.