Arterial Blood Supply of the Brain

Arterial Blood Supply of the Brain• Although it accounts for only about 2.5% of

body weight, the brain receives about one sixth of the cardiac output and one fifth of the oxygen consumed by the body at rest.

• The blood supply to the brain is derived from the internal carotid and vertebral arteries which lie in the subarachnoid space.

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…Supply of the Brain• Internal Carotid Arteries• The internal carotid arteries arise in the

neck from the common carotid arteries. The cervical part of the artery ascends vertically through the neck, without branching, to the cranial base. Each internal carotid artery enters the cranial cavity through the carotid canals in the petrous part of the temporal bones

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…Supply of the Brain• The internal carotid arteries course anteriorly

through the cavernous sinuses, with the abducent nerves (CN VI) and in close proximity to the oculomotor (CN III) and trochlear (CN IV) nerves, running in the carotid groove on the side of the body of the sphenoid.

• The terminal branches of the internal carotids are the anterior and middle cerebral arteries

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…Supply of the Brain• The terminal branches of the internal

carotids are the anterior and middle cerebral arteries

…Supply of the Brain• Vertebral Arteries• The vertebral arteries begin in the root of the

neck (the prevertebral parts of the vertebral arteries) as the first branches of the first part of the subclavian arteries. The two vertebral arteries are usually unequal in size, the left being larger than the right.

…Supply of the Brain• The cervical parts of the vertebral arteries ascend

through the transverse foramina of the first six cervical vertebrae.

• The atlantic parts of the vertebral arteries (parts related to the atlas, vertebra C1) perforate the dura and arachnoid and pass through the foramen magnum.

• The intracranial parts of the vertebral arteries unite at the caudal border of the pons to form the basilar artery. The vertebrobasilar arterial system and its branches are often referred to clinically as the posterior circulation of the brain.

…Supply of the Brain• Cerebral Arteries• In addition to supplying branches to deeper parts of

the brain, the cortical branches of each cerebral artery supply a surface and a pole of the cerebrum. The cortical branches of the:

• Anterior cerebral artery supply most of the medial and superior surfaces of the brain and the frontal pole.

• Middle cerebral artery supply the lateral surface of the brain and the temporal pole.

• Posterior cerebral artery supply the inferior surface of the brain and the occipital pole

The cerebral arterial circle (of Willis)• It is an important anastomosis at the base of the brain

between the four arteries (two vertebral and two internal carotid arteries) that supply the brain.

• The arterial circle is formed sequentially in an anterior to posterior direction by the:

1. Anterior communicating artery.2. Anterior cerebral arteries.3. Internal carotid arteries.4. Posterior communicating arteries.5. Posterior cerebral arteries.• The various components of the cerebral arterial circle

give numerous small branches to the brain

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Anastomoses of Cerebral Arteries and Cerebral Embolism

• Branches of the three cerebral arteries anastomose with each other on the surface of the brain; however, if a cerebral artery is obstructed by a cerebral embolism (e.g., a blood clot), these microscopic anastomoses are not capable of providing enough blood for the area of cerebral cortex concerned. Consequently, cerebral ischemia and infarction occur and an area of necrosis results

Strokes• An ischemic stroke denotes the sudden

development of focal neurological deficits that are usually related to impaired cerebral blood flow. An ischemic stroke is generally caused by an embolism in a major cerebral artery.

• Hemorrhagic stroke follows the rupture of an artery or a saccular aneurysm, a sac-like dilation on a weak part of the arterial wall

Venous Drainage of the Brain• Venous drainage occurs via cerebral and

cerebellar veins that drain to the adjacent dural venous sinuses.

• The thin-walled, valveless veins draining the brain pierce the arachnoid and meningeal layer of dura to end in the nearest dural venous sinuses, which ultimately drain for the most part into the IJVs.

Venous Drainage of the Brain• The superior cerebral veins on the superolateral surface

of the brain drain into the superior sagittal sinus

Venous Drainage of the Brain• The inferior and superficial middle cerebral veins from

the inferior, posteroinferior, and deep aspects of the cerebral hemispheres drain into the straight, transverse, and superior petrosal sinuses.

SAV

SMC

Venous Drainage of the Brain• The great cerebral vein (of Galen) is a single, midline

vein formed inside the brain by the union of two internal cerebral veins; it ends by merging with the inferior sagittal sinus to form the straight sinus

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Venous Drainage of the Brain• The cerebellum is drained by superior and inferior

cerebellar veins, draining the respective aspect of the cerebellum into the transverse and sigmoid sinuses.