Blood supply of the brain ARTERIES OF THE BRAIN The brain is supplied by the two internal carotid and two vertebral arteries. The four arteries lie within the subarachnoid space, and their branches anastomose on the inferior surface of the brain to form the circulus arteriosus (circle of willis).
1-internal carotid artery ICA:
The ICA begins at the bifurcation of the common carotid artery, where it usually possess a localized dilatation, called carotid sinus ,it ascend the neck and perforates the base of the skull passing through the carotid canal of the temporal bone. The artery then run horizontally forward through the cavernous sinus, then it enters the subarachnoid spaces running on medial side of anterior clinoid process, where it divides into anterior cerebral artery ACA and middle cerebral artery MCA.
Branches of the cerebral portion of ICA:
Arise as the ICA emerges from the cavernous sinus. It enters the orbit through optic canal. It supplies the eye, frontal area of the scalp the ethmoid, frontal sinus and the dorsum of nose.
2-posterior communicating artery (PCoA)
PCoA is a small artery that originates from the ICA close to its terminal bifurcation. the PCoA runs posteriorly above the oculomotor nerve to join the posterior cerebral artery PCA .
ACA runs forward and medially superior to the optic nerve and enter the longitudinal fissure of the cerebrum. Here it is joined the ACA of the opposite side by the anterior communicating artery ACoA. It Curves backward over the corpus callosum, and finally anastomose with the PCA.
ACA supplies the medial surface of cerebral cortex as far back the parieto-occipital sulcus, also supply a strip of cortex about one inch(2.5cm)wide on the adjoining lateral surface, thus the ACA supplies the leg area of the precentral gyrus.
5-middle cerebral artery (MCA):
The largest branch of ICA runs laterally in the lateral cerebral sulcus.
MCA supply the entire lateral surface of the hemisphere, except of the narrow strip supplied by the ACA, the occipital pole, and the inferolateral surface of the hemisphere which are supplied by the PCA.
That it is to say MCA supplies all the motor area except the leg area.
2-vertebral artery V.A
The vertebral artery, a branch of the first part of the subclavian artery, ascends the neck by passing through the foramina in the transverse process of the upper six cervical vertebras.
It enters the skull through the foramen magnum and then passes upward, forward and medially on the medulla oblongata.
At the lower border of Pons, it joins the vertebral artery of the opposite side to form the basilar artery.
Are small branches and supply the bone and dura in the posterior cranial fossa .
2-posterior spinal artery:
It descends as two branches, one anterior and one posterior to the posterior roots of the spinal nerves.
3-anterior spinal artery:
Is formed from contributory branch from each vertebral artery near its termination.
Anterior spinal artery descends on the anterior surface of the medulla oblongata and spinal cord.
4-posterior inferior cerebellar artery (PICA):
Is the largest branch of the vertebral artery, it supplies the cerebellum, medulla oblongata and the choroid plexus of the fourth ventricle.
Are very small branches that are distributed to the medulla oblongata.
The basilar artery, formed by the union of the two vertebral arteries, ascends in a groove on the anterior surface of the Pons. At the upper border of the Pons. It divides into two posterior cerebral arteries PCA.
1-pontine arteries –supply Pons.
2-labyrinthine artery –supply the internal ear.
3-anterior inferior cerebellar artery (AICA):
Supplies the anterior and inferior parts of cerebellum, few branches pass to the Pons and medulla oblongata.
4-superior cerebellar artery:
Arise close to the termination of the basilar artery.
5-posterior cerebral artery (PCA):
PCA joined the ICA by its branch the posterior communicating artery (PCoA)
PCA supply the infero-lateral and medial surface of the temporal lobe and the lateral and medial surface of the occipital lobe. Thus PCA supplies the visual cortex. The Circle of Willis lies at the base of brain. It's formed by the anastomosis between the two ICA and two vertebral arteries, the anterior communicating, PCA, and basilar arteries all contribute to the circle.
Cicle of willis allow the blood that enters be either ICA or vertebral arteries to be distributed to any part of both cerebral hemispheres.
Cortical and central branches arise from the circle and supply the brain substances.
VEINS OF THE BRAIN: They emerge from the brain and lies in the subarachnoid space. They pierce the arachnoids matter and meningeal layer of the dura and drain into the cranial venous sinuses.
1-external cerebral veins: include:
A-superior cerebral veins: pass upward over the lateral surface of the cerebral hemisphere and empty into the superior sagittal sinus.
B-superficial middle cerebral vein: drains the lateral surface of cerebral hemisphere .it runs inferiorly in the lateral sulcus and empties into the cavernous sinus.
C-deep middle cerebral vein: drains the insula and is joined by the anterior cerebral and striate veins to form basal vein which in turn joins the great cerebral vein that drains into straight sinus.
2-internal cerebral veins: include
Both run beneath the splenium of corpus callosum to form the great cerebral vein, which empties into the straight sinus.
Clinical notes :
Vascular lesion of the brain is common and the resulting neurological deficit will depend on the size of artery occluded, the state of collateral circulation, and the area of the brain involved.
0Impairment of cerebral flow may be caused by many conditions like:
1-diseases that produce an alteration in blood pressure as:
-postural hypotension (in patient get up after long time confined to bed).
-cardiac diseases (like atrial fibrillation that result in marked fall in cardiac out put and reduction in cerebral blood flow.
2- Disease of arterial wall.
The most common cause of narrowing of the lumen of the arteries that supply the brain is atheroma from atherosclerosis.
3-Blockage of cerebral arteries can occur by emboli as in fat embolism that usually follows sever fracture of one of the long bones.
Aneurysm is a localized dilatation in the arterial wall. Congenital aneurysm occur most commonly at the site, where two arteries joint in the circle of willis resulting in compressive force on neighboring structure such as optic nerves, or third, fourth, or sixth cranial nerves and produce signs and symptoms, or may suddenly rupture into subarachnoid space causing subarachnoid hemorrhage.
C-intra cranial hemorrhage:
Intra cranial hemorrhage may result from trauma or cerebral vascular lesion resulting in the following types of hemorrhages: