Blood Supply Of Brain

The brain is supplied by two systems namely

1. Carotid system(70%)

2. Vertebrobasilar system(30%)

Carotid System:

Carotid system consists of an internal carotid artery, a branch of the common carotid artery. Internal carotid artery originates from the common carotid artery at the level of C4.

After originating from the common carotid artery ascends upward through the carotid canal of the temporal bone then passes anterior through the cavernous sinus and enters the subarachnoid space.

At lateral sulcus, ICA divides into 

Anterior cerebral artery.

Middle cerebral artery.

Following are the branches of ICA which supplies the brain 

1.ANTERIOR CEREBRAL ARTERY

It curves backwards over corpus callosum and does an anastomosis with posterior cerebral artery.

Cortical branches Supply the medial surface of hemisphere while central branches supply lentiform caudate and internal capsule.

2.OPHTHALMIC ARTERY 

Supplies orbital structures.

3.MIDDLE CEREBRAL ARTERY

Runs laterally in the lateral cerebral sulcus.

Supplies the entire lateral surface of cerebral hemispheres except for the leg area and visual cortex. 

4. POSTERIOR COMMUNICATING ARTERY 

Run posteriorly above the oculomotor nerve to join the posterior cerebral artery.

5. CHOROIDAL ARTERY 

lies close to the optic tract and enters the lateral ventricle.

Supplies lateral geniculate body, optic tract and internal capsule. 

Vertebrobasilar system

Originate from the first part of the subclavian artery.

Ascends through the neck by passing through the foramina in the transverse process of upper six cervical vertebrae.

Enters the skull through the foramen magnum and then enters the subarachnoid space.

At the lower border of the pons joins the opposite vertebral artery to form BASILLAR ARTERY.

Following are the branches that supply the brain.

VERTEBRAL ARTERY BRANCHES 

1.ANTERIOR SPINAL ARTERY 

Descend on the anterior surface of the spinal cord and medulla, supplies the anterior two-thirds of the spinal cord.

2.POSTERIOR SPINAL ARTERY 

May arise from a vertebral artery or posterior inferior cerebral artery.supplies posterior one-third of the spinal cord.

3. MININGEAL BRANCH 

supplies the falx cerebri.

4. POSTERIOR INFERIOR CEREBRAL ARTERY 

passes between medulla and cerebellum.

Supplies cerebellum.

5.MEDULLARY ARTERY 

Supplies some part of the medulla.

BASILLAR ARTERY BRANCHES

1.ANTERIOR INFERIOR CEREBRAL ARTERY 

Supplies anterior and inferior part of the cerebellum.

2.LABRYINTHINE ARTERY 

Accompanies the 7th and 8th cranial nerve in internal acoustic meatus.

Supplies internal ear.

3.PONTINE ARTERY 

Numerous pontine arteries supply pones.

4.SUPERIOR CEREBRAL ARTERY 

Supplies superior surface of the cerebellum.

5.POSTERIOR CEREBRAL ARTERY 

Supplies occipital and temporal lobe thus is supplies visual cortex.