Ojvensha E learning Resources-Prepared by Dr.B.B.Gosai

Blood supply of Brain (Long Question)

Introduction:

Blood supply of brain and spinal cord is derived from the branches of Internal carotid and vertebral arteries. Branches of these arteries also form circle of Willis at the base of brain and supply brain.

(No need to draw this diagram- only for understanding)

Circle of willis

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Internal carotid artery: (***Important - Viva)

It is branch of common carotid artery at the level of upper border of thyroid cartilage.

Parts of Internal carotid artery:

1. Cervical part: In neck.

2. Petrous part: In petrous temporal bone

3. Cavernous part: In cavernous sinus

4. Cerebral part: at base of brain supplying brain

Branches of Cerebral part of Internal carotid artery:

Ophthalmic artery: Supply orbit and eye (Central artery of Retina is End artery and blockage of this artery leads to blindness)

Middle Cerebral artery: Supply following parts of cerebrum (*****Important - Viva)

1. All superolateral surface up to parietooccipital sulcus except narrow strip along superomedial border supplied by anterior cerebral artery. ( all motor area except leg area)

Applied Anatomy:

Middle Cerebral Artery Occlusion (Blocakge):

• Contralateral hemiparesis and hemisensory loss of face and arm(precentral and postcentral gyri).

• Aphasia if left hemisphere is affected (Broca’s motor area of speech).

• Contralateral homonymous hemianopia (Optic radiation).

• Anosognosia- loss of stereognosis if right hemisphere is affected.

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Anterior Cerebral artery: Supply following parts of cerebrum(*****Important - Viva)

1. All medial surface up to parietooccipital sulcus.

2. 1 inch(2.5cm) strip on superolateral surface (leg area of motor area)

Applied Anatomy:

Anterior Cerebral Artery Occlusion (Blockage):

1. Contralateral hemiparesis and hemisensory loss of leg and foot(paracentral lobule).

2. Inability to identify objects and Personality changes(frontal and parietal lobes).

Anterior choroidal artery: Form choroid plexus and help in formation of cerebraospinal fluid (CSF)

Posterior communicating artery: Communicates with posterior cerebral artery and help in formation of circle of WIllis

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(Draw this diagram- only for long question of Blood supply of brain but important for viva to know arteries supplying parts of Brain)

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Verebral artery: (***Important - Viva)

It is branch of subclavian artery in the neck.

Parts of Vertebral artery:

1. 1st part: In neck from origin to foramen of 6th cervical vertebra.

2. 2nd part: In foramina transversarium of 6th to 1st cervical vertebra

3. 3rd part: on posterior arch of atlas vertebra

4. 4th part: In cranial cavity

Branches of Cranial part of Vertebral artery: (***Important - Viva)

Anterior spinal artery: Supply anterior two third of spinal cord

Posterior inferior cerebellar artery: supply cerebellum, medulla oblongata and give posterior spinal artery which supply posterior one third of spinal cord

Two vertebral arteries unite at the lower border of pons and form Basilar artery.

Basilar artery is located in basilar sulcus of pons and terminates by dividing in to posterior cerebral arteries.

Branches of Basilar artery:

Anterior inferior cerebellar artery: Supply cerebellum

Pontine arteries: Supply pons

Labrynthine artery: Supply Internal ear

Superior cerebellar artery: supply cerebellum

Posterior cerebral artery: Help in formation of circle of Willis.

Posterior cerebral artery supply: (*****Important - Viva)

1. Inferolateral and medial surface of temporal lobe.

2. Lateral and medial surface of occipital lobe (Visual cortex).

Applied Anatomy:

Posterior Cerebral Artery Occlusion (Blockage):

1. Contralateral homonymous hemianopia (calcarine cortex). Macula is spared-not affected due to it’s dual blood supply also from middle cerebral artery.

2. Impairment of memory (Medial part of temporal lobe).

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Circle of Willis (Circulosus arteriosus cerebri):

(***** Very Important Short note)

(Draw this diagram- for short note with labels with Red circles)

Introduction: Circle of Willis is vascular anastmotic circle formed between branches of two internal carotid and two vertebral arteries.

Location: Interpeduncular fossa at the base of brain.

Arteries contributing formation of circle of Willis:

Anteriorly: Anterior communicating artery (Branch of Internal carotid artery).

Anterolateraly: Anterior cerebral artery(Branch of Internal carotid artery).

Posterolateraly: Posterior communicating artery (Branch of Internal carotid artery).

Posteriorly: Posterior cerebral artery (Branch of Basilar artery)

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Importance: Circle of Willis is end to end functional anastomosis and allow blood to supply both cerebral hemisphere in case of blockage of any of the arteries forming circle.

Normally streams of all the vessels do not mix. At a point where opposite vessels meet, the pressure is zero.

Applied anatomy:

During blockage of one of the internal carotid or vertebral artery the blood will be supplied by the circle of Willis.

Carotid angiography: Radioopaque dye is injected in the common carotid artery will show blood vessels of one side only (Due to Zero point as At this point pressure is Zero normally and Blood do not cross to opposite side). If the circle of willis is completely seen and arteries of opposite side are seen, it indicated blockage in one of the vessels forming circle of willis:

Vertebral angiography: Similar like carotid angiography done for vertebral artery.

…………………

Veins of the brain:

External Cerebral Veins:

Superior cerebral veins: From lateral surface of cerebrum and drains into superior sagittal sinus.

Superficial middle cerebral vein: From lateral surface of cerebrum and drains into cavernous sinus.

Deep middle cerebral vein: Drains insula and joined by anterior cerebral and striate veins to form basal vein. Basal vein joins with great cerebral vein which ultimately drains into straight sinus.

Internal Cerebral Veins:

Two internal cerebral veins: Formed by union of thalamostriate vein and choroid vein. These veins drain into straight sinus.

Ojvensha E learning Resources-Prepared by Dr.B.B.Gosai

(No need to draw this diagram- only for understanding)

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