Download MBBS Anterior Circulation and Localisation New Lecture PPT

ARTERIAL SUPPLY OF BRAIN
The blood reaches the brain through 2 systems of blood vessels.
1.Carotid system - Internal carotid artery
2.Vertebral system - Vertebrobasilar arteries

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CIRCLE OF WILLIS
Branches of ICA & branches of VB system of arteries
anastomose in the base of brain to form the arterial circle
of willis.

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FORMATION

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-Ant.communicating artery,which connects Rt & Lt ACA ,forms anterior part
of circle of willis.
- ACA forms anterolateral part on each side.
- Lateral part is formed by termination of ICA on each side.
- Circle is completed posteriorly by bifurcation of basilar artery into Rt & Lt PCA.

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- Posterolaterally , post. communicating artery is the connecting link b/w ICA &
PCA.
MCA does not take part in the formation of circle of willis.

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FUNCTIONAL IMPORTANCE
- This arterial circle equalises pressure of blood flow to 2 sides of brain.

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- Arterial anastomosis provides an alternative route through which blood
entering the ICA or basilar artery may be distributed to any part of cerebral
hemisphere.
- If 1 of major arteries forming circle of willis is blocked,it is through this
anastomosis that blood can be supplied to area of blocked artery.

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ANTERIOR CIRCULATION OF BRAIN
q Internal carotid artery and its
branches

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ANTERIOR CIRCULATION

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INTERNAL CAROTID ARTERY

? Each ICA arises as one of the 2 terminal branches at
the bifurcation of CCA in the neck at the level of C4
vertebra.

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? Artery then ascends up in the carotid sheath &enters
cranial cavity through carotid canal & upper part of
foramen lacerum.

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? ICA - 4 parts
1.Cervical part

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2.Petrous part
3.Cavernous part
4.Cerebral part

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? BRANCHES OF CEREBRAL PART
? Ophthalmic artery

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? Anterior choroidal artery
? Posterior communicating artery
? ANTERIOR CEREBRAL ARTERY
? MIDDLE CEREBRAL ARTERY
ACA & MCA supply entire forebrain except occipital lobe.

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ANTERIOR CEREBRAL ARTERY
It is divided into two segments
? Precommunal(A1) circle of willis or stem which connects ICA
to anterior communicating artery

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? Postcommunal (A2) segment distal to anterior communicating
artery

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A1 SEGMENT SUPPLY
A1 give rise to several deep penetrating branches that supply
? Anterior limb of internal capsule

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? Anterior perforate substance
? Amygdala
? Anterior hypothalamus
? Inferior part of head of caudate nucleus

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A2 SEGMENT SUPPLIES

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? Orbital branches supply medial half of orbital surface of the frontal
lobe
? Frontopolar branch supplies the anteriormost part of the frontal lobe
on Inferior surface
? Callosomarginal and Pericallosal branches supply the medial surface of

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the frontal and parietal lobes
? The functional areas that receive blood from A2 segment of ACA are
the motor and sensory areas for lower limb and perineum

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DISTRIBUTION OF ANTERIOR CEREBRAL ARTERY

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MIDDLE CEREBRAL ARTERY

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? Proximal MCA (M1) segment give rise to penetrating branches
(lenticulostriate arteries)
? In the sylvian fissure MCA divides into superior and inferior
divisions (M2 branches)
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SUPPLY OF M1 SEGMENT
? Putamen
? Outer globus pallidus
? Posterior limb of internal capsule
? Adjacent corona radiata

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? Most of the caudate nucleus

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M2 BRANCHES
? Superior division supplies frontal and superior parietal
cortex
? Inferior division supplies inferior parietal and temporal

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cortex

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SUPPLY OF M2
? Orbitofrontal branches supply the lateral half of orbital surface of the
frontal lobe
? Frontal branches (precentral and central) supply the superolateral surface of

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the frontal lobe excluding the area supplied by the ACA
? Parietal branches supply the Postcentral gyrus, Inferior parietal lobule and
superior parietal lobule excluding the area supplied by the ACA
? Temporal branches supply the lateral surface of the temporal lobe excluding
the Inferior temporal gyrus but the temporal pole

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The functional areas that receive blood from MCA are motor and sensory
areas, premotor area, frontal eye field, auditory area, speech centres in
dominant hemisphere

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DISTRIBUTION OF MIDDLE CEREBRAL ARTERY

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FUNCTIONAL AREAS OF CORTEX

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A.FRONTAL LOBE
1. Motor area ( Area 4 )
2. Premotor motor (Area 6 )
3. Area of voluntary conjugate eyemovements ( Area 8 )
4. Broca's area ( Area 44 )

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5. Exner's area ( Area 45 )
6. Prefrontal area
7. Paracentral lobule

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B. PARIETAL LOBE
1.Cortical sensory area (Area 3,1,2 )

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2.Angular gyrus ( Area 39 )
3.Supramarginal gyrus ( Area 37 )

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C.TEMPORAL LOBE
1. Auditory sensory area ( area 41,42 )
2. Auditory associative area ( area 22)

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3. Limbic system

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D. OCCIPITAL LOBE
1.Visual sensory area ( area 17 )
2. Visual associative area (area 18 ,19 )

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