Download MBBS (Bachelor of Medicine and Bachelor of Surgery) Anterior Circulation and Localisation PowerPoint PPT presentation
The blood reaches the brain through 2 systems of blood vessels.
1.Carotid system - Internal carotid artery
2.Vertebral system - Vertebrobasilar arteries
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.
FORMATION
-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.
- Posterolaterally , post. communicating artery is the connecting link b/w ICA &
PCA.
MCA does not take part in the formation of circle of willis.
FUNCTIONAL IMPORTANCE
- This arterial circle equalises pressure of blood flow to 2 sides of brain.
- 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.
ANTERIOR CIRCULATION OF BRAIN
q Internal carotid artery and its
branches
ANTERIOR CIRCULATION
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.
? Artery then ascends up in the carotid sheath &enters
cranial cavity through carotid canal & upper part of
foramen lacerum.
? ICA - 4 parts
1.Cervical part
2.Petrous part
3.Cavernous part
4.Cerebral part
? BRANCHES OF CEREBRAL PART
? Ophthalmic artery
? Anterior choroidal artery
? Posterior communicating artery
? ANTERIOR CEREBRAL ARTERY
? MIDDLE CEREBRAL ARTERY
ACA & MCA supply entire forebrain except occipital lobe.
ANTERIOR CEREBRAL ARTERY
It is divided into two segments
? Precommunal(A1) circle of willis or stem which connects ICA
to anterior communicating artery
? Postcommunal (A2) segment distal to anterior communicating
artery
A1 SEGMENT SUPPLY
A1 give rise to several deep penetrating branches that supply
? Anterior limb of internal capsule
? Anterior perforate substance
? Amygdala
? Anterior hypothalamus
? Inferior part of head of caudate nucleus
A2 SEGMENT SUPPLIES
? 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
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
DISTRIBUTION OF ANTERIOR CEREBRAL ARTERY
MIDDLE CEREBRAL ARTERY
? Proximal MCA (M1) segment give rise to penetrating branches
(lenticulostriate arteries)
? In the sylvian fissure MCA divides into superior and inferior
divisions (M2 branches)
?
SUPPLY OF M1 SEGMENT
? Putamen
? Outer globus pallidus
? Posterior limb of internal capsule
? Adjacent corona radiata
? Most of the caudate nucleus
M2 BRANCHES
? Superior division supplies frontal and superior parietal
cortex
? Inferior division supplies inferior parietal and temporal
cortex
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
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
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
DISTRIBUTION OF MIDDLE CEREBRAL ARTERY
FUNCTIONAL AREAS OF CORTEX
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 )
5. Exner's area ( Area 45 )
6. Prefrontal area
7. Paracentral lobule
B. PARIETAL LOBE
1.Cortical sensory area (Area 3,1,2 )
2.Angular gyrus ( Area 39 )
3.Supramarginal gyrus ( Area 37 )
C.TEMPORAL LOBE
1. Auditory sensory area ( area 41,42 )
2. Auditory associative area ( area 22)
3. Limbic system
D. OCCIPITAL LOBE
1.Visual sensory area ( area 17 )
2. Visual associative area (area 18 ,19 )
THANKYOU..
This post was last modified on 12 August 2021