Cerebrum Sulci and Gyri and Circle of Willis

8/10/2019 Cerebrum Sulci and Gyri and Circle of Willis

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CEREBRUM

SULCI & GYRI

FUNCTIONAL AREAS


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Cerebrum Cerebrum is a highly

convoluted bilobed

structure. Situatedin the

cranial fossae


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CEREBRUM

Median longitudinal

fissure

3 poles frontal,

occipital, temporal

3 borders

superomedial,

inferomedial, inferolateral

3 surfaces

superolateral, medial,

inferior

Superolateralsurface

Inferior surface

Medial surface


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SUPEROLATERAL SURFACEFive lobes on the basis of

1.Central sulcus (Rolando)2.Lateral sulcus posterior

ramus & line extending

backwards4.Parieto-occipitalis sulcus

5.Pre-occipital notch

6.Line joining 4 & 5


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LOBES OF THE CEREBRUM


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Angular & Supramarginal gyrus


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Central sulcus (of Rolando)


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InsulaLies within lateral sulcus

Overlying cortical areas are called 'Operculum'


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MEDIAL SURFACE


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INFERIORSURFACE


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INFERIOR SURFACE


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Functional areas of the Brain Cerebral cortex demarcated

into large number of areaswhich differ from each other

in their functions

Divided by Brodmann into 47areas


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FUNCTIONAL AREAS

Brodmannsclassification

Types of cortical areas:-

Motor areas- corticospinal & corticonuclear tracts.

Sensory areas:- receive afferent fibers fromthalamic nuclei.

Association areas:-associative, cognitive &integrative functions.


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MOTOR AREA

Primary motor area-4 ofBrodmann.

precentral gyrus, anteriorpart of the paracentral lobule.

Controls voluntary motoractivities of the opposite halfof the body.

Lesion of primary motor

area in one hemisphereproduce paralysis of theextremities of the oppositehalf of the body.


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PRIMARY SENSORY AREA

3, 1 & 2 Postcentral gyrus, extend to

posterior part of the paracentrallobule on the medial surface.

Concerned with perception of

sensations from opposite half ofthe body.

Receives projections fromthalamus.

Lesion- loss of sensation fromopposite half of the body.


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Speech centres

Motor speech areas/Brocasarea 44 & 45

Sensory speech area/ area

22,39,40 (wernickesarea22)

Sensory speech areareceives input from

hearing, vision, touch &proprioception & thenprojected to brocasareathrough arcuate fasciculus.


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BROCAS AREA

Pars triangularis-45 & pars

opercularis- 44 of inferiorfrontal gyrus of the frontallobe of the left hemisphere.

Production of expressive

speech / Vocalization.Formation of words withconnections to adjacentprimary motor area.

Lesions- Motor aphasia.Agrammatical & nonfluentspeech.

Expressive aphasia.


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SENSORY SPEECH AREAArea 39 of Angular gyrus, stores

visual images & recognises objects bysight.

lesion- word blindness. Words areseen but not comprehended.

ALEXIA, AGRAPHIAArea 40 of supramarginal gyrus ofthe inferior parietal lobule,recognises familiar objects with help

of touch & proprioceptionLesion produces astereognosis

conduction aphasia- arcuatefasciculus is inv repetition of spoken

language is difficult


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WERNICKES AREAArea 22 of superior temporal

gyrus Comprehends spokenlanguage, recognises familiarsounds & words

Lesion produces worddeafness/ sensory aphasia,unable to interpret spokenwords.

Lesions inv both motor &sensory areas result in loss ofproduction of speech as well asloss of understanding of thespoken & written speech.

Global aphasia.


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Speech areas


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AUDITORY AREA 41 & 42

Primary auditory area 41, insuperior surface of thesuperior temporal gyrus

lesions-word deafness.


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visual area Primary visual area-17 in

walls & floor of calcarinesulcus. Perception ofisolated visual impressionslike color, size, form,motion & illumination.

Loss of vision


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Visual & its association areasArea 18/ parastriate area,

Area 19/ peristriate area.Together called asoccipital eye field.Receives afferent fromprimary area.

Relates visual

information to pastexperiences & responsiblefor recognition of objects.


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Brain is sensitive to hypoxia & hypoglycemia.

10 secs of cessation of blood flow consciousnessis lost

More than 4 mins IRREVERSIBLE brain

damage starts.

Brain 2% of total body weight receives about15% of cardiac output and utilizes 25% of total

oxygen consumption of body

Per minute, 750 ml of blood circulates throughbrain of an average weight.


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Arteries of Brain

Vertebral system

Carotid System


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1.Internal carotid artery

Branch of common carotid artery given in neck.

Enters cranial cavity through carotid canal.

Internal carotid artery- branches (terminal) Anterior cerebral artery and

Middle cerebral artery.


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Internal carotid artery


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BASILAR ARTERY


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CIRCLE OF WILLIS/Circulus arteriosus


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Location

In Interpeduncular fossa

Around optic chiasma

Branches


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Branches

1.Central branches numerous, slender & arise ingroups. Immediately they pierce brain to supply

internal parts

Do not anastomose & are called end arteries.

Supplies diencephalon, corpus striatum & internal

capsule.

2.Cortical branches Ramify over cortex toanastomose on piamater.

Numerous branches enter cortex at right angles &these do not anastomose.

3. Choridal Branches

supplies the ventricles


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ANT.CER.A

POST.CER.A

MID.CER.A

LATERAL SURFAC


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CORTICAL BRANCHES- MEDIAL SURFACE


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MEDIAL SURFACE

ANT.CER.A

POST.CER.A

MID.CER.A


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CORTICAL BRANCHES- INFERIOR SURFACE


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Cerebral circulationfunctional significance

Internal carotid artery &posterior cerebral artery in

posterior communicatingartery.

Two vertebral arteries inbasilar artery

Two anterior cerebralarteries in anteriorcommunicating artery.

Normally there is little or no mixing of blood streams

between


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Right half of brain is supplied by rightvertebral & right Internal carotid artery

Left half of brain is supplied by left vertebraland left internal carotid artery

However, if internal carotid artery or vertebralartery or their branches get occluded, blood

passes forward or backward across variousalternative routes for Collateral Circulation.


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Cerebrum Sulci and Gyri and Circle of Willis