CEREBRUM CEREBRUM ANDAND

BASE OF THE SKULLBASE OF THE SKULL

BYDR MANAH CHANDRA CHANGMAI

IMS

Able to describe the general structure of the Cerebrum and Cerebral Cortex.

Able to identify the Cerebrum, the Lobes of the Brain, the Cerebral Cortex, and its major regions/divisions.

Able to describe the primary functions of the Lobes and the Cortical Regions of the Brain.

Objectives

INTRODUCTIONINTRODUCTION

The cerebrum is the largest part of the brain with two hemisphere.The two cerebral hemisphere are linked by commisural fibres of corpus callosum.

Each cerebral hemisphere contains externally highly convulated cortex of grey matter and internal mass of white matter or medulla.

Each cerebral hemisphere contains lateral venticle continous with the third ventricle through interventricular foramen.

The cerebral hemispheres contains motor and sensory areas and the limbic system.

Each cerebral cortex is often divided phylogenetically into old allocortex,consisting of archicortex and paleocortex and a newer neocortex.

Longitudinal Fissure

Cerebral hemisphere

Cortex and medullaCortex and medulla

Surfaces of cerebral hemisphereSurfaces of cerebral hemisphere

Each cerebral hemisphere has three surfaces

I. Superolateral surfaceII. Medial surfaceIII. Inferior surface. Inferior surface further

divided into twoi. Orbital surfaceii. Tentorial surface

Surfaces of cerebral hemisphere………contd.

Superolateral surface It follows the concavity of the cranial vault Medial surface It is flat and vertical and seperated from its fellow by the great

longitudinal fissure and falx cerebri. Inferior surface Inferior surface or the basal surface is irregular and divided

into orbital and tentorial surface.

SuperolateralMedial surface

Surfaces of the brain

Inferior surface

Orbital surface

Tentorial surface

Borders of cerebral hemisphereBorders of cerebral hemisphere

Superomedial border

Inferior border

Occipital pole

Frontal pole Temporal

pole

Poles of the brainPoles of the brain

Lobes of the brainLobes of the brainFour lobes

are present• Frontal• Parietal• Occipital• Temporal Occasionally

insula is considered as the fifth lobe

Gyrus and sulcusesGyrus and sulcuses

Each cerebral hemisphere shows a complex pattern of convulation called Gyrus

The gyruses are separated by furrows of varying length called Sulci.

The convulated structure increases the cortical volume to three times what it would be if the surface is smooth.

The area of the cerebral cortex is 2200cm²

Sulci(Groove)

Fissure(Deep groove)

Gyri(Elevation)

Important sulci and gyriImportant sulci and gyri

In the suprolateral surface:i. Lateral sulcuso Deep cleft on the lateral

and inferior surfaceo It has a stem which divides

into three rami:anterior,ascending,p-osterior.

o The floor of the posterior ramus is the insula which is hidden cortex.

Lateral sulcus

Central sulcus

Important sulcus and gyrus…….contd.

ii. The central sulcuso It is the boundary between frontal and parietal lobeso It starts at the superomedial border, a little behind the

midpoint between frontal and occipital poles.It runs downards and forwards for about 8-10cm to end little above the posterior ramus of lateral sulcus.

o It demarcates the motor and sensory area of the cerebral cortex.

iii. The other known sulcuses are superior frontal sulcus Inferior frontal sulcus Precentral sulcus Postcentral sulcus

Medial surfaceMedial surface

In the medial surface The commisural fibres of

the corpus callosum lies in the depth of longitudinal fissure

Parts of corpus callosuma. Rostrumb. Genuc. Trunk or bodyd. Splenium The anterior part divided

into outer and inner zone by cingulate sulcus

splenium

Body or trunk

GenuRostrum

Medial surface with corpus callosum

Cingulate sulcus

Parieto-occipital sulcus

Calcarine sulcus Collateral sulcus

Sulcus in the medial surface

Sulcus and gyrus………contd.

The posterior region of the medial surface is traversed by parieto-occipital and calcarine sulcus.The parieto-occipital sulcus marks the boundary between parietal and occipital lobes.

The visual cortex lies above and below the calcarine sulcus.

In the inferior cerebral surface Olfactory sulcus Rhinal sulcus Occipitotemporal sulcus Collateral sulcus

Orbital sulcus

Occipitotemporal sulcus

Collateral sulcus

Rhinal sulcus

Sulcus and important structures on inferior surface of cerebral hemisphere

Olfactory sulcus

Insula

-Present within the lateral sulcusBetween temporal and frontalLobe.

-The overlying cortical areas are called opercula formed from the parts of frontal,temporal and parietal lobe

-Functions linked to emotion and body’s homeostasis

-i.e perception,motor control,self awarness,congnitive functioning interpersonal experience

Insula

Cerebral cortexCerebral cortex

Cerebral cortex is an intricate blend of nerve cells and fibres,neuroglia and blood vessels.

Microscopically the cortex consists of six layers or laminae lying parallel to the surface.

From outside to insideI. Molecular or plexiform layerII. The external granular layerIII. External pyramidal laminaIV.Internal granular layerV. Internal pyramidal cell layerVI.Multiform or pleiomorphic layer

Pyramidal cells

Neocortex has 6 layers designated I, II, III, IV, V, VIPyramidal cells predominate in layers III and VGranule cells in layers II and IV

Pyramidal cells

Granule cells

Cerebral cortex

Pyramidal cells have large apical dendrite and basal dendritesAxon projects downward into subcortical white matter; may have collateralsPyramidal cell is the primary output neuron

Pyramidal cell

Pyramidal cell

Pyramidal cell

Broadmann’s areasBroadmann’s areas These areas were defined and

numbered by korbinian broadmann

The areas are based on the cortical cytoarchitectonic organisation of neurons

Many of the broadmann’s areas are defined on neurological function coorelated closely to diverse cortical functions.

For example Area 1,2,3 – primary

somatosensory area Area 4 – Motor area Area 41,42 – Auditory area Area 44,45 – Broca’s area,etc

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legs

toes

ankle

MotorCortex

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toes

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foot

SensoryCortex

Mapping of sensory and motor areas to the body

•Primary Motor Cortex (Precentral Gyrus) – Cortical site involved with controlling movements of the body.•Broca’s Area – Controls facial neurons, speech, and language comprehension. Located on Left Frontal Lobe.

Broca’s Aphasia – Results in the ability to comprehend speech, but the decreased motor ability (or inability) to speak and form words.

Orbitofrontal Cortex – Site of Frontal Lobotomies

* Desired Effects:- Diminished Rage- Decreased Aggression- Poor Emotional Responses

* Possible Side Effects:- Epilepsy- Poor Emotional Responses- Perseveration (Uncontrolled, repetitive actions, gestures, or words)

Frontal lobes cortical regions

Primary motor cortex

Broca’s area

Orbitofrontal cortex

Primary Somatosensory Cortex (Postcentral Gyrus) – Site involved with processing of tactile and proprioceptive information.

Somatosensory Association Cortex - Assists with the integration and interpretation of sensations relative to body position and orientation in space. May assist with visuo-motor coordination

Primary Gustatory Cortex – Primary site involved with the interpretation of the sensation of Taste.

Parietal lobe cortical areas

Associated somatosensory area(7)

Primary gustatory area (40)

Primary somatosensory area(3, 1, 2)

Primary Visual Cortex – This is the primary area of the brain responsible for sight -recognition of size, color, light, motion, dimensions, etc.

Visual Association Area – Interprets information acquired through the primary visual cortex.

Occipital lobe and cortical regions

White matter of cerebrumWhite matter of cerebrum Consists of myelinated nerve

fibres which are categorized on the basis of their course and connections

A. Association fibres• It links different cortical areas

of the same hemisphere• Two typesi. Short association fibres They are entirely intracotical Some merely pass from one

wall of the sulcus to other.ii. Long association fibres They are present in bundles Example: uncinate

fasciculus,cingulum,superior longitudinal fasciculus,etc

White matter of cerebrum………contd.White matter of cerebrum………contd.

B. Commissural(transverse) fibres

• Commisural fibres cross the midline,linking corresponding areas in the two cerebral hemisphere.

• The largest commissure is the corpus callosum.Other commisures are

a. Anterior b. Posteriorc. Habenulard. Commissure of the fornix.

White matter of cerebrum……..contd.

C. Projection fibres• Projection fibres

connect cerebral cortex with lower levels in the brain and spinal cord.

• Consists of both coticofugal and corticopetal fibres

• Corticofugal fibres converge from all directions to form corona radiata.Corona radiata continous with the internal capsule.

Corpus callosum

Anterior commissure

Habenular commissure

Posteriorcommissure

Commissures of brain

Commissure of fornix

CT SCAN OF THE BRAIN

CT scan of the brain showinga tumour in the right cerebral hemisphere

CT scan of brain…….contd

MRI OF BRAIN

.A non-progressivedisorder• Caused by brain injurypre (70-80%), peri, orpost natally• Injure occurs beforeCNS reaches maturity• Patients often have greatpotential masked by their connections

Cerebral palsy

• Malfunction of motor centers• Postural and balancedifficulties• Normal life expectancypossible• Early death respiratory

Manifestation

Spastic • 52-70% of all CPs• Hyperirritability of muscles• Arms flexed, legs internally rotated• Difficulty bending into a sitting position• Difficulty with head control• Postural difficulty• May not have protective extension

Athetoid or Dyskinetic Type• 25- 30% of CPs• Uncontrollable writhing movements ofopposing muscle groups• All four extremities involved• Neck and face involved• Voluntary movements are flailing• Difficulty uprighting and balancing•Grimacing

• Tremors (rare form) of CP• Rigid 5 -10% of CPs• Flaccid (Hypotonicity)• Mixed 15 - 40% of CPs

• 5 to 10 %• Affects balance and coordination.• They may walk with an unsteady gait with feetfar apart, and they have difficulty withmotions that require precise coordination,such as writing.

Ataxic cerebral palsy

Other types

BASE OF THE SKULLBASE OF THE SKULL

SKULL BASESKULL BASE

Skull base boundaries: Upper surface of the ethmoid bone,orbital plate of the frontal

bone upto the ethmoid bone

Key bones: Orbital Plate of frontal bone Ethmoid bone Sphenoid bone Occipital bone

Skull base……contd.

Divided into three cranial fossa: a. Anterior cranial fossab. Middle cranial fossac. Posterior cranial fossa

Key openings in base of the skull

Foramen spinosumForamen ovaleForamen lacerumForamen rotundumForamen magnumJugular foramenSuperior orbital fissureInferior orbital fissure

Optic canalHypoglossal canalPterygopalatine fossa

Skull base……contd.

Foramen rotundumPresent at the anterior and medial part of sphenoid bone.Structures passinga.Maxillary nerveb.Emissary veins

Foramen ovaleLocated in the anterior part of sphenoid bone,posterolateral to foramen rotundumStructures passing• Mandibular nerve• Accessory meningeal artey• Lesser petrosal nerve• Emissary veins

Foramen spinosumForamen spinosum may be absent in 2% of the cases.Situated posterolateral to foramen ovaleTransmits following structures• Middle meningeal artery•Nervous spinosus from mandibular nerve• Middle meninigeal vein

Foramen magnum Latin”great hole” is present in the occipital boneIt transmits• Medulla oblongata,vertebral arteries• Anterior and Posterior spinal arteries• Spinal accessory nerve•Membrana tectoria,Alar ligaments.

Superior Orbital Fissure

• CN III, IV, V1, VI

• Middle meningeal artery- orbital branch

• Recurrent meningeal artery

• Superior opthalmic vein

Jugular foramen Anterior compartment• Inferior petrosal sinus intermediate compartment• Cranial nerve IX,X,XI Posterior compartment• Internal jogular vein• Meningeal branches of occipital and ascending pharyngeal artery

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