Anatomy of the Cerebrum

Cerebrum-ANATOMY

Shittu LAJ

Lerning objectivesOverview of the CNSCerebral anatomyDiscuss the various parts and functionsApplied anatomy

The human brain

The brain contains roughly ~20 billion neurons- excitatory and inhibitory interactions ensure that theIts response can vary to meet changing circumstances- adaptability requires multiple processing steps- every synapse adds to the delay between stimulus and

response- spinal reflexes provide an immediate response

Organization of the Brain

• Adult human brain contains ~95% of all neural tissue

- weighs about 1.4kg (~3lb)- considerable individual variation exist- brains of males are on average ~10% larger

Organization of the BrainThe basic parts of the brain are as follows:

The cerebrumThe diencephalonThe brain stemThe cerebellum

The brain is organized into groupings of cell bodies (the gray matter) and fibers (the white matter).

The cerebrum & the cerebellum contain gray matter on the outer edges w/white matter below this surface.

While the diencephalon & brain stem have the white matter superficially surrounding internal pockets of gray matter

CerebrumLargest portion of brain (>=80% mass).Responsible for higher mental functions.. The cerebrum is divided into left and right hemispheres by the

longitudinal fissure.The cell bodies in the outer cortex require more surface area

than the underlying white matter which results in much folding. The upfoldings are called gyri (gyrus, singular).The infoldings are called sulci (sulcus, singular).

Corpus callosum:Major tract of axons that functionally interconnects right

and left cerebral hemispheres.

Other parts of the brain

The diencephalon:The epithalamusThe thalamusThe hypothalamus

The brain stemThe midbrainThe ponsThe medulla oblongata

The cerebellum

The Brain

MedullaPons

Cerebellum

MidbrainDiencephalon

Cerebral hemisphere

CerebrumLargest part of the brain

Situated in the anterior and middle cranial fossae

Two parts are involved embryologically: Diencephalon – central coreTelencephalon – cerebral hemispheres

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Fig. 14-5, p. 422

Cerebral hemispheres

General Appearance:Separated by a deep midline sagittal fissure –

longitudinal cerebral fissureThe fissure contains falx cerebri and the anterior

cerebral arteriesIn the depth of the fissure, the corpus callosum

connects the hemispheres across the midlineGyri – the folds of the surface of hemispheresSulci – the fissures separate the gyri

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Cerebral Cortex-histologySurface layer of gray matter -- 3 mm thickNeocortex (six-layered tissue)

newest part of the cortex (paleocortex & archicortex)layers vary in thickness in different regions of brain

2 types of cellsstellate cells

have dendrites projecting in all directions

pyramidal cells have an axon that passes

out of the area

Cerebral cortex -functionsThe is particularly well developed in humans is responsible for many higher brain functions,including manual dexterity (eg to move the fingers

individually so as to play the piano); conscious, discriminative aspects of sensation; cognitive activity, including language, reasoning, and many other aspects of learning and memory.

Lobes of Cerebral Hemispheres

Cerebral hemispheres are divided into lobes by the central, parieto-occipital, lateral and calcarine sulci

Lobes are named according to the cranial bones under which they lie

Lobes are:FrontalParietal TemporalOccipital

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The cerebral hemispheresThe cerebral cortex (consists of six lobes on

each side:frontal, parietal, temporal,occipital,insular, and limbic).

the underlying cerebral white matter, the basal ganglia: a complex of deep gray

matter masses.

cerebrum

The main sulci include

1. Central sulcus:Indents the superior medial border of the

hemisphere, 1 cm behind the mid-pointIt runs downward, forward and toward the

lateral sulcus across the lateral aspect of the hemisphere

The central sulcus is the only sulcus that indents the superior medial border

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cerebrum

2. Lateral sulcus:

Deep cleft on the inferior and lateral surfaces of the cerebral hemisphere

It consists of a short stem and three rami.

3. Parieto-occipital sulcus:

Begins on the superior medial border of the hemisphere, about 5 cm anterior to the occipital pole

It passes downward and anteriorly on the medial surface to meet the calcarine sulcus

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Calcarine sulcus:Found on the medial surface of the hemisphereIt begins under the posterior end of the corpus

callosumIt ascends upward and backward to reach the

occipital pole

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Surfaces of Cerebral Hemisphere

Three surfaces are identifiable:Superolateral surfaceInferior surfaceMedial surface

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Superolateral surface

Frontal lobe – anterior to central sulcus and superior to lateral sulcus

Superolateral surface of frontal lobe is divided by three sulci into four gyri

Precentral sulcus and gyrusSuperior and inferior frontal sulciSuperior, middle and inferior frontal gyri

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Cerebral CortexFrontal lobe:

Anterior portion of each cerebral hemisphere.Precentral gyri:

Contains upper motor neurons.Involved in motor control.

Body regions with the greatest number of motor innervation are represented by largest areas of motor cortex.

Superolateral surfaceTemporal lobe – inferior to lateral

sulcusTwo sulci and three gyriOccipital lobe – small area behind the

parieto-occipital sulcus

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Cerebral Cortex Temporal:

Contain auditory centers that receive sensory fibers from cochlea.

Interpretation and association of auditory and visual information.

Occipital: Primary area responsible for vision and coordination of eye

movements.Insula:

Implicated in memory encoding.Integration of sensory information with visceral responses.Coordinate cardiovascular response to stress.

Superolateral surfaceParietal lobe –

posterior to central sulcus and superior to lateral sulcus, extends upto the parieto-occipital sulcus

Two sulci and three gyri

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Lateral sulcus

Parietal LobePrimary area

responsible for perception of somatesthetic sensation.

Body regions with highest densities of receptors are represented by largest areas of sensory cortex.

Figure 8-7

Medial and Inferior Surface

Important areas are:Corpus callosum

Cingulate sulcus and gyrus

Paracentral lobule

Precuneus and cuneus

Occipitotemporal, collateral and calcarine sulcus

Parahippocampal, medial and lateral occipitotemporal gyrus and uncus

Olfactory sulcus, gyrus rectus and orbital gyri

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inferior-medial surface of Cortex46

Inferior view of cortex

Internal structure of Cerebral Hemispheres

Gray matter – cerebral cortexLateral ventriclesBasal nuclei – masses of gray

matterWhite matter – nerve fibers

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Lateral ventricles

Two lateral ventricles – one is in each cerebral hemisphere

It communicates with the third ventricle through interventricular foramen

C – shaped

Body – lies in the parietal lobe

Anterior horn – frontal lobe

Posterior horn – occipital lobe

Inferior horn – temporal lobe

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Basal gangliaAnatomically, the basal ganglia include the caudate nucleus, the putamen, and the globus pallidus.

(Together they are called the corpus straitum)

Functionally, the basal ganglia and their interconnections and neurotransmitters form the extrapyramidal system.

Basal nuclei

Corpus striatum

Amygdaloid nucleus

Claustrum

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Basal ganglia nuclei

White matterComposed of mylinated nerve fibersClassified into three groups:Commissural fibersAssociation fibersProjection fibers

NB: “ CAP”

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Corpus callosum

Largest commissure

Parts:RostrumGenuBodySplenium

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Rostrum

Genu

Body

Splenium

Fig. 14-5, p. 422

Commissural fibers

Connect corresponding regions of two hemispheres

They are:Corpus callosumAnterior commissurePosterior commissureFornix Habenular commissureHippocampal commissure

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Association fibersConnect various cortical regions within the same

hemisphereThey are:Short association fibers - connect adjacent gyriLong association fibers – collected into named

bundles. They are:Uncinate fascicullusCingulumSuperior longitudinal fascicullusInferior longitudinal fascicullusFronto-occipital fascicullus

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Association fibers

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Projection fibers

Afferent and efferent nerve fibers passing to and from the brainstem to the entire cerebral cortex

They are:Internal capsuleCorona radiataOptic radiation

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Projection fibers

Areas of the cerebrumBrodmann numbers to identify functions-

down to individual sulciQuestion localisation now that we know

more about connectionism and we have a more dynamic view of how the brain works

Broadman number of brain

HomunculusMap of motor and sensory controlReflects the bodySizes indicate the amount of ‘brain’ needed

for various functions Note vast area for the face- why?

Anatomy of the Cerebrum

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