Anatomy of the Cerebrum
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Cerebrum-ANATOMY
Shittu LAJ
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Lerning objectivesOverview of the CNSCerebral anatomyDiscuss the various parts and functionsApplied anatomy
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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
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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
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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
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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.
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Other parts of the brain
The diencephalon:The epithalamusThe thalamusThe hypothalamus
The brain stemThe midbrainThe ponsThe medulla oblongata
The cerebellum
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The Brain
MedullaPons
Cerebellum
MidbrainDiencephalon
Cerebral hemisphere
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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
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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
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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.
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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.
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cerebrum
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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
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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.
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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.
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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
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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
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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
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Inferior view of cortex
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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.
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Basal nuclei
Corpus striatum
Amygdaloid nucleus
Claustrum
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Basal ganglia nuclei
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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
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Fig. 14-5, p. 422
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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
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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
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Broadman number of brain
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Broadman number of brain
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Broadman number of brain
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HomunculusMap of motor and sensory controlReflects the bodySizes indicate the amount of ‘brain’ needed
for various functions Note vast area for the face- why?