Dr. Zeenat ZaidiDr. Zeenat Zaidi

CEREBRUCEREBRUMM

Cerebrum Largest part of the forebrainLargest part of the forebrain Derived from Derived from telencephalontelencephalon Divided into two halves, the Divided into two halves, the

cerebral hemipherescerebral hemipheres The two hemispheres are The two hemispheres are

separated by a deep separated by a deep median median lingitudinal fissure lingitudinal fissure which which lodges the falx cerebrilodges the falx cerebri

In the depth of the fissure, In the depth of the fissure, the hemispheres are the hemispheres are connected by a bundle of connected by a bundle of fibers called the fibers called the corpus corpus callosumcallosum

Median longitudinal fissure

Corpus callosum

Right hemisphere

Left hemisphere

SuperolateralSuperolateral

MedialMedial

Inferior

SurfacesSurfaces

The The structure of cerebral structure of cerebral hemiphereshemipheres includes: includes: Superficial layer of grey Superficial layer of grey

matter, the matter, the cerebral cortex Deeper to the cortex, axons Deeper to the cortex, axons

running to and from the running to and from the cells of the cortex form an cells of the cortex form an extensive mass of extensive mass of white white mattermatter

Burried within the white Burried within the white matter lie a number of matter lie a number of nuclear masses (nuclear masses (caudate, caudate, putamen, globus pallidusputamen, globus pallidus) ) collectively known as the collectively known as the basal ganglia

CortexBasal ganglia

WMWM

WMWM

The superficial layer of grey matter is highly convoluted to The superficial layer of grey matter is highly convoluted to form a complex pattern of ridges form a complex pattern of ridges (gyri)(gyri) and grooves and grooves (sulci)(sulci)

This arrangement This arrangement maximize the surface area maximize the surface area of the cerebral of the cerebral cortex (about 70% is hidden within the depths of sulci)cortex (about 70% is hidden within the depths of sulci)

G

SG G

Three sulci,consistent in their position, divide each hemisphere into 4 lobes (named after overlying bones)

motor function, motivation, aggression, smell and mood

reception and evaluation of sensory information

smell, hearing, memory and abstract thought

visual processing

Parieto-occipital sulcus

It is responsible for:It is responsible for: establishing emotional statesestablishing emotional states linking conscious intellectual functions with the linking conscious intellectual functions with the

unconscious autonomic functions unconscious autonomic functions facilitating memory storage and retrievalfacilitating memory storage and retrieval

Functionally each hemisphere contains a ‘limbic limbic lobe’lobe’ on the medial surface.

Central sulcus Central sulcus An uninterrupted vertical sulcus An uninterrupted vertical sulcus

running from the lateral fissure running from the lateral fissure to the median longitudinal to the median longitudinal fissurefissure

Extending for a short distance Extending for a short distance on the medial surface of the on the medial surface of the hemispherehemisphere

Separates the frontal lobe from Separates the frontal lobe from parietal lobeparietal lobe

Lateral sulcus Lateral sulcus Deepest cleft on the lateral Deepest cleft on the lateral

surfacesurface Separates the temporal lobe Separates the temporal lobe

from the frontal and parietal from the frontal and parietal lobeslobes

Parieto-occipital sulcusParieto-occipital sulcus Separates the occipital lobe Separates the occipital lobe

from the parietal lobe on the from the parietal lobe on the mdial surfacemdial surface

FF PP

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PP

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Frontal lobe: Frontal lobe: Precentral gyrusPrecentral gyrus Superior & inferior Superior & inferior

frontal sulcifrontal sulci divide the divide the lobe into lobe into superior, superior, middle & inferior middle & inferior frontal gyrifrontal gyri

Parietal lobe: Parietal lobe: Postcentral gyrusPostcentral gyrus Intraparietal sulcusIntraparietal sulcus

dividing the lobe into dividing the lobe into superior & inferior superior & inferior parietal lobulesparietal lobules

Superior parietal lobule

Inferior parietal lobule

Temporal lobe: Temporal lobe: Superior & inferior Superior & inferior

temporal sulcitemporal sulci giving giving rise to rise to superior, superior, middle & inferior middle & inferior temporal gyritemporal gyri

InsulaInsula: : the gyri in the the gyri in the depth of depth of lateral lateral fissurefissure, covered by , covered by parts of frontal, parts of frontal, parietal & temporal parietal & temporal lobes called the lobes called the operculaopercula (removed in (removed in lower pic.)lower pic.)

Insula

(Lateral)

Medial Surface SulciSulci: Cingulate, Parieto-occipital, Calcarine : Cingulate, Parieto-occipital, Calcarine GyriGyri: Cingulate, Parahippocampal: Cingulate, Parahippocampal

Histological Structure of Cerebral Cortex

Contains nerve Contains nerve cell bodies, dendritic cell bodies, dendritic arborizations, synapses, neuroglia, blood arborizations, synapses, neuroglia, blood vesselsvessels

ArchicortexArchicortex and and PaleocortexPaleocortex (hippocampus (hippocampus and parts of temporal lobe associated with and parts of temporal lobe associated with olfactory functions) have olfactory functions) have three layered three layered structurestructure

NeocortexNeocortex, generally consists of , generally consists of six layerssix layers, , although the detailed cytological structure although the detailed cytological structure varies from region to regionvaries from region to region

Histological Structure of Cerebral Cortex Layer ILayer I: few nerve cells, many : few nerve cells, many

processes and synaptic interactionsprocesses and synaptic interactions Layer IILayer II: many small neuron, which : many small neuron, which

establish intercortical connectionsestablish intercortical connections Layer IIILayer III: medium sized neurons giving : medium sized neurons giving

rise to rise to association & commissural fibersassociation & commissural fibers Layer IVLayer IV: site of termination of : site of termination of afferent afferent

fibersfibers from the specific thalamic nuclei from the specific thalamic nuclei Layer Layer VV: origin of : origin of projection fibers to projection fibers to

extracortical targetsextracortical targets. In primary motor . In primary motor cortex, this layer contains giant Betz cortex, this layer contains giant Betz cells which give rise to pyramidal fiberscells which give rise to pyramidal fibers

Layer VILayer VI: contain : contain association and association and projection neuronesprojection neurones

Brodmann's numbering of these cortical locations has become one of the standard ways in which clinicians identify brain areas.

The basis of Brodmann's cortical localization is its subdivision into 'areas''areas' with similar cellular and laminar structure

BrodmannBrodmann produced a produced a numberednumbered, cytological map of cerebral , cytological map of cerebral cortex based upon its regional histological characteristicscortex based upon its regional histological characteristics

Functions of the Cerebral Cortex Is necessary for conscious awareness and thought, Is necessary for conscious awareness and thought,

reasoning & intellect, emotions, behaviour & memory reasoning & intellect, emotions, behaviour & memory (stores information and retrieves when needed)(stores information and retrieves when needed)

Receives all sensory modalities (mostly through Receives all sensory modalities (mostly through thalamus), consciously perceives and interprets in the thalamus), consciously perceives and interprets in the light of previous experiencelight of previous experience

Is the highest level where motor system is represented.Is the highest level where motor system is represented. Controls & directs the conscious or volitional motor Controls & directs the conscious or volitional motor

functions of the body functions of the body Is the site where the actions are conceived and initiated Is the site where the actions are conceived and initiated

Functional Areas Functional Areas of the of the

Cerebral CortexCerebral Cortex

Frontal LobePrimary motor cortexPrimary motor cortex Located in Located in precentral gyrus precentral gyrus

(Brodmann area 4)(Brodmann area 4) Controls Controls voluntary, skilled voluntary, skilled

movementsmovements (fractionated (fractionated movements)movements)

AfferentsAfferents: from ventral : from ventral lateral (VL) nucleus of lateral (VL) nucleus of thalamusthalamus

EfferentsEfferents: Corticospinal : Corticospinal (30%) and corticobulbar (30%) and corticobulbar fibers. 3% of corticospinal fibers. 3% of corticospinal fibers arise from Betz cellsfibers arise from Betz cells

The body is represented The body is represented contralaterallycontralaterally, in a precise , in a precise somatotopic fashion, depicted as somatotopic fashion, depicted as a a ‘motor homunculus‘motor homunculus’’

The representation of body is The representation of body is invertedinverted, with the head area in the , with the head area in the most inferior part of the most inferior part of the precentral gyrus and then precentral gyrus and then progressing superiorlyprogressing superiorly

The The lower limb is represented on lower limb is represented on the medial surfacethe medial surface

The area of the cortex devoted to The area of the cortex devoted to a particular body parts is a particular body parts is proportional to proportional to the degree of the degree of precision with which movements precision with which movements can be executedcan be executed (and not to the (and not to the size)size)

Larynx, tongue, face & digits of Larynx, tongue, face & digits of hand are represented by relatively hand are represented by relatively large regionslarge regions

Premotor cortexPremotor cortex Located in the region immediately Located in the region immediately

anterior to the precentral gyrus anterior to the precentral gyrus (Brodmann’s area 6)(Brodmann’s area 6)

On the On the lateral surfacelateral surface, this includes , this includes the the posterior parts of superior, posterior parts of superior, middle and inferior frontal gyrimiddle and inferior frontal gyri

On the On the medial surfacemedial surface, it includes , it includes region of region of supplementary motor supplementary motor cortex.cortex.

In supplementary motor cortex, In supplementary motor cortex, body is represented body is represented somatotopicallysomatotopically and this representation is and this representation is bilateral.bilateral.

Premotor area functions in Premotor area functions in programming of, and programming of, and preparationpreparation for, for, movementmovement & & in the in the control of posturecontrol of posture

AfferentsAfferents: from ventral : from ventral anterior (VA) nucleus of anterior (VA) nucleus of thalamusthalamus

EfferentsEfferents: : Short association fibersShort association fibers to to

primary motor cortexprimary motor cortex CorticospinalCorticospinal and and

corticobulbarcorticobulbar fibers. There fibers. There are no Betz cells in are no Betz cells in premotor cortexpremotor cortex

Frontal eye fieldFrontal eye field Located in the Located in the middle middle

frontal gyrusfrontal gyrus immediately immediately in front of premotor cortex in front of premotor cortex (Brodmann’s area 8)(Brodmann’s area 8)

Controls Controls voluntary voluntary conjugate deviation of the conjugate deviation of the eyeseyes while scanning the while scanning the eye fieldeye field

Damage to this area Damage to this area results in conjugate results in conjugate deviation of the eyes deviation of the eyes toward the side of lesion toward the side of lesion

Broca’s (motor speech) areaBroca’s (motor speech) area Located in the Located in the inferior frontal inferior frontal

gyrusgyrus of the dominant of the dominant hemisphere (usually left)hemisphere (usually left)

Brodmann’s area 44 & 45Brodmann’s area 44 & 45 Involved in Involved in language language

functionsfunctions Interconnected with parts of Interconnected with parts of

ipsilateral temporal, parietal ipsilateral temporal, parietal and occipital lobesand occipital lobes

Prefrontal cortexPrefrontal cortex Extensive region of the frontal Extensive region of the frontal

lobe lobe anterior to premotor areaanterior to premotor area Has Has cognitive functionscognitive functions of high of high

order e.g. intellectual, order e.g. intellectual, judgemental and predictive judgemental and predictive faculties and the planning of faculties and the planning of behaviourbehaviour

AfferentsAfferents: mediodorsal and : mediodorsal and anterior nuclei of thalamusanterior nuclei of thalamus

EfferentsEfferents: to parietal, occipital : to parietal, occipital and temporal cortex through long and temporal cortex through long association fibersassociation fibers

Parietal lobePrimary somatosensory cortexPrimary somatosensory cortex

Located in Located in postcentral gyrus postcentral gyrus (Brodmann’s area 1, 2, 3)(Brodmann’s area 1, 2, 3)

It is the final relay station for It is the final relay station for general sensations to a conscious general sensations to a conscious levellevel

AfferentsAfferents: Thalamocortical : Thalamocortical projections from the projections from the ventral ventral posterior nucleus posterior nucleus

The body is represented The body is represented contralaterallycontralaterally, in a precise , in a precise somatotopic fashion, depicted as a somatotopic fashion, depicted as a ‘sensory homunculus‘sensory homunculus’’

The representation of body is The representation of body is invertedinverted, with the head area in the , with the head area in the most inferior part of the most inferior part of the precentral gyrus and then precentral gyrus and then progressing superiorlyprogressing superiorly

The The lower limb is represented on lower limb is represented on the medial surfacethe medial surface

The area of the cortex devoted to The area of the cortex devoted to a particular body parts is a particular body parts is proportional to proportional to the richness of its the richness of its sensory innervationsensory innervation (and not to (and not to the size)the size)

Larynx, tongue, face, lips & Larynx, tongue, face, lips & palmer surface of the hand and palmer surface of the hand and digits are represented by digits are represented by relatively large regionsrelatively large regions

Adjascent to mouth area is a Adjascent to mouth area is a region where region where tastetaste is perceived is perceived

Parietal association cortexParietal association cortex Located posterior to Located posterior to primary primary

somatosensory cortexsomatosensory cortex Superior parietal lobule Superior parietal lobule

responsible for:responsible for: Interpretation of general Interpretation of general

sensory informationsensory information Conscious awareness of Conscious awareness of

contralateral half of the body contralateral half of the body Inferior parietal lobule interfaces Inferior parietal lobule interfaces

between somatosensoryy cortex between somatosensoryy cortex and the visual & auditory cortices and the visual & auditory cortices (and speech area in dominant (and speech area in dominant hemisphere)hemisphere)

Temporal LobePrimary auditory cortexPrimary auditory cortex

Located in the Located in the superior surface superior surface of the superior temporal gyrus of the superior temporal gyrus (Brodmann’s area 41, 42)(Brodmann’s area 41, 42)

Composed of small transverse Composed of small transverse gyri called gyri called Heschl’s convolutionsHeschl’s convolutions

Responsible for Responsible for conscious conscious perception of soundperception of sound

There is There is bilateral, tonotopic bilateral, tonotopic representation of the cochlear representation of the cochlear ductduct

Afferents: from Afferents: from medial medial geniculate nucleus of thalamusgeniculate nucleus of thalamus

Auditory association cortexAuditory association cortex Located immediately Located immediately

posterior to the primary posterior to the primary auditory cortexauditory cortex

It is called It is called Wernick’s areaWernick’s area in in dominant hemispheredominant hemisphere

Plays major role in Plays major role in understanding of the spoken understanding of the spoken wordswords, has important , has important connections with other connections with other language areaslanguage areas

Parahippocampal gyrus:Parahippocampal gyrus: Located in the Located in the

inferomedial part of inferomedial part of temporal lobetemporal lobe

Deep to this gyrus lies the Deep to this gyrus lies the hippocampushippocampus and the and the amygdalaamygdala, which are , which are parts of limbic systemparts of limbic system

Occipital LobePrimary visual cortexPrimary visual cortex

Located on the Located on the medial surface of medial surface of the hemisphere, in the gyri the hemisphere, in the gyri surrounding the calcarine sulcus surrounding the calcarine sulcus (Brodmann’s area 17)(Brodmann’s area 17)

Responsible for Responsible for visual perceptionvisual perception AfferentsAfferents: from lateral geniculate : from lateral geniculate

nucleus through optic radiationnucleus through optic radiation Each Each lateral half of visual fieldlateral half of visual field is is

represented in the represented in the primary visual primary visual cortex of the contralateral cortex of the contralateral hemispherehemisphere

Upper half of visual field Upper half of visual field represented represented below the calcarine below the calcarine sulcussulcus, and the , and the lower half above lower half above the sulcusthe sulcus

Visual association cortexVisual association cortex Responsible for the Responsible for the

interpretation of visual interpretation of visual imagesimages

Lesion results in Lesion results in deficits in visual deficits in visual interpretation and interpretation and recognitionrecognition

Language Area Organized around the lateral Organized around the lateral

fissurefissure Broca’s areaBroca’s area: concerned with : concerned with

expressive aspects of languageexpressive aspects of language Wernick’s areaWernick’s area: responsible for : responsible for

comprehension of the spoken comprehension of the spoken wordswords

Nearby regions of Nearby regions of temporal lobe temporal lobe and parietal lobeand parietal lobe ( (angular gyrusangular gyrus & & supramarginal gyrussupramarginal gyrus of the of the inferior parietal lobule) are inferior parietal lobule) are important in naming, reading, important in naming, reading, writing and calculation writing and calculation

Hemispheric Dominance The localization of speech centers & mathematical The localization of speech centers & mathematical

ability is the criterion for defining the dominant ability is the criterion for defining the dominant cerebral hemispherecerebral hemisphere

In 96% of normal right-handed individuals and In 96% of normal right-handed individuals and 70% of normal left-handed individuals, the left 70% of normal left-handed individuals, the left hemisphere contains the language centers. These hemisphere contains the language centers. These are are left hemisphere dominant. left hemisphere dominant.

Cerebral dominance becomes established during Cerebral dominance becomes established during the first few years after birththe first few years after birth

Verbal Memory

Shape Memory

Hemispheres communicate via the corpus Hemispheres communicate via the corpus callosumcallosum

CLINICAL NOTES

Focal Cerebral Lesions (vascular or tumor)

Give rise to 3 kinds of symptoms:Give rise to 3 kinds of symptoms: Partial epileptic seizures, due to repetitive Partial epileptic seizures, due to repetitive

discharges of group of neurons in the cerebral discharges of group of neurons in the cerebral cortex. Patient may show abnormal movements, cortex. Patient may show abnormal movements, sudden change in behavior, perception and sudden change in behavior, perception and mood, or may trigger generalized seizuresmood, or may trigger generalized seizures

Sensory/motor deficitsSensory/motor deficits Psychological deficits (language, memory, Psychological deficits (language, memory,

perception) perception)

Unilateral cerebral hemisphere lesionUnilateral cerebral hemisphere lesion causes: causes: Mental impairment e.g. aphasiaMental impairment e.g. aphasia Contralateral spastic hemiparesis, hyperreflexia & an Contralateral spastic hemiparesis, hyperreflexia & an

extensor motor response (upper motor neuron lesion)extensor motor response (upper motor neuron lesion) Contralateral hemisensory lossContralateral hemisensory loss

Bilateral cortical disordersBilateral cortical disorders:: Alzheimer’s disease: atrophy of parietal and temporal Alzheimer’s disease: atrophy of parietal and temporal

lobes, leads to disorientation in space, aphasia, lobes, leads to disorientation in space, aphasia, amnesiaamnesia

Neurosyphilitic infection: involves both frontal lobes, Neurosyphilitic infection: involves both frontal lobes, results in total change of personality, loss of judgment results in total change of personality, loss of judgment & planning, with bizarre behavior & planning, with bizarre behavior

Left frontal lobe lesionLeft frontal lobe lesion: Jacksonian seizures, : Jacksonian seizures, contralateral hemiplegia, Broca’s aphasia (poor contralateral hemiplegia, Broca’s aphasia (poor articulation of speech)articulation of speech)

Parietal lobe lesionsParietal lobe lesions: paraxysmal attacks of : paraxysmal attacks of abnormal sensations spreding to the contralateral abnormal sensations spreding to the contralateral side of body, contralateral hemisensory loss, side of body, contralateral hemisensory loss, inferior visual field loss, & (in left lobe lesions: inferior visual field loss, & (in left lobe lesions: anomia, alexia, agraphia, acalculia; in right lobe anomia, alexia, agraphia, acalculia; in right lobe lesions:constructional apraxia)lesions:constructional apraxia)

Temporal lobe lesionTemporal lobe lesion: contralateral superior : contralateral superior visual field loss, Wernicke’s aphasiavisual field loss, Wernicke’s aphasia

Occipitl lobe lesionsOccipitl lobe lesions: visual disturbances: visual disturbances