Transcript 13. Cerebrum cortical areas.ppt

CEREBRUM
Dr. Zeenat Zaidi
Cerebrum
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Largest part of the forebrain
Derived from telencephalon
Divided into two halves, the
cerebral hemipheres
The two hemispheres are
separated by a deep median
lingitudinal fissure which
lodges the falx cerebri
In the depth of the fissure,
the hemispheres are
connected by a bundle of
fibers called the corpus
callosum
Corpus callosum
Left
hemisphere
Right
hemisphere
Median longitudinal fissure
Surfaces
Superolateral
Medial
Inferior
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The structure of cerebral
hemipheres includes:
 Superficial layer of grey
matter, the cerebral cortex
 Deeper to the cortex, axons
running to and from the
cells of the cortex form an
extensive mass of white
matter
 Burried within the white
matter lie a number of
nuclear masses (caudate,
putamen, globus pallidus)
collectively known as the
basal ganglia
Cortex
Basal
ganglia
WM
WM
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The superficial layer of grey matter is highly convoluted to
form a complex pattern of ridges (gyri) and grooves (sulci)
This arrangement maximize the surface area of the cerebral
cortex (about 70% is hidden within the depths of sulci)
G
S
G
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
visual
processing
smell, hearing,
memory and
abstract thought
Parieto-occipital
sulcus
Functionally each
hemisphere
contains a ‘limbic
lobe’ on the medial
surface.
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It is responsible for:
 establishing emotional states
 linking conscious intellectual functions with the
unconscious autonomic functions
 facilitating memory storage and retrieval
Central sulcus
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An uninterrupted vertical sulcus
running from the lateral fissure
to the median longitudinal
fissure
Extending for a short distance
on the medial surface of the
hemisphere
Separates the frontal lobe from
parietal lobe
F
P
T
Lateral sulcus
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Deepest cleft on the lateral
surface
Separates the temporal lobe
from the frontal and parietal
lobes
Parieto-occipital sulcus
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Separates the occipital lobe
from the parietal lobe on the
mdial surface
F
P
O
Frontal lobe:
 Precentral gyrus
 Superior & inferior
frontal sulci divide the
lobe into superior,
middle & inferior
frontal gyri
Parietal lobe:
 Postcentral gyrus
 Intraparietal sulcus
dividing the lobe into
superior & inferior
parietal lobules
Temporal lobe:
 Superior & inferior
temporal sulci giving
rise to superior,
middle & inferior
temporal gyri
 Insula: the gyri in the
depth of lateral
fissure, covered by
parts of frontal,
parietal & temporal
lobes called the
opercula (removed in
lower pic.)
(Lateral)
Insula
Medial Surface
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Sulci: Cingulate, Parieto-occipital, Calcarine
Gyri: Cingulate, Parahippocampal
Histological Structure of Cerebral Cortex
Contains nerve cell bodies, dendritic
arborizations, synapses, neuroglia, blood
vessels
 Archicortex and Paleocortex (hippocampus and
parts of temporal lobe associated with olfactory
functions) have three layered structure
 Neocortex, generally consists of six layers,
although the detailed cytological structure
varies from region to region
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Histological Structure of Cerebral Cortex
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Layer I: few nerve cells, many
processes and synaptic interactions
Layer II: many small neuron, which
establish intercortical connections
Layer III: medium sized neurons giving
rise to association & commissural fibers
Layer IV: site of termination of afferent
fibers from the specific thalamic nuclei
Layer V: origin of projection fibers to
extracortical targets. In primary motor
cortex, this layer contains giant Betz
cells which give rise to pyramidal fibers
Layer VI: contain association and
projection neurones
Brodmann produced a numbered, cytological map of cerebral
cortex based upon its regional histological characteristics
The basis of Brodmann's
cortical localization is its
subdivision into 'areas' with
similar cellular and laminar
structure
Brodmann's numbering of
these cortical locations has
become one of the standard
ways in which clinicians
identify brain areas.
Functions of the Cerebral Cortex
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Is necessary for conscious awareness and thought,
reasoning & intellect, emotions, behaviour & memory
(stores information and retrieves when needed)
Receives all sensory modalities (mostly through
thalamus), consciously perceives and interprets in the
light of previous experience
Is the highest level where motor system is represented.
Controls & directs the conscious or volitional motor
functions of the body
Is the site where the actions are conceived and initiated
Functional Areas
of the
Cerebral Cortex
Frontal Lobe
Primary motor cortex
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Located in precentral gyrus
(Brodmann area 4)
Controls voluntary, skilled
movements (fractionated
movements)
Afferents: from ventral
lateral (VL) nucleus of
thalamus
Efferents: Corticospinal
(30%) and corticobulbar
fibers. 3% of corticospinal
fibers arise from Betz cells
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The body is represented
contralaterally, in a precise
somatotopic fashion, depicted as
a ‘motor homunculus’
The representation of body is
inverted, with the head area in the
most inferior part of the
precentral gyrus and then
progressing superiorly
The lower limb is represented on
the medial surface
The area of the cortex devoted to
a particular body parts is
proportional to the degree of
precision with which movements
can be executed (and not to the
size)
Larynx, tongue, face & digits of
hand are represented by relatively
large regions
Premotor cortex
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Located in the region immediately
anterior to the precentral gyrus
(Brodmann’s area 6)
On the lateral surface, this includes
the posterior parts of superior,
middle and inferior frontal gyri
On the medial surface, it includes
region of supplementary motor
cortex.
In supplementary motor cortex,
body is represented
somatotopically and this
representation is bilateral.
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Premotor area functions in
programming of, and
preparation for, movement &
in the control of posture
Afferents: from ventral
anterior (VA) nucleus of
thalamus
Efferents:
 Short association fibers to
primary motor cortex
 Corticospinal and
corticobulbar fibers. There
are no Betz cells in
premotor cortex
Frontal eye field
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Located in the middle
frontal gyrus immediately
in front of premotor cortex
(Brodmann’s area 8)
Controls voluntary
conjugate deviation of the
eyes while scanning the
eye field
Damage to this area
results in conjugate
deviation of the eyes
toward the side of lesion
Broca’s (motor speech) area
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Located in the inferior frontal
gyrus of the dominant
hemisphere (usually left)
Brodmann’s area 44 & 45
Involved in language
functions
Interconnected with parts of
ipsilateral temporal, parietal
and occipital lobes
Prefrontal cortex
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Extensive region of the frontal
lobe anterior to premotor area
Has cognitive functions of high
order e.g. intellectual,
judgemental and predictive
faculties and the planning of
behaviour
Afferents: mediodorsal and
anterior nuclei of thalamus
Efferents: to parietal, occipital
and temporal cortex through long
association fibers
Parietal lobe
Primary somatosensory cortex
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Located in postcentral gyrus
(Brodmann’s area 1, 2, 3)
It is the final relay station for
general sensations to a conscious
level
Afferents: Thalamocortical
projections from the ventral
posterior nucleus
The body is represented
contralaterally, in a precise
somatotopic fashion, depicted as a
‘sensory homunculus’
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The representation of body is
inverted, with the head area in the
most inferior part of the
precentral gyrus and then
progressing superiorly
The lower limb is represented on
the medial surface
The area of the cortex devoted to
a particular body parts is
proportional to the richness of its
sensory innervation (and not to
the size)
Larynx, tongue, face, lips &
palmer surface of the hand and
digits are represented by
relatively large regions
Adjascent to mouth area is a
region where taste is perceived
Parietal association cortex
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Located posterior to primary
somatosensory cortex
Superior parietal lobule
responsible for:
 Interpretation of general
sensory information
 Conscious awareness of
contralateral half of the body
Inferior parietal lobule interfaces
between somatosensoryy cortex
and the visual & auditory cortices
(and speech area in dominant
hemisphere)
Temporal Lobe
Primary auditory cortex
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Located in the superior surface
of the superior temporal gyrus
(Brodmann’s area 41, 42)
Composed of small transverse
gyri called Heschl’s
convolutions
Responsible for conscious
perception of sound
There is bilateral, tonotopic
representation of the cochlear
duct
Afferents: from medial
geniculate nucleus of thalamus
Auditory association cortex
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Located immediately
posterior to the primary
auditory cortex
It is called Wernick’s area in
dominant hemisphere
Plays major role in
understanding of the spoken
words, has important
connections with other
language areas
Parahippocampal gyrus:
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Located in the
inferomedial part of
temporal lobe
Deep to this gyrus lies the
hippocampus and the
amygdala, which are
parts of limbic system
Occipital Lobe
Primary visual cortex
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Located on the medial surface of
the hemisphere, in the gyri
surrounding the calcarine sulcus
(Brodmann’s area 17)
Responsible for visual perception
Afferents: from lateral geniculate
nucleus through optic radiation
Each lateral half of visual field is
represented in the primary visual
cortex of the contralateral
hemisphere
Upper half of visual field
represented below the calcarine
sulcus, and the lower half above
the sulcus
Visual association cortex
 Responsible for the
interpretation of visual
images
 Lesion results in
deficits in visual
interpretation and
recognition
Language Area
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Organized around the lateral
fissure
Broca’s area: concerned with
expressive aspects of language
Wernick’s area: responsible for
comprehension of the spoken
words
Nearby regions of temporal lobe
and parietal lobe (angular gyrus
& supramarginal gyrus of the
inferior parietal lobule) are
important in naming, reading,
writing and calculation
Hemispheric Dominance
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The localization of speech centers & mathematical
ability is the criterion for defining the dominant
cerebral hemisphere
In 96% of normal right-handed individuals and
70% of normal left-handed individuals, the left
hemisphere contains the language centers. These
are left hemisphere dominant.
Cerebral dominance becomes established during
the first few years after birth
Verbal
Memory
Shape
Memory
Hemispheres communicate via the corpus callosum
CLINICAL NOTES
Focal Cerebral Lesions
(vascular or tumor)
Give rise to 3 kinds of symptoms:
 Partial epileptic seizures, due to repetitive
discharges of group of neurons in the cerebral
cortex. Patient may show abnormal movements,
sudden change in behavior, perception and
mood, or may trigger generalized seizures
 Sensory/motor deficits
 Psychological deficits (language, memory,
perception)
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Unilateral cerebral hemisphere lesion causes:
 Mental impairment e.g. aphasia
 Contralateral spastic hemiparesis, hyperreflexia & an
extensor motor response (upper motor neuron lesion)
 Contralateral hemisensory loss
Bilateral cortical disorders:
 Alzheimer’s disease: atrophy of parietal and temporal
lobes, leads to disorientation in space, aphasia,
amnesia
 Neurosyphilitic infection: involves both frontal lobes,
results in total change of personality, loss of judgment
& planning, with bizarre behavior
Left frontal lobe lesion: Jacksonian seizures,
contralateral hemiplegia, Broca’s aphasia (poor
articulation of speech)
 Parietal lobe lesions: paraxysmal attacks of
abnormal sensations spreding to the contralateral
side of body, contralateral hemisensory loss,
inferior visual field loss, & (in left lobe lesions:
anomia, alexia, agraphia, acalculia; in right lobe
lesions:constructional apraxia)
 Temporal lobe lesion: contralateral superior
visual field loss, Wernicke’s aphasia
 Occipitl lobe lesions: visual disturbances
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