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PARIETAL LOBE DR ARUN S

Parietal lobe

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Page 1: Parietal lobe

PARIETAL LOBE

DR ARUN S

Page 2: Parietal lobe

Introduction No independent existence as anatomical / physiological unit Operates in conjunction with brain as a whole Strategically situated b/w other lobes Greater variety of clinical manifestations

than rest of the hemisphere Dysfunction likely to be overlooked

unless special techniques used

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History

In 1874 Bartholow recorded odd sensation from legs on stimulating post central gyrus through skull wounds

Cushing in 1909 --- Electrical stimulation in conscious human beings under LA –– mainly tactile hallucinations

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Critchley (1953) – monograph on “ The Parietal Lobes” Djerine – alexia , agraphia -- angular

gyrus lesion Liepmann--- ideomotor & ideational

apraxia in (L) sided lesion

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Neuroanatomy

Occupies middle third of cerebral hemispheres

Situated b/w frontal ,temporal ,occipital lobes with anatomical & functional continuity

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Boundaries

Anterior –Central sulcus & its imaginary continuation over inner paracentral lobule medially

Posterior- parieto occipital sulcus on mesial aspect & its continuation (imaginary) to join pre occipital notch inferolaterally

Lower- Sylvian fissure & its imaginary extension backwards

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Lateral surface

2 well defined sulci

Post central sulcus –parellel to Fissure of Rolando

Inter parietal sulcus- runs AP from post central sulcus to occipital lobe

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Lateral surface

Gyri Post central gyrus- primary sensory

area(3,1,2) Superior parietal lobule(5,7) Inferior parietal lobule ( Ecker’s

lobule ) Supramarginal gyrus (area 40)

arches over Sylvian fissure Angular gyrus (area 39 ) - arches

over the superior temporal sulcus

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Mesial surface

Paracentral lobule- mesial part of post central gyrus

Precuneus- behind post central gyrus

Subjacent part of cingulate gyrus- below sub parietal sulcus

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Vascular supply

Lateral - MCA

Artery of Rolandic fissureArtery of inter parietal fissure Artery of post parietal fissure Inter opercular parietal arteryArtery to angular gyrus

Mesial - ACA mainly & PCA to a slight extent

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Venous drainage

Superficial middle cerebral vein –lies in lateral fissure

Vein of Trolard (superior anastomotic vein) - connects sup middle cerebral vein to SSS

Vein of Labbe’ ( inferior anastomotic vein ) - connects sup middle cerebral

vein to Transverse sinus

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Post central gyrus

Granular cortex Receives most of its afferents from VPL

nucleus of thalamus Projects to somatosensory association

cortex (area 5) Some parts (except hand & foot )

connected to opposite somatosensory cortex via corpus callosum

Representation of C/L side of body

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Postcentral gyrus

Superior part represent the LL Middle part -- the trunk & UL and Lower part --the face Amount of cortex devoted to any

particular body area – proportional to sensory acuity

Tips of fingers & lips larger area of representation

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Posterior parietal region Superior & inferior Parietal lobule

Connections Post central gyrus

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Superior parietal area

Area 5b- occupies large portion of Sup parietal lobule

Extends over medial surface to include pre cuneus

No large pyramidal cells in layer V Granular layer – great depth &

density

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Inferior parietal area

Supra marginal & angular gyrus No pyramidal cells Granular cortex well developed Close proximity to occipital & temporal

lobe

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Parietal lobe functions

Difficult to describe due to bewildering range of symptoms

Simple functional division Anterior region- post central

gyrus / sensory strip Posterior region – lies behind post

central gyrus & is composed of tertiary cortex

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Functions of anterior region Somato sensory perception Tactile perception Body sense Visual object recognition

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Functions of posterior region

Language Reception of spoken language

Reading Spatial orientation & attention

Route following L- R discrimination

CalculationIntentional movementPraxis Constructional ability

DrawingShort term auditory memory

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Optic radiation passes to Occipital Lobe via deep region . Lesion --- VF defects

Angular & supramarginal gyri of dominant hemisphere – imp in language & related functions

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APRAXIA

Definition Difficulty in performing skilled motor

acts which can not be explained by an elementary sensory or motor deficit or language comprehension disorder

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Apraxia

Limb apraxia – Limb kinetic / melokinetic Ideomotor Ideational

Disassociation Conduction Conceptual Constructional & dressing –often

associated with neglect & visual perceptual disorders

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Scattered , fragmented

Loss of spatial relations

Faulty orientation

Energetic drawing

Addition of lines to make drawing correct

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Coherent , simplified

Preservation of spatial relations

Correct orientation

Slow & laborious

Gross lack of details

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Tests

Pressure sensitivity Two point discrimination Point localisation Position sense Tactual object recognition

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Two point discrimination

Use a compass / calibrated 2 point esthesiometer 1mm tip of tongue 2-4 mm finger tips 4-6 mm dorsum of fingers 8-12 mm on palm 20-30 mm on dorsum of palm

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AmorphosynthesisInability to synthesize separate tactile

sensations into perception of form Lack of recognition of C/L body & of

space

Astereognosis Loss of ability to recognize object by

touch Unable to name objects, describe or

demonstrate their use Primary sensations intact

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Asomatognosia

Agnosia relates to patient’s own body

TypesAnosognosia

Autotopagnosia

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Anosognosia

Ignorance of existence of disease More with (R ) PL lesions U/L neglect may co exist

Deny weakness /sensory loss of affected limb

Extreme cases- disowns limb

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Autotopagnosia

Impairment in localization / naming of parts of own body

Patient unable to point to body parts named by examiner / move them

May not be able to identify them on examiner’s body / on diagram

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Finger agnosia

Inability to recognize , name & point to individualized fingers on self & others – usually middle 3 fingers

Form of autotopagnosia B/L lesion Central feature of Gerstmann

syndrome

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Language dysfunction

Dominant PL lesion Defect in reception of spoken

language & reading Conduction aphasia

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Agraphia

Spontaneous writing & writing on command more affected than copy righting

Irregular & tremulous script, misspelling , semantic & syntactial errors

Site – inferior parietal lobule

Page 38: Parietal lobe

Apractic agraphia- agraphia despite normal sensory, motor & visual feed back, word & letter knowledge

Lesion- Dom sup parietal lobule Visuo spatial agraphia- neglect of (U)

side of paper in writing Lesion -- (R) temp- parietal

junction

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Effects of unilateral disease of the parietal lobe, right or left

A. Corticosensory syndrome and sensory extinction

B. Mild hemiparesis (variable), unilateral muscular atrophyin children, hypotonia, poverty of movement, hemiataxia

C. Homonymous hemianopia or inferior quadrantanopia(incongruent or congruent) or visual inattention

D. Abolition of optokinetic nystagmus with target movingtoward side of the lesion

E. Neglect of the opposite side of external space

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Effects of unilateral disease of the dominant (left) parietallobe

A. Disorders of language (especially alexia)B. Gerstmann syndrome (dysgraphia, dyscalculia, finger agnosia, right-left confusion)C. Tactile agnosia (bimanual astereognosis)D. Bilateral ideomotor and ideational apraxia

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Effects of unilateral disease of the nondominant (right) parietal lobe

A. Visuospatial disorders

B. Topographic memory loss

C. Anosognosia, dressing and constructional apraxias

D. Confusion

E. Tendency to keep the eyes closed, resist lid opening,and blepharospasm

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Effects of bilateral disease of the parietal lobes

A. Visual spatial imperception, spatial disorientation, andcomplete or partial Balint syndrome

Page 45: Parietal lobe