The parietal lobe is strategically located between other lobes and has a greater variety of clinical manifestations than other parts of the brain. It is involved in somatosensory processing, spatial awareness, language, praxis, and more. Damage can cause syndromes like Gerstmann syndrome, apraxia, agraphia, acalculia, hemispatial neglect, and others, depending on whether the left or right lobe is affected. The parietal lobe works in conjunction with other brain regions to carry out its diverse functions.

1. PARIETAL LOBE DR ARUN S

2. 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

3. 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

4. Critchley(1953) – monograph on “ The Parietal Lobes” Djerine– alexia , agraphia -- angular gyrus lesion Liepmann--- ideomotor & ideational apraxia in (L) sided lesion

5. Neuroanatomy Occupies middle third of cerebral hemispheres Situated b/w frontal ,temporal ,occipital lobes with anatomical & functional continuity

6. 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

8. 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

9. Lateral surface Gyri Post central gyrus- primary sensory area(3,1,2) Superior parietal lobule(5,7) Inferior parietal lobule ( Ecker’s lobule ) Supramarginalgyrus (area 40) arches over Sylvian fissure Angular gyrus (area 39 ) - arches over the superior temporal sulcus

10. Mesial surface Paracentral lobule- mesial part of post central gyrus Precuneus- behind post central gyrus Subjacent part of cingulategyrus- below sub parietal sulcus

12. Vascular supply Lateral - MCA Artery of Rolandic fissure Artery of inter parietal fissure Artery of post parietal fissure Inter opercular parietal artery Artery to angular gyrus Mesial - ACA mainly & PCA to a slight extent

14. 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

15. 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

17. 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

18. Posterior parietal region Superior & inferior Parietal lobule Connections Post central gyrus

19. 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

20. Inferior parietal area Supra marginal & angular gyrus No pyramidal cells Granular cortex well developed Close proximity to occipital & temporal lobe

21. 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

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

24. Intentional movement

25. Praxis

27. APRAXIA Definition Difficulty in performing skilled motor acts which can not be explained by an elementary sensory or motor deficit or language comprehension disorder

28. Apraxia Limb apraxia– Limb kinetic / melokinetic Ideomotor Ideational Disassociation Conduction Conceptual Constructional & dressing –often associated with neglect & visual perceptual disorders

29. Scattered , fragmentedLoss of spatial relationsFaulty orientation Energetic drawing Addition of lines to make drawing correct

30. Coherent , simplifiedPreservation of spatial relationsCorrect orientation Slow & laborious Gross lack of details

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

32. 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

33. Amorphosynthesis Inability 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

34. Asomatognosia Agnosia relates to patient’s own body Types Anosognosia Autotopagnosia

35. 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

36. 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

37. 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

38. Language dysfunction Dominant PL lesion Defect in reception of spoken language & reading Conduction aphasia

39. Agraphia Spontaneous writing & writing on command more affected than copy righting Irregular & tremulous script, misspelling , semantic & syntactial errors Site – inferior parietal lobule

40. 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

43. Effects of unilateral disease of the parietal lobe, right or leftA. Corticosensory syndrome and sensory extinction B. Mild hemiparesis (variable), unilateral muscular atrophyin children, hypotonia, poverty of movement, hemiataxiaC. Homonymous hemianopia or inferior quadrantanopia(incongruent or congruent) or visual inattentionD. Abolition of optokineticnystagmus with target movingtoward side of the lesionE. Neglect of the opposite side of external space

44. 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

45. Effects of unilateral disease of the nondominant (right) parietal lobeA. Visuospatial disordersB. Topographic memory lossC. Anosognosia, dressing and constructional apraxiasD. ConfusionE. Tendency to keep the eyes closed, resist lid opening,and blepharospasm

46. Effects of bilateral disease of the parietal lobes A. Visual spatial imperception, spatial disorientation, andcomplete or partial Balint syndrome

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