Cerebral Hemispheres

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Gross Anatomy - Lobes Laid Bare

  • Cerebral Hemispheres: Two; separated by longitudinal fissure; connected by corpus callosum.
  • Lobes (4 per hemisphere):
    • Frontal: Anterior to central sulcus. Motor control, planning.
    • Parietal: Posterior to central sulcus. Somatosensation, spatial processing.
    • Temporal: Inferior to lateral sulcus. Auditory, memory, language comprehension.
    • Occipital: Posterior-most. Visual processing.
  • Key Sulci:
    • Central Sulcus (Rolando): Frontal from Parietal.
    • Lateral Sulcus (Sylvian): Temporal from Frontal & Parietal.
    • Parieto-occipital Sulcus: Parietal from Occipital (medial).
  • Key Gyri:
    • Precentral (Frontal): Primary motor cortex.
    • Postcentral (Parietal): Primary somatosensory cortex.

Diagram of cerebral lobes and sulci

⭐ The central sulcus (of Rolando) separates the frontal lobe from the parietal lobe.

Functional Areas - Brain's Busy Zones

Brodmann Areas Map

LobeBA No.Area NameFunctionNote/Mnemonic
Frontal4Primary MotorVoluntary movement
6Premotor/SMAPlan movement
8Frontal Eye FieldConjugate eye movement
44, 45Broca's Area (Dom)Motor speech📌 Broca's = Broken speech
Parietal3,1,2Primary SomatosensorySensation (touch, pain etc.)
39Angular Gyrus (Dom)Reading, writing, calculationLesion → Gerstmann Syndrome
40Supramarginal Gyrus (Dom)Language, spatial sense
Temporal41,42Primary AuditoryHearing
22Wernicke's Area (Dom)Language comprehension📌 Wernicke's = Word salad
Occipital17Primary VisualVision
18,19Visual AssociationVisual interpretation

White Matter - Neural Highways

  • Composed of myelinated axons, forming tracts for rapid signal transmission.
  • Classified by connections:
Fiber TypeExamplesKey Function/Location
Association FibersSuperior/Inferior longitudinal fasciculus, Arcuate, CingulumConnect different cortical areas within same hemisphere.
Commissural FibersCorpus callosum (largest), Anterior/Posterior commissureInterconnect both cerebral hemispheres.
Projection FibersInternal capsule, Corona radiata (corticospinal/bulbar)Connect cortex with subcortical nuclei, brainstem, spinal cord.

⭐ The internal capsule's posterior limb carries corticospinal tract fibers.

Blood Supply & Dominance - Vital Flow & Brain Boss

Cortical vascular territories of cerebral arteries

Cerebral Arterial Territories & Deficits:

ArteryTerritoryDeficit (Occlusion)
ACA (Anterior Cerebral A.)Medial frontal/parietal lobes; leg motor cortexContralateral leg > arm weakness/sensory loss. 📌 "A for Anterior leg"
MCA (Middle Cerebral A.)Lateral hemisphere; arm/face motor cortex; speech (dominant) / neglect (non-dominant) areasContralateral face/arm > leg weakness/sensory loss; aphasia (dominant) / neglect (non-dominant).
PCA (Posterior Cerebral A.)Occipital lobe, medial temporal lobeContralateral homonymous hemianopia; memory loss.
  • Left Hemisphere (Typically Dominant): Language (Broca's: motor speech; Wernicke's: sensory speech), analytical thought, calculations.
  • Right Hemisphere (Typically Non-Dominant): Visuospatial skills, facial recognition, emotional prosody, music.

⭐ Middle cerebral artery (MCA) is the most commonly affected artery in stroke, often leading to contralateral hemiplegia and hemisensory loss, predominantly affecting the upper limb and face.

High‑Yield Points - ⚡ Biggest Takeaways

  • Frontal lobe: Precentral gyrus (motor), Broca's area (motor speech), executive functions.
  • Parietal lobe: Postcentral gyrus (sensory), spatial orientation, Gerstmann's syndrome (dominant parietal).
  • Temporal lobe: Wernicke's area (sensory speech), auditory cortex, hippocampus (memory), Kluver-Bucy syndrome.
  • Occipital lobe: Primary visual cortex (calcarine sulcus), visual association areas.
  • Dominant (Left) Hemisphere: Key for language (Broca's, Wernicke's), calculation, praxis.
  • Non-Dominant (Right) Hemisphere: Excels in visuospatial skills, facial recognition, music, emotional prosody.
  • Corpus Callosum: Largest commissure connecting hemispheres; lesions can cause split-brain syndrome.
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Practice Questions: Cerebral Hemispheres

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Not seen in case of hemorrhage in MCA territory is:

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Types of white matter:_____ fibers: fibers passing to and from the brainstem to the cerebral cortex.

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Types of white matter:_____ fibers: fibers passing to and from the brainstem to the cerebral cortex.

Projection

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Cerebral Hemispheres - Free Indian Medical PG High-Yield