Cerebral Cortex

Cerebral Lobes - Brainy Boundaries

• Four Major Lobes: 📌 Mnemonic: "Frankfort Plays Tough Opponents" (Frontal, Parietal, Temporal, Occipital).
  • Frontal Lobe: Motor control (precentral gyrus), executive functions, Broca's area (speech). Anterior to central sulcus.
  • Parietal Lobe: Somatosensation (postcentral gyrus), spatial awareness, attention. Posterior to central sulcus.
  • Temporal Lobe: Audition (primary auditory cortex), memory (hippocampus), Wernicke's area (language comprehension). Inferior to lateral sulcus.
  • Occipital Lobe: Vision (primary visual cortex around calcarine sulcus). Most posterior.
• Key Anatomical Dividers (Sulci):
  • Central Sulcus (Rolandic Fissure): Separates Frontal from Parietal lobe.
  • Lateral Sulcus (Sylvian Fissure): Separates Temporal lobe from Frontal & Parietal lobes.
  • Parieto-occipital Sulcus: Separates Parietal from Occipital lobe (most distinct on medial surface).

⭐ The central sulcus is a critical landmark, separating the primary motor cortex (precentral gyrus in frontal lobe) from the primary somatosensory cortex (postcentral gyrus in parietal lobe).

Brodmann's Map - Area Codes

Key areas by cytoarchitecture.

• Frontal Lobe:
  • Area 4: Primary Motor Cortex (Precentral gyrus)
  • Area 6: Premotor/Supplementary Motor Cortex
  • Areas 44, 45: Broca's Area (Motor speech; 📌 Broca = Broken speech)
  • Areas 9-12, 46, 47: Prefrontal Cortex (Executive fn.)
• Parietal Lobe:
  • Areas 1, 2, 3: Primary Somatosensory (Postcentral gyrus)
  • Area 39: Angular Gyrus (Reading, math)
  • Area 40: Supramarginal Gyrus (Language)
• Temporal Lobe:
  • Areas 41, 42: Primary Auditory (Heschl's gyrus)
  • Area 22: Wernicke's Area (Sensory speech; 📌 Wernicke's = Wordy nonsense)
• Occipital Lobe:
  • Area 17: Primary Visual (Striate cortex)
  • Areas 18, 19: Visual Association

⭐ Area 22 (Wernicke's area) lesion causes fluent (receptive) aphasia: impaired comprehension, fluent but nonsensical speech.

Functional Zones - Cortical Command Centers

• Motor Control:
  • Primary Motor (Area 4): Executes voluntary movement; homunculus.
  • Premotor/SMA (Area 6): Plan, sequence movements.
  • Frontal Eye Field (Area 8): Saccadic eye movements.
• Sensory Input:
  • Somatosensory (Areas 3,1,2): Touch, pain, temp, proprioception.
  • Visual (Area 17): Basic visual processing.
  • Auditory (Areas 41,42): Basic auditory processing.
• Language:
  • Broca's (Areas 44,45): Speech production. (📌 "Broca = Broken speech")
  • Wernicke's (Area 22): Speech comprehension.
• Higher Functions:
  • Prefrontal Cortex (PFC): Executive functions (planning, decisions, working memory).
  • Parieto-occipito-temporal Assoc. Cortex: Sensory integration, spatial awareness, attention.

⭐ Lesion in Broca's area (dominant hemisphere) leads to expressive (non-fluent) aphasia; Wernicke's area lesion causes receptive (fluent) aphasia.

Vascular Strokes - Cortex Under Attack

• Ischemic (majority) vs. Hemorrhagic. Focus: Cortical deficits.
• Key Arteries & Syndromes:
  • ACA (Anterior Cerebral Artery): Contralateral leg/foot > arm/face motor/sensory loss. Urinary incontinence. Frontal lobe signs (abulia, grasp reflex).
  • MCA (Middle Cerebral Artery): (Most common) Contralateral face/arm > leg motor/sensory loss.
    • Dominant hemisphere: Aphasia (Broca's - expressive, Wernicke's - receptive).
    • Non-dominant hemisphere: Neglect syndrome.
    • Homonymous hemianopia. Gaze preference towards lesion.

    ⭐ Gerstmann syndrome (dominant parietal MCA infarct): agraphia, acalculia, finger agnosia, R-L disorientation.

  • PCA (Posterior Cerebral Artery): Contralateral homonymous hemianopia (macular sparing common). Alexia without agraphia (dominant occipital + splenium). Memory loss.
• Diagnosis: NCCT head (r/o bleed first), MRI (confirms ischemia, extent).
• Management: IV thrombolysis (e.g., Alteplase) if within 4.5 hours; Mechanical thrombectomy up to 24 hours for Large Vessel Occlusion (LVO).

High‑Yield Points - ⚡ Biggest Takeaways

• Frontal lobe: Precentral gyrus (Primary Motor Cortex, Area 4), Broca's area (Motor Speech, Areas 44, 45).
• Parietal lobe: Postcentral gyrus (Primary Somatosensory, Areas 3,1,2), part of Wernicke's area.
• Temporal lobe: Primary Auditory Cortex (Areas 41, 42), Wernicke's area (Sensory Speech, Area 22), Hippocampus (memory).
• Occipital lobe: Primary Visual Cortex (Area 17) around calcarine sulcus.
• Dominant hemisphere (usually left) for language (Broca's, Wernicke's).
• Corpus callosum: Major interhemispheric commissure.
• Homunculus: Somatotopic organization of motor/sensory cortex_