Cerebral Cortex

Question 1

Cerebral Cortex:

Anatomical organization

Answer 1

1. Embryologically derived from the telencephalon
2. Can be subdivided into:
   
   1. Archicortex (3 layers)
      
      • Hippocampus and Dentate gyrus
   2. Paleocortex
      
      • ​Olfcatory cortex
   3. Neocortex (6 layers)
3. Made up of 3 poles (frontal, occipital, and temporal) and 6 lobes

Question 2

6 Anatomical Lobes:

Answer 2

1. Frontal lobe
2. Parietal lobe
3. Temporal lobe
4. Occipital lobe
5. Insular lobe
   
   • The Insula
6. Limbic lobe:
   
   • includes Cingulate gyrus, Parahippocampal gyrus, and Hippocampus

Question 3

Blood supply to the cerebral cortex:

Answer 3

1. Anterior cerebral
2. Middle cerebral
3. Posterior cerebral
4. Anterior communicating
5. Posterior communicating arteries

• all of which form the Circle of Willis

Question 4

Drainage of the cerebral cortex:

Answer 4

1. Superior Sagittal sinus
2. Inferior sagittal sinus
3. Straight sinus
4. Transverse sinuses
5. Sigmoid sinuses

• which drain into the Internal jugular veins

Question 5

6 Layers of the Neocortex:

Answer 5

1. Layer I: Molecular layer
2. Layer II: External granular layer
3. Layer III: External pyramidal layer
4. Layer IV: Internal granular layer
   
   • well-developed in sensory areas
5. Layer V: Internal pyramidal layer
   
   • well-developed in motor areas
6. Layer VI: Multiform layer
   
   • project back to the thalamus

Question 6

How are myelinated axons organized in the cortex?

Answer 6

horizontal bands and vertical bundles

Question 7

What are the major cell types of the cortex?

Answer 7

Pyramidal and Non-pyramidal

Question 8

Functional units: Columns and Modules

Answer 8

1. Each column extends through the 6 layers that share similar functions
2. Functional columns form modules in various cortical areas
   
   • especially the primary somatosensory, visual, and auditory cortices
3. Columns of cortical neurons are interconnected within the same hemisphere and between the two hemispheres

Question 9

Areas 3, 1, 2 (Postcentral gyrus):

Answer 9

Primary somatosensory cortex

• Somatotopic organization (contralateral)
• Sensory homunculus
• Greater representation of the face and hand
• Lower limb representation is medial
• Lesion:
  
  • Contralateral loss of somesthetic sensation

Question 10

Area 4 (Precentral gyrus):

Answer 10

Primary motor cortex

• Somatotopic organization (contralateral)
• Motor homunculus
• Greater representation of the face and hand
• Lower limb representation is medial
• Lesion:
  
  • ​Contralateral spastic paralysis

Question 11

Area 17 (Cuneus and Lingual gyri):

Answer 11

Primary visual cortex

• Visuotopic organization
  
  • Central visual field: Most posterior
  • Peripheral visual field: most anterior
  • Vertical meridian: border of areas 17 and 18
  • Horizontal meridian: bisect horizontally
• Lesions:
  
  • Contralateral hemianopia
  • If restricted to upper or lower banks of the Calcarine fissure ⇒ contralateral inferior or superior quadrantanopia

Question 12

Areas 41 and 42: Transverse gyri (of Heschl)

Answer 12

Primary auditory cortex

• Tonotopic organization
• Biaural representation
• Lesions:
  
  • Bilateral lesions lead to loss of hearing

Question 13

Areas 44 and 45: part of the **Inferior frontal gyrus **

Answer 13

Motor area of speech (Broca’s area)

• mostly dominant in the left hemisphere
• Lesions:
  
  1. Dominant side (left) ⇒ motor aphasia, Broca’s aphasia, or expressive aphasia
  2. Non-dominant (right) ⇒ difficulty in expressing emotional aspect of language

Question 14

Main functional areas of the frontal cortex:

Answer 14

• Primary motor cortex: area 4
• Premotor cortex: area 6
• Supplementary motor cortex
• Frontal eye field
• Broca’s area
• Prefrontal cortex:
  
  • Dorsolateral prefrontal cortex: working memory
  • Ventromedial prefrontal cortex (orbitofronal cortex): limbic

Question 15

Association cortical areas of the parietal lobe:

Answer 15

• Posterior parietal lobe: polymodal convergence
• Superior parietal lobule: areas 5 and 7
• Inferior parietal lobule: Supramarginal gyrus (area 40) and Angular gyrus (area 39)

Lesions:

• **Dominant (usually left) hemisphere: **
  
  • astereognosis (area 40)
    
    • lose the meaning of touch
  • aphasia, alexia and agraphia (area 39)
    
    • inability to read and write
• Non-dominant (usually right) hemisphere:
  
  • spatial distortion
  • contralateral neglect

Question 16

Assciation cortical areas of the occipital lobe:

Answer 16

• Secondary visual cortex: area 18 or V2
• Association cortical areas: V3, V4, etc.
• 32 visual areas in the primate cortex (in the occipital, parietal, and temporal cortices)

Lesions:

• A variety of visual deficits

Question 17

Association cortical areas of the temporal lobe:

Answer 17

• Wernicke’s area: Posterior part of the superior temporal gyrus (area 22)
  
  • language comprehension (dominant on the left)

Lesions:

• Wernicke’s area (dominant hemisphere)
  
  • sensory aphasia, Wernicke’s aphasia, or receptive aphasia
• Wernicke’s area (non-dominant hemisphere)
  
  • ​difficulty in comprehending the emotional aspect of language

Question 18

Cortico-cortical connections within the same hemisphere and between the two hemispheres:

Answer 18

1. Short association fibers
2. Long association fibers
3. Callosal fibers

Question 19

GENERAL FUNCTIONAL SIGNIFICANCE OF THE CEREBRAL CORTEX:

Answer 19

1. Perception of special sensations: somatic, visual, auditory, olfaction
   
   • Multiple cortical maps for each of the major sensory representation
2. Planning and execution of voluntary movements
3. Emotions and behavior
4. Mental functioning
5. Memory

Question 20

DYSFUNCTIONS OF THE CEREBRAL CORTEX:

Answer 20

• Dysfunction is usually caused by vascular hemorrhage, thrombosis, or tumor
• Tumor is generally of glial origin
• Symptoms are related to specific region(s) of the cortex being affected

Question 21

Examples of cortical dysfunction:

Answer 21

1. Lesion of primary motor cortex:
   
   • Contralateral paralysis
2. Lesion of primary sensory cortex:
   
   • Contralateral loss of somatic sensation
3. Lesion of primary visual cortex:
   
   • Contralateral hemianopia
4. Lesion of the supramarginal gyrus (area 40):
   
   • astereognosis
5. Lesion of the angular gyrus (area 39):
   
   • alexia and agraphia
6. Lesion of the Broca’s area (44 and 45) on the dominant hemisphere:
   
   • motor aphasia