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The structure and functional localization of the cerebral cortex

  • Cerebral cortex is composed of grey matter (10 billion neurons are present)
  • Types of cells present in the cerebral cortex
Cell type
Special points
  • Pyramidal cells  
  1. Cell bodies are pyramidal shape
  2. Largest cell type
  3. Found in the precentral gyrus of the frontal lobe
  4. Axons enter the white matter
  5. Present throughout the levels of the cortex
  • Stellate cells
Smallest cell type
  • Fusiform cells
Axons enter the white matter
  • Horizontal cells of Cajal
Runs parallel to the surface of the cortex
  • Cells of Martinotti  
Present throughout the levels of the cortex

  • Nerve fibers of the cerebral cortex are arranged radially & tangentially (Runs parallel to the surface of the cortex)
  • Layers of the cerebral cortex (Superficial to deep)
image
i. Molecular layer (Plexiform layer)
ii. External granular layer
iii. External pyramidal layer
iv. Internal granular layer
v. Internal pyramidal layer (Ganglionic layer)
vi. Multiform layer (Layer of polymorphic cells)
A: Golgi neuronal stain. B: Nissl cellular stain.
C :Weigart myelin stain. D: Neuronal connections

  • In some areas the 6 layer arrangement is absent (Heterotypical; if 6 layers are present it’ homotypical) and there are 2 heterotypical types




      1. Granular type (Granular layers are well developed) : Post central & Superior temporal gyri
      2. Agranular type (Granular layers are not well developed) : Precentral gyrus
Cortical areas

Functional localization of the cerebral cortex
image
Lateral aspect of the cerebrum. The cortical areas are shown according to Brodmann with functional localizations
image
Medial aspect of the cerebrum. The cortical areas are shown according to Brodmann with functional localizations
The cortical lobes & their areas
Lobe
Areas
Function
Frontal lobe Precentral area (In precentral gyrus) Posterior region (1stry motor area – B 4)
  1. Carry out individual movements of different parts of the body (Contra lateral side of the body as inverted
  2. It only converts the design into execution of movements
Anterior region (2ndry motor area – B 6)
  1. Store programs of motor activity according to past experiences
  2. Programs the activities of 1stry motor area
Supplementary motor area
  1. Movements of the contra lateral limbs
  2. Removal of this area doesn’t produce permanent loss of movements
Frontal eye field
Control voluntary scanning movements of the eye & it’s independent of visual stimuli
Motor speech areas of Broca (B 44 & 45)
  1. Important in the dominant hemisphere
  2. Important for the formation of words
  3. Damage to this area will cause paralysis of speech (Speech is not fluent)
  4. If the Broca’s area of the non dominant hemisphere is damaged, won’t have no effect on speech  
Prefrontal area
Important in making up the individual’s personality & judgment
Parietal lobe 1stry somesthetic area (In post central gyrus)
  1. Anterior region (B 3) & Posterior region (B 2 & 1)
  2. Receive projection fibers from the ventral posterior lateral & ventral posterior medial nuclei of the thalamus (The opposite ½ of the body is represented as inverted)
2ndry somesthetic area
Less important than the 1stry sensory area (Function of this area is not understood)
Somesthetic association area (B 5 & 7)
  1. Receive & integrate different sensory modalities (Enables to recognize objects placed on the hand without the help of vision)
  2. Receives size & shape of an object + relates to past sensory experiences
Occipital lobe 1stry visual area (B 17)
  1. Receives afferent from the lateral geniculate body
  2. Receives fibers from temporal ½ of the ipsilateral retina & nasal ½ of the contra lateral retina (Right ½ of the visual field is represented in the visual cortex of the left cerebral hemisphere)
  3. The macula lutea (The central area of the retina – the area for most perfect vision) is represented by the posterior part of area 17
2ndry visual area (B 18 & 19)
Relate the visual information received by the 1stry visual area to past experiences (Enable to recognize things which are seen)
Occipital eye field
  1. Situated in the 2ndry visual area in human
  2. Reflex movements
  3. Associated with movements of the eye when it’s following an object
Temporal lobe 1stry auditory area (B 41 & 42)
  1. Receives fibers from medial geniculate body & auditory radiation of the internal capsule
  2. Anterior part        : Reception of sounds of low frequency
  3. Posterior part       : Reception of sounds of high frequency
  4. Unilateral lesion will cause partial deafness of both ears (Greater loss being in the contra lateral ear)
2ndry auditory area (B 22)
  1. Receives impulses from the 1stry auditory area & from the thalamus
  2. Important in interpreting sounds & to associate auditory input with other sensory information
Sensory speech area of Wernicke
  1. Localized in the dominant hemisphere
  2. It’s connected to Broca’s area (By arcuate fasciculus)
  3. Receives fibers from the visual cortex (B 17) & from the auditory cortex
  4. Enables to understand written & spoken language
  5. Enables to read a sentence, understand it & say it loud
  6. If it damaged (Sensory aphasia) the speech is fluent but speak nonsense
Other cortical areas
Taste area
At the lower end of the post central gyrus
(B 43)
Fibers from the nucleus solitarius ascend through the ventral posterior medial nucleus of the thalamus
Vestibular area
Situated near the part of the post central gyrus concerned with the sensation of the face
Concerned with appreciation of the position & movement so the head in space
Influence the movements of the eyes, muscles of the trunk & limbs in maintaining posture
Insula
Important in planning & coordinating the articulatory movements necessary for speech

imageThe nerve pathway involved in hearing a question & answering it
image
The nerve pathway involved in reading a sentence & repeating it out loud

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The structure and functional localization of the cerebral cortex The structure and functional localization of the cerebral cortex Reviewed by Radiology Madeeasy on August 10, 2010 Rating: 5
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