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 Cel...

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	Cell bodies are pyramidal shape Largest cell type Found in the precentral gyrus of the frontal lobe Axons enter the white matter 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)

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

Granular type (Granular layers are well developed) : Post central & Superior temporal gyri
Agranular type (Granular layers are not well developed) : Precentral gyrus

Cortical areas

Functional localization of the cerebral cortex

Lateral aspect of the cerebrum. The cortical areas are shown according to Brodmann with functional localizations

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)	Carry out individual movements of different parts of the body (Contra lateral side of the body as inverted) It only converts the design into execution of movements
		Anterior region (2ndry motor area – B 6)	Store programs of motor activity according to past experiences Programs the activities of 1stry motor area
	Supplementary motor area		Movements of the contra lateral limbs 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)		Important in the dominant hemisphere Important for the formation of words Damage to this area will cause paralysis of speech (Speech is not fluent) 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)		Anterior region (B 3) & Posterior region (B 2 & 1) 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)		Receive & integrate different sensory modalities (Enables to recognize objects placed on the hand without the help of vision) Receives size & shape of an object + relates to past sensory experiences
Occipital lobe	1stry visual area (B 17)		Receives afferent from the lateral geniculate body 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) 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		Situated in the 2ndry visual area in human Reflex movements Associated with movements of the eye when it’s following an object
Temporal lobe	1stry auditory area (B 41 & 42)		Receives fibers from medial geniculate body & auditory radiation of the internal capsule Anterior part : Reception of sounds of low frequency Posterior part : Reception of sounds of high frequency Unilateral lesion will cause partial deafness of both ears (Greater loss being in the contra lateral ear)
	2ndry auditory area (B 22)		Receives impulses from the 1stry auditory area & from the thalamus Important in interpreting sounds & to associate auditory input with other sensory information
	Sensory speech area of Wernicke		Localized in the dominant hemisphere It’s connected to Broca’s area (By arcuate fasciculus) Receives fibers from the visual cortex (B 17) & from the auditory cortex Enables to understand written & spoken language Enables to read a sentence, understand it & say it loud 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