DR PRATIK MISTRY

Allocortex – 10 % (also called Limbic Cortex)

i. Archipallium – hippocampus & Dentate gyrus.

ii. Paleopallium – Uncus & part of Parahippocampal gyrus.

iii. Mesocortex. – transitional zone.

Neocortex (Isocortex) -Rest of 90% of cerebral cortex.

Six layers

1. Molecular

2. Outer granular

3. Outer pyramidal

4. Inner granular

5. Inner pyramidal

6. Pleomorphic

Cells:

1. Pyramidal cells of betz

2. Granule (stelate) cells

3. Cells of martinoti

4. Horizontal cells of cajal

AGRANULAR CORTEX

Pyramidal cells – large, Betz cells

Granule cells absent or less in number

Seen in Motor cortex (4) & Boca's motor speech area (44)

GRANULAR CORTEX

Excess granule cells

Few pyramidal cells

Seen in sensory cortex & visual area, auditory area

FRONTAL CORTEX

Small and medium pyramidal cells

Few stellate cells

Pre-frontal cortex of frontal lobe

PARIETAL CORTEX

More stellate cells

Seen in most of parietal lobe & junction of parietal, temporal & occipital lobes

POLAR CORTEX

Thinnest of all

All layers reduced depth.

Seen in frontal & occipital pole

For functional analysis, cerebral cortex is divided into number areas,

20 areas of Campbell

109 areas of Economo

200 areas of Vogt

52 areas of brodmann- frequently used

Subdivided into motor, sensory and association areas

Subdivided into

Primary motor area (area 4)

Pre-motor area (area 6)

Frontal eye field (area 8)

Supplementary motor area

Pre-frontal area (areas 9 to 12)

Location:

Precentral gyrus (area 4)

Extends to the ant. part of paracentral lobule

Agranular cortex

Afferents :

Premotor area (Area 6)

Somesthetic or somatosensory cortex

Ant. Part ventral nucleus of thalamus(which receives info. from cerebellum

Basal ganglia

Efferents : Fibres from area 4 and

area 6 forming… 1. Corticospinal 2. Corticonuclear3. Corticobulbar tracts. Regulate the voluntary

movements of opposite side of body

Fronto-pontine fibres Corpus striatum, red

nucleus

Control movements of voluntary muscles of opposite side

Movements represented with head end below and leg end up (INVERTED MOTOR HOMUNCULUS)

Centres from below are: lips, tongue, larynx, pharynx, face, head & neck, upper limb with large area for fingers and hand, trunk, lower limb above knee.

Ant. Part of paracentral lobule

Extent of area depend on skill of movement and not on the bulk of muscle

Somewhat sensory. Receive some sensations like tingling and numbness

Known as MSI

Muscles of forehead, tongue, mastication, larynx, pharynx, extra ocular bilaterally represented

Only movements not muscles

LESION: initially flaccid paralysis

Location (area 6):

In front of area 4, include post. Part of sup., middle and inf. Frontal gyri

On medial side, continue with supplementary motor area

Agranular & motor

Integrates voluntary movements to perform skilful act.

Writing centre

Concerned with programming which is executed by area 4

LESION:

Produce difficulty in the performance of skilled movements.

Apraxia: loss of the ability to do simple or routine acts in the absence of paralysis.

Agraphia: when writing is also involved.

PRIMARY SOMATOMOTOR AREA (MSI)

=

PRIMARY MOTOR AREA

PREMOTOR AREA

Lie in front of area 6

Involve posterior part of middle frontal gyrus

Agranular cortex

Regulate voluntary conjugate movements of eye. Deviation of eyes to the opposite side

Controls voluntary scanning movements of the eyes and is independent of the visual stimuli.

Connected to the visual area of occipital cortex by association fibres.

Lesion of the area cause two eye to deviate to the side of lesion

Located on medial surface of cerebrum in the post. part of medial frontal gyrus anterior to the paracentral lobule

Afferents from VA and VL of thalamus

Efferents to area 4

Function is to control complex movements. Produce sensation of “URGE TO MOVE’

Receive some senses (MSII)

Lesion of area produce AKINESIA

Rest of frontal lobe ant. to pre-motor area which include orbital surface also

Fibres from thalamus, hypothalamus, limbic system, all areas of cortex

Concerned with individual’s personality

Regulate depth of feeling, thinking, mature judgement, orientation, concentration, pleasure and displeasure, right or wrong.

Bilateral damage due to trauma or tumour: change in personality, loss of concentration, judgement, inappropriate social behaviour like vulgarity of speech, improper clothing

Primary Secondary Sensory Association

Somesthetic (sensory) Visual Auditory

Primary somesthetic areas (areas 3,1,2)

Secondary somesthetic area

Somesthetic association are (areas 5,7)

Located in the post-central gyrus and extends into the posterior part of the paracentral lobule on the medial surface.

Granular cortex

Afferents from VPL and VPM of thalamus and other areas of cortex

Localise, analyse, discriminate all modalities of sensations

Sensations represented with head end below (INVERTED SENSORY HOMUNCULUS)

Paracentral lobule receive sense of distension from bladder and rectum

Hand, face, tongue, lips having larger representation in cortex

Lower part act as taste centre (area 43)

Modulate sensory input

Secondarily motor (SMI)

Located on the posterior part of posterior ramus of lateral sulcus

Involve lower part of pre and post-central gyri

Receive mainly pain sensation

Somewhat motor in function (SMII)

Located in the superior parietal lobule

Connected with higher association area in supra-marginal gyrus (area 40)

Concerned with the perception of shape, size, roughness, and texture of the objects

Stereognosis- ability to identify known objects in hand with closed eyes

Astereognosis or Tactile agnosia

Primary visual area

(area 17)

Visual association area (area 18 & 19)

Higher visual association area (area 39)

Located in the lips and walls of posterior part of calcarine sulcus which include cuneus and lingual gyrus

Thinner and granular cortex

Stria of gennari

Afferents from optic radiation

Temporal half of same retina and nasal half of opposite retina

Register opposite field of vision

Macular area-

occupying approximately posterior one-third of the visual cortex.

is the central area of retina and responsible for maximum visual acuity (keenest vision) has extensive cortical representation

Connected to area 18, 19 of both sides

Concerned with reception and perception of simple visual impressions like colour, size, form, transparency etc.

Unilateral lesion due to thrombosis, trauma produce partial blindness (hemianopia) with macular vision retained

Macular sparing because it is supplied by both MCA and PCA

Occupy rest of occipital lobe and calcarine sulcus

Afferents from area 17

Occipital eye field-produce involuntary deviation of eyes reflexly

Located in the angular gyrus of inferior parietal lobule

It relate visual information to the past experience, thus enabling person to recognize and identify the object by vision

Lesion of this area- visual agnosia- inability to recognize known objects by vision

Sensory aphasia (word blindness)- inability to recognize written word

Primary auditory area (area 41)

Auditory association area (area 42)

Higher auditory association area (Wernicke's area) (area 22)

Involve anterior transverse temporal gyrus (of Heschl), on the upper part of sup. temporal gyrus

Granular cortex

Afferents from MGB as auditory radiation

Detect the changes in frequency and direction from where sound originates

Unilateral lesion no deafness due to bilateral presentation

Lie behind area 41

Involve posterior transverse temporal gyrus of superior temporal gyrus

Granular cortex

Same function

Wernicke’s area

Rest of the area

Afferents from area 41 & 42

Interpretation of sounds and comprehension of spoken language from past auditory experiences

Lesion produce sensory aphasia (word deafness)-unable to interpret the spoken words.

Taste area (area 43)-lower part of inf. parietal lobule

Vestibular area- lower part post-central gyrus near face area

Olfactory area (area 28)-anterior part of parahippocampus gyrus and uncus

Speech- highly complex function

Speech function performed by dominant hemisphere

In 90%, left one, DOMINANT (TALKING BRAIN) & right one, NON DOMINANT (MUTE BRAIN)

FOUR SPEECH CENTRES: 3 sensory & 1 motor

Sensory speech areas:

1. Area 22 (Wernicke's area)

2. Area 39

3. Area 40

Broca’s motor speech area (area 44 & 45)

Area 22 (Wernicke’s area)

Interpret spoken language & recognize familiar words

Congenital deaf child-dumb

Area 39 of angular gyrus-store visual images and recognize them by sight

Area 40 of supramarginal gyrus- recognize familiar objects by touch and proprioception

All these 3 areas receive input from hearing, vision, touch and process it in the area 22 &

Then project it to Broca’s area through ARCUATE FASCICULUS

Located in the pars triangularis and pars posterior of inferior frontal gyrus

Afferents from area 22

Efferents to the muscles of tongue, lips, larynx, pharynx, palate, face for production of speech

Area 22- word deafness- unable to interpret spoken words. Speak fluently with incorrect and useless words

Area 39- word blindness- inability to recognize written words even written by self

Alexia, Agraphia

Area 40- Astereognosis

Area 44 & 45- motor aphasia- cannot speak properly although he understand everything. Slow speech with many grammatical mistakes

Conduction aphasia- arcuate fasciculus damage