2. CEREBRAL CORTEX
Introduction:
Cerebral cortex is involved in different motor and sensory function
Cerebral cortex area is about 2.2 square meter
It has two cerebral hemisphere right and left
The characteristic feature of cerebral cortex is Sulci and Gyri
Sulci are the depression present on cerebral cortex
Gyri are the elevations present on cerebral cortex
3. The two cerebral hemisphere are separated by a deep vertical fissure fissure
These two halves separated fully at anterior and posterior and partially in the
middle part due to the presence of Corpus callosum its is a connecting fibers of
these two halves
And each half of cerebral hemisphere divided into 4 lobes namely
Frontal lobe
Parietal lobe
Temporal lobe
Occipital lobe
4. The main fissures or sulci which separate these lobes are
1.Centaral sulcus
is in between frontal and parietal lobe
2.Parieto occipital sulcus
is in between parietal and occipital lobe
3.Lateral sulcus or sylvian fissure
is in between parietal and temporal lobe
4.Callosomarginal fissure
is in between temporal and limbic area of frontal lobe
5.
6. Brodmann area:
Brodmann areas are the regions of cerebral cortex based on its microscopic structures
and organisation of cells
Brodmann areas are 52 in number i.e from area no 1,2,3------to------area no 52
7. Frontal lobe:
Frontal lobe is situated in between frontal pole and central sulcus inferiorly up to
lateral sulcus
It occupies 1/3 rd of cerebral cortex
It has pre central gyrus,superior,middle,inferior frontal gyrus
Functionally this lobe divided into two parts namely
1.Prefrontal cortex
2.Precentral cortex
Precentral cortex further divided in to 3 parts
1.Primary motor area
2.Premotor area
3.Supplementary motor area
8. Prefrontal cortex:
It is also called Orbito frontal cortex
It is situated anteriorly in between anterior pole and precentaral are of
frontal lobe
It has lateral medial and inferior surfaces
Areas present in pre frontal cortex are 9,10,11,12,13,14 on lateral surface
23,24,29,32 areas on medial surface
Inferior surface has Orbital gyri
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10
11 12
9. Connections of Prefrontal cortex:
Afferent connections
Receives fibers mainly from
Dorsomedial nucleus of thalamus
Hypothalamus
Corpus striatum
amygdala
Mid brain
Efferent connections
Send fibers to
Thalamus
Hypothalamus
Tegmentum
Caudate nucleus
Pons
Temporal lobe
Area 13 along with hippocampus send fibers to mammillary body via fornix this area related with
Emotions
10. Functions of Prefrontal cortex:
This area is center for higher functions like Emotions,learning,memory,social
behaviour
Short term memories stored
Center for planned actions
Center for intelligence
Bilateral removal of these area leads to lack of mental alertness and lack of
intiation very little changes in memory judgement and intelligence
12. Precentral cortex:
It is posterior part of frontal lobe
It is situated anteriorly in between central sulcus and prefrontal cortex ,posterior
portion of middle,superior and inferior frontal gyri
It extend to medial surface also
It is also called excito motor cortex
Precentral cortex again divided into
Primary motor area
Pre motor area
Supplementary motor area
13. Primary motor area:
This area present through out the area of pre central gyrus adjoining area of
central sulcus
Area no. 4 and 4s are present in it
Connections of Primary motor area:
Afferent connections
Receives fibers from
Dentate nucleus via red nucleus
Thalamus
Efferent connections
Send fibers to
Corticospinal tract to spinal cord of opposite side
Frontopontine fibers to pontine nuclei of same side
Corpus striatum
Red nucleus
Thalamus
Subthalamus
Reticular formation
Association fibers to this area to other area of cortex
14. Functions of Primary motor area:
This area is involved in voluntary movements and speech
Area 4:
Area situated just in front of central sulcus on pre central gyrus as a strip
Area has broad end at superiorly
Most of efferent fibers arised from primary motor area and these fibers involved in voluntary movements
of opposite side on stimulation
Area 4S:
This is called suppressor area
It is present in front of area no.4 on precentral gyrus
It inhibited the movements created by the area no 4 so that it control exaggerated movements
• Lesion in this area leads to paralysis of contralateral side(opposite side of body)
• Lesion of this area both side leads to total paralysis
• Recovery is late while recovering upper limb recovered first than lower limbs
16. Pre motor area:
This area present anterior to primary motor area
Area involved in postural movements of body sent efferent fibers to axial muscles of body
Areas involved are 6,8,44 and 45
Area 6:
Area no 6 divided in to 6a and 6b on frontal gyri, infront of area no 4
This area also send efferent fibers through corticospinal tract along with area 4
Functions of Area 6:
Coardinate the movements intiated by area 4,that is it involved in skilled movements to perform
accurate
lesion of this area leads to loss of skilled movements opposite side
Lesion along with area 4 leads to severe hemiplegia
17. Area 8:
This area also called Frontal eye field
Present anterior to the area no 6
It is concerned with eye ball movements
Send fibers to i.e efferent connection with Occulomotor nuclei of midbrain
Receive fibers from i.e afferent connection with Thalamus and Occipital lobe
Functions of Area 8:
this area involved in eye ball movements,open and closure of eyelids,dilatation of
pupil and lacrimation of opposite side of eye
lesion of this area leads to loss of eye ball movements but not effect eyelids and pupil
18. Area 44 and 45:
It is also called as Broca’s area
It is a Motor area of speech
Situated on inferior frontal gyrus of frontal lobe
Functions of Broca’s area:
area responsible for movements of tongue,lips,and larynx which area
involved in speech
lesion of this area leads to Motor aphasia or Broca’s aphasia
In this person has idea about his statement but he is unable to talk fluently
Supplementary motor area:
This area present medial surface of frontal lobe
Exact function of this area not understood clearly
It suggested that it is concerned with coordinate skilled movements
20. Homunculus arrangement of motor areas in cerebral cortex
The muscles of various parts of body represent in motor area 4 from medial to lateral
surface
In this the lower part of body present at lateral surface and upper parts of body present
at medial surface
The order of representation from medial to laeral cortex is
Toes-->ankle-->knee-->hip-->trunk-->shoulder-->arm-->elbow-->wrist-->hand-->fingers-->face
From their respective are the efferent fibers send to respective muscles of opposite side
except face
Face receives efferents from both side cortex
21.
22. Parietal lobe:
Frontal lobe is situated in between frontal lobe,occipital lobe and temporal lobe
separated by Central sulcus,parieto occipital sulcus and sylvian fissure respectively
Parietal lobe divided into 3 areas
Somesthetic area I
Somesthetic area II
Somesthetic association area
Along with it has nother area present namely sensory motor area
Parietal lobe mainly involved in sensory functions
23. Somesthetic area I:
It is also called Primary somesthetic area or Primary sensory area
It is situated posterior to the central sulcus on post central gyrus and on paracentral lobule
of medial side
Areas:
It has three areas 3,1 and 2
Anteriorly on post central gyrus has area 3 and posteriorly has area 1 and 2
Connections:
It receives afferent fibers from Thalamus as thalamic radiation
24. Functions of Somesthetic area I :
It receives sensory impulses like pain,touch,temperature,pressure and proprioception from
opposite side
Area 1 involved in sensory perception and area 2 and 3 in integration of sensory impulses
These area send feedback to pre motor area
Apart from this it has also involved in
Spatial recognition:
Tactile localization and two point discrimination
Recognition of intensity of stimuli
Recognition of similarities and difference between stimuli
If lesion in this area without involvement of thalamus leads to loss of discrimination but
patient able perceive the stimuli
If lesion in this area along with thalamus leads to loss of sensations opposite side
26. Somesthetic area II:
It is situated on post central gyrus below the somesthtic area I some part of
this area present in sylvian fissure
Connections:
It receives afferent fibers from Thalamus and somesthetic area directly
Exact role of this area not clear but it concerned with perception of sensation
28. Somesthetic association area:
It is situated posterior to post central gyrus infront of visual cortex and above auditory
cortexmedial side
Areas:
It has areas 5 and 7
Anteriorly on post central gyrus has area 3 and posteriorly has area 1 and 2
Function:
This area center for combined sesation like Stereognosis
Lesion of this area leads to Astereognosis
30. Sensory motor area:
Sensory area not limited to parietal lobe it extends in to motor area of pre central
gyrus
Similarly motor area not limited to frontal lobe it extends In to sensory area post
central gyrus
This combined area called as sensory motor area
Timing and programming of skilled movents involved in Corticocerebellum are stored
in sensory motor area
31. Homunculus arrangement of motor areas in cerebral cortex
The various parts of body represent in primary sensory area from medial to lateral
surface
In this the lower part of body present at lateral surface and upper parts of body
present at medial surface
The order of representation from medial to laeral cortex is
Toes-->ankle-->knee-->hip-->trunk-->shoulder-->arm-->elbow-->wrist-->hand-->fingers--
>face(eyelids-->nose-->cheek-->upper lip-->lower lip)
32.
33.
34. Temporal lobe:
Temporal lobe is situated below the fronto parietal lobe
Temporal includes 3 areas
Primary auditory area
Auditopsychic area
Area for equilibrium
35. Primary auditory area:
This area include area no 41,42
41’42areas are present on anterior transvers gyrus and anterior part of
superiortemporal gyrus
Connections:
This area receives afferent fibers from Medial geniculate body and Pulvinar
Send efferent fibers to medial geniculate body,inferior colliculus of mid brain
and pulvinar
Functions of primary auditory area:
primary auditory area involved in perception of auditory stimulus
but interpretation of sound i.e analysis of speech source of sound is done with
the help of Auditopsychic area
36. Auditory psychic area:
This area include area no 22
This is also called wernick’s area
It is situated on superior temporal gyrus posterior to area no 41,42
It is helpful in interpretation of sound
It is a sensory area of speech
Lesion of this area leads to Sensory aphasia or Wernick’s aphasia
In this patient able to talk clearly but not related
Area for equilibrium:
It is situated posterior to superior temporal gyrus
It is helpful maintainence of equilibrium
Stimulation of this area leads to dizziness,swaying,falling and feeling of rotation of
body
22
38. Occipital lobe:
It is posterior part of cerebral cortex
Temporal include visual cortex
Visual cortex includes
Primary visual area----- area no.17
Visual association area--area no.18
Occipital eye field-------area no.19
Connections:
It receives afferent fibers from latearal geniculate body
Send efferents to superior colliculus and lateral geniculate body
39. Functions of Visual cortex :
Primary visual are involved in perception of visual impulses
Visual association area involved in interpretation of visual impulses
Occipital eye field concerned with movement of eyes
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41. Histology of cerebral cortex
Cerebral cortex formed by nerve cells along with their processes and neuroglia
it does not have uniform thickness
Thickest part is at Precentral gyrus i.e 4.5cms and thinnest part is at frontal and occipital poles
Cerebral cortex is formed by six layers (from out side to in side)
Molecular or plexiform layer
External granular layer
Outer pyramidal layer
Internal granular layer
Internal pyramidal layer or Ganglionic layer
Fusiform cell layer