The Cerebral Cortex

1. Human Brain
(Encephalon)

2. Anatomic subdivisions of the brain
• Hindbrain
(rhombencephalon)
– Medulla oblongata
– Pons
– Cerebellum
– Cavity: 4th Ventricle
• Midbrain
(mesencephalon)
– Cavity: cerebral
aqueduct of Sylvius
• Forebrain
(prosencephalon)
– Telencephalon
– diencephalon
cerebe
-llum
Midbrain
Pons
Medulla
Oblongata
Cerebral hemisphere
4 V
L
3V

3. Forebrain (Prosencephalon)
Forebrain Telencephalon
(Endbrain)
Diencephalon
(interbrain)
Right cerebral
hemisphere
Epithalamus
Ventral
thalamus
(subthalamus)
Hypothalamus
Dorsal
thalamus
Left cerebral
hemisphere

4. Cerebral hemispheres (cerebrum)
• Dimensions
– Weight: 1400 g (males)
• About wt of liver
• About 10 times wt of cerebellum
– Weight: 1200 g (females)
– Volume: about 1500 cm3
– Surface area: about 2200 cm2
– Cortical thickness:
• As thick as 4.5 cm
• As thin as 1.5 cm
• The two hemispheres are
separated by a longitudinal
fissure

5. Lobes of the Cerebral hemisphere
• 4 lobes:
–Frontal
–Parietal
–Temporal
–Occipital

6. Parts of the Cerebral wall
• Cortex
– or grey
matter
• Medullary
substance
– or white
matter
• Basal ganglia
– or basal
nuclei
Basal nuclei

7. Lateral ventricle
• Cavity of
cerebral
hemisphere

8. Frontal pole
Temporal pole
Occipital pole
Surfaces and borders & poles of cerebral hem.
• Three surfaces
– Superolateral
– Medial
– Inferior
• Tentorial part
• Orbital part
• Borders
– Superomedial
– Inferolateral
– Medial
• Poles
– Fontal
– Occipital
– temporal

9. Cerebral Cortex (surface topography)
• Presence of
sulci
(grooves) &
gyri (ridges)
• Gyri increase
cortical
surface area
several folds
• Some sulci &
gyri are
named
Superolateral surface

10. Main sulci of the cerebral hemisphere
• Central
sulcus of
Rolando
• Lateral
sulcus of
Sylvius
– Stem
– Anterior
ramus
– Ascending
ramus
– Posterior
ramus
On the superolateral surface

11. • Calcarine
sulcus
• Parieto-
occipital
sulcus
• Cingulate
sulcus
Calcarine
sulcus
Main sulci of the cerebral hemisphere
On the medial surface
Cingulate sulcus

12. • Orbital sulcus
(H-shaped)
• Olfactory
sulcus
Main sulci of the cerebral hemisphere
On the inferior surface

13. FUNCTIONAL LOCALIZATION OF THE
CEREBRAL CORTEX

14. Specific cortical areas in the frontal lobe
Precentral gyrus
Central sulcus
• PRIMARY MOTOR AREA
– In the precentral gyrus &
paracentral lobule
• Brodmann area 4
• Agranular ctx, with Betz cells (80 um)
– Afferents:
• Cerebellum, basal nuclei
– via thalamus
• Somatosensory ctx & premotor area
– Destination
• Brainstem motor nuclei
• Lower motor neurons
– Function:
• Controls voluntary motor activity
(contralateral side)
• Source of corticospinal
(pyramidal) fibres
• Lesion:
• Contralateral spastic paralysis
• exaggerated stretch reflexes (as
occurs in stroke).

15. Motor Homunculus
• Somatotopically organized
• Has the lowest threshold
for eliciting motor activity
upon electrical stimulation
• Body regions with finely
controlled (fractionated)
movements have large
representations
– Fingers & face largest; trunk
smallest

16. Premotor area Central sulcus
Premotor area (secondary motor area)
• In the posterior parts of superior,
middle & inferior frontal gyri
– Brodmann area 6 (& parts of 8, 44,
45)
– Afferents:
• Basal ganglia, thalamus,
somatosensory ctx
– Destination
• Primary motor ctx, etc
– Function:
• Storage of motor activity related to
past experience
– It programs the activity of primary
motor ctx (based on past motor
experiences).
It elicits mvt similar to
primary motor ctx but
requires greater threshold

17. Supplementary motor area
• Location:
– Medial frontal gyrus (part of Brodmann areas 6 & 8)
• Function
– Controls contralateral body mvt, but higher threshold required
• Lesions may not produce permanent loss of mvt
• Contributes to
corticospinal fibres

18. Frontal eye field
• Localized in the postr
part of middle frontal
gyrus
– Brodmann areas 6, 8, &
9
• Connections:
– With occipital ctx, via
association fibres
(reciprocal)
– Efferent:
• to superior colliculus
– and via reticular fibres to
motor nuclei of nerves of
extraocular mm
Importance:
Controls voluntary
scanning conjugate mvt of
the eyes to opposite side
(independent of visual
stimulus)
Lesion results in the two eyes
deviating to the side of the lesion;
with inability to turn the eye to the
opposite side

19. Arcuate fasciculus
Motor speech area of Broca
• Located in the
dominant (often
left) hemisphere
– Brodmann areas
45, 44 in the
inferior frontal
gyrus
• Connections:
– With primary
motor ctx for ctrl of
muscles of tongue,
larynx, lips, etc.
• Lesion:
– Speech paralysis
(motor aphasia)
• Not paralysis of
laryngeal or
tongue muscles
Lesion in both Broca’s and Wernicke’s speech
areas would lead to global aphasia; in which the
person cannot produce nor understand speech.

20. Medial
PFC
Prefrontal cortex
• Include parts of supr, middle & infr
frontal, orbital, medial frontal & antr
part of cingulate gyri
– anterior to precentral area
– Largely Brodmann areas 9,10,11,12
• Reciprocal connections with thalamus,
hypoth, corpus striatum, other parts of
cortex
• Is linked with opposite PFC by corpus
callosum
• Importance:
– Mediates behaviour, attention, feelings
(affect); planning , initiative (executive
fxns), working memory
– Lesion: ADHD, antisocial behavior; lack
of initiative and judgment

21. S1
M1
• Primary somatosensory area
– Or primary somesthetic area
– Brodmann area 3, 1, 2
– In postcentral gyrus & paracentral
lobule
– granular type of ctx
• Afferent:
– Ventral posterior lateral/ventral
posterior medial nuclei
• Efferent:
– primary motor ctx
• So that proprioceptive input can
elicit proper motor responses
• Importance
– Conscious perception of
exteroception and proprioception
Specific cortical areas in the parietal lobe

22. Sensory homunculus
• S1 is somatotopically
organized
– Specific regions
represented on specific
loci of the ctx
• Size of representation
depends on the level of
sensitivity of a region
– Density of receptors
– Face, thumb, index
fingers, lips, have large
areas

23. Secondary somatosensory area
• At the
lowermost end
of S1
– Above lateral
fissure
posterior limb
& behind
central sulcus

24. Somatosensory association area
• Localized in the
superior parietal
lobule, extending
into medial surface
– Brodmann areas 5,
7
• Connections:
– Other sensory
areas of ctx
• Importance:
– Stereognosis:
• ability to identify
the shape and
character of an
object by touch
• Lesion:
– tactile agnosia

25. Taste Area
• Location:
– Lower end of
postcentral gyrus &
– superior wall of
lateral sulcus
• Afferent:
– ventral
posteromedial
nucleus of thalamus

26. VESTIBULAR AREA
• Location: adjacent to
the part of the
postcentral gyrus for
face
• Works in association
with the vestibular
apparatus for
appreciation of
position and
movement of the
head in space

27. 17
17
18
19
Specific cortical areas in the Occipital lobe
• PRIMARY VISUAL AREA
– Or striate cortex (area 17)
– Along the walls of postr part of calcarine
sulcus
– May extend onto lateral hem surface
around occipital pole
– Stria of Gennari in layer IV
– Granular type of ctx
• Relation to visual field
– Right ½ of visual field rep in left visual ctx
– Left ½ of visual field rep in right visual ctx
– Infr filed of vision is rep in supr wall of
calcarine sulcus
– Supr field of vision is rep in infr wall of
calcarine sulcus
– Macula lutea is rep in the postr part of
visual ctx, near occipital pole
• Afferent:
– From ipsilateral lateral geniculate
nucleus
• Vis retrolentiform part of internal
capsule (optic radiation)
17
17
18
19
• Efferent:
• V18, V19
• Wernicke’s area, superior colliculus, etc
• Importance
Conscious perception of vision

28. • lesion in the
visual cortex
– contralateral
homonymous
hemianopia

29. Visual association
area
• Surrounds striate
cortex on medial and
lateral surfaces of hem
– Parastriate and
peristriate areas (18,
19)
• Afferent
– From area 17
• Function
– Relates visual info
received by primary
visual cortex to past
visual experiences
17
17
18
19

30. • Primary auditory area
– On upper surface of
supr temporal gyrus
• convolutions of Heschl
or transverse temporal
gyri
– Areas 41, 42
– Granular type of ctx
• Afferents
– Medial geniculate
nucleus
• Via sublentiform part of
internal capsule
(auditory radiation)
Specific cortical areas in the temporal
lobe

31. Primary
auditory ctx
• Efferents
– Secondary aud. Area
– Sensory speech area of
Wernicke
• Importance
– perception of spoken words
– Tonotopically organized:
• High frequency sounds are
represented in the postr
part of this ctx; low
frequency sound in the
anterior part
• Lesion
– Partial deafness
• Greater on contralateral
side (why??)

32. Secondary auditory cortex
• Auditory association
area
– lateral surface of
superior temporal
gyrus
– Area 22
• Afferent
– From A1
• Importance
– Involved in the
interpretation of
sounds
22

33. Sensory speech area of Wernicke
• Location
– Left (dominant)
hemisphere
– Mainly in the
superior
temporal gyrus
• Extends into
inferior
parietal
lobule
– around
postr end
of lateral
sulcus
• Includes areas
39, 40 (angular
& supramarginal
gyri respectively)

34. • Afferents: auditory and
visual cortices, etc
• Efferents: Broca’s area,
via arcuate fasciculus, etc
• Importance
– Understanding of written
and spoken language
• Lesion
– Wernicke’s aphasia
(sensory aphasia,
receptive aphasia, or
fluent aphasia)
• Problems understanding
spoken & written
language
• Inability to express
language meaningfully
Arcuate
fasciculus
Lesion: in the angular gyrus of the
dominant hem. (part of Wernicke’s
speech area) results in alexia
(inability to read) and agraphia
(inability to write)
[owing to separation of
the visual association area
from Wernicke’s area]

35. Cerebral Dominance
• Dominant hemisphere
– For Handedness, language and
speech
– Usually left hemisphere
• In more than 90% of popn
• Non-dominant hemisphere
– For spatial perception, facial
recognition , & music
– Usually right hemisphere

36. Case study