CEREBRUM

Learning Objectives
A Different lobes and surfaces of Cerebral hemisphere

B. Blood supply of different regions of cerebral hemisphere

C Important sulci and gyri

D Different functional areas located in cerebral hemisphere

E. Lesions and its effects

 2

Cerebrum

Largest part of the brain

Heavily convoluted bilobed structure
 4

Cerebral hemispheres

General Appearance:
Separated by a deep midline sagittal fissure
– longitudinal cerebral fissure
In the depth of the fissure, the corpus
callosum connects the hemispheres across
the midline
Gyri – the folds of the surface of
hemispheres
Sulci – the fissures separate the gyri
 5

Surfaces of Cerebral Hemisphere

Three surfaces:
Superolateral surface
Inferior surface
Medial surface
Borders

1 Superomedial border

2 Superciliary border and inferolateral border

(Shows preoccipital notch)

3. Medial orbital border, hippocampal border or

inferomedial border and medial occipital border
 6

Lobes of Cerebral Hemispheres

Cerebral hemispheres are divided into lobes
by the central, parieto-occipital, lateral and
calcarine sulci
Lobes are named according to the cranial
bones under which they lie
Lobes are:
Frontal
Parietal
Temporal
Occipital
8
Cerebral
hemisphere
• the essential features can be
summarized by stating that:-
1

1. the frontal lobe lies in front of

the central sulcus (1) and above 2
the lateral sulcus (2) . 3
2. the parietallobe is behind
the
central sulcus andabove the
lateral sulcus.
3. the temporal lobe is below the
lateral sulcus
4. the occipital lobe lies below and P
behind the parieto-occipital F
sulcus (3) .
O
T
Main sulci 1
1. Central sulcus
3
2. Lateral sulcus
3. Parito-occipital sulcus
4. Calcarine sulcus 2
5. Cingulate sulcus
6. Callsosal sulcus ( Sulcus
of corpus callosum )
7. Orbital sulcus
8. Parahippocampal sulcus
9. Collateral sulcus
5
10. Occipiti-temporal sulcus
6

- First (6) can be seen in

sagittal sections
- Last 4 seen only in axial 4
sections
Main sulci 7
1. Central sulcus
2. Lateral sulcus
3. Parito-occipital
sulcus
4. Calcarine sulcus
5. Cingulate sulcus
6. Callsosal sulcus (
Sulcus of corpus 10 8
callosum ) 9
7. Orbital sulcus
8. Parahippocampa
l
sulcus
9.10. Occipiti-temporal
Collateral sulcus
sulcus
1. Central sulcus 2. Lateral sulcus 3. Parito-occipital
4. Calcarine sulcus sulcus
5. Cingulate
6. Callsosal sulcus ( Sulcus of corpussulcus
callosum )

1
3
5
6
2
4
 1. Orbital sulcus ( NOT
SHOWN / Above the
orbit !! ) 2
2. Parahippocampal sulcus
3. Collateral sulcus
4. Occipiti-temporal sulcus
3

4
 Main gyri 1 2
1. Precentral 3
2. Postcentral 3 4
3. Frontal (superior, middle & inferior) 3
4. Parietal (superior & inferior) 5- 5
5. Temporal (superior middle &
5
inferior) ,
6. Callosal 5
7. Medial frontal
8. Paracentral
lobule 7 8
9.
10. Precuneus
Cuneus 6
11. Lingual gyrus 9
12. Orbital gyri
13. Gyrus rectus 10
14. Parahippocampal
11
15. Occipitotemporal (medial & lateral)
16. Uncus
 Main gyri 13
1. Precentral
12
2. Postcentral
3. Frontal (superior, le & inferior)
midd erior) 5-
4. Parietal (superior & inf middle
(superior
5. Temporal , &
inferior) 16
6. Callosal
15 15
7. Medial frontal
8. Paracentral lobule 14
10.
9. Cuneus
Precuneus
11. Lingual gyrus
12. Orbital gyri
13. Gyrus rectus
14. Parahippocampal
15. Occipitotemporal (med
16. Uncus
ial & lateral)
 1

1. Rectus gyrus
2. Uncus ( parahippocampus
gyrus ) 2

3. Hippocampal gyrus 3
 9

Main sulci
Central sulcus
Indents the superior medial border of the
hemisphere, 1 cm behind the mid-point
It runs downward, forward and toward the lateral
sulcus across the lateral aspect of the hemisphere
The central sulcus is the only sulcus that
indents the superior medial border
 10
-

Main sulci (Cont’d)

Lateral sulcus
Deep cleft on the inferior and lateral
surfaces of the cerebral hemisphere
It consists of a short stem and three rami-
Anterior horizontal , anterior ascending and
posterior
 11

Main sulci (Cont’d)

Parieto-occipital sulcus:
Begins on the superior medial border of the
hemisphere, about 5 cm anterior to the
occipital pole
It passes downward and anteriorly on the medial
surface to meet the calcarine sulcus
Main sulci (Cont’d)
Calcarine Sulcus- Medial surface
Insula/Island Of Reil
• portion of the cerebral corte
folded deep within x
sulcus. the latera
• Play a role l
in consciousness
and
emotions
• The cortical area overlying the
insula toward the lateral surface
of the brain is the operculum
(meaning lid).
• The opercula are formed from
parts of the enclosing frontal,
temporal, and parietal lobes.
• Insulaa is surrounded by circular
sulcus ( arrow !! )
Superior surface
of temporal
operculum
presents
anterior and
posterior
transverse
temporal gyri
Other Sulci and Gyri
Superolateral surface
12

Frontal lobe – anterior to central sulcus and

superior to lateral sulcus
Superolateral surface of frontal lobe is divided
by three sulci into four gyri
Precentral sulcus and gyrus
Superior and inferior frontal sulci
Superior, middle and inferior frontal gyri
Anterior and ascending rami of lateral sulcus
divide inferior frontal gyrus into
PARS ORBITALIS, PARS TRIANGULARIS
PARS OPERCULARIS
13
 15

Superolateral surface
Parietal lobe – POST
CENTRAL SULCUS AND
GYRUS

o INTRAPARIETAL SULCUS
AND SUPERIOR AND
INFERIOR PARIETAL
LOBULE
Lateral
sulcus
 Superolateral surface

o PARIETAL LOBE-Few sulci extend into inferior parietal

lobule and divided into
o SUPRAMARGINAL GYRUS AROUND LATERAL
SULCUS
o ANGULAR GYRUS AROUND SUPERIOR
TEMPORAL SULCUS
o ARCUS TEMPORO-OCCIPITALIS AROUND
INFERIOR TEMPORAL SULCUS
 14

Superolateral surface

Temporal lobe – inferior to lateral sulcus

Two sulci – SUPERIOR AND INFERIOR
SULCUS
Three gyri- SUPERIOR, MIDDLE AND
INFERIOR TEMPORAL GYRI
Superior surface of temporal operculum
(Superior temporal gyrus)presents anterior and
posterior transverse temporal gyri. Anterior
gyrus forming primary auditory area, also called
HESCHL’S GYRUS
Superolateral surface

Occipital lobe – small area behind the

parieto-occipital sulcus
LATERAL OCCIPITAL SULCUS
LUNATE SULCUS
TRANSVERSE OCCIPITAL SULCUS
MEDIAL SURFACE
CINGULATE SULCUS AND CINGULATE GYRUS
CALLOSAL SULCUS
PARACENTRAL LOBULE(CORTICAL CENTRE OF
MICTURATION AND DEFECATION) AND MEDIAL FRONTAL
GYRUS

CALCARINE SULCUS AND PARIETO-OCCIPITAL SULCUS

SUPRASPLENIAL SULCUS IN PRECUNEUS
 INFERIOR SURFACE
ORBITAL SURFACE- OLFACTORY SULCUS, GYRUS RECTUS

ORBITAL SULCUS AND ORBITAL GYRI

TENTORIAL SURFACE- MEDIAL COLLATERAL SULCUS AND LATERAL OCCIPITO-TEMPORAL

SULCUS

LINGUAL GYRUS – BETWEEN COLLATERAL SULCUS AND CALCARINE SULCUS

LINGUAL GYRUS ANTERIORLY CONTINUE WITH PARAHIPPOCAMPAL GYRUS WHOSE

ANTERIOR END HOOK LIKE LIMITED BY RHINAL SULCUS- UNCUS

MEDIAL AND LATERAL OCCIPITO- TEMPORAL GYRUS

BROADMANS AREAS AND
FUNCTIONAL AREAS OF CEREBRAL
HEMISPHERE
Specific
Sulci/Fissures:
Central Sulcus

Longitudinal
Fissure

Sylvian/Latera
l Fissure

Transverse Fissure

http://www.bioon.com/book/biology/whole/image/1/1 http://www.dalbsoutss.eq.edu.au/Sheepbrains_Me/human_bra
 Frontal Lobe - Cortical Regions
Primary Motor Cortex
/Brodmann,s area 4
Precentral Gyrus – it cntr all ols
voluntary movements o the f
contralateral side of th body e
Site where movements of the
various parts of the body are
initiated
Recieves sensory input fro
cerebellum and thalamus m
The body is represented
upside down along the
precentral gyrus
Investigation (Phineas Gage)

Primary Motor
Cortex/ Precentral
Gyrus

Broca’s Area

Orbitofrontal
Cortex

Olfactory Bulb

Regions

Modified from:
secondary motor area/6,8,44 and 45
Precentral gyrus,sup,middle,inf frontal gyri
It programs the activity of the PMA
Stronger stimulation is required to produce the
same degree of movement
Broca’s Area –44,45
Inf.frontal gyrus
Brings about the formation of words.
Located on Left Frontal Lobe
Broca’s Aphasia – Results in the ability to
comprehend speech, but the decreased motor
ability (or inability) to speak and form words
Frontal eye field 8,
Middle frontal gyrus
Voluntary eye movements towards
opposite side and the accomodation
pathway
also controls eyelid movements
Prefrontal cortex9,10,11,12
Concerned with the makeup of the
individual,s personality
Head rotation area
 Parietal Lobe - Cortical Regions

Primary sensorymotor Cortex

1,2,3(Postcentral Gyrus) – Site involved
with processing of tactile and proprioceptive
information.
•Somatosensory Association Cortex -5,7 sup
parietal assists with the integration and
interpretation of sensations.

•Primary Gustatory Cortex 43

•Inferior part of the post central gyrus– Primary site
involved with the interpretation of the sensation of
Taste.
Primary
Somatosensory
Cortex/ Postcentral
Gyrus

Somatosensory
Association Cortex

Primary Gustatory
Cortex

Modified from:
http://www.bioon.com/book/biology/whole/image/1/1-8.tif.jpg

Regions
 Occipital Lobe – Cortical
Regions
Primary Visual Cortex – This is the primary area of the
brain responsible for Vision

•Visual Association Area – Interprets

information acquired through the primary
visual cortex.
Primary Visual
Cortex

Visual Association
Area

Modified from:
http://www.bioon.com/book/biology/whole/image/1/1-8.tif.jpg Regions
Temporal Lobe – Cortical
Regions
Primary Auditory Cortex –41,42 mostly
hidden in the lateral sulcus
Responsible for hearing
Its anterior part recieves low freq sounds
Post part –high freq sounds
Sec. Auditory Cortex 22
Interpretation of sounds
 Temporal Lobe – Cortical
Regions
•Primary Olfactory Cortex – sense of smell
(Not visible on the superficial cortex)

•Wernicke’s Area superior and middle

temporal gyri
• Understanding of speech
- Wernicke’s Aphasia – Words and sentences are not
clearly understood, and sentence formation may be
inhibited.
Primary Auditory
Cortex

Wernike’s Area

Primary Olfactory
Cortex (Deep)
Conducted from Olfactory
Bulb

Modified from: Regions

http://www.bioon.com/book/biology/whole/image/1/1-8.tif.jpg
dominant hemisphere

95-left
Broca
90% right handed
BLOOD
SUPPLY
Anterior and middle cerebral artery
(internal carotid artery)
Posterior cerebral artery (basilar artery)
Physiological information about
brain
• Left hemisphere is dominant Which hemisphere
90% of the right handed
in and 64%
of the left handed
is dominant ?!
• Right hemisphere is dominant in
10% of righ handed and 20% of
left handed

• In the remaining 16% of

handed bothhemispheres left
dominant .. are

• Speech areas in brain usually in

the dominant hemisphere !! ( OF
CLINICAL IMPORTANT )
Brodmann areas
Motor areas of
cortex
• 1- primary motor area :-
-MSI area ( precentral gyrus MSII
)
MSI
-MSII area ( Anterior part of
paracentral lobule )
• 2- secondary motor area
– Posterior parts of
frontal gyri extending
medially
Primary motor
area
• Broadmann area 4
• The area Msl is where movements
of the various parts of the body MSII
are initiated,
• Afferent :- receives its main inputs MSI
from the cerebellum and
thalamus.
• Efferent :- the corticonuclear and
corticospinal (pyramidal) tracts.
• MSII area many
from the basal nuclei
receives fibresand is
concerned with postural
mechanisms, but this area is not
yet clearly understood.
Motor homunculus
• the body is represented upside
down along this cortex, although
the face itself is represented the
right way up.

• The face lies lowest, then the

hand (a very large area), then arm,
trunk and leg.

• The leg and perineum areas

overlap the superior border and
extend down on the medial
surface of the hemisphere

• Blood supply :-
• 1- middle cerebral artery
Primary motor
area

• Lesions to thisarea produce

contralateral paralysis
!!
• Organs that supplied
are the less affected …
bilaterally
• CNs are supplied bilaterally
?!!
Secondary motor area
• Or supplementary motor area
• Broadmann are 6
• Location :- Posterior parts of
frontal gyri extending medially
• The function of the secondary
motor area:
• 1- store programs motor
To of
activity resulted past
experiencefrom
• 2- Controls sequence of
movements
• 3- spatial & postural
orientation
Controls movements.
• 4- Controls bimanual movements.
• Blood supply: Middle &
anterior
secondary motor area
• Lesions :-

• Apraxia (inability to execute purposeful movements despite

having
learnedthe desire and the physical capacity to perform
them).

• There is no or little loss of strength

Boca's area
• The motor (anterior) speech area
(of Broca, areas 44 and 45) is
usually situated in the inferior
frontal gyrus on the left side (in
right-handed and in most left-
handed people), below and in
front of the face area and centred
on the pars triangularis between
the anterior and ascending rami of
the lateral fissure.

• Damage to it produces
aphasia — difficulty
motor in finding the
right words, but not paralysis of
laryngeal musculature.

• Blood supply :-
• Middle cerebral a.
Wernicke's
• The posterior speech area (of
area
Wernicke) is in the posterior parts of
the superior and middle temporal gyri
and extends into the lower part of the
parietal lobe.
- It is connected to the Broca’s, visual &
auditory cortex

• Function:
• To understand the written and spoken
• Its
language is necessary for
understanding the
integrity of speech.

• Lesion … dysphasia;
patient responds
Receptive by intact, the
irrelevant speech! but
• Blood supply:
• Middle cerebral artery
Prefrontal
cortex
• The prefrontal cortex is an
extensive area that lies anterior to
the precentral
• The prefrontal area is
concerned
1. with
the makeup the individual’s
of personality.
2. regulator of the person’s depth of
feeling.
3. It exert its influence
alsodetermining
s in initiative
the
and
judgment of an individual.
Prefrontal
• Lesions :-
cortex
• It is now generally that
agreed destruction of the
• region does not produce
prefrontal
any
marked loss of intelligence
• Tumour or traumatic destruction
of the prefrontal cortex result in
the person’s losing initiative and
judgment.
• Emotional changes that occur
include a tendency to euphoria.
• The patient no longer conforms to
the accepted mode of social
behavior and becomes careless of
dress and appearance.
• Bipolar disorders
Sensory areas
• 1- Primary somatosensory area
- The postcentral gyrus
1
- Posterior part paracentra 2
of lobule l
- Recieves primary from thalamus
- Sensations from the oral region,
pharynx, larynx & perineum are
received bilaterally

• 2- ( or association
somatosensory
Secondary area.
)
- Occupies the parietal
superior lobule
Primary sensory area

• Sensory homunculus:
• The amountof the cortex for a
particular part of bod
related the to its functionalis
importance & number of
receptors ( not to its size)

• Blood supply:
- Middle cerebral artery
- Anterior cerebral artery (leg area)
Primary sensory area
• Lesions :-
• Lesions of the primary
somesthetic of the cortex
result
area in contralateral sensory
disturbances, which are most
severe in the distal parts of the
limbs. Crude painful, tactile,and
thermal stimuli often return,but
this is believed to be due to the
function of the thalamus.
• The patient remains unable to
judge
• degrees of warmth, unable to
localize tactile stimuli accurately,
and unable to judge weights of
objects.
• Loss of muscle tone may also be a
symptom of lesions of the sensory
cortex.
Secondary somatosensory area
• Function:
- Receive different sensory
modalities & relate them to past
experience. e.g; object recognition
without vision.

- Lesions = asterognosis !!
- Inable to identifythings
without see them …
Primary visual
cortex
• Broadmann area 17

• Functions:
- Receives fibers from the opposite
field of vision
- It excludes &
alsounwantedmodulates
images!

• Blood supply:
- Posterior cerebral artery

• Lesions :-
• Crossed homonymous hemianopi
a
Secondary visual
cortex
• Brodmann area 18,19

• Surrounded by the primary visual

cortex …

• Functions to relate the visual

information to past experiences

• Lesions produce … Visual agnosia;

loss of ability to recognize objects
seen in the opposite field of vision
Primary auditory area
• Broadmann area 41,42

• In the inferior wall of lateral

sulcus
• Afferent: Principally from
the
medial geniculate body

• Blood supply:
-- Lesions produce artery… Partial
Middle cerebral
deafness in ears
inability to locate sound.
both with
- The greater lossbeing in the
opposite ear
- (cochlear nuclei send 2nd order to
the olivary nucleus & nuclei of
trapezoid body bilaterally)
Auditory
pathway

• Explaning why greter loss of

inability to hear on the
opposite site !!!

• Cochlear n. send fibers more

to the other side than the
same side …
Secondary auditory area
• Broadmann area 22
• Lies posterior to the primary
auditory area
• Function:
- To interpret sounds and associate
the auditory input with other
sensory information.

• Blood supply:
• Middle cerebral artery

• Lesions : auditory agnosia !!

The dominant angular gyrus
• This part is often
considered a part of the
Wernicke area

• Lesion here results in inability to

read (alexia) or write (agraphia).
Aphasia

Alexia
Sensory aphasia

Agraphia
Motor aphasia
A lesion resulting in a nonfluent expressive
aphasia would most likely be found in the
(A) temporal lobe
(B) parietal lobe
(C) frontal lobe
(D) occipital lobe
Alexia without agraphia and aphasia would
most likely result from occlusion of the
(A) left anterior cerebral artery
(B) right anterior cerebral artery
(C) left middle cerebral artery
(D) left posterior cerebral artery
(E) right posterior cerebral artery
A patient is asked to bisect a horizontal line
through the middle, to draw the face of a clock,
and to copy a cross. The patient bisected the
horizontal line to the left of the midline,
placed all of the numerals of the clock on the
right side, and did not complete the cross on
the left side. The most likely lesion site for this
deficit is the
(A) left frontal lobe
(B) right parietal lobe
(C) left parietal lobe
(D) right temporal lobe
(E) left occipital lobe
 White Matter
Underlies the cortex
Contains:
Nerve fibers
(predominantly myelinated)
Neuroglia
Blood vessels
The nerve fibers
originate, terminate or
sometimes both, within
the cortex
Depending on their origin & termination, these nerve fibers
are classified into three types:

A. Association

B. Projection

C. Commissural
 Association Fibers
Unite different parts of the
same hemisphere
Are of two kinds:
Short association fibers: those
connecting adjacent gyri,
Long association fibers: those
connecting more distant gyri
 Short Association Fibers
Lie immediately beneath the gray
substance of the cortex
Connect together the adjacent gyri.
 Long Association Fibers
Long fibers travel
through white matter to
connect distant areas of
cerebral cortex
Link the primary sensory
areas in parietal, temporal
and occipital lobes to the
association areas of the
cerebral cortex, and to
each other
Superior
longitudinal
fasciculus:
connects the
frontal, parietal,
temporal and
occipital lobes

Uncinate
fasciculus: Broca’s Arcuate

connects frontal to Area Fasciculus Arcuate fasciculus:

temporal lobe, connect gyri in
contributing to the frontal to temporal
regulation of lobes, important for
behavior language function
Wernicke’s Area
Cingulum: connects
frontal & parietal
lobes to the
para-hippocampal
gyrus and adjacent
temporal gyri

Inferior longitudinal
fasciculus: connects
occipital to temporal
pole & contributes to
visual recognition
 Commissural Fibers
Connect the corresponding Corpus Callosum

regions of the two hemispheres

Include:
Corpus callosum
Anterior commissure
F
Hippocampal commissure (commissure of
fornix)
*(Posterior commissure, not a cerebral
commissure)
P
 Commissural Fibers
Connect the Anterior commissure------> small fiber ,
corresponding regions of below anterior part of corpus
the two hemispheres. callosum
Include: Posterior commissure-----> just above
1. Corpus callosum. superior colliculus
2. Anterior Hippocampal commissure (commissure
commissure. of fornix).------> deeper
3. Posterior within parahippocampalgyrus ( when
commissure. you open
4. Hippocampal parahippocampalgyrus you will find tow
commissure swelling (hippocampi) ,
(commissure of connect whith each other by
forni Hippocampal commissure
 Corpus Callosum
Is a fibrous bridge located in the
depth of the median longitudinal
fissure
Connects the two cerebral
hemispheres together
Shorter craniocaudally than is
the hemisphere
Cranial end is nearer to the
frontal pole of hemisphere as
compared to caudal end to the
occipital pole
 Corpus Callosum
Connects the corresponding Antero-posterior lenghth of corpus scallosum shorter
regions of the two than
hemispheres except the Antero-posterior lenghth of hemisphere because of
temporal lobes, that are that :
connected by anterior The fiber that connect the anterior pole of frontal
commissure lobes ,
It is shorter craniocaudally will pass backward reach anterior part of corpus
than is the hemisphere callosum
then go to opposite side and reach anterior pole of
The callosal fibers linking the
corpus callosum
frontal poles curve forward The anterior end of corpus callosum ---- form forceps
forming anterior forceps The fibber that connect the tow occipital lobe run
(forceps minor) forward reach corpus callosum then to opposite
The callosal fibers linking the hemisphere go backward to reach corresponding
occipital poles curve backward area in
forming posterior forceps occipital lobe
(forceps major The posterior end of corpus callosum ---- form
forceps
 Parts of Corpus Callosum

Genu Body

Splenium
Rostrum
Anterior Commissure
Bundle of fibers runs fornix

transversely in front of IVF

the anterior columns of

Anterior
fornix column of
fornix
Connects the inferior
and middle temporal
gyri & the olfactory
regions of the two
hemispheres
 Hippocampal Commissure
Bundle of fibers runs transversely
between the crura of the fornix
Connect the two hippocampi with each
other
(notethat
hippocampo-mamillary fibers
do not cross)
 Posterior Commissure
Rounded band of white
fibers
Crossing the midline on the
dorsal aspect of the upper
end of the cerebral aqueduct
(located between superior
P
colliculus & pineal body)
Connects the left and right SC

midbrain. Plays important IC

role in the bilateral pupillary Cerebral

aqueduct

reflex
 Projection Fibers
Fibers running vertically through the
hemispheres
Consist of:
Cortical afferent fibers conveying
impulses to the cerebral cortex:
(mainly thalamo-cortical fibers)
Cortical efferent fibers carrying
impulses away from the cortex to the
lower centers: (corticostriate,
corticobulbar, corticopontine,
corticospinal, & descending
autonomic fibers)
Deeper to the cortex, these fibers are
arranged radially as the corona
radiata
Then the fibers converge to form a corona
radiata
sheath, called the internal capsule,
that passes between the thalamus
and the basal ganglia
Continue in the:
Crus of the midbrain
Basilar part of pons
Pyramid of medulla oblongata
Continue in the spinal cord as the
corticospinal tracts
Internal Capsule BG

Bundle of projection
fibers, passes through
the interval between
the thalamus and the
Th
basal ganglia
Has 5 parts:
1. Anterior limb: between
caudate (C) &
lentiform (L) nuclei
2. Genu
3. Posterior limb: between thalamus (TH) & C
1
lentiform nucleus (L)
2 L
4. Retrolenticular part: caudal to lentiform
3
nucleus Th
5. Sublenticular part: below lentiform nucleus 4

(can not be seen in this section)

Anterior limb contains:
Thalamocortical projections that connect
mediodorsal nucleus of thalamus with the
prefrontal cortex
Frontopontine fibers
Genu contains:
Corticobulbar fibers which connect the cortex
with cranial nerve motor nuclei in the
brainstem
Posterior limb contains:
Corticospinal
Corticobulbar
Thalamocortical projections from:
VPN to the primary
somatosensory cortex
VAN & VLN to motor
regions of cortex
Retrolenticular part contains
thalamocortical projections:
Geniculocalcarine fibers (visual
radiation), from the lateral
geniculate nucleus of thalamus
to the visual cortex in the
occipital lobe
& few Geniculotemporal fibers
(auditory radiation) from the
medial geniculate nucleus of
thalamus to the auditory cortex
in the temporal lobe
Sublenticular part contains
thalamocortical projections:
geniculo-temporal fibers
(auditory radiation) from the
medial geniculate nucleus of
thalamus to the auditory
cortex in the temporal lobe
 Clinical Notes
Bilateral lesion of the inferior longitudinal fasciculus (as in
carbon monoxide poisoning), leads to:
Loss of identification of the:
Nature of objects (object agnosia)
Individual faces (prosopagnosia)
The elementary vision remains intact
Damage to corpus callosum leads to split-brain syndrome.
The two half of the brain behave relatively autonomously
Damage to splenium of corpus callosum leads to posterior
disconnection syndrome of alexia (cannot understand written
material) without agraphia (can speak and write without
difficulty)