 The average human brain weighs about
1,400 grams (3 lb). When the brain is
removed from the skull, it looks a bit like a
large pinkish-gray walnut.
 The two really large and deep ones are
usually called fissures (but one of these, the
Sylvain fissure, is sometimes called the
lateral sulcus). These two fissures plus the
Central Sulcus divide the cortex into its main
divisions.
The most prominent is the
Interhemispheric Fissure, which divides
the cerebral cortex into two hemispheres,
right and left.
 Each hemisphere of the cerebral cortex is
divided into four lobes by various sulci
and gyri.
 The sulci (or fissures) are the grooves
and the gyri are the "bumps" that can be
seen on the surface of the brain.
The folding of the cerebral cortex
produced by these bumps and grooves
increases the amount of cerebral cortex
that can fit in the skull. (In fact, the
total surface area of the cerebral cortex
is about 324 square inches - about the
size of a full page of newspaper!).
Although most people have the same
patterns of gyri and sulci on the
cerebral cortex, no two brains are
exactly alike.
MAIN SULCUS
1.CENTRAL SULCUS
2.LATERAL SULCUS OR
SYLVIAN fISSURE
3.PARITO-OCCIPITAL SULCUS
Different lobes & Sulci Gyri on
Supero Lateral Surface
 Located in front of the central sulcus.
Sulci on this lobe 1.PRE CENTRAL SULCUS
2.SUPERIOR & INFERIOR
FRONTAL SULCUS
Gyri On This Lobe
1. Pre-central gyrus
2. Superior frontal gyrus
3. Middle frontal gyrus
4. Inferior frontal gyrus
FUNCTIONAL AREAS OF
FRONTAL LOBE
Precentral Cortex :- Area 4 ,6,8,44
Prefrontal Cortex :- Area 9,10,11,12,32
4
Situation :- The Precentral Gyrus.
Repersentation of body parts :- Centres for the
various parts of body are arranged upside down,
From above downwards- Toes, Foot, Leg,Thigh
,Abdomen , Thorax, Shoulder, Arm, Hand,
Fingers, Thumb, Neck, Face, Head.
Function :-
 Center for Volition. Control voluntary activities
of the half of body.
Effect of lesion :- Contralateral paralysis &
Jacksonian fits.
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Situation:- Posterior parts of superior , middle
& inferior frontal gyri.
Functions:1.Frontal Adversive Field :- Stimulation causes
movements of eye, head & body towards the
opposite side.
2.Extra-pyramidal Activity :- Controls the
movements of eyeballs & complex
movements of body & limbs. Also
responsible for tone , posture & equilibrium.
3.Writing Centre (Area 6aα) :- On the left side,
in right handed people & vise-versa.
4.Controls complex movements of jaws, tongue
,pharynx, larynx & also the activity of the
respiratory muscles.
Effect of Lesion:-
Complex movements of body & limbs
disturbed.Also tone , posture & equilibrium
disturbed.
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Situation:- Posterior part of middle frontal
gyrus.
Function: Controls the horizontal conjugate
movements of eye balls to the opposite side,
opening & closing of the eye-lids & sometimes
dilatation of pupils & lacrimation.
Effect of Lesion :i. Lesion of this area turns the eyes to the
affected side.
ii.Horizontal conjugate movements of eyes are
lost.
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45 45
Situation :- Pars Triangularis & Pars
Opercularis.
Functions :I.Controls the Spoken Speech.
II.Responsible for movements of tongue
,lips & larynx which are involved in
speech.
Effect of lesion :-
 Lesion in Broca’s area leads to
Aphasia.
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10
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Situation :- Anterior part of frontal lobe.
Function:1.Seat of intelligence. It is unresponsive to
electrical stimulation. Hence called Silent
Area.
2.It controls emotion , concentration ,
attention & judgement
3.It helps in complex intellectual activities ,
e.g.working-out mathematical problems,
giving judgement , etc.
Effect of Lesion:i.The injury of pre-frontal cortex lead to a
condition called frontal lobe syndrome.
The features of this syndrome are :i. Emotional instability :- There is lack of
restraint leading to hostility, aggressiveness &
restlessness .
ii.There is alteration in behavior.
iii.Impairment of memory, loss of learning
power.
iv. Lack of Self control.
v.Distractibility (Difficulty of attention)
vi.Fright of irregular linkless ideas.
vii.Loss of memory,especially for the recent
events.
viii.Alteration in the social behavior,loss of
moral & social sense.
Owing to this functions , the
prefrontal region is called the organ of
mind.
Located behind the central sulcus.
Chief sulci on this lobe 1.Post Central Sulcus
2.Intraparietal Sulcus
Gyri On This Lobe
1.Post Central Gyrus
2.Superior Parietal Lobule
3.Inferior Parietal Lobule
3
2
1
Situation:- Postcentral gyrus & paracentral
lobule.
Representation of the body parts:-The
centers for the different parts of the body are
arranged upside-down.
Functions:1. Appreciation of general senses such as touch
,pain ,heat ,cold & kinaesthetic from the
opposite side of the body.
2. Appreciation of size, shape, texture ,weight
of the objects - Stereognosis.
3. Appreciation of the relative intensity of the
different stimuli.
4. Tactile localisation ,Tactile discrimination of
two points, Recognition of position & passive
movements of limbs - Spatial Recognition
Effect of Lesion:- Lesion of this area results in
disturbances of these faculties.
 Loss of appreciation of the impulse received.
 There will be Astereognosis.
 Loss of spatial recognition & appreciation of
relative intensity of different stimuli.
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7
Situation :-
 Superior Parietal Lobule.
Functions :-
 Stereognosis i.e. appreciation of shape ,size
& texture of an object without aid of vision.
 Sensory Speech.
Effect of Lesion :-

Astereognosis & Sensory Aphasias.
Located at the back of the brain, behind
the parietal lobe and temporal lobe.
Sulci on this lobe1.Lateral Occipital Sulcus
2.Transverse Occipital Sulcus
3.Lunate Sulcus
Gyri On This Lobe
1.Superior Occipital Gyrus
2.Inferior Occipital Gyrus
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Situation :Medial surface of Occipital lobe &
around the Postcalcarine sulcus.
Representation of body parts : Macular area has largest
representation.
Function : Cortical visual centre .
 Reception & perception of the isolated
visual impressions of colour ,size ,form
.motion ,illumination & transparency.
Effect of Lesion :-
 Homonymous Hemianopia of opposite side
with macular sparing.
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18
17
Situation :-
 Surround the Striate area { 18 Parastriate,
19 Peristriate }
Function :-
 Visuopsychic area.
 Correlation of visual impulses with past
memory & recognition of objects seen & also
the depth.
 The exact meaning of a image is
interpreted & integrated such as the
meaning of written language.
Effect of Lesion : Visual Agnosia { Inability to recognise
objects}
 Subjects with lesion in this area will fail
to understand written language.
Located below the lateral fissure.
Sulci on this lobe 1. Superior Temporal Sulcus
2. Inferior Temporal Sulcus
Gyri On This Lobe
1.Superior Temporal Gyrus
2.Middle Temporal Gyrus
3.Inferior Temporal Gyrus
Situation :-
 Posterior part of Sup. Temporal Gyrus & Anterior
Transverse Temporal Gyrus [mostly hidden in the
Sylvian Fissure]
Functions :-
 Centre for Hearing.
 Reception & perception of auditory impulses.
Analysis of pitch & determination of intensity of
sound , source of sound & quality of sound.
Effect of Lesion :-
 Impaired Hearing.
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Situation :-
 Superior Temporal Gyrus.
Function :-
The auditopsychic area is represented
unilaterally. In right-handed person it is on
the left side & in the left-handed person it is
on the right side.
 Correlation of auditory impressions with
past memory & identification { interpretation
} of the sounds heard.
Effect of Lesion : Auditory Agnosia
 Disturbances of smell Auditory hallucinations
with sounds like buzzing or ringing.
 Dreamy states.
TEMPORAL LOBE SYNDROME : Inability to recognise objects [ visual
agnosia ].
 Tendency to examine all the objects by
putting them into the mouth [ oral
tendencies ].
Peculiar attention to different objects
[hypermetamorphosis].
 Changes in emotional behaviour.
 Striking increase in sexual behaviour
& its diversity [hypersexuality].