The average human brain weighs about 1 400

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 f. ISSURE 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.

6

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 6 aα) : - 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.

8

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.

44 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.

9 10 11

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.

5 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 lobe 1. Lateral Occipital Sulcus 2. Transverse Occipital Sulcus 3. Lunate Sulcus

Gyri On This Lobe 1. Superior Occipital Gyrus 2. Inferior Occipital Gyrus

17

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.

19 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.

20 22

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].