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CEREBRUM Introduction: Cerebrum is the largest part of central nervous system and highest in the functional hierarchy. It is formed by right and left cerebral hemispheres partly connected in the midline by band of corpus callosum.

Location: Located in the cranial cavity.

(Above diagram is for explanation only)

External Features:

Cerebrum has two cerebral hemispheres partly connected by corpus callosum and partly separated by Medial longitudinal fissure. Longitudinal fissure contains falx cerebri (Fold of dura mater).

On the surface of cerebrum large size folds are seen.

Depressions on the surface of cerebrum are known as Sulci.

Elevations between sulci is known as Gyri.

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Surfaces of Cerebrum:

Three surfaces:

Superolateral surface: Between Superomedial border and inferolateral border.

Medial Surface: Between Superomedial and inferomedial border.

Inferior Surface: Between Inferolateral and inferomedial border.

Three borders:

Superomedial border: between superolateral and medial surface.

Inferolateral border: between superolateral and inferior surface.

Inferomedial border: between inferior and medial surface.

Three poles:

Frontal pole: Anterior most part of cerebrum (frontal lobe)

Occipital pole: Posterior most part of cerebrum (Occipital lobe)

Temporal pole: Anterior most part of temporal lobe.

Sulci, Gyri and Important Functional areas of Cerebrum:

Cerebrum on superolateral surface is divided into three lobes by certain sulci and imaginary lines.

Main sulci for demarcation of lobes are:

1. Central sulcus: Starts from 1 cm behind the midpoint on superomedial border and runs obliquely on superolateral surface without interruptions and ends just above the lateral sulcus.

2. Lateral sulcus: It is also seen on superolateral surface.

It has a stem and three rami. Stem is near the anterior end of temporal lobe.

Three rami:

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Anterior ramus runs forwards.

Ascending ramus runs upwards

Posterior ramus is longest and runs backwards.

3. Parieto-occipital sulcus: It is predominantly seen on Medial surface. Its small part is seen on superolateral surface.

SUPEROLATERAL SURFACE: It is divided into four lobes:

1. Frontal lobe

2. Parietal lobe

3. Temporal lobe

4. Occipital lobe

1. Frontal lobe: Part of cerebrum in front of central sulcus.

2. Parietal lobe: Part of cerebrum behind the central sulcus.

3. Occipital lobe: Behind the imaginary line joining parito-occipital sulcus and preoccipital notch.

4. Temporal lobe: Below the posterior ramus of lateral sulcus.

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Frontal pole (Black arrow)

Temporal pole (Red arrow)

Occipital pole (Green arrow)

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Important Figure for Sulci and gyri on superolateral surface

(All Labels are to be mentioned)

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Important Figure for Functional areas in superolateral surface

(All labels are to be mentioned)

Sulci, Gyri and functional areas in Frontal lobe:

Sulci:

Pre-central sulcus: in front of central sulcus and runs parallel to it.

Superior and inferior frontal sulci: In front of pre-central sulcus and runs horizontally.

Anterior and ascending rami of lateral sulcus: in the lower aspect of anterior part of frontal lobe.

Gyri:

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Pre-central gyrus: Located between the central and pre-central sulcus. It contains Motor areas of cerebrum.

Superior, Middle and Inferior frontal gyri: The part of frontal lobe in front of precentral gyrus is divided into superior, middle and inferior frontal gyri by superior and inferior sulci.

Functional areas:

Motor Areas of Cerebrum: (*****Short note)

1. Motor Area of cerebrum: Location: It is located in the pre-central gyrus between the central sulcus and pre-central sulcus.

Important characteristics:

a. Body is represented upside down in the area. i.e. head and neck is represented in the lower part of area and lower limbs are represented in the upper part of the area.

b. In the area movements are represented and not the individual muscles. i.e. for example flexion movement is represented and not the individual muscle causing flexion.

c. The parts having fine movements are represented larger compared to parts having coarse movements. i.e. Thumb, fingers, lips tongue and eyes are represented larger compared to trunk and limbs.

d. Upper 1.5 cm area is supplied by Anterior cerebral artery and rest of the area is supplied by middle cerebral artery.

e. It controls opposite half of body (Contralateral control). i.e. Right side of area control left side of the body and left side area control right side of body.

Function: It is responsible for the execution of the movements of body.

Applied Anatomy:

a. Damage to this area in compression by collection of hematoma in fracture of skull leads to paralysis of the muscles of opposite half of body.

b. Blockage of anterior cerebral artery leads to paralysis of lower limb muscles and loss of control on sphincters while rest of the body is not affected. (Anterior cerebral supply upper part of area).

c. Blockage of Middle cerebral artery leads to paralysis of the all the muscles of body except the lower limb and sphincters.

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2. Pre-motor area: In front of motor area. Function: Planning of the movements.

3. Broca’s motor area of speech: Located in triangular area between anterior and ascending rami of lateral sulcus (Pars Traingularis).

Function: Motor speech of person i. e. articulation of words.

Applied: Damage to this area leads to Motor Aphasia. ( Loss of speech).

Silent Area of Brain (Prefrontal cortex): It is anterior part of frontal lone.

Earlier it was believed to be silent but now it is know that it is part of limbic system and concerned with social and emotional behaviour of person.

Damage to this area leads to Anti-social behaviour.

Sulci, Gyri and Functional areas in Parietal lobe:

Sulci:

Post-central sulcus: behind the central sulcus and runs parallel to it.

Intraparietal sulcus: Curved sulcus in the middle of parietal lobe.

Gyri:

Post-central gyrus: Located between central and post central sulcus. It contains primary sensory area.

Superior parietal lobule: Part above the intraparietal sulcus.

Inferior parietal lobule: Part below the intraparietal sulcus.

Functional areas:

1. Primary Sensory area ( Primary somesthetic area) : Located in post central gyrus between central and post central sulcus.

Function: Identification of all general sensations and taste sensation.

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2. Secondary sensory area (Secondary somesthetic area) : Located behind the primary sensory area.

Function: It keeps the memory of all sensations experienced by person and coordinated with incoming new sensations.

3. Wernick’s sensory area of speech: It is cap like area on the posterior end of posterior ramus of lateral sulcus.

Function: Identification of text from the images and sound and send it to Broca’s area for articulation.

Applied aspect: Damage to Wernick’s area leads to inability to identify text from images and sound i.e. Sensory Aphasia. Person can speak but unable to read aloud from book and repeat spoken words.

Sulci, Gyri and Functional areas in Temporal lobe: Sulci:

Superior and Inferior Temporal sulci.

Gyri:

Superior, middle and inferior temporal gyri: Temporal lobe ins divided in to superior, middle and inferior gyri by superior and inferior temporal sulci.

Functional Areas:

1. Primary Auditory area: Located in superior temporal gyrus.

Function: Identification of sound. (Hearing)

2. Auditory association area: Located outer to primary auditory area.

Function: Keeps memory of all sound heard by person and coordinated with new incoming sound.

Applied anatomy:

Damage to auditory area leads to partial hearing loss.

Abnormal stimulation of Auditory association area leads to Auditory Hallucinations i.e. person complains of hearing non-existent sound.

Sulci, Gyri and Functional areas in Occipital lobe: Sulci:

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Small part of calcarine sulcus: Most of the sulcus is seen on medial surface.

Lunate sulcus: Curved sulcus in from of end of calcarine sulcus.

Functional area:

Primary visual area: Mostly seen on medial surface above and below the calcarine sulcus>

Function: Identification of image. ( Vision)

Damage to this area leads to Contralateral homonymous hemianopia.

Visual Association area: located outer to visual area.

Function: Keeps memory of all images seen by person and coordinated with new incoming images.

Abnormal stimulation of visual association area leads to visual Hallucinations i.e. person complains of seeing non-existent images.

MEDIAL SURFACE:

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Sulci:

Callosal sulcus: Closely related to corpus callosum.

Cingulate sulcus: Runs parallel to corpus callosum.

Parieto-occipital sulcus and calcarine sulcus forms “Y” shape on posterior aspect of medial surface.

Upper limb of “Y” is Parieto-occipital sulcus. (Red Arrow)

Lower limb of “Y” is Calcarine sulcus. (Black arrow)

Gyri:

Cingulate gyrus: Between callosal sulcus and cingulated sulcus. It is part of limbic system concerned with social, emotional behaviour and memory.

Cuneus: part between calcarine and parieto-occipital sulcus.

Pre-cuneus: part in front of parieto-occipital sulcus.

INFERIOR SURFACE:

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Divided in to two parts:

1. Orbital part: Related to roof of orbit. (Anterior smallerpart)

Sulci:

Olfactory sulcus: related to olfactory tract.

Orbital sulci: “H” shaped.

Gyri:

Gyrus rectus: Medial to olfactory sulcus.

Orbital gyri: between orbital sulci.

2. Tentorial part: related to tentorium cerebella (fold of dura mater) (Posterior larger part)

Sulci:

Collateral sulcus: It is medial sulcus bounding the parahippocampal gyrus.

Occipito-temporal sulcus: It is lateral to collateral sulcus.

Rhinal sulcus: small sulcus in anterior part of parahippocampal gyrus.

Gyri:

Parahippocampal gyrus: Medial to collateral sulcus. Part of limbic system. Cocerned with social, emotional behaviour and memory.

Uncus: hook shaped anterior part of parahippocampal gyrus.

NOTE:

Describe sulci and gyri of cerebrum (only mention sulci and gyri and draw the diagram for the same)

Describe functional cortical areas of cerebrum ( mention the functuional areas in the superolateral surface with functions and applied aspect)

Short note:

Motor areas of cerebrum (Mention motor area, premotor area and Broca’s motor area of speech

with diagram showing only these areas)

Motor area of cerebrum (only Motor area to be mentioned with diagram)

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