11 Cerebrum MBBS, BATCH 17 Year II DR. WAI WAI KYI

Objectives:  To discuss the external features, functional areas and blood supply of the cerebrum Learning outcomes:  Describe the external features of cerebrum: surfaces, borders, poles, lobes, sulci and gyri.  Discuss the functional areas of cerebrum: position and function  Explain the blood vessels of cerebrum 22

Brain  The brain can be divided into three main parts. The forebrain, midbrain and hindbrain. The midbrain and hindbrain are collectively know as the brain stem. Forebrain (Prosencephalon)  Telencephalon (cerebrum)  Diencephalon (thalamus, hypothalamus, pineal body). Midbrain (Mesencephalon) Hindbrain Rhombencephalon  Pons  Cerebellum. Metencephalon  Medulla oblongata. 3

44 Cerebrum (Telencephalon) Introduction The cerebrum is the highest center in the brain. It perceives sensations, commands skilled movements, provide awareness of emotions and is necessary for memory, thinking, language abilities and all other mental functions.  There are right & left cerebral hemispheres separated by longitudinal fissure & connected to one another across the midline by corpus callosum.  Largest part of the brain  Tentorium cerebelli separates the cerebral hemispheres from the cerebellum..

Cerebrum ; Introduction Cont. ▪ It is composed of gray and white matter. Surface layer of gray matter is called cortex. Gray matter: Grayish nerve tissue of the central nervous system containing neuron cell bodies, neuroglia, and unmyelinated axons. White Matter: Lies underneath the outer layer of gray matter, containing myelinated axons. Basal nuclei/ganglia: gray matter nuclei located deep within the white matter of the cerebral hemisphere that help coordinate subconscious skeletal muscular movement; composed of caudate nucleus, putamen, globus pallidus, and amygdala. 5

Borders ( Cerebrum)  Superomedial border  Inferior border 6 Inferior border Superomedial border Transverse cerebral fissure Poles (Cerebrum) Three poles can be recognized-  Frontal or anterior pole  Occipital or posterior pole  Temporal pole Temporal pole Occipital pole Frontal pole

Surfaces The borders divide the brain into three large surfaces: Superolateral Medial Inferior surface Inferior surface is further divided into an anterior orbital part and posterior tentorial part. Superolateral surface Medial surface Tentorial part Orbital part 7

88 Surface features of the cerebral hemispheres To increase the surface area of the cerebral cortex, each hemisphere has formed folds (gyri) which are separated by sulci (fissures) Sulcus - shallow groove Gyrus - ridge/ outward folds Fissure - larger groove

9 The major sulci On the superolateral surface of the hemisphere two prominent sulci :  Central sulcus(of Rolando)  Lateral sulcus (of Sylvius) On the medial surface of the hemisphere near the occipital pole:  Parieto-occipital sulcus separates parietal and occipital lobes on the med. surface; on the lat. surface by imaginary line joining the parietoccipatal sulcus & pre-occipital notch.  Calcarine sulcus 9 Parieto- occipital sulcus 9

Imaginary lines A little anterior to the occipital pole the inferolateral border shows a slight indentation called the preoccipital notch. The first imaginary line connects the upper end of the parieto- occipital sulcus to the preoccipital notch. The second imaginary line is a backward continuation of the posterior ramus of the lateral sulcus to meet the first line. Central sulcus Lateral sulcus 10 Post. ramus of lateral sulcus

Four lobes Each hemisphere is divided into 4 lobes named according to the cranial bones under which they lie. ▪ Frontal lobe ▪ Parietal lobe ▪ Temporal lobe ▪ Occipital lobe ▪ Insula - Considered to be the fifth lobe. 11

12 Insula 12 It is buried In the depth of the stem & posterior ramus of the lateral sulcus & surrounded by circular sulcus. Surface is divided into a number of gyri.

Surfaces of cerebral hemisphere 13

Medial surface of cerebral hemisphere Corpus callosum, Medial frontal gyrus, Cingulate gyrus, Cuneus, Callosal sulcus, Parieto-occipital sulcus, Paracentral lobule, Calcarine sulcus. 14 Cuneus

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Inferior surface Inter-peduncular fossa- bounded in front by the optic chiasma &on the sides by the optic tracts. Two swellings medial lateral geniculate bodies Mammilary bodies Tuber cinereum Anterior perforated substance Posterior perforated substance 16

Inferior surface sulci & gyri Orbital surface Olfactory sulcus Orbital sulcus Gyrus rectus Anterior gyrus Posterior gyrus Medial & lateral gyrus 17

Tentorial surface Collateral sulcus (medially) Occipitotemporal sulcus (laterally) Lingual gyrus Parahippocampal gyrus Uncus ( Rhinal sulcus) Medial & lateral occipitotemporal gyrus. 18 Inferior surface sulci & gyri Hippocampal sulcus

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Lobes of cerebrum (Location, sulci & gyri) 20

Frontal lobe – location The most anterior lobe of the brain. Its posterior boundary is the fissure of Rolando, or central sulcus, which separates it from the parietal lobe. Inferiorly, it is divided from the temporal lobe by the fissure of Sylvius/lateral fissure.

Pre central gyrus by the precentral sulcus Superior & inferior frontal sulcus divides into superior, middle & frontal gyri. Anterior & ascending rami of the lateral sulcus extend into the inferior frontal gyrus dividing into three parts. Pars orbitalis, Pars triangularis, Pars opercularis. 22 Frontal lobe – sulci & gyri \ Broca’s area (dominant hemisphere Pars Opercularis Pars Triangularis

Temporal lobe – location Lies below the posterior ramus of the lateral sulcus & the second imaginary line. It is separated from the occipital lobe by the lower part of the first imaginary line. Temporal lobe- sulci & gyri Major sulci & gyri – Superior & inferior temporal sulci. Superior, Middle, & Inferior temporal gyri.

Parietal lobe – location Lies behind the central sulcus. Bounded below by the posterior ramus of the lateral sulcus & the second imaginary line.& behind by the upper part of first imaginary line. Parietal lobe – gyrus & sulci Postcentral gyrus between central & post central sulcus. Superior parietal & inferior parietal lobule by the intraparietal sulcus. Supramarginal gyrus, Angular gyrus, & Arcus parieto -occipitalis

Occipital lobe location No natural boundaries, Is the area lying behind the first imaginary line Occipital lobe – Sulci & gyri Lateral occipital sulcus Superior & inferior occipital gyri. Lunate sulcus just in front of the occipital pole. Just in front of lunate sulcus is the gyrus descendens. Transverse occipital sulcus Arcus parieto- occipitalis (a curved gyrus which surrounds the termination of the parieto – occipital sulcus, on the superolateral surface of the hemisphere, 5 cm in front of the occipital lobe).

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Lobes of Cerebrum 27 Arcus parieto- occipitalis

Lobes of cerebrum (Functional areas) 28

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30 Brodmann areas and their functions

31 Frontal lobe ▪ Primary motor area (area 4 of Brodmann) - precentral gyrus; voluntary skilled movements /Initiates conscious motor control Lesion – contralateral paralysis and paresis ▪ Premotor area (area 6) – anterior part of precentral gyrus; contains programming necessary for movement Focal lesion – apraxia, inability to perform purposive movement even though no paralysis exists. ▪ Prefrontal cortex - Planning, emotion, judgment, behavior. ▪ Broca’s speech area - Dominant hemisphere  motor speech area is usually the left hemisphere; speech production and articulation. (Association areas are those responsible for interconnecting the various sensory and motor areas by means of association fibers) 31

Frontal lobe (Cont. ) Lesion of Broca’s speech area – expressive aphasia characterized as nonfluent, hesitant and poor articulation, short sentences. Person knows what to say but cannot speak. Broaca area has an important fiber link with the Wernicke’s area. Lesion to link – conduction aphasia; similar to receptive aphasia ▪ Frontal eye field (area 8) - control conjugate movement of the eye Lesion - unilateral damage causes deviation of the eyes towards the side of lesion ▪ Olfactory area (smell)- Orbital gyrus Lesion – inability to discrimanate odors 32

33 Parietal lobe ▪ Primary somatosensory (area 3,1,2); post central gyrus ▪ Secondary somatosensory- interpretation of the general sensory information ▪ Superior parietal lobule – interpretation of sensory information & for conscious awareness of contralateral half of the body Lesions - impair the interpretation & understanding of sensory input and neglect of contralateral side of the body; loss in the ability to recognize an object held in the hand if the eyes are closed. Neglect syndrome – Fails to recognize the opposite side of the body and surroundings. ▪ Inferior parietal lobule interrelates between somatosensory cortex and the visual and auditory association cortices. In dorminant hemisphere contributes to language function. ▪ Gustatory area (taste) - junctional region of the postcentral gyrus and insula Lesion – impairment of taste to contralateral side of tongue. 33

34 The body is representad on the motor and sensory cortex as an inverted person,called the motor and sensory homunculus Sensory homunculus Motor homunculus 34

Functional areas of the brain 35

36 Temporal lobe ▪ Primary auditory cortex, area 41&42, transverse temporal gyri (of Heschl) in the inf. wall of lat. sulcus Lesion - unilateral lesion results in no significant hearing loss because of the bilateralism of the auditory pathways. ▪ Memory / learning areas ▪ Wernicke’s area (Accessory auditory cortex, area 22) - sensory or receptive speech area Speech comprehension area; permits understanding written & spoken languages. Prefrontal cortex Motor association cortex Sensory asso. area Primary Somatosensory cortex Primary motor cortex Broca's area Auditory cortex Wernicke's area Visual cortex Visual asso. area 36

37 Temporal lobe (Cont.) Lesion of Wernicke’s area - receptive or fluent aphasia, able to speak but meaningless, can not comprehend language (faulty understanding) in any form - heard, read or spoken ie. both the auditory and visual compehension are lost.  Word deafness = Inability to understand spoken words  Word blindness = Inability to understand written words  Olfactory area (smell) Language areas of the cerebral hemisphere ▪ Broca’s area ▪ Wernicke’s area ▪ Angular gyrus and supramarginal gyrus of the inferior parietal lobule 37

Occipital lobe ▪ Primary visual cortex (area 17); occupies the gyri above and below the calcarine sulcus for visual perception ▪ Secondary visual cortex ( ares 18, 19) – visual interpretation Bilateral lesion – color agnosia, loss of spacial relationship Calcarine Sulcus - nerve fibers conveying visual impulses end in the cortex of its walls. This cortex can be recognised by its linear appearance and is termed the striate cortex. 38 Cuneus Calcarine sulcus Lingual gyrus Parietal-occipital sulcus 38

39 Language areas of the cerebral hemisphere Cortical areas of the dominant hemisphere play an important role in language production. 1.Visual input to visual cortex bilaterally 2. Visual association cortex 3.Left angular gyrus where the objects are recognized and named 4.Wernicke’s area where words are assembled into sentences 5.Impulses are sent via arcuate faciculus to 6. Broca’s area 7. Motor cortex which then elicits speech via the brainstem centers and the muscles under their control. 39 Motor cortex vocalization Broca’s speech area (44,45)

Language Centers 40 Supramarginal gyrus

41 Location of major limbic system structures Limbic lobe The portions of the frontal, parietal & temporal lobes on the medial surface form the limbic lobe that are involved with emotional states and memory. Comprised of: cingulate gyrus, parahippocampal gyrus,hippocampus, amygdala, mammillary bodies, uncus and other small portions of the adjacent cortex. Medial saggital section of the cerebral hemisphere Amygdala Septum Olfactory bulb Mammillary bodies Hippocampus Fornix Hypothalamus Parahippocampal gyrus Uncus Cingulate gyrus

42 Principal gyri and sulci

43 Functional areas

44 Results of lesions

45 Central sulcus Calcarine sulcus Principal gyri and sulci

46 Functional areas

47 Results of lesions Lt lower limb anaesthesia

Blood supply of cerebrum 48

Areas supplied by middle cerebral artery include:  Most of superolateral surface (except narrow strip along the superomedial border from the frontal pole to parieto-occipital sulcus, Occipital lobe, Inferior temporal gyrus) & insular lobe. ▪ Lateral part of orbital surface ▪ Anterior part of tentorial surface Superior division supplies lateroinferior frontal lobe (location of Broca's area i.e. language expression) Inferior division supplies lateral temporal lobe (location of Wernicke's area i.e. language comprehension) Deep branches supply the basal ganglia as well as the internal capsule. 49

Functional areas supplied by middle cerebral artery  Lower parts of Primary motor area (area 4) Premotor area (area 6) Somatosensory area (area 3 1 2) - Parietal lobe Prefrontal area (area 9,10,11,12) - Frontal lobe  Broca’s motor speech area (45,44) - Frontal lobe in the left hemisphere  Auditory area (41,42) - Temporal lobe  Supramarginal gyrus (40)  Angular gyrus (39)  Superior temporal gyrus (22) (Werneike's area) Inferior parietal lobule Frontal lobe 50

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Areas supplied by anterior cerebral artery include: Cortical branches supply the:  Orbital surface of the frontal lobe,  All medial surface of the cerebral cortex as far back as the  Parietooccipital sulcus and adjacent strip of the suprolateral surface of the cerebral hemisphere 52 Anterior cerebral artery PCA MCA

Functional areas supplied by anterior cerebral artery  Upper part of primary motor area(4)  Upper part of somatosensory area (3,1,2)  Upper part of premotor area (6)  Upper part of prefrontal cortex (9,10,11,12) 53

Posterior cerebral artery Cortical branches: ▪ Inferior surfaces of temporal lobe by temporal brs ▪ Medial surface of the occipital lobe by calcrine brs ▪ Medial surface of the post part of the parietal & part of the occipital lobes by parieto occipital brs Functional area supplied: ▪ Visual area (17,18,19) 54

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56 Applied anatomy ▪ Focal cerebral lesions Due to stroke, tumors may cause 1. Partial epileptic seizures – repetitive discharges of neurons of the cerebral cortex Sudden attacts of abnormal movements or sensations to generalizesd (tonic-clonic) seizures 2. Sensory/ motor deficits 3. Psychological deficits – breakdown in psychological processes such as language, perception, memory Seizure – sudden disturbance of consciousness or sensorimotor function ▪ A unilateral cerebral hemisphere lesion – due to stroke or harmorrhage which effects the internal capsule; aphasia, contralateral spastic hemiparesis, contralateral hemisensory loss ▪ Damage to the corpus callosum may result in "Split Brain" syndrome 56

57 Any Questions ?