CEREBRAL HEMISPHERE OR CEREBRUM By Prof Saeed Abuel

CEREBRAL HEMISPHERE OR CEREBRUM By Prof. Saeed Abuel Makarem

• It is the largest part of the forebrain. • It is highly developed in human. • It is derived from the telencephalon. • The 2 cerebral hemisphere are incompletely separated by the median or greater longitudinal fissure. • They are connected by the corpus callosum. • Each hemisphere has a cavity called the lateral ventricle. CEREBRUM

• • • Each hemisphere has 3 surfaces, 3 poles, 4 borders, 4 Lobes. Surfaces: • Lateral or superolateral: Convex and related to the skull vault. • Medial: • Flat & vertical and related to the falx cerebri & median longitudinal fissure. • Inferior: • Divided into orbital and tentorial parts by the stem of lateral sulcus. CEREBRUM : SURFACES

• Four borders: • 1 - Medial or Superomedial border: border Between lateral & medial surfaces. • 2 - Inferolateral border: Between lateral & inferior surfaces. • Its anterior part may be called superciliary border. • 3 - Medial orbital border. • 4 - Medial occipital border. CEREBRUM: BORDERS

CEREBRUM 3 POLES & 4 LOBES • Each hemisphere has 3 poles: • 1 - Frontal pole. • 2 - Occipital pole. • 3 - Temporal pole. • Also, each hemisphere has 4 lobes: • 1 - Frontal lobe. • 2 - Temporal lobe • 3 - Parietal lobe. • 4 - Occipital lobe

• • • Lateral sulcus or fissure: Separates the frontal and parietal lobes from the temporal lobe. Central sulcus: Begins from the superomedial border ½ inch behind the midpoint between the frontal and occipital poles. It descends downward & forward making an angle about 70▫ with the vertical line. It stops slightly above the lateral sulcus. Pre-central: a finger breadth anterior & parallel to the central sulcus. Post-central: a finger breadth behind & parallel to the central sulcus. Superior & inferior frontal sulci Superior & inferior temporal sulci. Interparietal sulcus. Lunate sulcus SULCI ON THE LATERAL SURFACE

• Pre-central gyrus: Between central & precentral sulci. • Postcentral gyrus : • Between central & post-central sulci. • Superior, middle & inferior frontal gyri. • Superior, middle & inferior temporal gyri. • Superior & inferior parietal lobules. • Angular gyrus GYRI ON THE LATERAL SURFACE

• Callosal sulcus: sulcus just above the corpus callosum. • Cingulate sulcus: sulcus one inch above & parallel to the callosal sulcus. • Parieto-occipital sulcus: sulcus begins in the upper border 4 cm in front of the occipital pole • It ends at the meeting of calcarine & postcalcarine sulci. • Calcarine: • Begins below the splenium then passes backwards and upwards to meet the parieto-ocipital sulcus then continuous as the postcalcarine sulcus. • Postcalcarine sulcus: It is an extension of the calcarine. SULCI ON THE MEDIAL SURFACE

• Cingulate gyrus: Between the callosal & cingulate sulci. • Paracentral lobule: lobule • It is the continuation of the precentral & postcentral gyri. • Precuneus: behind the paracentral lobule. • Cuneus: between the parieto-ocipital & postcalcarine sulci. GYRI ON THE MEDIAL SURFACE

• Olfactory sulcus: • Close & parallel to the medial orbital margin. • Orbital sulcus: • Irregular H- shaped lateral to olfactory sulcus. • Stem of lateral sulcus: • It divides the inferior Surface into, orbital & tentorial parts. • Rhinal sulcus: • A short sulcus on the temporal pole. • Collateral sulcus: • Behind the rhinal sulcus and extends to the occipital pole. • Occipitotemporal sulcus: • Lateral to the collateral sulcus • It extends from temporal to occipital poles. . SULCI ON THE INFERIOR SURFACE

• Gyrus rectus: rectus • Medial to the olfactory sulcus. • Orbital gyri; • Anterior, posterior, medial and lateral, orbital gyri. • Lateral occipitotemporal gyrus: Lateral to occipitotemporal sulcus. • Medial occipitotemporal gyrus: gyrus Medial to occipitotemporal sulcus. • Parahippocampal gyrus: • Medial to collateral sulcus. • Lingual gyrus: gyrus • Between collateral & calcarine sulci. • Uncus: Anterior end of the Parahippocampal gyrus • It is the smell center. GYRI ON THE INFERIOR SURFACE

IMPORTANT CENTERS OF THE CEREBRAL CORTEX OR MAIN FUNCTIONAL AREAS OF THE CEREBRAL CORTEX

The cerebral cortex is important for: Conscious awareness , Though, Memory and Intellect. Most sensory modalities ascend to the cortex from the thalamus, perceived & interpreted in the light of the previous experience.

Posterior part of the cerebrum receives sensory information in: 1 - Parietal lobe (Somatosensory), 2 - Occipital lobe (Vision), 3 - Temporal lobe (Hearing).

• Information is elaborated to the association cortex, ( at the meeting of the parietal, temporal & occipital) for identification by touch, sight & hearing. • The limbic system (medial part of cerebrum) enable storage & retrieval of the information processed in the posterior cortex. Storage & Retrieval of information

• The frontal lobe (anterior part of cerebrum) is concerned with • the organization of movement: • 1 -Primary motor area. • 2 -Premotor area. • 3 -Supplementary motor area. • 4 - Prefrontal area (guidance of complex motor behaviour). MOTOR AREA

• In precentral gyrus & anterior part of the paracentral lobule. • It corresponds to Brodmann’s area 4. • Body is represented upside down. • Size of the functional area is directly proportional to the skilled movement, not to the size of the muscle. • It is here that actions are conceived and initiated. • The principal subcortical afferent to PMC is from Lateral ventral nucleus (LVN) of thalamus. • LVN receives its input from globus pallidus & dentate nucleus. PRIMARY MOTOR CORTEX (PMC)

• Lesion: Upper 1/3 and paracentral lobule leads to affection of voluntary control in lower limb & perineum of the opposite side. • Lower 2/3 rds: affection of voluntary control of the head, neck & upper limb on the opposite side. • Isolated lesion of the premotor cortex leads to apraxia. • (Inability to perform skilled complex voluntary movement in spite of absence of muscle paralysis)

• Lies anterior to primary motor cortex. • Brodmann’s area 6. 6 • It includes the posterior parts of superior, middle & inferior frontal gyri. • Function: • Programming & preparing for movement and control of posture. • It receives its afferent from ventral anterior nucleus of thalamus. PREMOTOR CORTEX 6

• On the medial surface of the premotor cortex. • The principle subcortical input to premotor and supplementary motor cortex is the ventral anterior nucleus of the thalamus. • This nucleus receives its afferent from the globus pallidus & substantia nigra SUPPLEMENTARY MOTOR CORTEX

• It lies in posterior part of the middle fontal gyrus. • It is corresponding to; • Brodmann's area 8 • It controls conjugate movement of the eye. • Unilateral damage to area 8 causes conjugate deviation of the eyes to the side of the lesion. FRONTAL EYE FIELD

• In the inferior frontal gyrus in the dominant (usually left) hemisphere. • Brodmann’s areas 44 & 45 • It has connections with ipsilateral temporal, parietal, occipital lobes that share in language function. • Lesion: • (Left middle cerebral artery) • Expressive or motor aphasia (inability to express thought, answer or writing inspite of a normal comprehension) MOTOR SPEECH AREA BROCA’S AREA

• Lies anterior to premotor area. • It has rich connections with parietal, temporal and occipital cortex. • Functions: • Intellect. • Judgment. • Prediction. • Motivation • Planning of behaviour. PREFRONTAL CORTEX

• In the postcentral gyrus & posterior part of paracentral lobule. • It correspond to Brodmann’s areas 1, 2 and 3). • Here thalamocortical neurons terminate (3 rd order neuron). • Input comes from ventral posterior nucleus (VPN) of the thalamus. • Within the somatosensory cortex the contralateral half of body is represented upside down. PRIMARY SOMATOSENSORY CORTEX

• VPN receives: • • 1 -Medial lemniscus (Fine touch & proprioception). 2 -Spinal lemniscus (coarse touch & pressure). 3 -Spiothalamic tract (pain & temperature). 4 - Trigeminothalamic tract (general sensation from head)

• Lies in the superior bank of the middle of the superior temporal gyrus. • Hidden within the lateral fissure. • Brodmann's 41, 42. • Its precise location is marked by small transverse temporal gyri ( Heschl’s convolutions). • Input to Primary auditory cortex is from medial geniculate nucleus (MGN) of the thalamus. • Auditory radiation undergoes partial decussation in the brain stem before it reaches the (MGN). PRIMARY AUDITORY CORTEX

• Lies behind the primary auditory cortex. • Continuous posteriorly with the second motor speech (Wernicke’s) area. • Here the heard sounds or words are interpreted. • Lesion: • Sensory aphasia; (inability to recognize the meaning of sounds or words with hearing unimpaired. SECONDARY AUDITORY CORTEX or AUDITORY ASSOCIATION CORTEX

• Lies on medial surface of the occipital lobe. • In close relation to the calcarine sulcus. • It extends to the occipital pole. • Brodmann’s area 17 • It receives optic radiation from lateral geniculate nucleus (LGN) of the thalamus. • Each lateral half of the visual field is represented in the visual cortex of the contralateral hemisphere. • Lesion: Homonymous hemianopia. PRIMARY VISUAL CORTEX

• Brodmann’s areas 18, 19 are called visual association cortex. • They are interpretive to the visual image. • Lesion: visual agnosia, (inability to recognize a seen object). VISUAL ASSOCCIATION CORTEX

SECOND MOTOR SPEASCH AREA (Wernicke’s area) • Also, known as language area. • Lies in dominant hemisphere. • Lies in the inferior parietal lobule & auditory association area. • Lesion: • Sensory or receptive aphasia • (Lack of comprehension of words by vision or hearing)