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The Brain Dr Ayman G. Mustafa
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CNS = Brain + Spinal cord Brain is divided into 1.Forebrain 2. Midbrain 3. Hindbrain
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Hindbrain: 1.Pons 2. Medulla oblongata 3.Cerebellum Brainstem: Midbrain + Pons + Medulla oblongata
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Directional terms Above the brain stem: Dorsal means superior Ventral means inferior Rostral means anterior Caudal means posterior Within the brain stem and below: Dorsal means Posterior Ventral means Anterior Rostral means Superior Caudal means Inferior
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Coverings of the brain Brain is covered by three protective layers of connective tissue called meninges 1. Dura matter 2. Arachnoid matter 3. Pia matter
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Coverings of the brain 1.Dura matter: Tough fibrous membrane Avascular Composed of two layers -Endosteal layer -Meningeal layer The two layers adhere tightly except in certain areas to form Dural Sinuses
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Coverings of the Brain Dura matter has sheet like procesess (septa): -Falx cerebri: between cerebral hemispheres -Tentorium cerebelli: above cerebellum -Falx cerebelli: between cerebellar hemispheres
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Coverings of the brain 2. Arachnoid mater: Delicate avascular membrane Separated from pia mater by Subarachnoid space which contains Cerebrospinal fluid (CSF) Arachnoid villi: empty CSF into superior sagital sinus
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Coverings of the brain 3. Pia mater: - Innermost layer - Vascular layer - Tightly attached to the brain surface
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Forebrain Composed of : 1.The Diencephalon: masses of gray matter located around third ventricle Thalamus, situated dorsally Hypothalamus, situated ventrally Pineal gland
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Forebrain 2. Cerebrum: Largest part of the brain Composed of: Rt & Lt cerebral hemispheres Separated by longitudinal cerebral fissure connected by corpus callosum
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Cerebral hemispheres Each hemispheres is composed of : 1.Cerebral cortex: outer layer 4-6 mm of gray matter 2. White matter 3. Basal ganglia Masses of gray matter lie deep within white matter
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Each hemisphere is divided into lobes by: Central sulcus Parieto-occipital sulci Lateral sulcus And two imaginary lines
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Cerebral Hemispheres External appearance: Each hemisphere is organized into folds called Gyri Gyri are separated by fissures called sulci
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Insular lobe lies deep within the lateral sulcus
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Internal Structure of Cerebral Hemispheres White mater: composed of nerve fibers (axons) and glial cells Types of fibers: 1.Commissural fibers: connect regions of the two hemisphers e.g Corpus callosum, Anterior commissure, Posterior commissure
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Internal Structure of Cerebral Hemispheres 2. Association fibers: -Short association fibers: connect adjacent gyri -Long association fibers: bundled together to make named structures e.g Cingulum within cingulate gyrus Connects frontal and parietal lobes with temporal lobe
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Internal Structure of Cerebral Hemispheres 3. Projection fibers: Nerve fibers that pass from brainstem to the entire cortex Internal capsule, External capsule, Extreme capsule Corona radiata: optic radiation, auditory radiation
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Internal Structure of Cerebral Hemispheres Septum pellucidum: Thin sheet of gray and white matter Extend from corpus callosum to fornix Forms partition between anterior horns of lateral ventricles It is a double membrane
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Internal Structure of Cerebral Hemispheres Corpus callosum: Large bundle of commissural fibers Parts: 1.Rostrum 2.Genu 3.Body 4.Splenium 1 2 3 4
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Ventricles of the Brain Four CSF-filled cavities located within the brain Lined by ependyma Contain specialized vascular structure for CSF production (choroid plexus) - Lateral ventricles (2) -Third ventricle (1) -Fourth ventricle (1)
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Lateral Ventricle C – shaped Parts: 1. Body: in parietal lobe 2. Anterior horn: in frontal lobe 3. Posterior horn: in occipital lobe 4. Inferior horn: in temporal lobe Each lateral ventricle is connected to the third ventricle through foramina of monro
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Third Ventricle Narrow cavity located between the two thalami Communicates with lateral ventricles Communicates with fourth ventricle through cerebral aqueduct
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Cerebral Aqueduct ¾ inch long Connects third ventricle to fourth ventricle Does not contain choroid plexus
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Fourth ventricle Tent shaped cavity Anterior to cerebellum Posterior to pons and medulla oblongata Communicates with central canal of medulla and spinal cord Communicates with subarachnoid space through: -foramen of magendie -foramena of luschka
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Functional Localization of Cerebral Cortex
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Funtional Localization of Cerebral Cortex
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General Somatic Sensations Primary somesthetic area: - Postcentral gyrus - Posterior part of paracentral lobule (Brodmann areas 1,2,3) Somesthetic association cortex - Superior parietal lobule (brodmann areas 5, 7)
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Vision Primary visual cortex: - Surrounds calcarine sulcus (Brodmann area 17) Secondary visual cortex - Surrounds primary visual area (Brodmann areas 18, 19)
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Hearing Primary auditory cortex: - Inferior wall of lateral sulcus (Transverse Gyri of heschl’s) (Brodmann areas 41, 42) Secondary auditory cortex - Posterior part of superior temporal gyrus (Wernicke’s sensory speech area) (Posterior part of Brodmann’s area 22)
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Taste and Olfaction Primary gustatory cortex: - lower end of postcentral gyrus in the superior wall of lateral sulcus (Brodmann areas 43) Primary olfactory cortex - Insula and uncus (Brodmann area 34)
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Motor cortex Primary motor cortex - Precentral gyrus -Anterior part of paracentral lobule (Brodmann’ s area 4) Secondary motor cortex (Premotor area) - Lateral aspect of frontal lobe (Brodmann’ s area 6)
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Motor cortex Expressive speech area -Broca’s area -Consist of Opercular & triangular gyri) (Brodmann’s areas 44, 45) Frontal eye field -Lateral aspect of frontal lobe -Brodmann’ s area 8
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Motor cortex Supplementary motor area -Medial surface of frontal lobe -Brodmann’ s area 6
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