The Brain Dr Ayman G. Mustafa

CNS = Brain + Spinal cord Brain is divided into 1.Forebrain 2. Midbrain 3. Hindbrain

Hindbrain: 1.Pons 2. Medulla oblongata 3.Cerebellum Brainstem: Midbrain + Pons + Medulla oblongata

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

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

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

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

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

Coverings of the brain 3. Pia mater: - Innermost layer - Vascular layer - Tightly attached to the brain surface

Forebrain Composed of : 1.The Diencephalon: masses of gray matter located around third ventricle Thalamus, situated dorsally Hypothalamus, situated ventrally Pineal gland

Forebrain 2. Cerebrum: Largest part of the brain Composed of: Rt & Lt cerebral hemispheres Separated by longitudinal cerebral fissure connected by corpus callosum

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

Each hemisphere is divided into lobes by: Central sulcus Parieto-occipital sulci Lateral sulcus And two imaginary lines

Cerebral Hemispheres External appearance: Each hemisphere is organized into folds called Gyri Gyri are separated by fissures called sulci

Insular lobe lies deep within the lateral sulcus

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

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

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

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

Internal Structure of Cerebral Hemispheres Corpus callosum: Large bundle of commissural fibers Parts: 1.Rostrum 2.Genu 3.Body 4.Splenium

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)

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

Third Ventricle Narrow cavity located between the two thalami Communicates with lateral ventricles Communicates with fourth ventricle through cerebral aqueduct

Cerebral Aqueduct ¾ inch long Connects third ventricle to fourth ventricle Does not contain choroid plexus

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

Functional Localization of Cerebral Cortex

Funtional Localization of Cerebral Cortex

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)

Vision Primary visual cortex: - Surrounds calcarine sulcus (Brodmann area 17) Secondary visual cortex - Surrounds primary visual area (Brodmann areas 18, 19)

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)

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)

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)

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

Motor cortex Supplementary motor area -Medial surface of frontal lobe -Brodmann’ s area 6