Spinal Cord and Brainstem Anatomy PDF

## CHAPTER 1 ### ILOS: After this lecture, student should be able to: - Describe the external features of the spinal cord (levels, length, segments, enlargements, conus medullaris) - Define the spinal nerve roots and cauda equina. - Define the blood supply of the spinal cord. Describe the spinal me...

## CHAPTER 1 ### ILOS: After this lecture, student should be able to: - Describe the external features of the spinal cord (levels, length, segments, enlargements, conus medullaris) - Define the spinal nerve roots and cauda equina. - Define the blood supply of the spinal cord. Describe the spinal meninges. - Discuss the factors supporting the spinal cord within the vertebral canal. ## Spinal Cord ### I. External features - It occupies the upper 2/3 of the vertebral canal in the adult - **Length:** - 45 cm in length in adult males - 42 cm in adult females - **Extent:** - **Above:** it begins at the lower border of foramen magnum as a continuation of the medulla oblongata - **Below:** it ends by tapering into a conical structure called conus medullaris, the level of which differs with age: - By the 3rd month of intra-uterine life, it occupies the whole vertebral canal - At birth, it ends at the level of L3 vertebra - In the adult, it ends at the level of the disc (between L1 and L2 vertebrae) - These changes are due to differential growth between the spinal cord (slower) and vertebral column (faster). ### Shape - Spinal cord is nearly cylindrical and shows two enlargements - **Cervical enlargement:** from C5-T1 spinal segments, where the spinal cord gives origin to the brachial plexus of the upper limb - **Lumbar enlargement:** from L1-S3, where the spinal cord gives origin to lumbar and sacral plexuses of the lower limb - **Grooves of the spinal cord:** external surface of the spinal cord shows 6 longitudinal grooves or sulci: - Anterior median fissure or sulcus: is the deepest - Posterior median sulcus - Two anterolateral sulci: for exit of the ventral (motor) roots - Two postero-lateral sulci: for entry of the dorsal (sensory) roots. ## Spinal Cord ### Spinal Segments and nerves: - The spinal cord is divided into 31 segments, each segment gives origin to a pair (right and left) of spinal nerves (8 cervical, 12 thoracic, 5 lumbar segments, 5 sacral segments and 1 coccygeal). - Each spinal nerve is attached to the side of its corresponding spinal segment by two roots - **Ventral root (motor):** contains somatic efferent (motor) fibers, in addition to efferent sympathetic fibers - **Dorsal root (sensory):** contains somatic afferent (sensory) fibers, and carries an oval swelling called the dorsal root ganglion- sensory spinal nerves. - At the corresponding intervertebral foramen, the two roots (ventral and dorsal) unite together forming the spinal nerve trunk (mixed) which is very short and divides immediately after leaving the foramen into two primary rami (anterior and posterior), both rami are mixed. ### Vertebral levels of the spinal cord segments: - Spinal cord segments are present higher than their corresponding vertebrae. - The rule 1,2,3 is applied to the vertebral spines: - a) Cervical region: add one to the spine (C5 spine is opposite to C6 segment) - b) Upper thoracic region: add 2 to the spine (T3 spine is opposite to T5 segment) - c) Lower thoracic region: add 3 to the spine (T10 spine is opposite to L1 segment) - d) T11 spine is opposite to L2 to L5 segment - e) T12 spine is opposite to all sacral segments - Each cervical nerve from C1 to C7 emerges above its corresponding vertebra. i.e. C1 nerve emerges above atlas and C8 emerges above T1. - Each of the remaining spinal nerves from T1 emerges below the corresponding vertebra. - The gap in the length between the spinal cord and vertebral canal results in, gradual lengthening of the lumbar and sacral nerve roots which have to descend downward to reach their exit foramina as a leash of fibers called cauda equina. ## Spinal cord ### Coverings of the spinal cord (Spinal Meninges) - Spinal cord is surrounded by three membranes called the meninges, from inwards outwards they are, pia mater, arachnoid mater and dura mater. ### 1) Spinal Pia Mater: - It is a delicate vascular membrane that is closely adherent to the spinal cord. - **Thickenings of the spinal pia mater:** - **a) Denticulate ligaments:** - Two lateral extensions which arise from the sides of the pia mater. - The lateral edge of each ligament is serrated and has 21 processes which pierce the arachnoid mater and finally attach to the dura - Each ligament extends midway between the ventral and dorsal spinal nerve roots, from the foramen magnum (above) down to the level of L1 vertebra (below) - **b) Subarachnoid septum:** is a backward extension arising from the pia mater at the posterior median sulcus to get attached to the dura mater. - **c) Linea splendens:** is a median glistening band of pia mater that extends along the anterior median fissure, surrounding the anterior spinal artery - **d) Filum terminale:** - It is a silvery glistening band of pia mater which extends downward from the tip of conus medullaris among the roots of cauda equina. - At the level of S2 vertebra it pierces the arachnoid and dural tubes, and acquires a dural sheath to get finally attached to back of coccyx ### 2) Spinal Arachnoid Mater: - It is a delicate membrane which lies between pia and dura maters. - It is connected to the pia mater by delicate fibers that resemble a spider's web, hence its name. - **Above:** it is continuous with the arachnoid mater of the brain. - **Below:** it ends at the level of the S2. - **Internally:** it is separated from the pia mater by the subarachnoid space. - **Externally:** it is separated from the dura mater by the subdural space. ### Contents of the subarachnoid space: - Cerebro-spinal fluid (CSF) - Spinal blood vessels - Spinal nerve roots - Denticulate ligaments, subarachnoid septum - Cauda equina in lumbar cistern (see below) ### Dura begin byattach to the margin or foramen magnum. ### Fixation of the Spinal Cord: - **Filum terminale:** it attaches the spinal cord down to the back of the coccyx (the most important stabilizing factor). - **Denticulate ligaments:** they anchor the spinal cord to the dura mater on each side. - **Subarachnoid septum:** it attaches the spinal cord to the dura mater posteriorly. - **Dura mater:** it is attached above to the margin of the foramen magnum and on each side to the margins of the intervertebral foramina. ### Lumbar cistern: - It is the lower part of spinal subarachnoid space that is devoid of spinal cord. - It extends from L2 to S2 vertebrae. - **Contents:** CSF and cauda equina (filum terminale surrounded by the lumbar, sacral and coccygeal nerve roots) - **Clinical Importance:** it is used for performance of lumbar puncture. ### Lumbar puncture: - It is the procedure by which a needle is inserted into the subarachnoid space either to obtain a sample of CSF or to inject a drug. - The needle is inserted at the level of L3/L4 or L4/L5 to avoid injury of the spinal cord. ## Spinal Cord ### II. Blood Supply of the spinal cord #### A - Arterial Supply 1. **Single Anterior Spinal Artery:** - It is formed by the union of 2 anterior spinal arteries, each of which arises inside the skull from the 4th part of each vertebral artery. - It leaves the skull through foramen magnum and continues downwards along the anterior median fissure of the spinal cord - It gives central branches to supply the anterior 2/3 of the spinal cord (ventral, lateral horns as well as the anterior and lateral white funiculi). 2. **Two Posterior Spinal Arteries:** - Each artery arises inside the skull from the 4th part of the vertebral artery or its (posterior inferior cerebellar branch). - Each artery leaves the skull through foramen magnum and descends as 2 branches along the dorsal roots of the spinal nerves (the posterolateral sulcus). - They supply the posterior 1/3 of the spinal cord (the dorsal horn and the posterior white funiculus). Anastomosis between anterior and posterior spinal arteries occurs around the conus medullaris. 3. **Radicular Spinal Arteries:** - They arise from the vertebral arteries, the posterior intercostal arteries, lumbar arteries, and lateral sacral arteries on either side. - They enter the vertebral canal through the intervertebral foramina and divide into anterior and posterior branches which run along the ventral and dorsal spinal nerve roots. - they are main source of blood supply to the lower part of the spinal cord. - They end by anastomosing with both anterior and posterior spinal arteries. - One of the lower radicular arteries is very large and supplies the lumbar enlargement (the arteria radicularis magna). #### B - Venous Drainage - Spinal cord id drained by 6 longitudinal venous channels which end into the internal vertebral venous plexus: - Anteromedian and posteromedian channels. - Right and left anterolateral channels. - Right and left posterolateral channels. ## CHAPTER 2 ### ILOS: After this lecture, student should be able to: - Describe the external features and blood supply of pons, medulla and midbrain. - Define the cranial nerves attached to them and the internal location of their nuclei ## Brain stem - From below upwards it is formed of medulla oblongata, pons and midbrain. - Above it is directly continuous with the diencephalon. - Below it is directly continuous with the spinal cord. ## Medulla Oblongata ### I- External structure - **Length:** about 3 cm long - **Shape:** conical - **Extensions:** Above, it is continuous with the lower border of the pons, while below it is continuous with the spinal cord. ### Parts: - a) **Open medulla (upper 1/2):** forms a part of the floor of the 4th ventricle. - b) **Closed medulla (lower 1/2):** is traversed by central canal which is continuous with that of the spinal cord. ### External features - **Ventrolateral surface** which presents from medial to lateral: - **1) Anterior median fissure:** continuous with that of the spinal cord - **2) Pyramid (on each side of anterior median fissure):** Is an elongated elevation produced by the cortico-spinal tract (bundle of fibers). - **3) Olive (posterolateral to the pyramid):** oval elevation overlying the inferior olivary nucleus, separated from pyramid by an anterolateral sulcus for the exit of hypoglossal nerve(12) (XII) - **4) Inferior cerebellar peduncle (posterior to the olives) :** Is a bundle of nerve fibers connecting the medulla with the cerebellum, separated from olive by a posterolateral sulcus for the exit of glossopharyngeal, vagus, and cranial root of accessory nerves. ### Dorsal Surface - **Dorsal surface of the open medulla:** - Forms the lower part of the floor of the 4th ventricle. - It is separated from back of pons by a bundle of fibers called medullary stria. - Bounded laterally by the inferior cerebellar peduncles. - It is traversed by a vertical median sulcus, lateral to it an inverted v shaped depression called the inferior fovea, On each side the inferior fovea divides the medullary part into 3 triangular areas, from medial to lateral: - Hypoglossal trigone: overlies the nucleus of the hypoglossal nerve. - Vagal trigone: overlies the dorsal nucleus of the vagus nerve. - Vestibular area: overlies the inferior and medial vestibular nuclei. - **Area prostrema** (vomiting center): a protuberance at the infero/ posterior limit of the 4th ventricle. - **Dorsal surface of closed medulla** presents from medial to lateral: - A posterior median sulcus which is continuous with that of the spinal cord. - Gracile tract and tubercle (overlying gracile nucleus) on each side of the sulcus. - Cuneate tract and tubercle (overlying cuneate nucleus). - **Tuberculum cinereum:** overlies spinal nucleus of trigeminal. - **Inferior cerebellar peduncle (ICP)** on either side as 2 bundles which extend upwards and laterally along the sides of the 4th ventricle till they reach the lower border of the back of the pons where it bends sharply to enter the cerebellum. ### III. Blood supply of medulla - **Anterolateral surface:** supplied by anterior spinal and 4th part of vertebral arteries - **Postero-lateral surface:** supplied by posterior inferior cerebellar artery - **Gracile and cuneate tracts and nuclei:** supplied by posterior spinal artery ## Pons - **Length:** 1 inch = 2.5 cm - **Extensions:** It is the part of the brain stem which lies between the medulla and the midbrain, it lies anterior to the cerebellum. - Its name pons, came from the appearance presented on the anterior surface, which is like a bridge connecting the right and left cerebellar hemispheres. - The pons is divided into two parts : - a) **Ventral part:** called basis pontis - b) **Dorsal part:** called tegmentum. ### I-External structure - **Ventral (Basilar) surface:** shows the following features : - **i. Basilar groove:** A shallow median groove which lodges the basilar artery. - **ii. Transverse pontine fibers,** they are thick ridges which collect on either side to form middle cerebellar peduncle (mcp), connecting pons to cerebellum. - **iii. Exit of the middle four cranial nerves:** - **Trigeminal nerve (V):** consists of large sensory (lateral) and small motor (medial) roots and emerge from the lateral part of the front of pons close to its upper border. - **Abducent nerve (VI):** exits from the sulcus between pyramid and pons. - **Facial (VII) and Vestibulo-cochlear (VIII) nerves:** exit from the cerebello- pontine angle. - **Dorsal (Tegmental) surface:** - The posterior surface of the pons is hidden by the cerebellum. - It is bounded on either side by superior cerebellar peduncles. - It is separated from the back of open medulla by medullary stria. - Forms upper part of the floor of the 4th ventricle. - **It presents:** - **Medial eminence and facial colliculus** which is present at the lower end of the medial eminence and is produced by the abducent nucleus and the encircling facial nerve fibers. - **Sulcus limitans:** lateral to medial eminence its lower part lies lateral to the facial colliculus and forms superior fovea. - **Vestibular area:** Lateral to the sulcus limitans overlies superior, lateral yestibular nuclei. - **Basis pontis:** is supplied by the pontine branches of the basilar artery. - **Tegemntum:** - In lower pons: by the posterior inferior cerebellar artery. - In upper pons: by the superior cerebellar artery. ## Midbrain - **Length:** 0.8 inch (2 cm) connects the pons and cerebellum with the forebrain. - **Extension:** lies between the pons and the diencephalon. - **It contains a narrow canal** called cerebral aqueduct of sylvius (which connects third and fourth ventricles) and occupies the notch of the tentorium cerebelli. - The cerebral aqueduct of sylvius divides the midbrain into anterior part called cerebral peduncle and posterior part called tectum. ### I. External structure - It has 4 surfaces (ventral, dorsal and 2 lateral) - **A. The ventral surface:** presents: - Two cerebral peduncles. 2 large bundles of fibers that emerge from the upper surface of the pons and ascend to disappear in the substance of the cerebral hemispheres. - All cranial nerve that emerge from brain stem except trochlear nerve (IV) emerge from dorsal aspect. - **Crus cerebri of midbrain** - Optic tract - Mammillary body - Posterior perforated substance - Oculomotor nerve - Trochlear nerve - Interpedencular fossa - **B. The posterior surface:** presents: - **Four colliculi** (corpora quadrigemina): 4 rounded elevations divided into: - Two superior colliculi. which overlie visual reflexes. - Two inferior colliculi: which overlie lower auditory reflexes - **2 Superior cerebellar peduncles:** they run downwards, backwards and laterally along the sides the 4th ventricle to enter the cerebellum. - **iii. Trochlear (IV) nerve:** emerges immediately below the inferior colliculi. It is the only cranial N. that emerges from the dorsal aspect of the brain stem. - **C. The lateral surface of midbrain (lateral surface of the cerebral peduncle): ** - **Superior brachium** (of superior colliculus): connects superior_colliculus with the lateral geniculate body. - **Inferior brachium** (of inferior colliculus); connects inferior colliculus with the medial geniculate body. - In addition the lateral surface of the midbrain is crossed by: - Three arteries : posterior cerebral, superior cerebellar, anterior choroidal arteries. - Two nerves: trochlear and optic tract - One vein: basal vein draining into great cerebral vein - **N.B. The lateral surface is related to the tentorial notch of the tentorium cerebelli.** - **III. Blood supply of midbrain** - **Central branches of posterior cerebral artery** - **Superior cerebellar and posterior communicating** ### II. Internal structure ## Cerebellum ### ILOS: After this lecture, student should be able to: - Describe the external features of cerebellum and define its anatomical and functional divisions. - Name the cerebellar peduncles, their connections and the types of fibers passing in each of them. - Describe the position, boundaries, connections, relations foramina and recesses of the fourth ventricle. ## Cerebellum ### I. External structure - **Site and relations:** it is the largest part of the hindbrain which lies in the posterior cranial fossa and is related to: - Above: the tentorium cerebelli separating it from the cerebral hemispheres. - In front: back of pons and medulla separated from them by the 4th ventricle. - Laterally: To the sigmoid dural venous sinus, mastoid antrum and mastoid air cells. - **Parts of the cerebellum:** Grossly, it is composed of: - **i. Two large lateral cerebellar hemispheres** formed of many gyri called folia separated by deep fissures (sulci). - **ii. Vermis:** is a narrow median part joining the two cerebellar hemispheres. It is divided into superior and inferior vermis. - **Shape:** The cerebellum has - **1) Two notches:** - **a- The anterior notch:** A wide notch related to the back of the brain stem. - **b- The posterior notch:** A narrow notch which receives the falx cerebelli. - **2) Two surfaces:** - **a) Superior surface:** shows: - **Superior vermis:** is a median longitudinal ridge which merges with the cerebellar hemisphere. it is formed of five lobules: lingula, central lobule, culmen, declive and folium (from forward backward). - **Fissura prima (primary fissure):** is a wide V-shaped fissure which separates the anterior lobe from the middle lobe (posterior lobe) of superior cerebellar hemisphere. - **b) Inferior surface:** shows: - **Inferior surface of each cerebellar hemisphere** is separated from the other by a deep median longitudinal groove called the vallecula. - **Inferior vermis,** a longitudinal ridge which lies in vallecula. The inferior vermis is divided from before backwards into 4 parts: nodule, uvula, pyramid and tuber vermis. - **Flocculus:** lies on each side, along the anterior border of the inferior surface of the cerebellar hemisphere. It is almost isolated from the cerebellar hemisphere by the postero-lateral fissure. The two flocculi are connected to the nodule forming the flocculo-nodular lobe. - **Tonsil** is a small part of the cerebellar hemisphere, on either side of the uvula of the inferior vermis. The tonsil is partly separated from the inferior surface of the hemisphere by a fissure called the retrotonsillar fissure. - **Fissures of the cerebellum:** - **1. Primary fissure:** it runs between culmen and declive on the superior surface separating the anterior lobe from the posterior lobe (middle lobe) - **2. Posterolateral fissure:** intervenes between the flocculo-nodularlobe from the rest of the cerebellar hemisphere. - **3. The horizontal fissure:** intervenes between superior and inferior surfaces of the cerebellum - **Subdivisions of the cerebellum:** - **A- Anatomical division:** - The cerebellum is divided into 3 lobes by the primary and postrolateral fissure: - **1. Anterior lobe:** the area on the superior surface cranial to the primary fissure. - **2. Posterior lobe:** the large area between the primary and the postrolateral fissures. It lies in the superior and inferior surfaces. - **3. Flocculo-nodular lobe:** Consists of right and left flocculi and a median nodule. It lies caudal to the postrolateral fissure. - **B- Functional division:** the cerebellum is divided into 3 functional zones: - **1. Vestibulo-cerebellum (Archi-cerebellum)** - Is formed of the flocculo-nodular lobe. - Phylogenetically, it is the oldest part of the cerebellum. - It is connected with the vestibular system of the internal ear. - It is concerned with equilibrium. - **2.Spino-cerebellum (Paleo-cerebellum)** - It is formed the vermal zone (midline vermis) and paravermal zone (the part of the cerebellar hemisphere which is adjacent and parallel to vermis). - It is connected with the spinal cord and brain stem. - It is concerned with regulation of muscle tone and muscle coordination. - **3. Cerebro-cerebellum (Neo-cerebellum):** - It is the remaining largest part of the cerebellum. - Phylogenetically, it is the last and recent part of the cerebellum. - It is connected with the cerebral cortex. - It is concerned with planning and control of movements. - **Arterial supply:** - **1. Superior cerebellar artery:** arises from basilar artery and supplies superior surface - **2. Anterior inferior cerebellar artery:** arises from lower part of basilar artery and supplies small anterior part of the inferior surface - **3. Posterior inferior cerebellar artery:** arises from vertebral artery and supplies large posterior part of inferior surface ## Fourth ventricle, very, very important, - **A- Site:** - It is the cavity of the hindbrain. - It is situated between the cerebellum (behind) and the pons and upper part of the medulla (in front). - **B- Shape:** - It is diamond (rhomboid) shaped. - It has 4 angles: - Upper angle: continuous with the aqueduct of sylvius. - Lower angle: continuous with the central canal - 2 Lateral angles: each angle lies at the meeting of the superior and inferior cerebellar peduncles of its own side. - **Boundaries** - It has Four boundaries: roof, floor, 2 lateral borders. - **A. Lateral borders :** - Superior cerebellar peduncles (above). - Lateral angle forming lateral recesses. (in the middle). - Inferior cerebellar peduncle, cuneate and gracile tubercles (below). - **B. Floor: (diamond-shaped)** - The floor is divided into 2 similar halves by a median logitudinal sulcus. - The floor is divided transversly by transverse nerve bundles called the medullary stria, into upper (pontine) and lower (medullary) parts. - **The upper (pontine) part:(see before)** - infer medial eminence-Facial colliculu - sulcuslimitans-superiorfol - vestibulararea of Pons - **The lower (medullary) part: (see before)** - inferior fovea - hypoglossal trigone - vestibular area - **C. Roof of the 4t ventricle:** - **Superiorly:** The superior medullary velum (thin sheet of white matter connecting the 2 superior cerebellar peduncles). - **Inferiorly:** - **a. Upper area** is formed by nodule part of the cerebellum in the middle and inferior medullary velum connecting the 2 inferior cerebellar peduncles. - **b. Lower area** is formed by telachoroidea of the 4th ventricle where the choroid plexus invaginates the 4th ventricle and where pia mater comes in_contact with the ependyma. - **Recesses of the roof of 4t ventricle: (3 recesses)** - **a. Median recess:** The roof of the 4th ventricle is drawn backwards towards the cerebellum forming a median recess with an upper wall formed by the the nodule superior Medullary velum and a lower wall formed by the cerebellum. - **b. Two lateral recesses:** At the lateral angles of the 4th ventricle. Each lateral recess runs forward around medulla to open anteriorly into the subarachnoid space by a lateral aperture (foramen of Luschka). - **Communications of the 4th ventricle:** - **At its upper angle:** communicates with the 3rd ventricle above through the aqueduct of sylvius. - **At its lower angle:** communicates with the central canal of medulla, - **With the subarachnoid space:** by a median (foramen of Magendie) (opens in cisterna magna) and 2 lateral apertures (foramina of Lushka) opens into ponto- medullary cistern). - **Choroid plexus of the 4th ventricle:** - **Site:** it invaginates the lowermost area of the roof of 4th ventricle above the median aperture of magendie. - **Shape:** T shaped with a median stem and 2 arms extending to the lateral recess. - **Blood supply:** posterior inferior cerebellar arteries - **Fleave 4 thuentricle to Sub Arachnoid space by medianan da lateral Apertures** ## CHAPTER 4 ### ILOS: By the end of this chapter the student should be able to: - Describe the external features of the cerebral hemispheres (surfaces, borders, lobes, sulci and gyri). - Define the important functional areas of each lobe. - Describe the boundaries and contents of the interpeduncular fossa. - Describe the positions, relations and functions of the basal nuclei of the brain. - Describe the white mater of the cerebrum and the types of fibers (associative, commissural and projection) - Describe the position, parts, connections, relations and blood supply of the corpus callosum. - Describe the position, parts, relations and blood supply of the internal capsule. - Name the types of fibers passing in each part of the internal capsule. ## Cerebrum - The cerebrum consists of: - **1- Two cerebral hemispheres** which are separated from each other by the median longitudinal fissure that contains the falxcerebri. They are connected at the bottom of the median longitudinal fissure by corpus callosum. - **2- Diencephalon** ### Cerebral Hemisphere - **1. Position:** - The cerebral hemispheres occupy the anterior, the middle and the upper part of the posterior cranial fossae of the skull (supratentorial part). - The 2 cerebral hemispheres are separated from the cerebellum by a horizontal fold of dura mater called the tentorium cerebelli. - **2. Surfaces:** - Each cerebral hemisphere has 3 surfaces: - **i. Lateral (supero-lateral) surface:** Is convex and related to the cranial vault. - **ii. Medial surface:** Is flattened and related to its fellow of the opposite hemisphere with falx cerebri in between. - **3. Inferior surface:** Is irregular and divided by lateral sulcus into orbital part which lies on the roof of orbit, and tentorial that lies on tentorium cerebelli. - **4. Borders:** - **i. Superior (supero-medial) border:** that separates the lateral from the medial surfaces. It is related to the superior sagittal venous sinus of the dura. - **ii. Superciliary border:** that separates the lateral from the orbital part of inferior surfaces. - **iii. Inferior (infero-lateral) borders:** that separates the lateral from the tentorial part of the inferior surfaces. A slight depression called the preoccipital notch is seen on this border about 2 inches in front of the occipital pole. - **5. Division of the hemisphere into lobes:** - **A- The sulci** which divide the hemisphere into lobes: 3 major sulci or fissures: - **i. The central sulcus (sulcus of Rolando):** - It runs obliquely downwards and forwards across the lateral surface and its upper end usually cuts the upper border of the hemisphere and turns down a little on its medial surface. - It separates the motor area (in the frontal lobe) from the sensory area (in the parietal lobe). - **ii. The lateral fissure:** Fissure of sylvius: - The stem of the lateral fissure begins on the inferior surface of the hemispher and extends laterally between the temporal pole and the orbital surface of the frontal lobe to reach the lateral Surface where it divides into 3 rami: - **Posterior ramus** (the longest and deepest): runs backwards on the latera surface almost parallel to the inferior border. Its posterior end turns upward cutting into the parietal lobe. - **Anterior horizontal ramus:** Runs forwards cutting into the frontal lobe. - **Anterior ascending ramus:** Runs upwards cutting into the frontal lobe. - **iii. The parieto-occipital sulcus:** - It is present on the medial surface near to the occipital pole. Its upper end cuts the upper border about 2 inches in front of the occipital pole and turns down a little on the lateral surface of the hemisphere. - **B- Lobes of the cerebral hemisphere:** - Each hemisphere is divided into 4 lobes and the insula. On the lateral surface of the hemisphere the 4 lobes are bounded as follows: - **ii. The frontal lobe:** Is bounded by: - The central sulcus (behind). - The superior border. (Above). - Frontal pole (in front). - Superciliary border and the lateral sulcus (Below) - **iii. The occipital lobe:** Forms the posterior extremity of the lateral surface; it lies behind an imaginary line drawn from the upper end of the parieto-occipital sulcus down to the preoccipital notch. It is bounded posteriorly by the occipital pole. - **iv. The parietal lobe:** Is a quadrilateral area bounded by: - The central sulcus (in front). - The upper border (above). - The upper 1/2 of the line joining the parieto-occipital sulcus and the pre-occipital notch (behind). - The posterior ramus of lateral fissure and an imaginary line joining the posterior ramus with the middle of the line between the parieto-occipital sulcus and the preoccipital notch (below). - **v. The temporal lobe:** Is bounded by: - The inferior border (below) - The posterior ramus of the lateral fissure (above). - The lower 1/2 of the line joining the parieto-occipital sulcus and the pre- occipital notch (behind) - Temporal pole (in front). - **I. Frontal Lobe:** - **Sulci:** - **1- The precentral sulcus:** Is nearly parallel to the central sulcus and about one finger's breadth anterior to it. - **2- The superior frontal sulcus:** Usually begins in the upper part of the precentral sulcus and runs forwards nearly parallel to the upper border. - **3- The inferior frontal sulcus:** Usually begins in the lower part of the precentral sulcus and runs forwards and then downwards. - **Gyri:** - **1- The precentral gyrus:** Lies between the central and the precentral sulci. - **2- The remaining part of the frontal lobe:** Is divided into superior, middle and inferior frontal gyri by the superior and inferior frontal sulci. - **3- The inferior frontal gyrus:** Is subdivided by the anterior horizontal and the anterior ascending rami of the lateral fissure into 3 parts: - a- Orbital part: Below the anterior horizontal ramus. - b- Angular or triangular part: Between the 2 rami. - c- Opercular part: Between the anterior ascending ramus and the precentral sulcus. It covers part of the insula. - **II. Parietal Lobe:** - **Sulci:** - **1- The postcentral sulcus:** Runs nearly parallel to the central sulcus and about one finger's breadth behind it. - **2- The intraparietal sulcus:** Begins from the postcentral sulcus and runs backwards, nearly parallel to the upper border, towards the occipital lobe. - **Gyri:** - **1- The postcentral gyrus:** Lies between the central and the postcentral sulci. - **2- The remaining part of the parietal lobe:** Is divided by the intraparietal sulcus into: - A smaller superior parietal lobule. - A larger Inferior parietal lobule:- which has - a- The supramarginal gyrus: that surrounds the upturned posterior end of the posterior ramus of lateral sulcus. - b- The angular gyrus: Which surrounds the upturned posterior end of the superior temporal sulcus - **III. Temporal Lobe:** - **Sulci:** - **1- The superior temporal sulcus:** Begins near the temporal pole and_runs backwards about one finger breadth below and parallel to the posterior ramus of lateral fissure. - **2- The inferior temporal sulcus:** It runs parallel to the superior temporal sulcus about one finger breadth