Neuroanatomy Notes.pdf 72241i

Anatomy notes collection Gross anatomy of the brain, spinal cord and meninges

Haytham Bayadsi 2011/2012

Gross anatomy of the brain: The brain is the part of the CNS that lies within the cranial vault, the encephalon. its hemispheric surface is convoluted (Gyrencephalic) and has gyri & sulci The brain consists of: ● Cerebrum (cerebral hemispheres & diencephalon) ● Brainstem (midbrain, pons & medulla) ● Cerebellum Weights about 1400 g in the adult, covered by 3 connective tissue membranes called the Meninges & surrounded by the cerebrospinal fluid (CSF), which s it and protects it from trauma. The brain is classified into 6 post-embryonic divisions: ● Telencephalon ● Diencephalon ● Midbrain (Mesencephalon) ● Pons ● Medulla oblongata (Myelencephalon) ● Cerebellum

A. Telencephalon: Consists of the cerebral hemispheres & the basal ganglia and contains the lateral ventricles. 1. Cerebral hemispheres: separated by the longitudinal cerebral fissure & falx cerebri, interconnected by

the corpus callosum & consist of 6 lobes and the olfactory structures. For orientation, the best starting point is the central sulcus of Rolando: ○ A transverse sulcus on the outer surface of the hemispheres, separating the frontal lobe from the parietal lobe ○ Bordered by anteriorly by the precentral gyrus (main ‘’primary’’ motor cortex, belongs to the frontal lobe, giving rise to the fibers of the pyramidal tract) ○ Bordered posteriorly by the postcentral gyrus (main ‘’primary’’ sensory cortex, belongs to the parietal lobe) Another important sulcus to be located is the lateral sulcus of Sylvius: o Divides the frontal lobe & parietal lobe above from the temporal lobe below o Has a number of side branches, but 2 of the most prominent are: o The ascending (vertical) ramus o The horizontal ramus, which further subdivide the inferior frontal gyrus into 3 parts

a. Frontal lobe: i. Extends from the frontal pole to the central sulcus of Rolando, laying above the lateral

sulcus of Sylivus (Sylvian fissure) ii. The convex (outer) surface contains: 1. Precentral gyrus (primary motor area, Brodmann’s 4,6) ○ Precentral sulcus 2. Superior frontal gyrus ○ Superior frontal sulcus 3. Middle frontal gyrus ○ Inferior frontal sulcus 4. Inferior frontal gyrus, divided by the horizontal ramus of the lateral sulcus into: ○ Orbital part ○ Triangular part ○ Opercular part (covers the insula as the orbital operculum) ■b & c contain Broca’s speech area in the dominant hemisphere iii. The basal surface contains (from medial to lateral): 5. Straight gyrus (gyrus rectus) 6. Olfactory tract & bulb (laying in the olfactory sulcus) 7. Orbital gyri (above the orbit) iv. The medial surface contains: 8. Anterior paracentral lobule: continuation of the precentral gyrus on the medial

surface ○ paracentral sulcus: forming the anterior border of the paracentral lobule 9. Medial frontal gyrus (the continuation of the superior frontal gyrus on the medial

surface of brain) 10. Parolfactory area (Subcallosal area) 11. Paraterminal gyrus (subcallosal gyrus, peduncle of the corpus callosum) ○ The subcallosal area and the paraterminal gyrus belong to the frontal lobe

morphologically, but to the limbic lobe functionally b. Parietal lobe: i. Extends from the central sulcus to the occipital lobe (Parieto-occipital sulcus) and lies

superior to the temporal lobe ii. The convex (outer) surface contains: 1. Postcentral gyrus (primary somatosensory area, Brodmann’s 3,1,2) ○ postcentral sulcus 2. Superior parietal lobule ○ Intraparietal sulcus: divides the 2 parietal lobules 3. Inferior parietal lobule, composed of: ○ Supramarginal gyrus: can be found by placing the finger in the posterior

ramus of lateral suclus of Sylivus ○ Angular gyrus: can be found by placing the finger in the posterior part of the superior temporal sulcus ○ Parietal operculum: the portion of the parietal lobe on the outside surface of the brain bordering the lateral sulcus, and the extension of this cortex which forms the posterior ceiling of the lateral sulcus

iii. The medial surface contains: 1. Posterior paracentral lobule: the continuation of the postcentral gyrus on the

medial surface ○ Marginal sulcus: separates the posterior paracentral lobule from the precuneus 2. Precuneus

c. Temporal lobe: i. Extends from the temporal pole to a line connecting the parieto-occipital sulcus & the

preoccipital notch, lying below the lateral suclus, from which it extends up to the collateral sulcus ii. The convex (outer) surface contains: 1. Transverse temporal gyri of Heschl: lie buried within the lateral suclus, extending

from the superior temporal gyrus toward the MGB (Brodmann’s area 41,42) 2. Superior temporal gyrus: contains the Wernicke speech are in the dominant hemisphere ○ Superior temporal sulcus 3. Middle temporal gyrus ○ Middle temporal sulcus 4. Inferior temporal gyrus ○ Inferior temporal sulcus

iii. The basal surface contains (from lateral to medial): 1. Lateral occipitotemporal gyrus (Fusiform gyrus) 2. Collateral (Occipitotemporal) suclus d. Occipital lobe: i. Extends from a line connecting the parieto-occipital sulcus and the preoccipital notch

up to the occipital pole ii. The convex (outer) surface contains: 1. Lateral occipital gyri ○ Lateral occipital sulcus 2. Lunate sulcus (inconstant) 3. Transverse occipital sulcus: running from the intraparietal sulcus iii. The medial/inferior surface contains: 1. Cuneus: between the parietooccipital sulcus and the calcarine sulcus 2. Lingual gyrus (Medial occipitotemporal gyrus) ○ Calcarine sulcus/fissure: separates the cuneus from the lingual gyrus.

projects into the medial wall of the occipital horn of the lateral ventricle as the Calcar avis. (contains the Bordmann’s areas 16,17,18 for visual field)

e. Insular lobe (Insula, Island of Reil) i. Covered by the orbital, frontal, parietal & temporal opercula deep within the lateral

sulcus of the brain ii. Contains: 1. Short insular gyri (anterior group) ○ Central insular sulcus 2. Long insular gyri (posterior group) 3. Circular insular sulcus 4. Limen: an elongation of the olfactory stria which begins in the olfactory trigone, runs into the depth of the lateral fossa to end on the parahippocampal gyrus. Separates the anterior perforated substance from the basal surface of the insula f.

Limbic lobe (Cingulate lobe): i. A C-shaped structure of the medial hemispheric surface that encircles the corpus callosum & the lateral aspect of the midbrain ii. Includes the following: 1. Cingulate gyrus: merges with the parahippocampal gyrus at the isthmus ○ Cingulate sulcus: terminates posteriorly as the Marginal sulcus 2. Parahippocampal gyrus: seen on the basal surface, terminates in the Uncus ○ Limbus Giacomini: the uncus ligament, a smooth area which turns upward at right angle and keeps medially to get lost on the outer surface of the uncus

○

Hippocampal sulcus

3. Hippocampal formation: ○ Between the choroidal & hippocampal fissures, rolled into the

parahippocampal gyrus and connected to the hypothalamus via the fornix, it includes: ■ Dentate gyrus ■ Hippocampus 1. Pes hippocampi in front (digitations) 2. Fimbria hippocampi behind, the beginning of the fornix ■ Subiculum 4. Paraterminal gyrus & subcallosal area (Functionally): the bilateral

paraterminal gyri converge anteriorly and continue into the induseum griseum which is a grey sheet covering the corpus callosum. At the splenium, the induseum griseum continues as the gyrus fasciolaris, proceeds into the dentate gyrus and terminates in the limbus Giacomini i. The fornix: a C-shaped bundle of fibers that carries signals from the hippocampus to the

mamillary bodies and septal nuclei, has the following parts: 1. Fimbria: thin sheath that begins at the hippocampus 2. Crura (Posterior pillars): left & right, has the hippocampal commisure between them (see white matter description later) 3. Body: formed by the 2 crura in the mid-line of the brian

4. Columns (Anterior Pillars): left & right, ends at the mamillary bodies, has 2 parts, a. Visibile part (Pars libera): around the interventricular foramen of Monro b. Hidden part (Pars tecta): between the interventricular formaen and the

mamillary bodies

g. Olfactory structures (Olfactory lobe, Rhinencephalon): i. Olfactory bulb & tract: out-pouching of the telencephalon, lying in the olfactory sulcus,

the olfactory bulb receives the olfactory nerve (CN-I) ii. Olfactory trigone and striae: 1. Medial olfactory stria - terminates in the subcallosal area at the beginning of the cingulate gyrus 2. Lateral olfactory stria - goes towards the lateral sulcus of the brain, bends around the limen of the insula to terminates at the terminal part of the parahippocampal gyrus 3. Intermediate stria: terminates anteriormedial to the anterior perforated substance, at the olfactory tubercle iii. Olfactory tubercle: A small, oval area between the diverging medial and lateral olfactory striae, in the anteromedial part of the anterior perforated substance iv. Anterior perforated substance: by the penetrating striate arteries v. Diagonal band of Broca: interconnects the amygdaloid nucleus and the septal area

2. The Basal ganglia (nuclei): a. Subcortical nuceli (Grey matter) of the telencephalic origin mainly (some diencephalic &

mesencephalic elements) found within the cerebral hemispheres that includes: i. Caudate nucleus, C-shaped, divided into: 1. Head 2. Body 3. Tail

ii. Putamen iii. Globus pallidus (Paleostriatum, Pallidum), divided by the medial medullary lamina

into: 1. Internal (Medial) segment (GPi): adjacent to the internal capsule 2. External (Lateral) segment (GPe): adjacent to the putamen iv. Amygdaloid nuclear complex (Amygdala) v. Claustrum: located between the putamen & the insular cortex and between the

external capsule & the extreme capsule vi. Subthalamic nucleus of Luys (STN): functionally part of the basal ganglia, but anatomically is part of the subthalamus vii. Substantia Nigra: functionally part of the basal ganglia, but anatomically lies in the midbarin, dorsal to the cerebral peduncles, has 2 parts: 1. Pars compacta (SNc) 2. Pars reticulata (SNr) b. Organization of the basal ganglia: i. Putamen + Caudate nucleus = Striatum ii. Putamen + Globus Pallidus = Lentiform nucleus iii. Striatum + Globus Pallidus = Corpus striatum

3. White matter: a. Cerebral commissures: white matter fibers that inter-connect the cerebral hemispheres, i. Corpus callosum: the largest commissure of the brain, has four parts: 1. Rostrum 2. Genu 3. Body 4. Splenium

The corpus callosum consists of a mass of transversely travelling commissural fibers that the superficial ones appear in the form of the transverse striae → The supracallosal gyrus (induseum griseum; gyrus epicallosus) consists of a thin layer of grey matter in with the dorsal surface of the corpus callosum and continuous laterally with the grey matter of the cingulate gyrus. It contains two longitudinally directed strands of fibers termed the medial and lateral longitudinal striae respectively The supracallosal gyrus is prolonged around the splenium of the corpus callosum as a delicate lamina, the fasciolar gyrus which is continuous below with the dentate gyrus, and anteriorly it terminates after the splenu of corpus callosum in the paraterminal gyrus (see the description of the paraterminal gyrus in the limbic lobe) ii. Anterior commissure: located in the mid-sagittal section between the lamina

terminalis, lamina ventralis & the column of the fornix iii. Posterior commissure (Epithalamic commissure): located on the dorsal aspect of the

upper end of the cerebral aqua-duct iv. Habenular commissure: connecting the habenular nuclei within the habenular

trigones together

v. Hippocampal commissure (commissure of the fornix): contained within a thin

triangular lamina, named the psalterium (Lyra of David), ventral to the splenium of the corpus callosum, between the crura of the fornices b. Internal capsule: white matter located between the basal ganglia and the thalamus, has 3 parts: i. Anterior limb: between the caudate nucleus & the putamen ii. Genu: between the anterior & posterior limbs iii. Posterior limb: between the thalamus & the lentiform nucleus c. External capsule: white matter fibers that run between the most lateral segment of the lentiform

nucleus and the claustrum, eventually ing the internal capsule around the lentiform nucleus d. Extreme capsule: just lateral to the claustrum, beneath the insular cortex

B. Diencephalon: Located between the telencephalon & mesencephalon and between the interventricular foramen & the posterior commissure, consists of: 1. Epithalamus: a. Pineal body (Epiphysis cerebri) b. Habenular trigone: a small depressed triangular area bordered by, i. Medially: tenia thalami + habenular commissure ii. Laterally: thalamus iii. Posteriorly: Superior colliculus c. Medullary stria of the thalamus d. Tela choroidea and choroid plexus of the 3rd ventricle (+ tenia thalami) 2. Thalamus: separated from the hypothalamus by the hypothalamic sulcus a. Pulvinar b. Metathalamus: i. Medial geniculate body (MGB): belongs to the auditory system, communicates with the

inferior colliculus via the the brachium of inferior colliculus ii. Lateral geniculate body (LGB): belongs to the visual system, communicates with the superior colliculus via the brachium of superior colliculus c. Anterior tubercle d. Interthalamic adhesion (massa intermedia) 3. Hypothalamus: a. Optic chiasm b. Mamillary body c. Infundibulum d. Tuber cinereum: a hollow eminence of gray matter situated between the mammillary bodies and

the optic chiasm 4. Subthalamus (Ventral thalamus): lies ventral to the thalamus and lateral to the hypothalamus, not

visible on the midsagittal section! a. Subthalamic nucleus of Luys b. Zona incerta and fields of Forel 5. Third ventricle & associated structures: a. Lamina terminalis b. Tela choroida + choroid plexus of 3rd ventricle + tenia thalami c. Interventricular foramen of Monro: connects the lateral ventricles with the 3rd ventricle,

bordered by: i. Anteriorly: Free part of the columns of the fornix (pars libera) ii. Posteriorly: Anterior tubercle of the thalamus d. Lamina rostralis: A whitish line appearing on perfectly median sections of the brain as a thin

bridge connecting the rostrum of the corpus callosum with the lamina terminalis; the rostral

lamina contains no commissural fibres; instead, it corresponds to the line along which the pia mater reflects from the medial surface of one hemisphere to that of the other e. Recesses of the 3rd ventricle: i. Optic recess: At the junction of the floor and anterior wall of the third ventricle,

immediately above the optic chiasm ii. Infundibular recess: a prolonged downward funnel-shaped recess into the infundibulum iii. Suprapineal recess: overlying the habenular commissure iv. Pineal recess: a small recess that projects into the stalk of the pitutary gland v. Triangular recess: An evagination of the anterior wall of the third ventricle of the brain bordered by: 1. Inferiorly: the anterior commissure 2. Laterally: the diverging pillars (columns) of the fornix on both sides 3. Ventrally (anteriorly): lamina terminalis

C. Mesencephalon (Midbrain): Located between the diencephalon & the pons and extending from the posterior commissure to the frenulum of the superior medullary velum 1. Contains: the cerebral aquaduct of Sylivus (mesencephalic duct) that connects the 3rd ventricle with

the 4th ventricle 2. Ventral surface: a. Cerebral peduncle (crus cerebri) b. Lateral sulcus of the mesencephalon: indicating the border between the tegmentum & the

peduncle c. Interpeduncular fossa i. Oculomotor nerve (CN-III) (see the cranial nerves table for exact location) ii. Oculomotor sulcus (medial sulcus of the mesencephalon) iii. Posterior perforated substance: created by the penetrating branches of the posterior cerebral and posterior communicating arteries 3. Dorsal surface: a. Quadrigeminal plate (Tectal plate): i. Superior colliculus ii. Inferior colliculus b. Brachium of the superior colliculus (superior brachium) c. Brachium of the inferior colliculus (inferior brachium) d. Trochlear nerve (CN-IV): the only cranial nerve that exists the brainstem from the dorsal aspect e. Lemniscal trigone: a small grayish area bordered by: i. Anteriorly: inferior brachium (brachium of the inferior colliculus) ii. Posteriorly + inferiorly: superior cerebellar peduncle iii. Laterally: the lateral sulcus of the mesencephalon + cerebral peduncle

D. Pons: Located between the midbrain & the medulla and extends from the superior pontine sulcus (at the pontomesencepahlic junction) up to the inferior pontine sulcus (at the ponto-medullary junction) 1. Ventral surface: a. Base of the pons (Basis pontis): the anterior part of the pons b. Basilar sulcus: for the lodgement of the basilar artery; this sulcus is bounded on either side by an

eminence caused by the descent of the cerebrospinal fibers through the substance of the pons c. Cranial nerves: (see the cranial nerves table for exact location) i. Trigemnial nerve (CN-V) ii. Abducent nerve (CN-VI) iii. Facial nerve (CN-VII) iv. Vestibulocochlear nerve (CN-VIII)

2. Dorsal surface: is the upper part (or superior pontine portion) of the Rhomboid fossa (above the

medullary striae) a. Locus ceruleus: a bluish-gray area which owes its color to an underlying patch of deeply pigmented nerve cells, termed the substantia ferruginea. contains the highest density of norepinephrine secreting neurons in the CNS b. Facial colliculus: contains the abducent nerve nucleus and the internal genu of the facial nerve c. Sulcus limitans: separates the alar plate from the basal plate d. Dorsal median sulcus e. Medial eminence f. Superior fovea g. Vestibular (Acoustic) area: the area lateral to the limiting sulcus & medial to the restiform body (I) on the floor of the rhomboid fossa overlying mainly the vestibular nuclei h. Acoustic tubercle (Trigone of the acoustic nerve): a small eminence in the lateral recess of the 4th ventricle corresponding to the underlying nuclei of the acoustic & vestibular nerves i. Striae medullares

E. Medulla oblongata (Myelencephalon): Located between the pons and the spinal cord, extending from the inferior pontine sulcus up to the 1st cervical nerve (C1) 1. Ventral surface: a. Pyramids: contain the corticospinal tract b. Pyramidal decussation c. Foramen cecum d. Olive: contains the inferior olivary nucleus i. Lateral paraolivary sulcus (posterior), 3 cranial nerves exit here (from most superior to

most inferior): 1. Glosspharyngeal nerve (CN-IX) 2. Vagus nerve (CN-X) 3. Accessory nerve (CN-XI) ii. Medial paraolivary suclus (anterior), 1 cranial nerve exits here: 1. Hypoglossal nerve (CN-XII) 2. Dorsal surface: a. Inferior medullary portion of the Rhomboid fossa: i. Striae medullares ii. Sulcus limitans iii. Vagal trigone (Ala cinerea) iv. Hypoglossal trigone v. Area postrema (Vomiting center) vi. Funiculus Separans: An oblique ridge separating the area postrema from the vagal trigone

vii. Inferior fovea: a small depression in the limiting sulcus below the medullary striae of

either side, generally lateral to the hypoglossal and vagal trigones viii. Obex: a small transverse fold overhanging the calamus scriptorius marking the caudal

angle of the rhomboid fossa and the beginning of the central canal of spinal cord ix. Taenia of the 4th ventricle b. Gracile tubercle (Calva): contains the gracile nucleus, continues in the spinal cord as the

Gracile fasiculus (of Goll’s) c. Cuneate tubercle: contains the cuneate nucleus, continues in the spinal cord as the Cuneate fasiculus (of Burdach’s) d. Calamus Scriptorius (Arantius ventricle): the narrow lower end of the fourth ventricle between the 2 calvae (gracile tubercles) e. Trigeminal tubercle (Tuberculum Cinerum): a raised area between the rootlets of the accessory nerve and posterolateral sulcus. It overlies the spinal tract of trigeminal nerve

F. Cerebellum: Located in the posterior cranial fossa attaching to the brainstem by three cerebellar peduncles. it forms the roof of the fourth ventricle and separated from the occipital & temporal lobes by the tentorium cerebelli. The surface of the cerebellum consists of numerous parallel narrow convolutions, the Folia, on its outer surface and contain the following structures: 1. Hemispheres: made up of 2 lateral lobes

** Arbor Vita (Tree of life): the appearance of the cerebellar white matter on the mid-sagittal section (branched, tree-like) 2. Vermis: a mid-line unpaired structure ** Vallecula of the cerebellum: a fossa created between the hemispheres, with the Vermis being its floor → Morphological Anatomy of the cerebellum: Superior Vermis

Superior Hemisphere

Lingula

Vinculum of the lingula

Central lobule

Wing (Ala) of the central lobule

Moticle: ● Culmen ● Declive

Quadrangular (lunate) lobule ● Anterior part ● Posterior part (simple lobule)

Folium

Superior semilunar (Anseriform) lobule Inferior Vermis

Inferior Hemisphere

Tuber

Inferior semilunar lobule + upper part of gracile lobule

Pyramid

Biventral lobule + lower part of gracile lobule

Uvula

Tonsil

Nodulus

Flocculus

The cerebellum is sub-divided into 2 main parts separated by the posterolateral fissure: 1. Flocculonodular lobe 2. Cerebellar body, further subdivided by the primary fissure (deepest fissure on the mid-saggital section) into: a. Anterior lobe (Rostral to the primary fissure) b. Posterior lobe (Caudal to the primary fissure)

A. The flocculonodular lobe: 1. Consists of: a. Nodulus (midline structure) b. Flocculus (bilateral structure) 2. Together with the lingula (midline structure) it consists the Archicerebellum (oldest portion) 3. Functionally its connected to the vestibular nuclei → Vestibulocerebellum B. Anterior lobe of the cerebellar body: 1. Consists of: a. Lingula + Vinculum b. Central lobule + Wing of the central lobule c. Culmen + Quadrangular (lunate) lobule (anterior part) d. Paraflocculus: a lateral accessory part of the flocculus 2. Together with the pyramid & the uvula iIt forms the Paleocerebellum 3. Responsible mainly for proprioception → Spinocerebellum C. Posterior lobe of the cerebellar body: 1. Consists of: a. Declive + simple lobule b. Folium + Superior semilunar lobule c. Horizontal fissure (large & deep that separates the semilunar lobule into superior & inferior) d. Tuber + Inferior semilunar lobule e. Gracile lobule f. Biventral lobule g. Tonsils 2. It makes the Neocerebellum (New portion) 3. Receives the large corticocerebellar tracts from the cerebral cortex via the pontine nuclei for fine tuning of voluntary movements→ Pontocerebellum D. Nuclei of the cerebellum: 1. Dentate: heavily folded, with medial part open as the hilum of dentate nucleus 2. Fastigial: lies close to the median line in the white matter of the vermis 3. Emboliform: at the hilum of dentate nucleus 4. Globose: between the fastigial and emboliform nuclei 5. Interposed (nucleus interpositus): Globose + Emboliform nuclei D. Other structures in the cerebellum: 1. Tonsils: rounded lobule on the inferior surface of the each cerebellar hemisphere. in the case of the increased pressure in the skull, the medulla and tonsil are invaginated into the foramen magnum and can press the medulla against the basilar bone. The medulla contains important vegetative centers (CV & Respiratory control centers) which can be compromised and eventually lead to death! 2. Superior medullary velum & frenulum 3. Superior cerebellar peduncle (S, Brachim Conjuctivum): connects the cerebellum to the pons & midbrain 4. Middle cerebellar peduncle (M, Brachium Pontis): connects the cerebellum to the pons

5. Inferior cerebellar peduncle (I, Restiform body): connects the cerebellum to the medulla 6. Inferior medullary velum

Upper surface of the cerebellum (Superior view)

Lower surface of the cerebellum (inferior view)

Blood supply of the brain: The brain receives 15% of the cardiac output and 20% of the oxygen used by the body. The blood supply to the brain is derived mainly from 4 large vessels, lying in the subarachnoidal space: - 2 Internal carotid arteries (forming the anterior circulation) - 2 Vertebral arteries (forming the posterior circulation, or the vertebrobasilar system)

A. The internal carotid artery: Begins at the bifurcation of the common carotid artery (level of C4), having no branches in the neck (that’s how we distinguish it from the external carotid), it ascends within the carotid sheath accompanying the Vagus nerve and the internal jugular vein and enters the cranium together with the carotid sympathetic plexus through the carotid canal at the tip of the petrous part of the temporal bone into the middle cranial fossa via foramen lacerum. The internal carotid artery has 7 anatomical segments described by Bouthiller: - Cervical segment (C1) - Petrous segment (C2) - Lacerum segment (C3) - Cavernous segment (C4) - Clinoid segment (C5) - Ophthalmic or supraclinoid segment (C6) - Communicating or terminal segment (C7) The cervical segment (C1): Begins at the bifurcation of the common carotid artery (C4) and extends to the base of the skull where the artery enters the cranium. It has no branches in the neck. At its origin, the internal carotid artery is somewhat dilated. This part of the artery is known as the carotid sinus or the carotid bulb. The ascending portion of the cervical segment occurs distal to the bulb, when the vessel walls are again parallel. The petrous segment (C2): Extends from the base of the skull to the apex of the petrous bone through the horizontal carotid canal (it first ascends a short distance, then curves anteriorly and medially), entering the cranium via foramen lacerum. (It is erroneously stated that the internal carotid artery es through the foramen lacerum. This at best has only ever been a partial truth in that it es through the superior part of the foramen on its way to the carotid canal. As such it does not exit the skull through it. The inferior part of the foramen is actually filled with fibrocartilage!) Branches of the petrous segment of the internal carotid artery: • Vidian artery or artery of the pterygoid canal: supplying the contents and wall of the canal, the mucous membrane of the upper pharynx, the auditory tube, and the tympanic cavity • Caroticotympanic artery: for the tympanic cavity

The lacerum segment (C3): A short segment that begins above the foramen lacerum and ends at the petrolingual ligament, a reflection of periosteum between the lingula and petrous apex. The lacerum portion is still considered to be 'extradural', as it is surrounded by periosteum and fibrocartilage along its course. Normally, it has no named branches The cavernous segment (C4): es tortuously in the cavernous sinus, it first ascends toward the posterior clinoid process, then es forward by the side of the body of the sphenoid bone (next to the lateral thin wall of the sphenoidal sinus on both sides of the sella turcica, causing high risk of injury during sphenoidal sinus operations) and again curves upward on the medial side of the anterior clinoid process, and perforates the dura mater forming the roof of the sinus. This pathway of the artery is the so called Carotid siphon Branches of the cavernous segment: • Meningohypophyseal artery which gives: o Dorsal meningeal artery: dorsal part of the dura o Inferior hypophysial artery: for the hypophysis o Tentorial artery (artery of Bernasconi-Casinary) •

Inferolateral trunk: It provides blood supply to the 3rd, 4th, and 6th cranial nerves, as well as to the Gasserian ganglion. It anastomosis with branches of the internal maxillary artery, providing a collateral circulation between the ECA and the ICA systems.

The clinoid segment (C5): Short segment begins after the artery exits the cavernous sinus at the proximal dural ring and extends distally to the distal dural ring, after which the carotid artery is considered 'intra-dural' and has entered the subarachnoid space The ophthalmic (supraclinoidal) segment (C6): Begins after penetration of the dura (Diaphragm sellae, distal dural ring) and continues until the bifurcation into anterior and middle cerebral arteries. The named branches of the ophthalmic segment are: • Ophthalmic artery: Supplies branches to supply the eye and other structures in the orbit. It enters the orbit together with the Optic nerve through the Optic canal. • Superior hypophyseal artery: Supplying the pars tuberalis, the infundibulum of the pituitary gland and the median eminence. The communicating (terminal) segment (C7): es between the optic and oculomotor nerves to the anterior perforated substance at the medial extremity of the lateral cerebral fissure. The named branches of the communicating segment are: • Posterior communicating artery: s the posterior cerebral artery, supplying the optic chiasm & tract, crus cerebri, hypothalamus, subthalamus and anterior half of ventral portion of the thalamus • Anterior choroidal artery: supplies the choroidal plexus of lateral and third ventricles, optic chiasm and tract, internal capsule (Genu, posterior limb, retrolentiform limb), lateral geniculate

body, globus pallidus, tail of caudate nucleus, hippocampus, amygdaloid body, tuber cinereum, hypothalamic nuclei, thalamic nuclei, substantia nigra, red nucleus, and crus cerebri •

Anterior cerebral artery (ACA), a terminal branch: it es anteriorly, loops around the genu of the corpus callosum, then posteriorly in the interhemispheric fissure along with its fellow of the opposite side, and the two being ed by the Anterior Communicating artery. It is divided into 2 segments: o Precommunicating segment (A1) (before the anterior communicating artery), which gives the Anteromedial group of central arteries, which enters the most medial part of the anterior perforated substance, consisting of:  Supraoptic artery  Anterior perforating arteries  Preoptic arteries o Postcommunicationg segment (A2) (after the anterior communicating artery until the bifurcation forming the pericallosal and callosomarginal arteries):  Medial striate artery (Recurrent artery of Heubner): runs backward and laterally to enter the anterior perforated substance supplying the anterior caudate and putamen and anterior limb of internal capsule  Medial frontobasal (Orbitofrontal) artery: basal part of frontal lobe  Polar frontal (Frontopolar) artery o Pericallosal artery (A3 segment): forms t he internal parietal arteries (superior, inferior) and the precuneal artery, gives also:  Callosomarginal artery: gives the paracentral artery for the paracentral lobule supplying the leg/foot area of the motor and sensory cortices

•

Middle cerebral artery (MCA), a terminal branch: it es laterally around the pole of the temporal lobe, then posteriorly in the depth of the lateral cerebral fissure; has 4 segments: o Sphenoidal segment (M1): supplying perforating branches to the Internal capsule, Thalamus (Thalamostriatal branches), and Striate body (Corpus Striatum) (Lenticulostriatal branches) via:  Anterolateral group of central arteries (Lateral Striate arteries 8-10 branches): enter the anterior perforated substance, ascend lateral to the lower part of the Lentiform nucleus, then they turn medially and trough the reach the internal capsule and caudate nucleus. On of these arteries is usually large and called Charcot's artery or Artery of cerebral haemorrhage o Insular segment (M2): supplying branches to the insula. In this segment the MCA might bifurcate or trifurcate into superior, inferior & middle divisions terminating into the adjacent cortical areas o Opercular segment (M3): extends laterally from the insula towards the cortex. Sometimes its grouped with M2 segment (then its called Sylvian segment) o Terminal or cortical segment (M4): supplying a large part of the central cortical convexity, lateral frontobasal branches and speech areas of Boca & Wernicke

B. The Vertebral arteries (Vertebrobasilar system): Arise from the 2 Subclavian arteries, the cervical part ascends through the transverse foramina of the first 6 cervical vertebrae, then performing an S-shaped turn (Vertebral Siphon) on the posterior arch of atlas bone (Can be seen dorsally in the floor of the suboccipial trigone), entering the vertebral canal by ing beneath the posterior atlantooccipital membrane, after that perforating the dura and arachnoid ing through the foramen magnum ventral to the Medulla Oblongata. On the border between Medulla and Pons the 2 vertebral arteries unite to form the Basilar artery. Branches of vertebral artery before uniting: • Anterior spinal artery: 1 formed by 2 roots from the 2 vertebral arteries and found on the spinal cord anterior to the Anterior median fissure supplying the anteromedial spinal cord and adjacent pia mater (Via sulcal branches) • Posterolateral (Posterior) spinal arteries: 2 arising from the 2 vertebral arteries, running on the posterolateral sulcus, supplying medulla, spinal cord, and adjacent Pia mater. • Posterior Inferior Cerebellar artery (PICA): supplying the lateral medulla, Choroid plexus of 4th ventricle (via posterior choroidal branches), and inferior surface of the cerebellum Basilar artery: formed by union of the intracranial portions of the two vertebral arteries; runs along the clivus in the pontine cistern of the subarachnoid space from the lower to the upper border of the pons on the Basilar sulcus, where it bifurcates into the two terminal posterior cerebral arteries. Branches: • Anterior Inferior Cerebellar artery (AICA): supplies the inferior surface of cerebellum, Cerebellar peduncles, choroid plexus in cerebellopontine angle (Bochdalek flower basket) and lateral part of medulla and Pons. In 85% it gives the Labyrinthine artery • Labyrinthine artery: in 15% from basilar artery. Runs together with the Facial (CN-VII) and Vestibulocochlear (CN-VIII) nerves through the internal acoustic meatus into the inner ear • Pontine arteries (rami ad pontem): penetrating and circumferential branches directly to the pons • Superior Cerebellar artery (SCA): runs along the upper margin of Pons and extends deep into the ambient cistern around the cerebral peduncles to supply the upper surface of cerebellum, colliculi, and most of the Cerebellar nuclei •

Posterior Cerebral Artery (PCA): formed by the bifurcation of the basilar artery; it es around the cerebral peduncle to reach the medial aspect of the hemisphere; it is divided into three segments: o Precommunicating segment (P1), branches:  Posteromedial group central (paramedian) arteries: enter the interpeduncular perforated region, supplying the posterior medial part of the midbrain  Thalamoperforating artery: supplying midbrain and thalamus  Collicular artery: Supplying the Superior and inferior colliculi (corpora quadrigemina) of tectum of midbrain o Postcommunicating segment (P2), branches:  Posterolateral group of central arteries (circumflex mesencephalic branches): Supply the lateral part of midbrain  Posterior medial choroidal branches: supply the choroid plexus of the third ventricle  Posterior lateral choroidal branches: supply parts of the choroid plexus of the lateral ventricle  Peduncular branches: for the cerebral peduncles  Thalamogeniculate artery: for the pulvinar and the Later & Medial geniculate bodies

o Terminal or cortical segment (P3), branches:  Lateral occipital artery: supplies medial and ventral portions of the temporal lobe via anterior, intermediate, medial, and posterior temporal branches  Medial occipital artery: distributed to the corpus callosum, medial aspects of the caudal aspect of the parietal lobe, and medial occipital lobe including the visual cortex by named branches that include the dorsal branch to the corpus callosum, parietal branch, parietooccipital branch, occipitotemporal branch, and calcarine branch

The pathway of the vertebral artery (pointed by the black arrows). Note the vertebral siphone formed on the posterior arch of atlas before piercing the posterior atlantooccipital membrane and entering the cranium

C. The cerebral arterial circle of Willis (Circulus arteriosus): Pentagonal shaped circle of vessels on the ventral aspect of the brain in the area of the optic chiasm, hypothalamus, and interpeduncular fossa; formed, sequentially and in anterior to posterior direction, by: • Anterior Communicating artery (x1) • Anterior Cerebral arteries (x2) • Internal Carotid arteries (x2) • Posterior Communication arteries (x2) • Posterior Cerebral arteries (x2)

E. Anastomoses between the anterior (internal carotid) & the posterior (vertebrobasilar) systems: 1. Posterior communicating artery: between the internal carotid artery (ICA) and the posterior cerebral artery (PCA) as part of the arterial circle of Willis, in the interpeduncular fossa 2. Glomus anastomosis: between the anterior choroid artery (branch of ICA, or sometimes MCA) and the posterior lateral choroid artery (branch of the PCA) inside the choroid glomus in the central part of the lateral ventricle 3. Parieto-ccipital anastomosis: between the pericallosal artery (ACA terminal branch) and the dorsal branch to corpus callosum (PCA terminal branch) at the parietooccipital fissure

D. Arteries supplying the interior of the cerebral hemispheres: Internal capsule: Main arteries supplying the internal capsule are: • Medial & Lateral striate branches of the MCA: supplying the upper parts of the anterior limb, the genu and the posterior limb • Heubner's Recurrent artery of ACA: lower part of the anterior limb • Direct branches of internal carotid artery and from the Posterior Communicating artery: supplying the lower part of Genu • Anterior Choroidal artery: supplying the lower part of the posterior limb & the retrolentiform part Thalamus: Mainly supplied by the perforating branches of the PCA • Posteromedial group of central arteries: supply the medial and anterior part via the Thalamoperforating arteries • Posterolateral groups of central arteries: supply the posterior and lateral parts of the thalamus via the Thalamogeniculate branches • Some branches from Posterior communicating, Anterior choroidal, Posterior Choroidal and MCAs (Thalamostriatal branches)

Hypothalamus: • Anteromedial group of central arteries (of ACA): anterior part of hypothalamus • Posteromedial group of central arteries (of PCA): posterior party of hypothalamus

Striate Body (Corpus Striatum): 1) Caudate nucleus & Putamen (Striatum): • Lateral & Medial Striate branches of MCA: give the main arterial supply to the caudate nucleus and putamen • Heubner's recurrent artery of ACA: head of caudate nucleus and anterior-most parts of putamen • Anterior choroidal artery: tail of caudate nucleus and posterior most parts of putamen

2) Globus Pallidus: • Anterior choroidal artery: supplies the central part • Posterior communicating artery: supplies the medial most part • Striate arteries: supplies the lateral part

Brian Stem: Medulla: • Anterior Spinal artery: supplies a triangular area next to the midline including the pyramids, medial lemniscus and hypoglossal nucleus • Posterior Spinal artery: supplies a small area including the gracile and cuneate nuclei • Posterior Inferior Cerebellar artery: supplies the retro-olivary region (behind the inferior olive) containing the rubrospinal tract, nucleus ambiguous, the dorsal vagal nucleus and part of the inferior cerebellar peduncle • Direct bulbar branches from the vertebral arteries Pons: by branches of Basilar artery, • Paramedian branches: supplying the medial portion of the ventral part of the pons • Short Circumferential branches: supplying the lateral portion of ventral part • Long Circumferential branches: supplying the dorsal portion of Pons Midbrain: mainly by branches of Basilar artery, • Posterior Cerebral artery: via posteromedial group central arteries, collicular branches (Quadrigeminal artery) • Superior Cerebellar artery: via paramedian and circumferenial branches winding around midbrain • Posterior Communicating artery

E. Summary of the areas supplied by the cerebral arteries: 1. Anterior cerebral artery (ACA) territory: o The medial surface of the frontal lobe by the medial orbito-frontal artery, and parietal lobes o The anterior 4/5 of the corpus callosum o Approximately 2 cm (finger-width) of the lateral surface of frontal and parietal lobe next to the medial longitudinal fissure o Supplies the leg & foot are of the motor and sensory cortices (Paracentral lobule) o Anterior portions of the basal ganglia and internal capsule o Optic chiasm o Olfactory bulb and tract . 2. Middle cerebral artery (MCA) territory: o The lateral convexity of the hemisphere + underlying insula; except for the superior 2 cm of the frontal and parietal lobes lateral to the median longitudinal fissure (anterior cerebral artery), and the inferior part of the temporal lobe o Supplies the trunk, arm, face areas of the motor and sensory cortices o Superior division supplies latero-inferior frontal lobe (location of Broca's area i.e. language expression) o Inferior division supplies lateral temporal lobe (location of Wernicke's area i.e. language comprehension) o Deep branches supply the basal ganglia as well as the internal capsule 3. Posterior cerebral artery (PCA) territory: o Provides major blood supply to the midbrain o Supplies the posterior ½ of the thalamus & MGB + LGB o Supplies the occipital lobe, visual cortex (calcarine fissure) and the inferior surface of the temporal lobe including the hippocampal formation o Supplies the dorsal thalamus, pineal body and choroid plexus of the 3rd and lateral ventricle

Outer surface of cerebral hemisphere, showing areas supplied by cerebral arteries. (Blue region is ACA, red region is MCA, yellow region is PCA)

Medial surface of cerebral hemisphere, showing areas supplied by cerebral arteries. (Blue region is ACA, red region is MCA, yellow region is PCA)

Venous Drainage of the Brain: The veins draining the brain open into the dural venous sinuses. Ultimately, the blood from all these sinuses reaches the sigmoid sinus, which becomes continuous with the internal jugular vein. The intracranial venous sinuses communicate with the veins outside the skull via the Emissary veins. The veins of the brain are valveless and lay in the subarachnoidal space and on the surface of the brain and communicate with the dural sinuses via the bridging veins

 Veins of the Cerebral hemisphere: Consists of 2 sets: 1) Superficial cerebral veins: drain blood into the nearby dural sinuses, they consist of: a. Superior cerebral veins: drain blood from the upper parts of the superolateral and medial surfaces (Parietal & Frontal lobes), and end in the superior sagittal sinus via the lateral lacunae b. Inferior cerebral veins: drain the lower part of the hemisphere (Temporal and Inferior occipital lobes) into the transverse and superior petrosal sinuses c. Superficial middle cerebral vein: found on the superolateral surface along the lateral sulcus, and terminates into the cavernous sinus. It has 2 anastomosing veins: • Superior anastomotic vein of Trolard: connects the posterior end of the middle cerebral vein to the superior saggital sinus • Inferior anastomotic vein of Labbe: connects the middle cerebral vein to the transverse sinus 2) Deep cerebral veins: Drain blood from the deep structures of brain into the straight sinus eventually a. Internal cerebral veins: formed near the foramen of Monro by the union of: i. Superior thalamostriate vein: runs in the sulcus terminalis covered by the lamina affixa between the thalamus medially and the caudate nucleus laterally in the floor of the lateral ventricle ii. Veins of septum pellucidum: anterior & posterior iii. Choroidal vein: from the choroid plexus of the inferior horn (Superior choroid vein) iv. Caudate nucleus veins: anterior, transverse & posterior b. Basal veins of Rosenthal's: arise at the anterior perforated substance, around the optic chiasm and wind around the midbrain. Formed by: i. Anterior cerebral vein: accompanying the ACA, from the anterior 2/3 of corpus callosum ii. Deep middle cerebral vein: in the insular area draining also the putamen and globus pallidus iii. Inferior thalamostriate veins: emerge via the anterior perforated substance, draining the corpus striatum and internal capsule as well iv. Interpeduncular vein v. Anterior pontomesencephalic vein c. Great cerebral vein of Gallen: a large, unpaired vein formed by the junction of the two internal cerebral veins in the caudal part of the tela choroidea of the third ventricle; it es caudally receiving the 2 basal veins of Rosenthal between the splenium of the corpus callosum and the pineal gland, curving dorsally to merge with the inferior saggital sinus to form the straight sinus

 Venous drainage of the cerebellum and brainstem: -

Veins from the upper surface of the cerebellum drain into the straight, transverse and superior petrosal sinuses. Veins from the inferior surface of the cerebellum drain into the right and left sigmoid and inferior petrosal sinuses and occipital sinus Veins of the midbrain drain into the great cerebral vein or into the basal vein of Rosenthal The Pons and medulla drain into the superior & inferior petrosal sinuses, the transverse sinus and the occipital sinus Inferiorly the veins of the medulla are continuous with the veins of the spinal cord and Basilar plexus

Cranial meninges: Mesodermal covering that covers the brain and the interior of the cranial cavity and has several functions: - Protect the brain - Form a ing framework of arteries, veins and sinuses - Enclose a fluid (CSF = Cerebrospinal fluid) filled cavity, in the sub-arachnoidal cavity It is made out of 3 membranous connective tissue layers forming the Pachy- and Leptomeninx: - Pachymeninx: o Dura mater: tough, thick fibrous - Leptomeninx: o Arachnoid mater: thin, intermediate o Pia mater: delicate, internal, vasculated

1. Dura Mater: A bilaminar membrane that is composed of 2 layers: 1) External periosteal (Endosteal) layer: adherent to the inner surface of the calvaria and continuous on the exterior cranium through the foramen magnum (as the periostieum of the skull) 2) Internal meningeal (Fibrous) layer: strong fibrous membrane continuous with the spinal dura mater at the foramen magnum The 2 layers are fused together and cannot be separated except where the dural sinuses and the infoldings are formed, the meningeal arteries can be found running between the 2 layers as well. The dura mater is strongly adherent and attached to the calvaria and skull especially at the base. Pathologically, any fluid or blood that accumulates between the dura and the skull forms the pathological Epi-dural space (usually as a result of trauma  skull fracture  injury to the meningeal arteries) (Note: in the vertebral canal, the spinal Epi-dural space is a physiological space found there and not pathological) A. The dural infoldings (folds) or plates: Divides the cranial cavity into compartments and provides mechanical for the brain: - Cerebral (Major) falx: lies in the longitudinal cerebral fissure separating the 2 cerebral hemispheres Attachments: o Crista Gali o Frontal crest of frontal bone o Internal occipital protuberance o Tentorium cerebelli (Upper surface, continuation) It contains: o Superior Saggital sinus (at the upper border) o Inferior Saggital sinus (at the lower free border)

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Cerebellar Tentorium: Tent like shaped Attachments: o Transverse sulcus of the occipital bone posteriorly o Upper margin of the petrous bone forming the forming the superior petrosal sinus o Clinoid processes of the Sella turcica as the:  Anterior Petro-clinoidal fold (with its free Tentrorial frenulum)  Posterior Petro-clinoidal fold o Cerebral falx It separates the posterior cranial fossa from the middle one (occipital cerebral hemispheres from the cerebellum, and occipital lobes from the temporal ones) dividing the cranial cavity into: o Surpatentorial compartment o Infratentorial compartment It forms the tentorial notch or incisure, through which the brain stem es

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Cerebellar (minor) falx: lies in the Infratentorial compartment attached to the internal occipital crest and partially separates the Cerebellar hemispheres

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Sellar Diaphragm: formed between the Clinoid processes forming the roof of the hypophysial fossa, it covers the pituitary gland and has an aperture called the diaphragmatic hiatus for the age of the hypophysial stalk (infundibulum) and hypophysial veins

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Trigeminal cave, Meckel cavity: covers the Gasserian (Semilunar) ganglion or the ganglion of Trigeminal nerve (CN-V) on both sides of the cavernous sinuses

B. Dural venous sinuses: Endothelial lined, valve-less venous channels between the periosteal and the meningeal layers of the dura. They receive blood from internal and external veins of the brain via the bridging veins, receive cerebrospinal fluid (CSF) from the subarachnoid space, and ultimately empty into the internal jugular vein: -

Superior sagittal sinus: extending from the Crista gali to the internal occipital protuberance, lies inside the superior margin of the Falx cerebri, then it s the confluence of sinuses. It receives the superior cerebral veins and communicates on both sides with the lateral venous lacunae

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Arachnoid granulations (Collection of Arachnoid villi): elongation of Arachnoid that protrudes through the meningeal layer of the dura mater into the dural sinuses

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Inferior sagittal sinus: runs in the inferior concave free border of the falx cerebri, ending up in the straight sinus

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Straight sinus (sinus rectus): formed by the union of the: o Inferior sagittal sinus & o Great cerebral vein of Galen Runs along the line of attachment of the falx cerebri to the tentorium ending up in the confluence of sinuses

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Transverse sinus: es laterally from the confluence of sinuses forming a groove in the occipital bones and then becomes The sigmoidal sinus. It drains blood from the confluence of sinuses

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Sigmoid sinus: S-shaped, continues inferiorly as the internal jugular vein as ing through the posterior venous part of the jugular foramen

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Occipital sinus: lies in the border of the Cerebellar Falx, connects the confluence of sinuses with the internal vertebral venous plexus

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Cavernous sinus: located on both sides of the Sella turcica, on the body of the sphenoid bone, above the Sphenoidal sinus. It's divided into a venous plexus by incomplete connective tissue septa. The double layer of the dura divides and surrounds this sinus, forming: o Medial lamina: attached to the body of the sphenoid bone (a continuation of the posterior petroclinoidal fold and the tentorial notch) o Lateral lamina: between the anterior & posterior clinoid processes (a continuation of the anterior petro-clinoidal fold) The 2 cavernous sinuses on both sides are communicating with each other by the inter-cavernous sinuses, going in front and behind the hypophysis. It receives blood from (inflow): o Superior ophthalmic vein: this connection is very important clinically in the transmission of upper lip & face infections. ** The anastomosis of the facial vein branches with the ophthalmic ones (via the angular vein near the medial corner of the eye) will give the chance to infections in the face, nose and upper lip areas (in the danger triangle of face area) to ascend in a retrograde fashion and reach the cavernous sinus and thus infecting the meninges (causing lethal meningitis) or damage to the nerves in the cavernous sinus or thrombosis (leading to ophthalmoplegia) o Inferior ophthalmic vein: either directly or via the superior ophthalmic vein o Sphenoparietal sinus: running along the posterior edge of the ala minor of sphenoid bone o Superficial middle cerebral vein o Inferior cerebral vein The outflow sinuses of the cavernous sinus are: o Superior petrosal sinus: taking the blood to the junction of transverse & sigmoid sinuses o Inferior petrosal sinus: taking the blood into the sigmoid sinus o Emissary veins (via foramen ovale or lacerum): to the pterygoid plexus The cavernous sinus communicates also with: o Basilar plexus: connecting the cavernous sinus to the internal vertebral venous plexus

 Inside the cavernous sinus we can find (contents): o Internal Carotid artery (ICA) + Carotid sympathetic plexus (surrounding it) o Abducent nerve (CN-VI) (in the middle) o In the lateral wall: • Oculomotor nerve (CN-III) • Trochlear nerve (CN-IV) • Ophthalmic nerve (CN-V1) • Maxillary nerve (CN-V2) (inside the wall)

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Superior petrosal sinuses: from the posterior end of the cavernous sinus to the transverse sinuses at the part where it becomes sigmoidal

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Inferior petrosal sinuses: runs in the groove between the temporal and basilar bones. It drains blood from the cavernous sinus directly to the beginning of the internal jugular veins

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Basilar plexus: connects the Internal vertebral (Epidural) venous network of the spinal cord with the cavernous sinus and inferior petrosal sinuses

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Emissary veins: channels of communication between the venous sinuses of the dura mater and the external veins of the diploe and the scalp

Translated & Modified from Dr. Milan Sibalin original work

C. Vasculature of the Dura matter: The meningeal arteries supply the intracranial dura mater and usually arise from branches of the external carotid artery. They are found between the meningeal and the periosteal layers of the dura. The veins accompany the arteries with the same names and drain the same areas into the pterygoid venous plexus: - Anterior meningeal artery: branch of the anterior (sometimes posterior) Ethmoidal artery and supply the anterior cranial fossa part of the dura mater - Middle meningeal artery: branch of the maxillary artery, enters through the foramen spinosum, then it gives 2 branches: Anterior and Posterior branches of middle meningeal artery. Supplies most of the dura matter - Posterior meningeal artery: branch of the ascending pharyngeal, vertebral or occipital arteries. Supplies the posterior small part of dura in the posterior fossa

D. Nervous supply of the dura mater: Innervated directly by branches of the Trigeminal nerve (CN-V): - Anterior meningeal branches of the Ethmoidal nerve (CN-V1): accompany the Anterior meningeal artery - Dural branches of the maxillary (CN-V2) and Mandibular (CN-V3) nerves accompany the middle meningeal artery branches and innervate the corresponding areas. The maxillary nerve dural branch accompanies the anterior branch of the middle meningeal artery, and the recurrent dural branch of the mandibular nerve is given outside the skull immediately after the Mandibular nerve exit through foramen ovale, then it comes back in through foramen spinosum together with the middle meningeal artery and s it's posterior branch - Posterior part is innervated by the Vagus (CN-X) nerve dural branches - The Tentorium cerebelli together with a small posterior portion of the Falx Cerebri is innervated by the tentorial nerve, which is a branch of the ophthalmic nerve (CN-V1)

2. Leptomeninx (Arachnoid & Pia Maters): A. Arachnoid: o Is avascular connective tissue containing fibroblasts, collagen and some elastic fibers, connected to the Pia mater by the Arachnoid Trabeculae, but not connected to the dura mater o Arachnoid granulations (Arachnoid villi) are small protrusions of the arachnoid through the dura mater. They protrude into the venous sinuses of the brain, and allow one-way flow of the cerebrospinal fluid (CSF) from the subarachnoid space into the venous circulation The largest granulations lie along the superior sagittal sinus, they are, however, present along other dural sinuses as well. Smaller granulations are called villi, large calcified ones are referred to as Pacchionian bodies. B. Pia mater: o A highly vascularized delicate membrane by a dense network of blood vessels that adheres to the surface of the brain and spinal cord, following all their contours o Connected to the arachnoid by trabeculae o In the spinal cord it forms the denticulate ligament & the flium terminal (Check the spinal cord anatomy) o It follows the blood vessels when it penetrates the cerebral cortex to form a pial coat around them and forms the Perivascular space of Virchow-Robin (Important in viral infections!!)

3. Meningeal spaces: - Cranial epidural space (between skull and dura, or to be more accurate between the 2 layers of dura matter): a potential space that normally contains the meningeal vessels. Can be pathological as a result of trauma leading to the rupture of the middle meningeal arteries and bleeding between the bone and dura mater separating them from each other and forming an epidural hemorrhage/hematoma - Spinal epidural space: which is a physiological (natural) space located between the spinal dural sac and the vertebral periosteum (Endorachis). It contains loose areolar tissue, internal vertebral venous plexus and lymphatics

- Subdural space (between dura and arachnoid): also a potential space that trasmitts the superior cerebral veins to the venous lacunae of the superior sagittal sinus via the bridging veins. It can be pathological due to the bleeding of the bridging veins do to rapid hydration/dehydration of brain tissue or acceleration/deceleration injury forming a subdural hemorrhage/hematoma - Subarachnoid space: is a natural physiological occurring space between the arachnoid and pia mater, surrounding the entire brain and spinal cord. • It contains CSF (Cerebrospinal spinal fluid), trabecular cells, cerebral arteries and veins • It can be enlarged at some places in the cranial cavity forming the Subarachnoid cisterns • Extends in adults below the level of conus medullaris up to the 2nd sacral vertebra as the lumbar cistern -

Subarachnoid cisterns: dilation of the subarachnoid space containing CSF. They are names after the structures over which they lie (e.g. chiasmatic, pontine etc.) (see the Dr. Hanics’s handout about the cisterns)

The walls of the cerebral ventricles (taken from Dr. Altdorfer’s and Dr. Somogyi’s handout)

LATERAL VENTRICLES: C-shaped cavities in substance of each hemisphere. Have „horns” radiating from a center which lies under the parietotemporooccipital junction. From here, the horns radiate to an anterior (frontal) horn, an inferior (temporal) horn and a posterior (occipital) horn. The interventricular foramina of Monro are found at the junction of anterior horns and central parts (bodies) and connect the lateral ventricles with the 3rd ventricle.

OPENINGS: interventricular foramina (of Monro) from lateral ventricles to 3rd ventricle.

A/ Anterior horn: situated rostral to interventricular foramen (of Monro). Walls: •

Lateral wall is formed by head of caudate nucleus.

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Medial wall is the septum pellucidum.

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Floor - anterior wall - roof are formed by the radiation of corpus callosum (the radiation of rostrum genu - and body).

B/ Central part (Body): found posteriorly from interventricular foramen to the level of the splenium of corpus callosum. Walls: •

Roof is formed by the corpus callosum (radiation of truncus corporis callosi).

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Floor is formed by the dorsal aspect of thalamus, covered by the lamina affixa (lamina affixa thalami extends from stria terminalis to tenia choroidea).

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Lateral wall: body of the caudate nucleus.

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Medial wall: choroid lamina epithelialis of the lateral ventricle, attached to the fornix (tenia fornicis) and to the thalamus (tenia choroidea). On the outer aspect of choroid lamina epithelialis the pia mater (together = choroid tela) and the choroid plexus can be found.

Central part of the lateral ventricle and the third ventricle (coronal section) 1. Corpus callosum 2. Fornix (body) 3. Tela choroidea with choroid plexus 4. Choroid lamina epithelialis 5. Central part of lat. ventr. 6. Stria terminalis+thalamostriate vein 7. Thalamus+hypothalamus 8. Third ventricle 9. Choroid lamina epithelialis of third ventr. 10. Tela choroidea with choroid plexus 11. Lamina affixa thalami 12. Body of caudate nucl.

C/ Posterior horn extends into occipital lobe. •

Lateral wall is formed by the tapetum of the corpus callosum.

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The other walls are formed by the occipital white matter.

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In the medial wall two longitudinal elevations are seen: the bulb of the posterior horn, formed by the radiation of the corpus callosum (forceps major) and the calcar avis, produced by the calcarine fissure.

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On the floor the collateral trigone (caused by the collateral sulcus) is found.

D/ Inferior horn curves ventrally and then rostrally into temporal lobe. •

The floor is formed by the hippocampus and the collateral eminence (caused by the collateral sulcus).

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The roof and lateral wall is formed by the white substance of the hemisphere (radiation of splenium corporis callosi: tapetum) and along its medial border are the stria terminalis and tail of caudate nucleus.

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Anteriorly: the amygdaloid nucleus bulges into the anterior end of the horn.

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Medial wall: the choroid lamina epithelialis (with choroid tela and choroid plexus) is attached to the fimbria of hippocampus (tenia fimbriae) and to the stria terminalis (tenia terminalis).

THIRD VENTRICLE: small, narrow, midline vertical cleft of diencephalon, bridged by interthalamic adhesion of thalamus. •

Lateral wall is formed by thalamus, hypothalamic sulcus and hypothalamus.

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Roof is formed by choroid lamina epithelialis of the 3rd venticle (+ choroid tela and choroid plexus). The attachments of choroid lamina epithelialis: tenia thalami (on stria medullaris thalami), habenulae and habenular commissure.

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Floor is formed by the hypothalamus with the optic chiasm, infundibulum, mamillary bodies, and subthalamus.

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Anterior wall contains anterior commissure, columns of fornix and lamina terminalis.

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At posterior end of the ventricle the habenular commissure and the posterior commissure are located (between them the pineal recess, above the habenular comm. the suprapineal recess).

OPENINGS: 2 interventricular foramina laterally, cerebral aqueduct posteriorly.

The ventricles are covered by a single epithelium: - ependyma or - regions having with choroid plexus: choroid lamina epithelialis and pia mater (together called the tela choroidea). In these areas a rich capillary plexus develops and invaginates the choroid lamina epithelialis into the ventricle. These invaginations are called the choroid plexuses (function: CSF production into the ventricles). The line of attachment of the choroid lamina epithelialis is called choroid taenia.

Choroid plexus locations: found in the roof of the 3rd and 4th ventricles and next to the central part and inferior horns of the lateral ventricles. (The choroid plexus is enlarged at the junction between inferior horn and central part; here it is called the choroid glomus). None is found in the anterior or posterior horns. The plexus in the lateral ventricle is the largest and most important and is continuous with that of the 3rd ventricle above the interventricular foramina. The lateral openings of the 4th ventricle (foramina of Luschka) also contain choroid plexus which protrude through them and secrete CSF into the subarachnoid space.

Teniae: tenia thalami indicates the line where the roof (choroid lamina epithelialis) of the third ventricle is attached to the thalamus (on the stria medullaris thalami). Tenia choroidea is the medial edge of lamina affixa thalami; this is the attachment of the choroid lamina epithelialis of the lateral ventricle to the thalamus. The continuation into the inferior horn is tenia terminalis. Tenia fornicis and tenia fimbriae attach the other margin of the choroid lamina epithelialis.

tenia choroidea

tenia terminalis

FOURTH VENTRICLE The fourth ventricle is best studied on a midsagittal section through the brain stem and cerebellum. •

The roof is tent-shaped; formed by the superior medu1lary velum, a thin plate, which extends between the two superior cerebellar peduncles. (Lingula, a midline part of the cerebellar cortex, is fused to the outer surface of the sup. medullary velum.) The lower part of the roof is formed by the inferior medullary velum, the nodule of cerebellum and a thin ependymal membrane, the choroid lamina epithelialis of the fourth ventricle from which the choroid plexus of the fourth ventricle is suspended. The inferior medullary velum is continuous with the superio medullary velum at the apex of the fourth ventricle, the fastigium.

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The floor of the fourth ventricie is shaped like a rhombus and is accordingly referred to as the rhomboid fossa. On each side of the median sulcus is a longitudinaily running ridge, the medial eminence. The medial eminence is bounded laterally by the sulcus limitans. The small medullary fold that overhangs the opening of the central canal at the inferior end of the rhomboid fossa is called the obex. Identify the following structures in the rhomboid fossa: 1. Striae medullares: group of medullated fibers. 2. Facial colliculus is the pronounced elevation on the medial eminence rostral to the striae medullares; overlies the abducens nucleus and the internal genu of the facial nerve. 3. Locus ceruleus, a bluish gray area rostral to the facial colliculus in the area of the sulcus limitans. The area overlies the nucleus of the locus ceruleus (its pigmented cells give rise to noradrenergic pathways). 4. Vestibular area overlies the vestibular and cochlear nuclei in the lateral part of the rhomboid fossa. 5. Hypoglossal trigone - caudally from the striae medullares is formed by the underlying nucleus of the hypoglossal nerve. 6. Vagal trigone, lateral and posterior to the hypoglossal trigone, overlies the ala cinerea (autonomous nuclei of the vagus and glossopharyngeal nerves). 7. Area postrema is situated more laterally.

The rhomboid fossa 1. Sulcus limitans 2. Facial colliculus 3. Medullary striae 4. Vestibular area 5. Obex 6. Area postrema 7. Vagal trigone 8. Hypoglossal trigone 9. Median sulcus 10. Sup. medullary velum 11. Medial eminence

The cerebrospinal fluid leaves the fourth ventricle to enter the subarachnoid space through the median aperture (foramen Magendie), and the two lateral apertures (foramina of Luschka). The relatively wide median aperture which opens into the cerebellomedullary cistern, can be seen on the dorsal side of the brain stem in the angle between medulla oblongata and the cerebellum.

The lateral aperture can be identified on one of the half brain stem-cerebellum preparations by gently probing in the direction of the tubular lateral recess of the fourth ventricle as it curves over the dorsal aspect of the brain stem. The lateral aperture, which is located in the cerebellopontine angle, is usually easy to identify from outside because a part of the choroid plexus of the fourth ventricle projects out into the subarachnoid space through this opening (forming the ”flower basket of Bochdalek”).

(Dr. György Somogyi and Dr. Károly Altdorfer, 2007.)

3 dimensional view of the borders of the lateral ventricle, viewing it from a posterior aspect,

4. The cerebrospinal fluid and its circulation: The Cerebrospinal fluid (cerebrospinal liquor) is a clear, colorless, salty bodily fluid that occupies the subarachnoid space and the ventricular system around and inside the brain and spinal cord. In essence, the brain "floats" in it o Production: a. By the choroid plexi of the ventricles. The main source is the choroid plexus of the lateral ventricle, especially the glomus, which is an enlarged tuft of choroid plexus, lying in the trigone (atrium) of the lateral ventricle, and can be calcified in adults b. Total CSF volume is 140 ml (30 ml in the ventricles, 30 ml in the cranium, 80 ml in the spinal subarachnoid space) c. Rate of production is 500 ml/day d. Normal pressure is 80-180 mm water (CSF) in the lumbar cistern in decubitus position o Circulation of the CSF: a. From the lateral ventricles, the liquid circulates into the third ventricle through the interventricular foramen of Monro b. From the third ventricle, it circulates to the cerebral aqueduct of the mesencephalon. From there, to the fourth ventricle c. From the fourth ventricle, it circulates out into the outer liquor space (subarachnoid space) via: i. Lateral apertures of the fourth ventricle (Foramina of Luschka): opens into the lateral pontine cistern (Pontocerebellar) (The choroid plexus of the 4th ventricle can be also seen protruding from it as well in a structure known as Bochdalek’s flower basket) ii. Median aperture of the fourth ventricle (Formaen of Magendi): opens into the cerebellomedullary cistern (Cisterna magna) between the cerebellum & medulla d. From the cisterns of the subarachnoid space, the fluid circulates onto the entire surface of the brain and downward onto the spinal cord (still in the subarachnoid space) e. The fluid also flows down the dorsal surface of the spinal cord, circulates between the denticulate ligaments, reaching the lumbar cistern and recirculates upward toward the brain f. The absorption of this fluid is done by the arachnoid villi. These villi absorb the fluid from the space into the sinuses (venous blood). Most of the granulations are along side the superior sagittal sinus, the main drainage of the cerebrospinal fluid g. Some CSF is also absorbed at the exits of the spinal nerves where the fluid enters into the dense venous plexuses and into the nerve sheaths (drainage into the lymphatic circulation)

5. The blood brain barrier (BBB): A selective barrier for numerous substances that are prevented from penetrating through the capillary wall into the brain tissue, sealing the brain from the rest of the body o Goldmann’s first & second expierments demonstrated the blood brain barrier using the trypan blue dye, and also demonstrated the blood-CSF barrier, which behaves in a different way o Components of the BBB: a. Capillary wall: consisting of endothelial cells, overlapping at their junction like roof tiles t together by zonulae occludentes (tight junctions) b. Basal lamina c. Astrocyte foot process covering

6. Cicumventricular organs: Chemosensetive zones that monitor varying concentrations of circulating hormones in blood & CSF located in the periphery of the 3rd ventricle and floor of the 4th. These are highly vascularized areas with fenestrated capillaries and no BBB (except for the sub-commissural organ), include: a. Organum vasculosum of the lamina terminalis o Considered to be a vascular outlet of LHR hormone and somatostatin b. Median eminence of the tuber cinereum o Contains neurons that elaborate releasing and inhibiting hormones into the hypophyseal portal system c. Subfornical organ o Located on the inferior surface of the fornix at the level of the interventricular foramen of Monro o Central receptor site for angiotensin II o Porjects to the supraoptic nuclei and the organum vasculosm d. Subcommissural organ o Located below the posterior commissure o Has BBB e. Pineal body: o Contains calcareous granules, in brain sand or acervulus o Has pinealocytes, innervated by the ANS to sythesize serotonin and melatonin f. Area postrema o 2 small subependymal oval areas on either side of the 4th ventricle rostral to the obex o Chemoreceptor zone that triggers vomiting in response to circulating emetic substances

The exits of cranial nerves (from brain, dura and skull) & their subarachnoid pathway (Taken from Dr. Altdorfer & Dr. Somogyi’s handout 2007) Brain exit I. Olfactory nerve II. Optic nerve

III. Oculomotor nerve

IV. Trochlear nerve

Dural exit Cribriform plate

Cribriform plate

Optic chiasma

At the posterior pole of the eyeball (!)

Optic canal

Chiasmatic cistern

Cavernous sinus (lateral wall) Enters btw. the ant. and post. petroclinoidal folds

Sup. orbital fissure

Interpeduncular cistern

Cavernous sinus (lateral wall) Enters within the ant. petroclinoidal fold

Sup. orbital fissure

1. Quadrigeminal cistern (initial part) 2. Ambiens cistern (encircling the brainstem)

V/1.: Sup. orbital fissure V/2.: For. rotundum V/3.: For. ovale

Lateral pontine cistern (pontocerebellar cistern)

Sup. orbital fissure

Median pontine cistern (pontomedullary cistern)

Oculomotor sulcus (=medial sulcus of crus cerebri) in the interpeduncular fossa; between post. cerebral a. and sup. cerebellar a. Below inferior colliculi; both sides of the frenulum of sup. medullary velum Note: n. IV. is the only cranial nerve which exits ont he DORSAL aspect of the brain!!

V. Trigeminal nerve

Btw. pons and brachium pontis, anteriorly - larger, sensory root inferiorly, motor root superiorly

VI. Abducent nerve

At the ponto-medullary junction, on both sides of foramen cecum

Cavernous sinus (freely!) Ascends in the clivus in the Dorello's canal; enters the cavernous sinus far below the post. petroclinoidal fold

VIII. Vestibulocochlear nerve

Btw. pons and brachium pontis, posteriorly - in the cerebello-pontine angle Btw. pons and brachium pontis, posteriorly - in the cerebello-pontine angle; laterally from n. VII.

IX. Glossopharyngeal nerve

In the lateral parolivary sulcus (superiorly)

X. Vagus nerve

In the lateral parolivary sulcus (below n. IX.)

XI. Accessory nerve

XII. Hypoglossal nerve

Subarachnoid pathway (Cistern)

Olfactory bulb

Trigeminal (Meckel's) cave V/1.: cavernous sinus (lateral wall) V/2.: cavernous sinus (lateral wall) V/3.: For. ovale

VII. Facial nerve*

Skull (cranial) exit

In the lateral parolivary sulcus (inferiorly) - the cranial roots of n. XI. From spinal segments C16 the cervical or spinal roots of n. XI. In the medial parolivary sulcus

The fundus of the internal acoustic meatus

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Lateral pontine cistern (pontocerebellar cistern)

Jugular foramen (anterior part: pars nervosa)

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Hypoglossal canal

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* nervus intermedius exits between n. VII. and n. VIII. but belongs to n. VII. (parasympathetic and taste fibres) The real cranial nerves (CN III-XII.) originate from the brainstem (=midbrain, pons, medulla). Ist and IInd cranial nerves are not real cranial nerves because they are extensions of the brain (CNS!).

Gross anatomy of the spinal cord (Spinal medulla) Derived from the caudal part of the neural tube, surrouned by meninges and weights about 30 g, comprising 2% of the wright of the adult brain A. Location: o Extends in adults from foramen magnum to the lower border of L1. In newborns, it extens up to L3 o Continuous with the medulla oblongata at the spinomedullary junction, a palane defined by: i. Foramen magnum ii. Pyramidal decussation iii. The emergence of the 1st cervical nerve ventral roots o Lies within the subarachnoid space, which extends caudally up to S2 B. Attachments: suspend and anchor the spinal cord inthe dural sac, arising from the vascular pia matter, o Denticulate ligaments: 2 flattened bands of pial tissue that attach to the spinal dura with about 21 attachments o Filum terminale: a pial filament extending from the conus medullaris to the end of the dural sac and to the sacral canal, it has: a. Filum terminale internum: fuses with the end of dural sac at S2 b. Filum terminale externum (coccygeal ligament): continues down to fuse at the coccyx o Spinal nerve roots: provide the strongest anchorage and fixation to the vertebral canal C. Shape: o Elongated nearly cylindrical structure, flattened dorsoventrally and approximatelly 1 cm in diameter o Has 2 enlarged places for the nerve supply of the upper and lower extremities a. Cervical (brachial) (C5-T1) intumescence: for brachial plexus b. lumbar (lumbosacral) (L1-S2) intumescence: for lumbosacral plexus o On average, its 45 cm in length, terminating caudally as the conus medullaris (L1/L2)

D. Surface structures & features: a. Ventral median fissure: deep ventral midline groove underlyin the ventral spinal artery b. Ventral lateral sulcus: a shallow groove from which the ventral rootlets emerge c. Dorsal lateral sulcus: a shallow groove into which the dorsal rootlets enter d. Dorsal intermediate sulcus: o A shallow groove continuous with the dorsal intermediate septum, found between the dorsal lateral & dorsal median sulci but only rostral to T6 o Separated the faciculus gracilis from the fasciculus cunatus e. Dorsal median sulcus: a shallow dorsal midline groove that is continous with the dorsal median septum

E. internal morphology: i. Gray matter: o In the center of the spinal cord, H or butterfly shaped (varies in different levels) o Has a central canal and subdivided into 10 cytoarchitectural areas called Rexed Laminae o Divided into: a. Dorsal horn (column): receives and processes sensory input, found at all levels b. Lateral horn (column): recieves viscerosensory input, extends from T1(C8)-L3 c. Ventral horn (column): contains predominantly motor nuclei, found at all levels ii. White matter: o Consists of bundles of myelinated fibers that surround the central grey matter and consists of ascending and descending fiber pahtways called tracts o Divided bilaterally by sulci into 3 major divisions: a. Dorsal funiculus (Dorsal column): located between the dorsal median sulcus and the dorsal lateral suclus, subdivided above T6 into: 1. Fasciculus gracilus (of Goll’s): located between the dorsal median septum and the dorsal intermediate sulcus & spetum, found at all levels 2. Fasciculus cuneatus (of Burdach’s): located between the dorsal intermediate sulcus & septum and the dorsal lateral sulcus, only found at the upper thoracic & cervical cord levels (C1-T6) b. Lateral funiculus: located between the dorsal lateral and ventral lateral sulci c. Ventral funiculus: contains the anterior white commissure, which is located between the central canal and the ventral median fissure F. Spinal nerves: Consists of 31 pair of nerves that emerge from the spinal cord: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal containing both motor & sensory fibers o Spinal nerves are numbered after the vertebra they exist above o The 1st cervical nerve and the coccygeal nerve usually have no dorsal (sensory) roots and no corrosponding dermatomes o The 1st cervical spinal nerve es between the atlas and the skull o The 2nd cervical spinal nerve es between the atlas and the axis o With the exception of C1, all spinal nerves exit the intervertebral canal via intervertebral or sacral foramina o Components & branches of the spinal nerves: formed by the union of dorsal and ventral roots within the intervertebral foramen, resulting in a mixed nerve: a. Dorsal root: enters the dorsal lateral suclus as dorsal rootlets, conveying sensory input from the body via the dorsal root ganglion (DRG) b. Ventral root: emerges as ventral rootlets from the ventral lateral sulcus, conveying motor output from visceral and somatic motor neurons c. Cauda equina: consists of lumbosacral (dorsal & ventral) nerve roots (L2-Co) that descend from the spinal cord through the subarachnoid space (lumbar cistern) to exit through their respective intervertebral or sacral foramina (because the spinal cord itself is shorter than the spinal canal!) d. Spinal nerve rami (branches): i. Dorsal primary ramus: innervates the skin & muscles of the back

ii. Ventral primary ramus: innervates the ventral lateral muscles and skin of the trunk, extremities and visceral organs iii. Meningeal ramus: innervates the meninges and vertebral column iv. Gray communicating rami: contain unmyelinated postganglionic sympathetic fibers, associated with all spinal nerves v. White communicating rami: contain myelinated preganglionic sympathetic fibers and myelinated GVA fibers (splanchnic nerves), found only in T1-L3 G. Spinal nerve innervation: 1 spinal nerve innervates the derivates from 1 somite, which includes: o Dermatome: a cutaneous area innervated by the fibers of 1 spinal nerve o Mytome: a group of muscles innervated by fibers of 1 spinal nerve o Sclerotome: a group of bones & ligaments innervated by fibers of 1 spinal nerve

H. Arterial supply of the spinal cord: 1. Vertebral artery: gives rise to, i. Anterior spinal artery: supplies the anterior 2/3 of the spinal cord, including the anterior and lateral horns, also the pyramids, medial lemniscus, hypoglossal nerve in the medulla ii. Posterior (Posteriolateral) spinal arteries: supply the posterior 1/3 of the spinal cord, including the posterior horns & columns, also the gracile + cuneate nuclei in the medulla 2. Segmental arteries: o Arise from the aorta, vertebral arteries and common iliac arteries as medullary (spinal) arteries, which supply the anterior and posterior spinal arteries after they enter the IV foramen o Provide the man blood supply to the spinal cord at the thoracic & lumbar levels o The 2nd lumbar artery gives rise to a large anterior medullary artery of Adamkiewicz (varies between T12-L4), usually on the left side o The most poorly vascularized segments are T1-T4 and L1 * The anterior spinal artery gives off numerous small arteries into the anterior sulcus called: sulcocommissural arteries * Vasocorona: anastomoses between the anterior & posterior spinal arteries so that a vascular ring surrounds the spinal cord H. Venous drainage of the spinal cord: o In general it follows the arterial pattern o es from the spinal veins within the subarachnoid space to the spinal epidural internal vertebral venous plexus (of Batson) before draining into the intracranial, cervical, thoracic, intercostal or abdominal veins or communicating with the external vertebral venous system o It is a valveless venous system that permits bidirectional flow, depending on the pressure gradients, thus allowing also the free transmission of infectious agents and tumor cells!!