The Meninges of Brain and Spinal Cord DR. S. H. KHAN

The Meninges of Brain and Spinal Cord The spinal cord and brain are surrounded by three membranes, the meninges. Named from the outside~ inward they are the dura mater, arachnoid, and pia mater. DURA MATER SUB-DURAL SPACE (filled with thin film of fluid) ARACHNOID MATER SUB-ARACHNOID SPACE (filled with CSF) PIA MATER

The meninges of spinal cord Spinal Dura mater Spinal Arachnoid mater Spinal Pia mater

Spinal dura mater Characters Dense, strong, fibrous membrane Encloses the sp. Cord & cauda equina Continuous above foramen magnum with the meningeal layer of Dura mater of brain Below, becomes thinner & ends at lower border of S2 invests filum terminale to attach at back of coccyx

Epidural space Subdural space: potential space Position: lies between spinal dura mater and periosteum & ligaments of vertebral canal Contents: loose connective tissue, semi liquid fat, spinal arteries, vertebral venous plexus, lymphatics and, the spinal nerves on each side pass through the epidural space which is applicable for block anesthesia Subdural space: potential space

Spinal arachnoid mater Characters A thin, delicate, tubular membrane loosely investing spinal cord Above, it is continuous with cerebral arachnoid mater Inferiorly extends as Dura ( lower border of S2)

Subarachnoid space Position: lies between pia and arachnoid maters containing cerebrospinal fluid. Extends upto low. Border of S2 Terminal cistern : the largest part of subarachnoid space extending from termination of spinal cord (low. Border of L1) to level of S2, where it is occupied by nerves of cauda equina, so it is the best site for a lumbar puncture

Lumbar puncture (spinal tap) Bet. L3 & L4 (adult), L4 & L5 (child)

Spinal pia mater A delicate vascular membrane that closely invests the spinal cord Denticulate ligament: consist of 21 pairs triangular ligaments extending from spinal cord on each side between anterior and posterior roots of spinal nerves to spinal dura mater; these ligaments help to fix position of spinal cord. Filum terminale: an extension of pia beyond conus medullaris

The Meninges of Brain Cerebral Dura mater (Pachymeninx) Cerebral Arachnoid mater Cerebral Pia mater Leptomeninges

Cerebral Dura mater Characters A thick and dense inelastic membrane Composed of two layers, an inner - meningeal and outer - endosteal Cranial venous sinuses lie between 2 layers

Endosteal layer of Cerebral Dura mater Lies just below the skull bone -Epidural Hge Continuous outside at sutures & foramina with the periosteum of skull bones Most strongly adherent to the bones over base of skull Meningeal layer of Cerebral Dura mater (Dura mater proper) Dense, strong fibrous membrane Continuous through the foramina magnum as Dura mater of Spinal cord Forms 4 septa which divide the cranial cavity

Falx cerebri Tentorium cerebri Falx cerebelli Diaphragma sellae Four septa of Dura mater Proper Falx cerebri － Lies in between the cerebral hemispheres. Tentorium cerebri － Roof over the posterior cranial fossa. － covers the upper surface of cerebellum . Falx cerebelli － Lies between the cerebellar hemispheres. Diaphragma sellae － Forms roof of the sellar/ hypophyseal fossa

Dural Artery Supply ICA Vertebral A. ECA Maxillary a. Middle meningeal artery (clinically important -Epidural hge) Ascending pharyngeal a. Occipital a.

Venous Sinuses of duramater Function: To receive blood from brain through cerebral veins To receive CSF from SA space through Arachnoid villi Superior sagittal sinus Inferior sagittal sinus Straight sinus Confluence of sinus

Transverse sinus Sigmoid sinus Superior petrosal sinuses inferior petrosal sinuses

Position: lies on each side of sella turcica (hypophyseal fossa) Cavernous sinus Position: lies on each side of sella turcica (hypophyseal fossa) Relations of cavernous sinus: Internal carotid artery and abducent nerve run through the sinus Oculomotor and trochlear nerves and ophthalmic & maxillary divisions of trigeminal nerve lie in the lateral wall of the sinus MCA Occul n. Pituitary gland Troch n. ICA Abducent n. Optha n. Maxil n. Sphenoid air sinus

The flowing of the blood in dural sinus Sup. sagittal sinus Inf. sagittal sinus Straight sinus Confluence of sinus Transverse sinus Sup. petrosal sinus Sigmoid sinus Cavernous sinus Inf. petrosal sinus Internal jugular vein

Cerebral Arachnoid mater Characters: A delicate membrane covering brain loosely, Passing over sulci and entering only cerebral longitudinal and transverse fissures. Separated from Dura by potential Subdural space Separated from Pia by the Subarachnoid space

Arachnoid villi : In certain areas arachnoid projects into venous sinuses to form arachnoid villi Most numerous along the sup. Sagital sinus serve as sites where CSF diffuses into bloodstream Aggregations of arachnoid villi called archnoid granulations, May give rise to Brain tumour (Meningioma)

Cerebral pia mater Thin vascular membrane Closely invests brain surface, Covers the gyri and descends into the sulci Folds of Pia mater enclosing tufts of capillaries form the Telachoroidea. Such pia mater lined by secretory ependyma form the Choroid plexuses

Tela choroidea and choroid plexus Capillaries Pia Ependyma

Sub Arachnoid Space (SAS) Interval between Arachnoid & Pia mater Contains : － CSF, large blood vessels of brain & cranial nerves Extension: － Along the olfactory n. to the mucoperiosteum of nose － Along the cerebral bl. Vessels, till they become an arteriole or venule － Beyond the lower end of spinal cord, ends between S2 & S3 Around the base of the brain the SAS expands to form SA cisterns

Subarachnoid cisterns In certain situations the Arachnoid & Pia are widely separated to form the SA cisterns Has free comunication with one another and with remainder SA Space Cerebellomedullary cistern / Cisterna magna (Bet. Inf. Surface of cerebellum and the medulla) Interpeduncular cistern (contain circle of Willi’s) Pre Pontine cistern (contain vert. & basillar a.) Quadrigaminal cistern / Cisterna ambiens (contain the great cerebral vein of Galen)

Cerebellomedullary cistern CISTERNAL PUNCTURE

Cerebrospinal fluid (CSF) Clear colorless fluid, Contained in the ventricular system & SA space Replaces lymph in the CNS Function: － Cushions & protects the CNS. － Nourishment of CNS. － Removes metabolites from CNS Production: － By the choroids plexuses within the lateral ventricle mainly and, third and fourth ventricles also Absorption: By arachnoid villi Amount: 150ml Rate of production: 0.5ml/min Density of brain is slightly greater than that of CSF.

Circulation of cerebrospinal fluid interventricular foramina CSF drains from lateral ventricle third ventricle mesencephalic aqueduct median and two lateral apertures fourth ventricle arachnoid granulations subarachnoid space superior sagittal sinus vein

Ventricular System Lateral (L&R) Cerebral Aqueduct 3rd 4th

The Blood vessels of Brain and Spinal Cord

Arteries of brain Two sources Internal carotid artery: supplies anterior 2/3 of cerebral hemisphere and parts of diencephalon. Divides into ant. & mid. Cerebral arteries. Vertebral artery: supplies posterior 1/3 of cerebral hemisphere and parts of diencephalon, brain stem and cerebellum At lower border of pons two VA join to form the basilar artery

Internal carotid artery Anterior cerebral artery Middle cerebral artery Anterior choroidal artery Posterior communicating artery ICA ACA MCA AChA PComA

Anterior cerebral artery Terminal br. Of ICA Joins the fellow of the opposite side by the anterior communicating artery supply all medial surface of the cerebral cortex up to the parietooccipital sulcus ACA

Middle cerebral artery Largest br. Of ICA Cortical branches: supply entire lateral surface of cerebral hemisphere, except occipital pole and inferolateral surface which is supplied by PCA Central branches: supply lentiform and caudate nuclei, internal capsule

Posterior communicating artery runs backward to join posterior cerebral artery

Vertebral artery Cranial branches Branches of basilar artery Anterior and posterior spinal arteries Posterior inferior cerebellar artery Branches of basilar artery Anterior inferior cerebral artery Labyrinthine artery Pontine arteries Superior cerebellar artery Posterior cerebral artery

Posterior cerebral artery Cortical branches: supply medial and inferolateral surfaces of temporal lobe and lat. & medial surfaces of occipital lobe Central branches: supply dorsal thalamus, midbrain, medial and lateral geniculate bodies,

Cerebral arterial circle ( circle of Willis ) Concept: － Arterial anastomosis. － Distribute blood to any part of the cerebral hemisphere. － Equalizes pressure in the arteries of the two sides of brain. Position: － lies in the interpeduncular fossa at the base of the brain.

Formation: Anteriorly: － Ant Formation: Anteriorly: － Ant. communicating artery Posteriorly: － Basilar artery that divides into posterior cerebral arteries On each side: － Anterior cerebral arteries, － Internal carotid arteries, － Posterior communicating arts, － Posterior cerebral arteries

VENOUS DRAINAGE － very thin wall － no valves 1.External cerebral veins － lie in the subarachnoid space － drain into the cranial venous sinuses － ultimately drain into internal jugular vein 1.External cerebral veins 2.Internal cerebral veins

Veins of brain External cerebral veins Drain blood from cortex and subcortical medullary substance and empty into adjacent sinuses of dura mater

Veins of brain Internal cerebral veins: Two veins drain deeper parts of hemispheres, basal nuclei, internal capsule, diencephalon and choroid plexus, ultimately two ICV form great cerebral vein of Galen which enter straight sinus

Blood vessels of spinal cord Arteries of spinal cord Two sources One Anterior and two posterior spinal arteries Branches of segmental arteries: ASA PSA

Blood vessels of spinal cord Spinal veins: drain into internal vertebral venous plexus Post. Sp. A. Segmental sp. A. Ant. Spinal artery

Optic/visual pathway Light falling on the cornea. Traverse the refractive medias of the eye. Stimulates the rods and cones of retina. Optic nerve ( nasal & temporal fibers) Optic chaisma ( nasal fibers cross) Optic tract Lateral geniculate body Optic radiation Visual cortex