Meninges and Brain Vessels

Exercise 8 Meninges & Vessels of the Brain Neuroanatomy Meninges The meninges support and protect the CNS they are three membrane that line the skull and vertebral canal and enclose the brain and spinal cord. There are two kinds of meninges: cranial meninges and spinal meninges. Differences between spinal and cranial meninges are: • Spinal meninges have not 2 layers of dura • Cranial meninges have not real epidural space • Denticulate ligament is not present in cranial meninges • Arachnoid trabeculae are only present in cranial meninges Cranial meninges Fibrous covering of the brain located internal to the cranium. It is a protective membrane that support the brain and is composed of 3 layers as: dura mater, arachnoid and pia mater. Dura mater Page 1 Outermost, thick, fibrous layer which fuses with the endocranium of the skull. It consists of 2 layers: • External or periosteal layer (periosteum) • Internal or meningeal layer (real dura) Dura mater forms four major folds or dural reflections and the walls of the Dural venous sinuses as a partition between a major part of the brain: falx cerebri, tentorium cerebelli, diaphragma sellae and falx cerebelli. Falx cerebri Lies between cerebral hemispheres in longitudinal cerebral fissure. Is attached anteriorly to frontal crest and crista galli and posteriorly to internal occipital protuberance. Contain superior and inferior sagittal and straight sinuses. Tentorium cerebelli It is as a roof of the posterior cranial fossa and separates the occipital lobes from the cerebellum. Tentorium is attached to ridge of transverse sinus posteriorly, to the superior border of petrous bones and posterior and anterior clinoid process anteriorly. Contain the tentorial notch on the anterior free border, through which the brainstem (midbrain) passes. Sinuses that run in tentorium are superior petrosal, transverse, and straight sinuses. Exercise 8 Meninges & Vessels of the Brain Neuroanatomy Diaphragma sellae Forms the roof of hypophyseal fossa. Contains an aperture through which the hypophyseal stalk passes Falx cerebelli Lies in the posterior cranial fossa and separate two cerebellar hemispheres. It is attached to the internal occipital crest. The occipital sinus runs in this fold. Dural venous sinuses Page 2 The Dural venous sinuses lie between the two Dural layers. Veins draining of the brain, diploe, scalp and orbit drain into these sinuses. Superior sagittal sinus lies in superior attached edge of falx cerebri in front of the crista galli and arches posteriorly to end at int occipital protuberance, usually turns to right to become right transverse sinus. Communicates with lacunae on either side. Venous lacunae: lies along side of the superior sagittal sinus as lateral extension and open to it. Lacunae receive arachnoid granulation. Inferior sagittal sinus in lower free edge of falx cerebri. Ends by uniting with great cerebral vein to become straight sinus. Straight rectus sinus lies in the long line of attachment of falx cerebri and tentorium cerebelli. receives the great cerebral veins and inferior sagittal sinus. Occipital sinus is located in attached margin of falx cerebelli, begins at foramen magnum and ends at confluence of sinuses. Confluence of sinuses lies at internal occipital protuberance where superior sagittal, straight and occipital sinuses drains. It drains to transverse sinuses. Transverse sinus paired; each begins at confluence of sinuses passes laterally in attached posterior margin of tentorium. It unites with superior petrosal sinus to form sigmoid sinus. Sigmoid sinus direct continuations of transverse sinuses, located in posterior cranial fossa, ends at the jugular foramen and become continuous with internal jugular vein. Sphenoparietal sinus paired, located on posterior border of lesser wing of sphenoid. it drains to cavernous sinus. Exercise 8 Meninges & Vessels of the Brain Neuroanatomy Cavernous sinus paired, lies on each side of body of sphenoid. Drains in two directions: superior petrosal and inferior petrosal sinus. Internal carotid artery and CN VI lies within, and some other cranial nerves (III, IV, V1, V2) are located at the lateral wall of the sinus. Superior petrosal sinus paired, along superior border of petrous within attached margin of tentorium. Drains part of blood from cavernous sinus. Unites with transverse sinus to form sigmoid sinus. Inferior petrosal sinus paired, along the suture between occipital and petrous bone. Drains part of blood from cavernous sinus. Drains into internal jugular vein with sigmoid sinus. Arachnoid mater Is the intermediate, transparent membrane which is attached to the dura. It has microscopic projection called arachnoid villi invaginated into the Dural superior sagittal sinus through which cerebrospinal fluid (CSF) enters the venous system. Pia mater Page 3 Internal vascular membrane which covers the surface of the CNS. It is connected to arachnoid layer by the arachnoid trabecula in subarachnoid space. Denticulate ligament the spinal cord is suspended in the Dural sheath by denticulate ligament which is made of pia-arachnoid tissue. The lateral edge of the ligament is attached at 21 point to the Dural sheath. Meningeal Spaces: Are the spaces between the meningeal layers which are epidural, subdural, and subarachnoid spaces. Epidural space located between the ligament that attaches the vertebrae and dura mater only inside the spinal canal contains fat and venous plexus. there is no epidural space in the cranial cavity because dura and periosteum are attached together. Subdural space potential space located between the dura mater and arachnoid. normally contains only a film of extracellular fluid Exercise 8 Meninges & Vessels of the Brain Neuroanatomy Subarachnoid space located between pia mater and arachnoid. Contains CSF and large vessels. The enlarged space that contain more amount of CSF are called subarachnoid cistern. Subarachnoid cisterns Dilation of subarachnoid space which separates the arachnoid and the pia mater. These cisterns are filled with cerebrospinal fluid and are named after the structure over which they lie. The major subarachnoid cisterns are: pontine, interpeduncular, quadrigeminal and cisterna magna. cerebellomedullary cistern (cisterna magna): the largest of the subarachnoid cisterns. It lies between the cerebellum and medulla (below the cerebellum). Interpeduncular cistern: it is situated at the base of the brain, between the two cerebral peduncles of midbrain. Pontine cistern: located at ventral aspect of the pons and medulla. quadrigeminal cistern (superior cistern): located just behind the corpus quadrigemina (superior and inferior colliculi of midbrain) and above the cerebellum. lumbar cistern: is large space extending from L2 to the S2 (2nd segment of sacrum). It contains cauda equina, formed by lumbar and sacral spinal nerves. Blood supply of the brain Page 4 The brain is supplied by the paired internal carotid and vertebral arteries. Internal carotid artery is terminal branch of common carotid artery. It enters the cranial cavity via the carotid canal in the petrous temporal bone. It has four parts as follows: 1. cervical, 2. petrous, 3. cavernous, 4. cerebral. The carotid siphon is located between 3rd and 4th parts of the artery. Ophthalmic, hypophysial, anterior choroidal and posterior communicating arteries are the lateral branches of the internal carotid artery, middle and anterior cerebral arteries are the terminal branches of internal carotid artery. Middle cerebral artery (MCA): Runs deep to the lateral sulcus and supplies the lateral surface of the hemisphere. MCA has frontal, parietal and temporal branches. Exercise 8 Meninges & Vessels of the Brain Neuroanatomy Anterior cerebral artery (ACA): Bends around the genu of corpus callosum to Page 5 supply the medial surface of the brain from frontal pole to parietooccipital sulcus. Two arteries (ACA) join together at the midline (ant. to optic chiasma) by the anterior communicating artery. The pericallosal artery on the upper surface of corpus callosum and callosomarginal artery which follows the cingulate sulcus are the branches of ACA. Vertebral artery is a branch of subclavian artery ascends in the transverse foramina of cervical vertebrae. the artery enters the cranial cavity via foramen magnum. A single anterior spinal, paired posterior spinal and PICA are branches of the vertebral artery. Posterior Inferior Cerebral Artery (PICA): supplies posterior part of the cerebellum and dorsolateral part of the medulla. Basilar artery: is formed by joining of two vertebral arteries at the inferior border of the pons. The artery runs in the midline and ends at the superior border of the pons by dividing into the posterior cerebral arteries (PCA). The AICA, labyrinthine, pontine and SCA are the branches of basilar artery. Anterior Inferior Cerebellar Artery (AICA): arising from caudal end of basilar artery and supply the inferior surface of the cerebellum. Superior Cerebellar Artery (SCA): arises before the terminal bifurcation of basilar artery, supplies the superior surface of cerebellum. Posterior Cerebral Artery (PCA): Originated from the terminal bifurcation of basilar artery at the junction of the pons and midbrain (interpeduncular fossa). The temporal branch of PCA supplies the inferior surface of temporal lobe. The calcarine and parietooccipital arteries which run along the corresponding sulci are the terminal branches of PCA. cerebral circle (Willis) is formed by internal carotid artery, anterior cerebral (ACA) and anterior communicating arteries (as the anterior part of the cerebral circle), posterior cerebral (PCA) and posterior communicating arteries (as posterior part of the circle). Exercise 8 Meninges & Vessels of the Brain Neuroanatomy Veins of the brain Page 6 Veins of the brain are usually drain into one of the Dural venous sinuses. Superficial veins that drains the cerebral hemispheres include superior cerebral veins, middle cerebral veins, and inferior cerebral veins. Superior cerebral veins: drain the supralateral and medial aspect and empty into superior sagittal sinus. Middle cerebral veins: drain the lateral hemispheres and empty into cavernous sinus. Inferior cerebral veins: drain inferior aspect of the brain and join either superior cerebral veins or basilar veins. Basilar veins: drain small anterior cerebral veins & deep middle cerebral veins. Internal cerebral veins: drains the 3rd and 4th ventricles and the deep part of the cerebrum. These unite to form great cerebral vein. Great cerebral vein: receives the basilar veins and merges with the inferior sagittal sinus to form straight sinus. Superior and inferior cerebellar veins drain the cerebellum.