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THE BRAIN- meninges, blood supply and venous drainage. By Francesca Pickwell The Brain • The different parts of the brain are the cerebrum, diencephalon, brainstem and cerebellum. • The cerebrum is divided into left and right cerebral hemispheres by the longitudinal fissure • Each cerebral hemisphere is divided into 4 lobes: FRONTAL, PARIETAL, TEMPORAL, OCCIPITAL. • Functions- intelligence, personality, motor function, planning, touch sensation, interpretation of sensory impulses. The brain The brain Parietal lobe Frontal lobe Temporal lobe Occipital lobe The brain The brain Corpus callosum Thalamus Hypothalamus Cerebellum MIDBRAIN PONS MEDULLA OBLONGATA Blood supply • The brain receives its blood supply from the: • INTERNAL CAROTID arteries - branches of the common carotid artery. Enter skull through the carotid canals • VERTEBRAL- branches of the subclavian arteries. Pass through transverse foramina of cervical vertebrae and enter skull through foramen magnum. • The arteries give off branches to form the CIRCLE OF WILLIS CIRCLE OF WILLIS Meninges • The meninges are protective layers that surround the brain • There are 3 of them: -DURA MATA- tough, thick outer layer -ARACHNOID MATA- thin, delicate intermediate layer -PIA MATA- inner layer adhered to brain surface Area between the pia mata and arachnoid mata is the subarachnoid space. This contains CSF. Dura Mata 2 layers: PERIOSTEAL layer: outer layer attached to internal surface of skull MENINGEAL layer: closely related to the arachnoid mata. In certain places, the inner meningeal layer separates from the outer periosteal layer to form DURAL PARTITIONS… Dural Partitions The dural partitions formed by the dural reflections divide the cranial cavity into different parts: 1.FALX CEREBRI- divides left and right hemispheres of brain. Anterior attachments: frontal crest of frontal bone and crista galli Posterior attachments: internal occipital protuberance Dural partitions 2. TENTORIUM CEREBELLI- Covers the cerebellum separating it from the occipital lobe of the brain. Anterior attachments: clinoid processes of the sphenoid bone Lateral attachments: pertrous parts of temporal bones Posterior attachments: internal surface of occipital bone Tentorium cerebelli divides cranial cavity into infratentorial and supratentorial parts. Tentorial notch: gap in the tentorium cerebelli which the midbrain passes through. Dural partitions 3. FALX CEREBELLI-divides cerebellum in half 4. DIAPHRAGMA SELLAE- covers posterior gland in hypophysial fossa. Dural venous sinuses • Dural venous sinuses are endothelial lined spaces between the two layers of dura mata • Important role in VENOUS DRAINAGE • The large veins of the brain empty into these sinuses • The sinuses empty into the internal jugular vein Dural venous sinuses • Superior saggital sinuslies in the superior border of the falx cerebri. Terminates posteriorly at at the confluence of sinuses. Receives the superior cerebral veins. • Inferior saggital sinuslies in the inferior border of the falx cerebri. Joins with the great cerebral vein to form the straight sinus. Dural venous sinuses • Straight sinus- formed by union of great cerebral vein and inferior saggital sinus. Empties into the confluence of sinuses. • Left and right transverse sinuses- receive venous blood from confluence of sinuses on either side. • Sigmoid sinuses- S shaped continuations of left and right sinuses. Drain into internal jugular vein Dural venous sinuses • Cavernous sinuses- lie either side of the side of sella turcica. Drain into the superior and inferior petrosal sinuses. Clinically important because of structures that pass through or alongside them. • Structures passing through: -internal carotid artery -abducent nerve Structures in lateral wall: ophthalmic nerve, maxillary nerve, oculomotor nerve, trochlea nerve Quick overview- sinuses Quick overview- sinuses CSF flow • Ventricular system: two lateral ventricles, 3rd ventricle and 4th ventricle • CSF produced in the choroid plexus of the third and forth ventricles • CSF drains from the forth ventricle into the subarachnoid space • CSF is absorbed into the venous system by arachnoid granulations. • Main source of venous drainage: superior saggital sinus Dura mata- blood supply & nervous innervation • BLOOD SUPPLY: • Anterior meningeal artery – supplies anterior cranial fossa • Middle meningeal artery- supplies the middle cranial fossa. • Posterior cranial artery- supplies posterior cranial fossa. • NERVOUS INNERVATION: • Trigeminal nerve!!! (Clinical relevance: dural origin of headaches.) INTRACRANIAL HAEMORRHAGES • Extradural haemorrhage- arterial in origin. Blood from damaged middle meningeal artery accumulates between skull and dura. Get brief concussion, lucid interval then go into coma!!! • Subdural haemorrhage- venous in origin. Blood from venous sinuses collects between dura and arachnoid layers. • Subarachnoid haemorrhage- arterial in origin. Can be caused by rupture of an aneurysm OR by severe head trauma. Blood collects in subarachnoid space which results in meningeal irritation and loss of consciousness. Questions • The vertebral arteries branch off the subclavian arteries T • The middle cerebral artery connects the two anterior cerebral arteries F • The inner layer of the dura is called periosteal and the outer layer is called meningeal F • The tentorial notch is a gap in the tentorium cerebelli through which the midbrain passes T • The inferior saggital sinus joins with the great cerebral vein to from the straight sinus T • The two structures that pass through the cavernous sinus are the abducent nerve and opthalmic nerve F • Nervous innervation to the dura is via the trigeminal nerve T • Subdural haemorrhages are venous in origin F