L12: Brain and Meninges Flashcards
What are the major parts of the brain?
- Cerebrum - Cerebellum - Brainstem
What separates the hemispheres from each other? What holds them together?
- Separated by falx cerebri at the longitudinal fissure - Held together/ connected by corpus callosum
What separates the cerebellum from the remaining brain structures? What unites the two hemispheres of the cerebellum?
- Tentorium cerebelli lies above the cerebellum, separating it from the cerebrum - Vermis unites the two hemispheres
What are the parts of the brainstem?
- Midbrain - Medulla oblongata and pons
What arteries supply blood to the brain?
- Vertebral arteries - Internal carotid arteries
Course of vertebral arteries. Branches
- Vertebral artery is first branch off of subclavian. - Travels through transverse foramina of cervical vertebrae - Enters into the cranium through the foramen magnum. - Gives off posterior inferior cerebellar artery laterally, anterior spinal artery, posterior spinal artery - Unites at lower border of pons to form the basilar artery
Course and branches of basilar artery.
- Arises from vertebral artery at lower border of pons - Lies in median groove of the pons - Gives rise to: Anterior inferior cerebellar arteries Pontine arteries Superior cerebellar arteries Posterior cerebral arteries (terminal branches)
What are the major arteries that supply blood to the cerebellum?
- posterior inferior cerebellar arteries (PICA) from vertebral arteries - anterior inferior cerebellar arteries (AICA) from basilar artery - superior cerebellar arteries (SCA) from basilar artery
Course and branches of internal carotid arteries.
- Common carotid branches into internal and external carotids at the superior level of thyroid cartilage (~ C5). - Internal carotid arteries enter the skull through the carotid canal and gives rise to its branches: Posterior communicating Middle cerebral Anterior cerebral – become joined with anterior communicating artery and disappear in median longitudinal fissure
Draw the Circle of Willis
What is the pontomedullary junction?
- Area where vertebral arteries join and become the basilar artery
List 3 cranial meninges. Describe
- Dura mater (tough, outer layer) - Arachnoid mater (thin, avascular intermediate layer) - Pia mater (vascular inner layer)
How is dura mater different in cranium than in spinal canal?
- Called cranial dura in cranium as it has two layers. - External layer = external periosteal layer (aka endocranium) continuous with periosteum - Internal layer = internal meningeal layer continuous at foramen magnum with spinal dura
What are dural folds? List dural folds present and explain.
- Dural folds refers to internal layer of dura that separates from external periosteal layer to form folds/partitions separating regions of brain. Falx cerebri: lies in longitudinal fissure separates two cerebral hemispheres Tentorium cerebelli: separates occipital lobe from cerebellum Falx cerebelli: partly separates the cerebellar hemispheres Diaphragma sellae: circular sheet of dura suspended bw ant and clinoid processes of sphenoid bone forming roof over hypophyseal fossa allows hypophyseal stalk/infundibulum to penetrate through.
Where is CSF generated? What are the chambers of the ventricular system of the brain?
- Chroid plexus in the ventricles - Chambers: 2 x lateral ventricles (in each cerebral hemisphere) 3rd midline ventricle 4th inferior posterior ventricle
Function of CSF?
- Cushioning brain and spinal cord - Transportation of chemicals - Clearing waste
Explain CSF circulation.
- CSF generated in lateral ventricles travel to 3rd ventricles via interventricular foramen of Monro - CSF generated and accumulated in 3rd ventricle (from lateral ventricles) travel to 4th ventricle via cerebral aqueduct of Sylvius - CSF generated and accumulated in 4th ventricle (from lateral and 3rd ventricles) travel to subarachnoid space via median aperture (aka foramen of Magendie) or lateral apertures (aka foramina of Luschka) - CSF moves into subarachnoid space in spinal cord in cranium
Large fissures in brain.
- Lateral fissure (sulcus of Sylvius) is large sulcus that separates frontal/parietal lobes from temporal - Central fissure/sulcus separates frontal from parietal lobes
What is the insula?
- Large portion of cerebral cortex folded deep within lateral sulcus.
Through what fissures do branches from the internal carotid travel?
- Middle cerebral arteries travel through lateral fissures - Anterior cerebral arteries travel through longitudinal fissures
What is the major blood supply to the dura?
- Minor by meningeal arteries (anterior and posterior) - Major by middle meningeal artery (from maxillary artery branch of external carotid artery)
Over what cranial landmark does one find the middle meningeal artery?
- Pterion
Why would injury to pterion be dangerous? What type of bleed can it lead to?
- Pterion overlies the middle meningeal artery, which overlies and supplies blood to the dura. - It could lead to an epidural bleed/hematoma.
What are venous sinuses of brain? List them and explain where they are located.
- Endothelial lines spaces between the periosteal and meningeal layers of the dura. Large veins from around the brain empty here and blood returned to venous circulation 1.) superior sagittal sinus: upper border of falx cerebri 2.) inferior sagittal sinus: inferior edge of falx cerebri 3.) straight sinus: junction of falx cerebri and tentorium cerebelli 4.) transverse sinuses: continuation of superior and straight sinuses 5.) sigmoid sinuses: at petrous bone, transverse sinuses end and become sigmoid sinuses which empty at jugular foramen 6.) occipital sinus: lies in attached border of falx cerebelli 7.) cavernous sinuses: located bilaterally on each side of sella turcica 8.) sphenoparietal sinuses: course along lesser wing of sphenoid bone 9.) superior petrosal sinuses: stretch between cavernous and transverse sinuses 10.) inferior petrosal sinuses: commence at cavernous sinus and drain into jugular foramen - Confluence of sinuses: junction between superior sagittal, straight, occipital and transverse is at the confluence of sinuses located at the internal occipital protuberance
How is CSF volume maintained? Where is it absorbed or drained to?
- CSF is drained into superior sagittal sinus via arachnoid granulations. This is one-directional flow from subarachnoid space into venous circulation.
What are arachnoid granulations?
- They are one-way valves between the arachnoid space and venous sinuses that move CSF into venous drainage. Largest granulations lie in the superior sagittal sinus.
What are the attachments for the falx cerebri?
- Crista galli of ethmoid bone anteriorly - Internal occipital protuberance of occipital bone posteriorly - Joins with tentorium cerebelli on posterior aspect, holding tentorium cerebelli up like tent
Attachments for tentorium cerebelli?
- Clinoid process of sphenoid bone anteriorly - Petrous ridge of temporal bone laterally - At occipital bone posteriorly
Attachment of falx cerebelli?
- occipital bone
What are emissary veins?
- connect venous dural sinuses with veins outside of skull
Course of middle meningeal artery.
- Branches of maxillary artery of external carotid artery and enters skull through foramen spinosum
What is the nerve supply to the dura mater?
- Largely by CN V - Some by CN X and XII
What does the superior sagittal sinus drain into?
- confluence of sinuses
What does the inferior sagittal sinus drain into?
- straight sinus and then into confluence of sinuses
What does the transverse sinuses drain into?
- confluence of sinuses and into sigmoid sinus
What do the confluence of sinuses drain into?
- into sigmoid sinuses
What do sigmoid sinuses drain into?
- Internal jugular veins
Through what foramen does the sigmoid sinus travel?
- Jugular foramen
What cranial nerves would be impacted if venous drainage backed up at sigmoid sinuses? Why?
- CN IX, X and XI - Sigmoid travels through jugular foramen with these cranial nerves.
What is problematic with venous sinus in comparison to veins?
- Sinuses do not have valves. Infections can move in a backward direction
