blood supply to the brain and the meninges Flashcards
what are the meningeal layers of the brain and spinal cord?
dura, arachnoid and pia mater
what is a characteristic feature of the dural mater?
dural infoldings
how can you detect blood supply to the brain?
branches, circle of willis and territories of supply can be seen on an angiogram
what are meninges?
they are protective airbags around the brain and spinal cord
what is the most superficial meningeal layer and where is it found?
the dural mater and is just deep to the skull and covers spinal cord as well
what is the arachnoid mater?
the intermediate layer
what is the pia mater?
it covers the cortex - it is microscopically thin and follows the sulci and gyri
what are the characteristics of dural mater?
tough, fibrous, protective layer
what are the characteristics of arachnoid mater?
spider web like, thin and delicate and vascular layer and cannot see all the sulci and gyri if this is still present `
how is the dural attached to the skull?
very tightly - no gap between the skull and layer or with the arachnoid. There is an outer periosteal layer and inner meningeal layer
what are dural infoldings?
there are specific places where these layers separate and reflect - double layered dura that protrudes into the cranial cavity at specific points
what is created by the dural infoldings?
channel/space - venous dural sinus - veins drain into these along with CSF - reabsorbed into the venous system through a projection of arachnoid called arachnoid villi/granulations - protrusions of the arachnoid layer
what is the space between the arachnoid and pia mater?
a space - subarachnoid space - CSF contained in here
what does CSF resemble?
plasma of blood - bathes all structures of the CNS
what are the functions of the CSF?
cushion the brain, shock absorber, and provides with nutrients
where is CSF produced?
ventricular system of the brain
what are the dural folds?
falx cerebri, falx cerebelli and tentorium cerebelli
what is the falx cerebri?
it is found the sagittal plane separating the right and the left hemispheres - crescent shaped and protrudes into cranial cavity
where is the tentorium cerebelli?
between the temporal and occipital lobe on top of the cerebellum
what is the falx cerebelli?
it is found between the two cerebellum hemispheres and is smaller protrusions of the dural mater
where is the transverse sinus?
it is found in the transverse plane on either side and is attached to the tentorium cerebelli
how will dural mater appear on MRI?
shiny
the falx cerebri has two points of attachment, where are these?
anteriorly (protrusion of the ethmoid bone on cribriform plate) and posteriorly (occipital bone)
where is the epidural space and what is it in SC?
it is a fat filled space that is found between the dural and the vertebrae
what is the subarachnoid space ?
space deep to arachnoid mater that is filled with CSF
what are denticulate ligaments?
they are lateral extensions of the pia mater that anchor the spinal cord to the arachnoid to prevent excessive movement
what are real spaces?
the epidural (SC only)and subarachnoid spaces as they are filled with fat or CSF
what are potential spaces?
the subdural or space above dura as it is not filled with anything except in pathology - potentially blood
where is the middle meningeal artery found?
in the subdural space
why does the brain need a large blood supply?
neural tissue has a high metabolic rate and therefore although the weight of the brain is only 2% of the total body weight it uses 20% of the blood supply
what is the epidemiology of stroke?
it is a common neurological deficit of vascular origin that occurs in 1 in 100 people over the age of 65
what are the two arteries that supply the brain?
internal carotids and vertebral - these are connected at the base of the brain and at the circle of Willis
internal carotids
where do the vertebals pass through?
the transverse foramen in the neck (cervical vertebrae) and the foramen magnum to enter skull with the SC
what is the fusion between the two vertebral arteries at the bottom of the brainstem called?
the basilar artery
what does the external carotid artery supply?
blood supply to the skin and the muscles of the face and then internal to the brain
where does the internal carotid course?
carotid canal at base of temporal bone
where does the internal travel?
wiggling path to the floor of the skull
what are the vertebral arteries branches of?
subclavian arteries
what is the internal carotid a branch of?
the common carotid
what is the optic chiasm?
it is where the two optic nerves fuse at the ventral surface of the brain
where is the basilar artery formed?
at the base of the pons
how is the anterior spinal artery formed?
it is a single artery made from the branches of the vertebral arteries that come down and fuse to form one - all the way down the surface of anterior spinal cord
what are the posterior spinal arteries formed from?
the paired arteries are also from the vertebral arteries - one off each down the posterior SC
what arteries supply the posterior cerebellum?
the posterior inferior cerebellar arteries - paired and branch off vertebrals
how are the transverse pontine arteries formed?
they come off the basilar artery and are paired and they travel horizontally along the pons
what supplies the superior cerebellum and how are they formed?
the superior cerebellar arteries - paired and branch off the basilar at the level of the end of the pons
what is the last branch of the basilar artery?
it is the branch that comes off above the level of the cerebellum and supplies the cerebrum - it is paired and is the posterior cerebral artery
what arteries come off at the level of the medulla - pontine junction in the brainstem?
the anterior inferior cerebellar arteries come off the basilar - paired
what branches come out of the internal carotid?
the internal carotids ascend in the neck and enter the skull through the carotid canal on either side of the optic chiasm. They send branches to the lateral brain (paired middle cerebral artery) and anterior branches to the base of the frontal lobes (anterior cerebral arteries) which are paired.
where is the circle of willis found?
surrounding the optic chiasm and hypothalamus
what does the circle of willis connect and why?
it connects the internal carotid and the basilar arteries, it ensures compensation of decreased blood flow when a vessel is occluded
what are the constituents of the circle of willis?
the internal carotid arteries and the basilar, the anterior, middle and posterior cerebral arteries and the anterior and posterior communicating arteries
what do the paired posterior communicating arteries connect?
the middle cerebral and posterior cerebral arteries
what does the anterior communicating arteries connect?
the anterior cerebral arteries
what is the importance of the circle of willis?
if one vessel is occluded then supplies collateral blood supply, and helps to distribute the blood evenly
what are some common variations of the circle of willis?
where the AICA arise from - basilar or vertebral, both anterior cerebral arteries leading into one
where are berry aneurysms likely to occur?
at branching points - points of weakness so prone to aneurysm
what is a berry aneurysm?
it is a thinning of the vessel walls and because of it’s shape it is called a berry. Rupture of these can cause haemorrhage which can be subarachnoid. This is a vascular stroke type.
what are common sites of berry aneurysm?
abnormal dilations around the circle of willies or at points of arterial branching
how can you see the bend in the internal carotid?
the bend as it enters the carotid canal is seen by an angiogram
what happens in an angiogram?
you inject dye into a vessel and follow its course
what are two branches of the posterior cerebral?
the temporal and the calcarine branch
where is the carotid canal?
in the cavernous sinus in nasal cavity
where are the coiled branches of the MCA found?
in the lateral sulcus
what does occlusion of a cerebral vessel lead to?
loss of function of that territorial area
where does the ACA supply?
it goes to the medial aspect of the frontal and parietal lobes, and some superior tips, and the corpus callosum
what supplies the lateral areas of the parietal frontal and temporal lobes?
the MCA
where does the PCA supply?
the occipital lobe and the inferior and medial surface of the temporal lobe
what is anterior to the central sulcus?
the pre-central gyrus which is a large amount of grey matter
what happens to the PCG if the artery is blocked?
mostly supplied by MCA - if this is blocked will result in loss of function
what are deep arteries?
they are branches of the main cerebral arteries that perforate areas of grey matter and supply deep grey matter nuclei in the brain
what are the characteristics of deep arteries and how can this be a problem?
they are small and delicate meaning that they are likely to rupture of occlude and therefore can result in loss of function in the area that they supply
what are some deep arteries called?
striate arteries
what is the internal capsule?
it is a major fibre bundle to and from the cerebral cortex
what structures are supplied bu the deep arteries inside the hemisphere?
deep nuclei, grey matter, internal capsule and supplies will include the descending motor pathways
what are watershed areas?
they are the portion of the brain that is supplied by the distal tips of two or more vessles
why are watershed regions susceptible to ischaemia?
systemic decrease in blood pressure means that these areas are vulnerable to damage as little blood in either vessel - watershed stroke
what are the two main watersheds in the brain?
the MCA-PCA and ACA-MCA watersheds
where are superficial veins?
they are covering the cortex
what drains the internal surfaces of the brain?
the deep veins
where does all blood from veins end up?
the internal jugular vein
what is a confluence?
where all the dural venous sinuses meet
what are sinuses?
they are channels formed at the point of separation between the periosteal layer and the meningeal layer of dural mater
where is the inferior sagittal sinus?
at the inferior border of the falx cerebri
what occurs in the sinuses?
venous blood flow
what directly connects with the IJV?
the sigmoid sinus which continues from the transverse sinus
how does blood from the veins reach the sinuses?
superficial - drain directly into the sinus which go to the confluence - transverse (if not straight there) - sigmoid sinus - IJV
deep - all drain into the great cerebral vein / great vein of Galen via internal cerebral veins - straight - confluence - transverse - sigmoid - IJV
where do the sinuses go after the sinus system?
the IJV
how does the IJV leave the skull?
the jugular foramen
what follows the tentorium cerebelli?
the transverse sinus
what can / cannot be seen in the arachnoid?
see all vasculature but not all sulci and gyri
where is the MMA?
supplies the dura - is found overlying a portion of bones called pterion and is just anterior to the upper ear
how does a epidural haemorrhage result?
pathological space filled with blood - middle meningeal artery rupture between dural layer and skull
what are bridging veins and what pathology are these associated with?
they are cerebral veins that drain into the sinus - will briefly pierce the arachnoid to enter the sinus - they are briefly in the subdural space and if these rupture then is a subdural haemorrhage
what can cause a subarachnoid heamorrhage?
cerebral arteries and veins below the arachnoid layer that rupture
what colour does leaking fluid appear and what does it do?
it appears white and can push the brain to the side
what is blood in the subdural space usually?
typically venous blood
what is the suture between frontal and parietal bone?
coronal suture
what is the suture between occipital parietal lobes?
lamboid suture
what projects into the sinuses?
the arachnoid villi
