Blood Supply to Brain & Meninges Flashcards
What are the 3 meningeal coverings?
What are they and what do they cover?
- Dura mater
- Arachnoid mater
- Pia mater
They cover the CNS (brain and spinal cord) and act as protective air bags
What is the composition of the dura mater like?
It is a tough fibrous protective layer
There are two layers of dura:
- Outer periosteal layer that is tightly attached to the surface of the skull
- Inner meningeal layer that is in direct contact with the arachnoid mater
What is the composition of the arachnoid mater like?
It is a thin, delicate layer that looks like a spider-web
It is vasular
It does not follow the grooves of the brain so you cannot see sulci and gyri through this layer
What is the composition of the pia mater like?
it is a microscopically thin layer that is closely attached to the cortex of the brain
It follows the gyri and sulci (they are visible through this layer)
Label the 3 meningeal layers
Label the meningeal layers of the brain
What is significant about having two layers of dura?
This allows for dural infoldings only at specific areas
the inner meningeal layer comes away from the outer periosteal layer to form a dural fold
various venous dural sinuses are located within the dural infoldings
What is found within a dural sinus?
Venous blood
Superficial veins drain into the sinuses
CSF enters the sinuses and is reabsorbed into the venous system via arachnoid villi
What are the functions of CSF?
It is produced in the ventricular system of the brain and resembles plasma
It bathes the structures of the CNS (brain and spinal cord) and cushions them
It provides nutrients to the brain and spinal cord
It acts as a shock-absorber
Where is the sub-arachnoid space and what is located within it?
It is between the arachnoid mater and the pia mater
It contains cerebrospinal fluid and blood vessels
What is shown in this image?
What is the purpose of the arachnoid villi?
They are protrusions of the arachnoid mater into the dural layer
Diffusion across the arachnoid granulations into the superior sagittal sinus returns CSF to the venous circulation
What are the 3 main dural folds?
Where are they located?
Falx cerebri:
- crescent shaped fold of dura
- located in the Sagittal plane between the right and left hemispheres
Tentorium cerebelli:
- located between the occipital and temporal lobes and the cerebellum
Falx cerebelli:
- located between the cerebellar hemispheres
What is located within the dural infoldings?
Venous dural sinuses
The main ones are the superior sagittal sinus and the transverse sinus
Label the dural folds and sinuses
Label the dural folds
What are the 2 sites of attachment of falx cerebri?
Anterior attachment:
- crista gali of the ethmoid bone
Posterior attachment:
- occipital bone
What is the relationship between the periosteal and meningeal layers of dura?
They are tightly fused together except at dural venous sinuses and various infoldings (reflections)
What are the 3 main reflections of the dura?
There are 2 large reflections of dura that extend into the cranial cavity:
- Between the cerebral hemispheres - falx cerebri
- Between the cerebrum and cerebellum - tentorium cerebelli
There is a smaller reflection of dura between the cerebellar hemispheres - falx cerebelli
Where is the sub-dural space located?
The space between the arachnoid and the dura
This is a very thin potential space
The dura is tightly attached to the arachnoid, but a space could be created if a vessel was to rupture
Label the meninges of the spinal cord
What is the purpose of the denticulate ligaments?
They are lateral extensions of the pia
They anchor the spinal cord to the arachnoid mater on either side
As the arachnoid is already tightly anchored to the dura, this prevents excessive movement of the spinal cord
What is the difference in the dura in the spinal cord, compared to the brain?
It has NO periosteal component (only meningeal)
It is separated from the bone of the vertebrae by the epidural space
This is a real space, filled with fat
What is located between the pia and arachnoid of the spinal cord?
Subarachnoid space
This is filled with cerebrospinal fluid
What is the difference between a ‘real’ and ‘potential’ space?
Potential space:
- A space between 2 adjacent structures which are usually tightly pressed together
Real space:
- A space which exists all the time
What are the real and potential cranial spaces?
Real spaces:
- subarachnoid space - contains CSF
Potential spaces:
- epidural space (between periosteal and meningeal layers of dura)
- subdural space (between arachnoid and dura)
Why is the cranial epidural and subdural space called a potential space?
Subdural:
- can be opened by the separation of the dura from the arachnoid
Epidural:
- can be opened by the separation of the 2 layers of the dura
This happens due to trauma or pathological processes
What are the real and potential spaces in the spinal cord?
real spaces:
- epidural space - contains fat
- subarachnoid space - contains CSF
potential spaces:
- subdural space (between arachnoid and dura)
What are the 2 pairs of arteries that supply the brain?
How are they connected?
Vertebral arteries and internal carotid arteries
They are connected by the circle of Willis at the base of the brain
Where to the vertebral arteries originate from?
What is their pathway into the skull like?
Origin:
- they are direct branches of the subclavian arteries
Pathway:
- they ascend in the neck through the transverse foramen of the cervical vertebrae
- they enter the skull via the foramen magnum
Fusion:
- the vertebral arteries fuse at the base of the brainstem to form basilar artery
What passes through the foramen magnum with the vertebral arteries?
spinal cord leaves through the foramen magnum
What is the passage of the internal carotid artery like?
Origin:
- it is a branch of the common carotid arteries
Passage:
- they enter the skull via the carotid canals
- They emerge at the floor of the skull, on either side of the optic chiasma
Label the bones and foramen in the inferior view of the skull
What structures pass through these foramina?
What arteries are shown in the drawing?
What are the 3 pairs of cerebellar arteries and where do they originate?
Originate from basilar artery:
- Superior cerebellar artery (SCA)
- Anterior inferior cerebellar artery (AICA)
Originate from vertebral artery:
- Posterior inferior cerebellar artery (PICA)
Label the vessels that make up the Circle of Willis
Label the arteries of the brain
What is the role of the Circle of Willis?
it interconnects the internal carotid and vertebral-basilar system
it ensures compensation of decreased blood flow if one vessel is occluded
(acts as a collateral blood supply)
What are the constituents of the Circle of Willis?
- Anterior, middle and posterior cerebral arteries
- anterior and posterior communicating arteries
- internal carotid arteries
- basilar artery
What is meant by a berry aneurysm?
Why does it occur?
abnormal dilations around the circle of Willis or at the points of arterial branching within the brain
it occurs due to thinning of blood vessel walls, leading to blood pressure causing the walls to balloon
What parts of the brain are more prone to aneurysm?
aneurysms are most common at branching points or where 2 vessels meet
sites prone to aneurysm will have lots of branches
What complication is associated with rupture of a berry aneurysm?
If the aneurysm ruptures, this causes bleeding into the arachnoid space
This is a sub-arachnoid haemorrhage
10% of vascular strokes are caused this way
Label the angiogram of a berry aneurysm
This angiogram shows the vertebral-basilar artery system
Label the angiogram
What system and significant features does it show?
Internal carotid system
it shows the internal carotid artery (ICA) bend as it enters the skull in the carotid canal
It shows the ACA supplying the medial aspect of the hemispheres and the MCA supplying the lateral aspect of the hemispheres
Which cortical areas are supplied by the anterior cerebral artery (ACA)?
- Superior and medial areas of frontal and parietal lobes
- Corpus callosum
(regions in blue)
Which cortical areas are supplied by the middle cerebral artery (MCA)?
- Lateral areas of the frontal, parietal and temporal lobes
(areas in pink)
Which cortical areas are supplied by the posterior cerebral artery (PCA)?
- Occipital lobe
- Inferior and medial surface of temporal lobe
(areas in orange)
Where do the cerebral arteries originate from?
Anterior cerebral artery (ACA) = internal carotid artery
Middle cerebral artery (MCA) = internal carotid artery
Posterior cerebral artery (PCA) = terminal branch of basilar artery
What is meant by deep (or perforating arteries) of the brain?
What are some of them called?
Some of these are called striate arteries
They are branches of the cerebral arteries that supply the grey matter and structures inside the hemisphere
What structures inside the hemisphere are supplied by deep or perforating arteries?
- Deep nuclei
- Deep grey matter
- Internal capsule (major fibre bundle to and from the cerebral cortex)
Identify which areas are supplied by which cerebral artery.
What striate artery is present?
What is meant by a ‘watershed area’ of the brain?
It is a portion of the brain supplied by the distal tips of 2 or more vessels
What condition are watershed regions susceptible to?
Why?
ischaemia (Watershed stroke)
they are susceptible to ischaemia (watershed stroke) when there is decreased systemic blood pressure
they do not receive much blood from either of the 2 vessels usually, so they receive even less when blood pressure falls
What are the 2 different types of veins which drain the brain?
Superficial veins:
- these cover the surface of the cortex
Deep veins:
- these drain the internal surfaces of the brain
Identify which veins are superficial and which are deep.
Label the sinuses
Where does all venous blood from the brain drain into?
Internal jugular veins
What are dural venous sinuses?
How do they form?
They are channels formed when the inner meningeal layer of the dura separates from the outer periosteal layer
They are located within the dural folds
Which vessels drain into the dural venous sinuses?
Vessels from superficial veins drain DIRECTLY into the sinuses
Deep veins bring all the blood into the great cerebral vein of Galen, which then connects to the sinus system
Which sinus connects with the internal jugular vein directly?
sigmoid sinus
Label the dural venous sinuses
What is meant by the ‘confluence of sinuses’?
It is a connecting point of:
- Superior sagittal sinus
- Straight sinus
- Occipital sinus
The blood then drains into the right or left transverse sinus
Label the veins and sinuses
Where do the dural sinuses drain into?
they receive venous blood from the brain and drain into the internal jugular vein
Complete the diagram showing the pathway of venous drainage
Where would the inferior sagittal sinus drain into?
The superficial veins drain into the inferior sagittal sinus
this then drains into the straight sinus
Label the meningeal layers and the blood vessels that pass through them
In what type of injury is the middle meningeal artery vulnerable?
In a fracture of the pterion
This is the area where the parietal, frontal, temporal and sphenoid bones join
Rupture of the middle meningeal artery leads to epidural haemorrhage and creation of a pathological space
What is meant by the bridging veins being briefly in the subdural space?
The subdural space is a potential space
The bridging veins are part of the superficial veins which pierce the arachnoid mater to enter the superior sagittal sinus
They pass through the subdural space
What is the role of the meningeal arteries and veins within the dura?
They supply and drain the dura
Label the joints and features of the lateral skull
Label the vessels, meninges and spaces
What are the 3 types of haemorrhage that can occur in the brain?
- Epidural
- Subdural
- Subarachnoid
What type of haemorrhage is shown here?
How is it caused?
Epidural haemorrhage
this is caused by a torn middle meningeal artery
it causes separation between the skull and the dura
What type of haemmorhage is shown here?
What causes it?
Subdural haemorrhage
This is caused by torn bridging veins
Blood enters the space between the dura and arachnoid
What type of haemorrhage is shown here?
What causes it?
Subarachnoid haemorrhage
Caused by torn cerebral arteries (may be through rupture of berry aneurysm)
It causes blood to leak through the brain tissue and into the subarachnoid space
