Week 1: Lecture 4 - Blood supply to the brain Flashcards
What % of our oxygen is used by the brain?
20%
What are 4 possible causes of focal cerebral lesions?
- Vascular (most common)
- Tumour
- Abscess
- Hydrocephalous - excess CSF causes increased intracranial pressure
What is a TIA ?
transient ischaemic attack
-stroke that lasts less than 24 hrs
what is a stroke?
neurological deficit of vascular origin, lasting more than 24hrs
What is herniation?
occurs when brain tissue, blood and cerebrospinal fluid shifts from their normal position inside the skull
What are the two main pairs of arteries that surround the brain and what are they connected by?
- vertebral artery
- internal carotid artery
connected by the circle of willis at the base of brain
Which artery does the vertebral artery branch of?
subclavian
Which foramina do the vertebral arteries travel through to reach the base of the brainstem?
- ascend through the transverse foramen of the cervical vertebrae in the neck
- enter skull via foramen magnum
Vertebral arteries fuse at the base of the brainstem to form what artery?
basilar artery
Which artery is the internal carotid a branch of?
common carotid artery
How does the internal carotid artery enter the skull
via carotid canals
Before the vertebral artery ascends through the foramen magnum and fuses into the basilar artery, what branches does it give off?
- PICA (posterior inferior cerebellar artery)
- Anterior spinal artery
- posterior spinal arteries
- AICA (anterior inferior cerebellar artery)
What does the anterior spinal artery supply?
anterior aspect of spinal cord
What is the origin of the PICA?
is variable
-can be from the PICA or straight from vertebral
What are the numerous tiny branches of the basilar artery called? where are they located?
- pontine branches
- in the pon
What arteries branch off from the basilar artery?
- SCA - superior cerebella artery
- PCA - terminal branch of the basilar artery
What do the SCA and PCA supply?
SCA- superior cerebellum
PCA - posterior cerebellum
What does the AICA and PICA supply?
AICA - Anterior, inferior aspect of cerebellum
PICA - Posterior, inferior aspect of cerebellum
What are the 3 branches from the internal carotid?
- ACA (anterior cerebral)
- ICA (inferior cerebral)
- MCA (middle cerebral)
Where is the ICA?
lateral to the optic chiasma
What does the MCA and ACA supply?
ACA - anterior and medial aspect of cerebrum
MCA - middle and lateral portions of cerebrum
What arteries is the circle of willis made up of?
- ACA, MCA, PCA
- Anterior and posterior communicating arteries
- internal carotid arteries
- basilar artery
What is the circle of willis and what is its function?
- a closed anastomotic loop at base of brain
- creates collateral circulation
- ensures compensation of decreased blood flow if one vessel is occluded
What structures does the circle of willis surround?
optic chiasma and hypothalamus
What are the 6 possible variations of the circle of Willis?
- Occasionally, the anterior communicating artery is absent
- Both anterior cerebral arteries may arise from one internal carotid artery (10%)
- The posterior communicating artery may be absent or hypoplastic (undeveloped) on one side (10%)
- Both posterior communicating arteries may be absent or hypoplastic
- The posterior cerebral artery maybe absent or hypoplastic on one side
- Both posterior cerebral arteries may be absent or hypoplastic, the anterior cerebral arteries may arise from a common trunk
What is an aneurysm?
when there is a weakening in the wall of a blood vessel, causing it to balloon or widen abnormally
Where are berry aneurysms more common?
Areas of branching e.g circle of willis
Where is there a characteristic bend in the ICA?
When the ICA enters the carotid canal
What is the relationship between the cranial nerves and blood supply?
If there is a blockage or rupture of one of these blood vessels, we will have functional impairment of the nerves supplied by these blood vessels
what is another word for the ACA and which cortical areas does it supply?
- orbitofrontal artery
- supplies superior and medial arteries of frontal and parietal lobes
- corpus callosum
what is another word for MCA and which cortical areas does it supply?
- frontobasal artery
- supplies lateral areas of frontal, temporal and parietal lobes
What does the PCA supply?
- occipital lobe
- inferior and medial surface of temporal lobe
What are the striate arteries?
- deep perforating arteries
- supply deeper structures of the brain
- branch from MCA
What do the deep perforating arteries/ striate arteries supply?
- deep nuclei
- deep grey matter
- some white matter - internal capsule
- major descending motor pathway
what is the internal capsule
major fibre bundle made of white matter
to and from cerebral Cortex
What is meant by watershed areas?
regions that receive dual blood supply from distal areas of adjacent cerebral arteries e.g ACA-MCA watershed or MCA-PCA watershed
why are watershed areas susceptible to ischaemia?
- if there is a decrease in systemic blood pressure
- blood will not reach these distal arteries
- watershed stroke
What are the two groups of veins that drain the brain?
superficial veins
deep veins
What do superficial veins drain?
the cortex of the brain and superior white mater straight into the dural sinuses
what do deep veins drain?
internal structures of the brain into the great cerebral vein then ultimately into the confluence of sinuses
Where are dural venous sinuses located?
within dural inholdings
what are the names of the 7 sinuses that drain into the confluence of sinuses?
- superior sagittal sinus
- inferior sagittal sinus
- straight sinus
- right and left transverse sinus
- sigmoid sinus
- cavernous sinus
What is the clinical significance of the cavernous sinus?
- many infections can reach ad spread here
- can have an effect on many structures e.g optic chiasm, pituitary gland, ICA, many CNs
- cuts in the ‘danger triangle’ of the face can cause infection
How are veins in the face connected to the cavernous sinus?
via ophthalmic veins
What are the symptoms of cavernous sinus thrombosis?
headaches, oedema of the eyeball, numbness of the face, palsies (motor deficits) of cranial nerves
A tear in which artery would cause an epidural haemorrhage?
torn meningeal artery - causes a separation between skull and dura
A tear in which artery would cause a subdural haemorrhage?
torn bridging vein- causes a separation between the dura and arachnoid
A tear in which artery would cause a subarachnoid haemorrhage?
torn cerebral artery
