Blood Supply to CNS Flashcards
Where does the common carotid ascend and where does it bifurcate?
Common carotid ascends on side of the neck and bifurcates at carotid sinus into external and internal carotids.
Where does the internal carotid ascend after bifurcating?
Through the carotid canal and it has a twisting path through foramen lacerum.
Why is the internal carotid so tortuous?
To accomodate for the twisting of the head
What are the branches of the internal carotid artery?
It gives 3 main branches:
The opthalmic artery
The posterior communicating artery
The anterior choroidal artery
It then continues before dividing into 2 terminal branches:
Middle cerebral artery (MCA)
Anterior cerebral artery (ACA)
What membranes does the internal carotid pierce?
The dura mater before moving forward and upward to pierce the arachnoid mater and enter the subarachnoid space.
Where do vertebral arteries ascend?
Along the transverse processes of the vertebrae before entering the cranial cavity through foramen magnum.
Which brain layers do the vertebral arteries pierce?
The dura and arachnoid mater.
What branches do the vertebral arteries give off?
Anterior spinal artery
Posterior spinal artery
Posterior inferior cerebellar artery
Both unite at pontomedullary junction to form the basilar artery.
Where does the basilar artery move?
Ascends along ventral groove of pons
What are the branches of the basilar artery?
Pontine arteries
Anterior inferior cerebellar artery
Superior cerebellar artery
Posterior cerebellar artery (exits midbrain at terminal branches)
Where do vertebral arteries arise from?
The subclavian arteries
Where do the vertebral arteries unite to form the basilar artery?
At the pontomedullary junction
Where are the anterior (carotid) and posterior (vertebral) systems connected?
At the circle of willis
What is the purpose of the circle of willis?
It provides redundancy for collateral circulation.
Which blood vessels form the circle of willis?
Anterior+posterior communicating arteries
Where is the circle of willis located?
Anterior to the midbrain
under the cerebral hemispheres
in interpeduncular fossa
within the subarachnoid layer.
What fraction of people have a complete circle of willis?
1/3rd of people
Which arteries supply the midbrain?
The basilar artery
Posterior cerebral artery
Superior cerebellar artery
Which arteries supply the pons?
Pontine branches of basilar artery
Superior cerebellar artery
Anterior inferior cerebellar artery
Which arteries supply the medulla oblongata?
Vertebral arteries
Basilar artery
Anterior spinal arteries
Posterior spinal arteries
Posterior inferior cerebellar artery
Which arteries supply the cerebellum?
Superior cerebellar artery
Anterior inferior cerebellar artery
Posterior inferior cerebellar artery
Where does the anterior spinal artery originate and where does it go?
Descends from vertebral arteries in anterior spinal fissure and supplies the ventral 2/3rds of the spinal cord
What does the anterior spinal artery supply?
The anterior 2/3rds of the spinal cord
Lower median medulla
Which spinal cord segments are underperfused by the anterior spinal artery?
T4/L1
Why are there underperfused structures in the spinal cord?
Due to the lack of pressure in the circulation (only 1 artery goes down this artery).
Where does the posterior spinal artery arise from and where does it go?
Arises from vertebral arteries or posterior inferior cerebellar arteries (variation) and descends the spinal cord behind posterior roots to supply dorsal 1/3rd of the spinal cord
Which spinal segments are underperfused by the posterior spinal artery?
T1, 2, and 3
What do segmental arteries do?
They enter intervertebral foramina to reinforce blood flow of anterior and posterior spinal arteries.
What arteries do segmental arteries give rise to?
Anterior and posterior radicular arteries
What is the largest segmental artery and where deos it arise from?
The artery of adamkiewicz which arises from the aorta and supplies T10/T11
Which arteries commonly cause ischaemic stroke?
The middle cerebral arteries are commonly involved.
What percentage of cerebrovascular accidents are strokes?
80%
What causes ischaemic stroke?
Clots decrease blood flow and lead to irreversible cell death
What are extracerebral haemorrhages?
Bleeding between calvaria and brain.
How can extracerebral haemorrhages be fixed?
It can be fixed by ligating the blood vessel and draining the blood out.
What are the types of extracerebral haemorrhages?
Epidural
Subdural
Subarachnoid
How do extracerebral haemorrhages cause damage?
They compress the brain increasing intracranial pressure
What causes intracerebral haemorrhage?
High blood pressure and damaged artery leaks into brain tissue. Vessel causing this can not be ligated.
Which artery is commonly involved in intracerebral haemorrhage?
The middle cerebral artery
What are the 3 types of extracerebral haemorrhages?
Extradural haematoma
Subdural haematoma
Subarachnoid haematoma
What causes extradural haematoma?
Blow to the temporal bone and rupture of the middle meningeal artery.
What is the characteristic symptom of extracerebral haemorrhages?
Lucid interval which is a brief loss of consciousness followed by hours of decreasing consciousness.
What happens to dural layers during haemorrhages?
They rupture to create space. (normally they are held together by sutural ligaments)
What typically causes subdural haematomas?
Minor injury such as sudden deceleration causing a rupture of bridging vein (cerebral vein).
What kind of shape do extradural haematomas take?
Lemon-shaped
What kind of shape do subdural haematomas take?
Crescent shaped (banana)
Is the leak fast or slow in subdural haematomas?
Slow (Vein)
Is the leak fast or slow in extradural haematomas?
Fast (artery)
What is the typical symptom associated with subdural haematomas?
Fluctuating levels of consciousness with fall history
What causes subarachnoid haematomas?
Sudden rupture of berry aneurysms (Most commonly in circle of willis) caused by bried rise in BP.
What symptom is associated with subarachnoid haematomas?
Blood in subarachnoid space detected in CSF and a sudden/severe headache (thunderclap headache).
Which blood vessel rupture is associated with bladder dysfunction?
Anterior cerebral artery occlusion
What dysfunctions are caused by anterior cerebral artery occlusion?
Motor cortex ischaemic damage results in contralateral weakness in lower limb and pelvic floor muscles. (hemiparesis and bladder dysfunction)
Sensory cortex ischaemic damage results in contralateral lower limb sensory deficits.
Damage to prefrontal cortex results in behavioral abnormalities associated with prefrontal cortex (organisation of complex behaviour, volition, motivation etc)
What dysfunctions are caused by middle cerebral artery occlusion?
Superficial branches:
Head neck arm weakness
Contralateral head, neck, arm sensory defects
Non-fluent aphasia (Broca’s area)
Fluent aphasia (Wernicke’s area)
Deep branches:
Movement disorders (Basal ganglia)
What important structures are supplied by the middle cerebral artery?
Superficial:
Motor cortex (head, neck, arms)
Sensory cortex (head, neck, arms)
Wernicke’s and Broca’s areas
Deep:
Basal ganglia
What important structures are supplied by the posterior cerebral artery?
Superficial:
Occipital lobe
Splenium of corpus callosum
Hippocampus/amygdala
Deep:
Thalamus
What deficits are associated with stroke caused by occlusion of the posterior cerebral artery?
Loss of half of the visual field input.
Visual interpretation defects (difficulty reading but not writing)
Possible emotional behaviour changes (amygdala and hippocampus)
Hemisensory loss
How are veins in the brain to the rest of the body?
Veins do not follow arteries in the brain.
Veins of the brain do not have valves (bidirectional flow is allowed)
What pathway does blood take from the brain to the lungs?
They drain brain parenchyma.
Meninges -> sinuses -> internal jugular veins -> brachiocephalic vein -> superior vena cava -> heart -> lungs
Which veins drain the brain?
Superficial cerebral veins
Deep cerebral veins
What do superficial cerebral veins drain?
Cortical surfaces (Superior, middle, and inferior cerebral veins)
What are the branches of the middle cerebral vein?
Vein of Trolard
Vein of Labbe
What structures do deep cerebral veins drain?
Deep internal structures (internal cerebral veins, basal vein, and great cerebral vein)
