Blood Supply to the Brain Flashcards
What 2 arteries is the blood supply to the brain derived from?
How do these arteries enter the skull?
Internal carotid artery:
- this is a branch of the common carotid artery
- it enters the skull via the carotid canal
Vertebral artery:
- this is a branch of the subclavian artery
- it enters the skull via the foramen magnum
What is the difference in how the subclavian artery arises on the right and left sides?
- the left subclavian artery (and common carotid) arise directly from the arch of the aorta
- on the right side, the brachiocephalic trunk arises from the arch of the aorta
- this then divides into the right subclavian and common carotid arteries
Where does the vertebral artery originate from?
How does it enter the cranium and what does it fuse once it is there?
- it is the first branch of the subclavian artery
- it enters the transverse foramen of C6 and ascends through the transverse foramina of higher vertebrae
- it enters the cranium via foramen magnum
- at the level of the pontomedullary junction, the 2 vertebral arteries fuse to form the basilar artery
Where does the posterior cerebral artery arise from?
the posterior cerebral artery arises from the basilar artery as it bifurcates
Where do the anterior and middle cerebral arteries arise from?
- the internal carotid artery terminates by dividing into the anterior and middle cerebral arteries
- the ACA is a smaller branch than the MCA
What is the role of the anterior and posterior communicating arteries?
they connect the cerebral arteries
Anterior communicating artery:
- connects the left and right anterior cerebral arteries
Posterior communicating artery:
- connects the middle cerebral artery with the posterior cerebral artery on each side
What are the 3 cerebellar arteries and where do they arise from?
Posterior inferior cerebellar artery (PICA):
- this is a branch of the vertebral artery
Anterior inferior cerebellar artery (AICA):
- this arises at the point where the 2 vertebral arteries fuse to form the basilar artery
Superior cerebellar artery:
- this arises from the basilar artery as it bifurcates at the level of the pontomesencephalic junction
Where does the middle cerebral artery arise from?
How does it travel in the brain and which regions does it supply?
- it is the larger of the 2 terminal branches of the internal carotid artery
- the other branch is the anterior cerebral artery
- it passes laterally to supply blood to the lateral convexity of the cerebral hemisphere, including parts of the temporal, parietal, frontal and occipital lobes
What are the branches of the middle cerebral artery?
- lenticulostriate branches
- orbitofrontal artery
- pre-central (pre-Rolandic) and central (Rolandic) branches
- anterior & posterior parietal arteries
- angular artery
- anterior, middle & posterior temporal arteries
What is the role of the lenticulostriate branches of the MCA?
- these are a group of small arteries that supply the putamen, caudate nucleus and anterior limb of the internal capsule
- they are the first branches of the MCA
What is supplied by the orbitofrontal artery of the MCA?
- it supplies part of the frontal lobe
- it supplies the orbital gyri and the inferior frontal gyrus
What is supplied by the pre-central (pre-Rolandic) and central (Rolandic) arteries?
- these arteries supply different regions of the frontal lobe
- the Rolandic branch runs alongside the central sulcus
What is supplied by the angular artery?
- this supplies the angular gyrus
- this is part of the inferior parietal lobule that has a role in language and number processing, memory and reasoning
How can the middle cerebral artery be divided?
It can be divided into 4 anatomical segments (M1-M4)
- M1 - horizontal segment
- M2 - insular segment
- M3 - opercular segment
- M4 - cortical segment
Where does the M1 (horizontal) segment of the MCA run to and from?
- it runs from the origin at the internal carotid artery to the bifurcation of the MCA at the limen insulae
- the limen insulae is located just as the MCA passes out through the lateral sulcus by the insula
Where does the M2 (insular) segment of the MCA run to and from?
- it runs from the bifurcation at the limen insulae to the cortical branches
- there are 2 branches formed at the limen insulae - one runs superiorly and one runs inferiorly
- both of these branches run along the insula
Where do the M3 (opercular) and M4 (cortical) segments of the MCA run?
- M3 describes the opercular branches that run within the lateral fissure
- M4 describes the cortical branches that emerge from the lateral fissure onto the surface of the cortex
Which branches arise from the M1 (horizontal) segment of the MCA?
- lenticulostriate arteries
- anterior and polar temporal arteries
- uncal artery
Which branches arise from the superior and inferior terminal branches of the M2-M4 segments of the MCA?
Superior terminal branch:
- orbitofrontal artery
- pre-Rolandic artery
- Rolandic artery
Inferior terminal branch:
- anterior & posterior parietal arteries
- angular artery
- anterior, middle & posterior temporal arteries
In general, what territories are supplied by the MCA?
- majority of the lateral surface of the hemispheres
- internal capsule
- basal ganglia
Where does the anterior cerebral artery arise from it?
How does it travel in the brain?
- it is the smaller of the 2 terminal branches of the internal carotid artery
- it passes anteromedially towards the midline in the longitudinal fissure
- it then passes anterior to the genu of the corpus callosum and then curves posteriorly
Which structures are supplied by the anterior cerebral artery?
- it supplies blood to the medial aspect of the hemisphere, including parts of the frontal and parietal lobes
- it supplies the precentral and postcentral gyri
- it supplies the olfactory bulb and tract, anterior hypothalamus, parts of the caudate nucleus, internal capsule and putamen
What are the 2 major branches of the ACA?
- callosomarginal artery
- pericallosal artery
What is supplied by the callosomarginal artery?
- the paracentral lobule and portions of the cingulate gyrus
What is supplied by the pericallosal artery?
- this continues along the dorsal margin of the corpus callosum to supply the precuneus
- this is part of the parietal lobe that is caudal to the paracentral lobule
What are the 3 segments of the anterior cerebral artery?
A1:
- from origin of ACA at internal carotid artery to the anterior communicating artery
A2:
- from the anterior communicating artery to the origin of the callosomarginal artery
A3:
- this runs distal to the callosomarginal artery and is also the pericallosal artery
What are the 2 main branching patterns of the anterior cerebral artery?
- A2 gives off the callosomarginal artery and continues as the pericallosal artery
Cortical branches arise from the callosomarginal artery
- The callosomarginal artery is absent
Cortical branches arise directly from the pericallosal artery
(Cortical branches go over by about 1cm onto the lateral aspect of the brain)
Why can occlusion of the anterior cerebral artery lead to paralysis and loss of sensation of the contralateral leg?
- the ACA supplies the precentral gyrus, which processes sensory information from the contralateral leg
- it also supplies the postcentral gyrus, which initiates motor control of the contralateral leg
- occlusion of the ACA leads to loss of motor control (paralysis) and loss of sensation of the contralateral leg
What are the main branches of the anterior cerebral artery?
- anterior communicating artery
- medial striate artery (recurrent artery of Heubner)
- orbital branches
- frontopolar branches
What is the function of the anterior communicating artery?
What arises from this vessel?
- it connects the right and left anterior cerebral arteries at the level of the optic chiasm
- a group of small arteries arise from the anterior communicating and anterior cerebral arteries and penetrate the brain tissue perpendicularly
these supply blood to the anterior hypothalamus - including preoptic and suprachiasmatic areas
Where do intracranial aneurysms commonly occur in the anterior circulation?
What can this present with?
- at the junction between the anterior communicating artery and anterior cerebral artery
- these aneurysms can cause visual defects due to their proximity to the optic chiasm
What is supplied by the medial striate artery (recurrent artery of Heubner)?
- anteromedial part of the head of the caudate nucleus
- parts of internal capsule
- putamen
- septal nuclei
it arises from the ACA at the level of the optic chaism and penetrates the perforated substance
What is supplied by the orbital and frontopolar branches of the ACA?
Orbital branches:
- supply the orbital and medial surfaces of the frontal lobe
Frontopolar branches:
- supply the medial aspects of the frontal lobe
- (Both orbital and frontopolar branches arise from the A2 segment of the ACA)*
What is the origin of the posterior cerebral artery?
How does it travel from its origin?
- it is formed from the terminal bifurcation of the basilar artery
- it courses around the midbrain towards the dorsal (posterior) aspect of the brain
What is supplied by the posterior cerebral artery?
- most of the midbrain
- thalamus
- subthalamic nucleus
How can the posterior cerebral artery be divided in to 4 segments?
P1:
- from origin at bifurcation of basilar artery to origin of posterior communicating artery
P2:
- from posterior communicating artery to the quadrigeminal cistern at the posterior border of the lateral midbrain
- can be divided into P2A and P2P segments
P3:
- from quadrigeminal cistern to the origin of the calcarine and parieto-occipital arteries
P4:
- this describes the terminal branches of the PCA - calcarine and parieto-occipital
What are the 4 major branches of the posterior cerebral artery?
What do they supply?
- anterior temporal branches
- posterior temporal branches
- parieto-occipital branches
These supply the temporal lobes and medial /inferior occipital lobe
- calcarine branches
These supply the primary visual cortex
What small arteries can arise from the P2 segment of the PCA to supply the midbrain?
Quadrigeminal arteries
- these supply the inferior and superior colliculi on the dorsal aspect of the midbrain
What is meant by the vertebro-basilar circulation and what does it supply?
- this system includes the 2 vertebral arteries, the basilar artery and their branches
- it supplies the medulla, pons, midbrain and cerebellum
At the level of the medulla, which 3 branches are given off by the vertebral artery?
- anterior spinal artery
- posterior spinal artery
- posterior inferior cerebellar artery (PICA)
What regions / structures are supplied by the PICA?
Regions of the lateral medulla:
- spinothalamic tract
- dorsal & ventral spinocerebellar tracts
- descending sympathetic tract
- descending tract of trigeminal nerve (V)
- nucleus ambiguus
Cerebellum:
- region of the vermis
- inferolateral surface of cerebellum
What syndrome results drom occlusion of the PICA?
Lateral medullary (Wallenberg’s) syndrome
- there is damage to the lateral medulla in the region supplied by the PICA
- damage to the nucleus ambiguus leads to dysphonia, dysarthria and dysphagia
- this is due to the nucleus ambiguus innervating the laryngeal muscles
- there is also loss of coordination / balance (ataxia) and vertigo
- there is loss of contralateral P&T sensation if lateral STT is involved
- sensory disturbances from contralateral side of the body and ipsilateral side of the face
What are the branches of the basilar artery?
- anterior inferior cerebellar artery (AICA)
- labyrinthine artery
- pontine arteries
- superior cerebellar artery (SCA)
- posterior cerebral artery
What is supplied by the AICA?
- ventral and inferior surface of the cerebellum
- some of the lateral surface of the pons
What is supplied by the superior cerebellar artery?
- it supplies the rostral pons, caudal midbrain and superior surface of the cerebellum, including:
- portions of the superior and middle cerebellar peduncles
- medial & lateral lemniscus
- part of spinal trigeminal nucleus & tract
- spinothalalmic tract
What is surrounded by the circle of Willis?
What forms this structure?
- it surrounds the optic chiasm and infundibulum of the pituitary gland
- it is formed by the anastomosis of the branches of the internal carotid artery and the terminal branches of the basilar artery
What is the clinical importance of the circle of Willis?
if the blood supply in either the internal carotid arteries or vertebro-basilar system is compromised, the circle of Willis provides a collateral blood supply
What are striate arteries and where do they arise from?
- they are small arteries that supply the deep tissue of the brain
- they arise from the posterior cerebral artery and both the anterior & posterior communicating arteries
What is a berry aneurysm?
Where are they most likely to rupture?
- a condition in which weakness in the wall of a cerebral artery or vein causes a localised dilation or ballooning of the blood vessel
- an aneurysm occurring in the posterior circulation is more likely to rupture
- this includes the basilar artery, vertebral artery & posterior communicating artery
What are some causes of berry aneurysms?
- connective tissue disorders
- polycystic kidney disease
- arteriovenous malformations
- untreated hypertension
- tobacco smoking
- cocaine & amphetamines
- head trauma
- heavy caffeine intake
- intravenous drug use
- infection of the arterial wall from bacteraemia
What are the symptoms of berry aneurysm?
- typically, they are asymptomatic until they rupture and then may cause:
- sudden and unusually severe headache
- nausea & vomiting
- vision impairment
- loss of consciousness
- no symptoms at all
What type of haemorrhage can a ruptured berry aneurysm lead to and what are the symptoms of this?
subarachnoid haemorrhage
- typically presents with a sudden onset “thunderclap” headache, as well as:
- nausea & vomiting
- drowsiness, confusion & loss of consciousness
- visual abnormalities
- meningism
- dizziness
Where, specifically, is CSF produced and how is this related to blood supply?
- CSF is produced by the choroid plexus within the ventricular system
- CSF production is an active process that requires a blood supply
- the lateral ventricle produces the most CSF as it is the largest and contains the greatest amount of choroid plexus
What is the blood supply to the lateral ventricle and IIIrd ventricle?
- anterior choroidal artery
this is a branch of the middle cerebral artery (MCA) at the junction between the MCA and ICA
- lateral posterior choroidal artery
- medial posterior choroidal artery
these are branches of the posterior cerebral artery (P2)
What is the blood supply to the IVth ventricle?
- anterior inferior cerebellar artery (AICA)
- posterior inferior cerebellar artery (PICA)
