Blood supply to the Brain Flashcards
Brain
- Has immense metabolic needs
Brain:
- 2% of body weight
- receives 17% of cardiac output
- uses 20% of oxygen consumed by whole body
RAPID LOSS OF CONSCIOUSNESS IF BLOOD SUPPLY INTERRUPTED
What are the 2 arterial routes to the brain?
- Internal carotids
- Vertebral Arteries
Internal Carotid Artery
Forms the Anterior circulation
Course: Very sinuous course lateral to body of sphenoid bone emerging adjacent to optic chiasm.
- Enters the Cranium via the Carotid Canal into the Middle Cranial Fossa
-
Opthalmic Artery
- pre-terminal branch; passes into orbit via the optic foramen
- major blood supply to the eye
-
Central artery of the retina
- end-artery; occulsion leads to blindness as it’s the only supply to there
- Hypophyseal arteries - arise from intra-cavernous section of ICA to supply the neurohypophysis
- 2 terminal branches (ICA terminates lateral to the Optic Chiasm and gives rise to):-
- Anterior cerebral - the two are linked by the anterior communicating artery
- Middle Cerebral
Vertebral arteries
Ascend through the upper six cervical vertebrae to enter the cranium via the FORAMEN MAGNUM
Course: Run along the lateral surface of the medulla before fusing together on the ventral surface of the Pons to form the Basilar artery.
Main branches:
-
Posterior cerebral artery-
- principal terminal branch of the basilar, supplies the occipital lobe of the cerebral hemisphere
- posterior communicating arteries pass between here and the internal carotid artery on each side
-
Basilar artery
- fusion of left and right vertebral artery
- Left & right verterbral arteries individually
Branches of the subclavian arteries in the root of neck
Circle of Willis:
- Connects the anterior and posterior circulations
- Surrounds the optic chiasm and pituitary on base of brain and lies under the Internal Capsule
- Arterial supplies from the Internal Carotid and the Vertebral Arteries anastomose together here
- Anastomoses provide an alternative route for arterial supply if normal route is occluded
Blood supply to the Cerebellum and the Peduncles
- Superior cerebellar artery,
- anterior cerebellar artyery
- inferior cerebellar artery
Why is the Basilar artery important to the PONS?
- It has lots of pontine branches that come off it (the Basilar) that supply the PONS
What is the blood supply to the inner ear?
Labryinthine Artery, which is a branch of the Anterior Inferior Cerebellar Artery
What from the Circle of Willis supplies the hypothalamic area, the basal ganglia and the internal capsule?
Small perforating arteries that arises from the Circle of Willis supply these areas
Middle Cerebral Artery
- Largest of the three cerebral arteries
- Passes into the lateral fissure and supplies the lateral aspect of the cerebral hemisphere
- Commonly affected in stroke
- Supplies the lateral cortical areas including; primary motor and sensory areas, receptive speech area, auditory area and Broca’s expressive speech area.
Occlusion of the MCA leads to:
- Contralateral paralysis & sensory and motor deficits of lower face area
- Aphasia (if dominant hemisphere, usually the left)
- Hemianopia (loss of part of visual field, not being able to see either the R or L from the centre of your field of vision) of contralateral visual fields (thalamo-visual cortex tract)
Anterior Cerebral Artery
- Courses medially above the optic nerve and passes into the great longitudinal fissure, between the frontal lobes of the cerebral hemispheres.
-
Supplies:
- motor and sensory cortices for the lower limb
- narrow lateral band of frontal and parietal cortices
- medial surfaces of the frontal and parietal lobes
- corpus callosum
Occlusion of the ACA leads to:
- Paralysis and sensory deficits to CONTRALATERAL leg and perineum
- Mental confusion and dysphasia
- *Sometimes contralateral face, tongue and upper limb due to internal capsule
Posterior Cerebral Artery
- Principal terminal branch of the basilar artery
-
Supplies
- occipital and temporal lobes of the cerebral hemisphere
Occlusion of the PCA leads to:
- Blindness in contralateral visual field
- Hippocampal memory problems, but usually only short term
What supplies the Medial rim of lateral surface of the Cerebral Hemispheres?
Anterior and posterior cerebral arteries
- rim is susceptible to watershed infarcts as it is supplied by the most distal branches that come off the cerebral arteries.
Watershed infarcts - around the rim; common in large heart attacks with large drop in B.P
What kind of shape is the Carotid canal?
S shaped
What supplies the Internal Capsule and parts of the Basal Ganglia?
- Supplied by relatively small “central” or “perforating” arteries that branch from the Circle of Willis, largely supplied by the anterior and middle cerebral arteries.
-
Occlusion or rupture of these arteries can cause:
- contralateral motor and sensory deficits
What supplies the Ventral Midbrain
- Posterior Central or
- perforating arteries (supply the inner tissues of the brain)
What are the Internal Capsule and Basal Ganglia supplied by?
Perforating Arteries
-
Recurrent Artery of Heubner
- comes off the Ant. Cerebral Artery
- @ lvl of Optic Chiasm usually
-
Lenticulostriate arteries
- arise @ commencement of the MCA
What makes up the Brainstem?
- Medulla
- Pons
- Cerebellum
What supplies the Pons and Cerebellum?
Basilar Artery
What supplies the Medulla?
Vertebral Artery
Occlusion of the Vertebral and Basilar arteries lead to?
- Instantly fatal due to coma (reticular formation) and loss of respiratory control
- Cerebellar defects
- Cranial nerve defects
- Deafness if labyrinthine artery affected
- Infarction of ventral pons, leads to loss of all voluntary movements except eyes, the senses are spared - LOCKED IN SYNDROME
Which artery supplies which bit of the brain?
ACA
MCA
PCA
Anastamoses
Good?
provide an alternative route for arterial supply if normal route occluded
When are anastamoses bad?
Aneurysms
Berry aneurysm:
- sub-arachnoid haemorrhage can occur if this bursts
- v high mortalitly and morbidity
- can occur anywhere around C of Willis
- it is a swelling of the blood vessel
coiling of the berry aneursym can clot off the aneurysm - surgical procedure
Hemiparesis
Weakness of the entire Left OR Right side of the body
Hemiplegia
most severe form of hemiparesis
complete paralysis of half of the body
Where do intracranial veins drain into?
Dural venous sinuses
e.g. Superior Sagittal venous sinus
Venous Drainage of the brain
- Deep and superficial veins of the brain drain into the dural venous sinuses then into internal jugular via the jugular foramen in posterior cranial fossa
Venous sinuses are enclosed by dural folds and lined by endothelium
How does the sigmoid sinus exit the skull?
via the Jugular foramen into the “superior jugular bulb” (inital dilated bit of) the Internal Jugular Vein
Middle Meningeal Artery
- branch of the maxillary artery
- enters the intracranial region via foramen spinosum
- supplies bones of the vault
What can usually happen to the Pterion and what are its consequences?
Usally fractured since it is weak
can lead to MMA damage and bleeding
causing an EXTRA-DURAL HAEMORRHAGE
What is the blood supply to the spinal cord?
comes from high up and has to travel all the way down the spinal cord
2 different sources:
- Spinal arteries
- posterior
- anterior
- Radicular arteries
This dual system makes stroke of the spinal cord v rare
Spinal Arteries
where do they come from?
Posterior spinal arteries:
- from the Vertebrals or Posterior Inferior Cerebellar
Anterior Spinal arteries:
- from the Vertebrals
Radicular arteries
where do they come from and what do they enter through?
- From segmental arteries;
- which branch from the aorta in thoracic and lumbar regions
- Enter via the Interverbral Formaina
- Come in with the nerve roots
- become more prominent the further away you go from the brain
*
Venous drainage of Spinal cord
- Posterior spinal vein
- Anterior spinal vein
- posteriolateral spinal vein
- radicular veins
All drain into the INTERNAL VERTEBRAL VENOUS PLEXUS
What are the 2 types of stroke?
Haemorrhagic:
- bleeding
Ischaemic:
- Lack of blood
- Occluded artery
Extradural haemorrhage
- between skull and dura,
- e.g. from meningeal arteries may be higher pressure, more prolonged, push onto brain
Subdural haemorrhage
- between dura and arachnoid,
- e.g. from superior cerebral vein, low pressure, slow accumulation, clots in subdural space and pushes on brain
COMMON IN THE ELDERLY
Sub-arachnoid haemorrhage
- between arachnoid and pia,
- e.g. from ruptured aneurysms in Circle of Willis, sudden, very painful, one cause of a “stroke”, bleeds into sub-arachnoid space
Intracerebral haemorrhage
- within brain tissue itself
- another cause of stroke
- usually occurs when on blood thinners etc
