Blood Supply to the Brain Flashcards
Why are strokes so serious
3rd most common cause of death in the UK
Leading cause of disabiltiy => 2/3 of stroke survivors become disabled
Huge mortality and morbidity due to
- occlusion of blood flow by clot
- haemorrhage
Both lead to neuronal death
Describe the importance of blood supply in the brain
17% of cardiac output
20% of O2 in the body used in the brain
If blood supply interrupted => rapid loss of consciousness
3mins of interrupted blood supply => irreversible damage
What are the 2 arterial routes into the brain
Internal carotids
Vertebral arteries
Describe the route of the internal carotids into the brain
Common carotid
Internal carotid
S shaped carotid canal into skull
Emerges lateral to sphenoid body next to optic chiasm
Branches into
- Central artery of retina => supplies retina (end artery)
- Opthalmic artery => supplies eye
- Ant cerebral
- Mid cerebral
Describe the route of the vertebral arteries into the brain
Subclavian artery L and R vertebral arteries Transverse cervical foramen Foramen magnum Fuse together into vertebral arteries => basilar arteries Post cerebral artery
What is the function of the transverse foramen in the cervical vertebrae
Ascend up C1-6, allows for safe protective passage of vertebral arteries
Vertebral arteries fuse on ventral pons => basilar artery
Where is the Circle of Willis found
Surrounds optic chiasm and pituitary at brain base
Found in the subarachnoid space
Name the arteries that come off the Circle of Willis
Ant communicating between ant cerebral
Mid cerebral comes off int carotid
Post communicating between int carotid and basilar
Name the arteries that branch off the basilar artery
Post cerebral Sup cerebellar Pontine branches Labyrinthine, supply inner ear Ant inf cerebellar Post inf cerebellar branches off vertebral
Describe the anatomical structure of the cerebellar arteries
All anastamose with each other to supply cerebellum
Describe the areas supplied by the middle cerebral artery
Supplies mainly the LATERAL regions of the cerebrum
- Primary motor (upper limbs and face)
- Primary sensory (upper limbs and face)
- Broca and Wernicke’s speech area in dominant hemisphere
- Part of visual field
What can happen when the MCA is occluded
Contralateral paralysis and sensory deficits of lower face and arm
Aphasia if dominant hemisphere affected
Hemianopia of contralateral visual field (affects thalamus visual cortex tract)
Describe the areas supplied by the anterior cerebral artery
Supplies mainly the MEDIAL regions of the cerebrum
- Frontal lobe (cognition, behaviour and emotion)
- Primary motor (lower limbs and perineum)
- Primary sensory (lower limbs and perineum)
- Internal capusule
What can happen when the ACA is occluded
Contralateral paralysis and sensory deficits of lower limbs and perineum
Cognitive behaviours and emotional problems
Sometimes contralateral face, tongue and upper limb due to inner capsule
Describe the areas supplied by the posterior cerebral artery
Supplies mainly the posterior regions of the brain
- Occipital (visuals)
- Temporal (language and memory)
- Thalamus
What can happen when the PCA is occluded
Memory affected
Contralateral visual field defects
Hemisensory deficits due to thalamus involvement
Describe the overlap in cerebral blood supplies
What can happen in a watershed infarct
ACA and PCA both supply medial rim of the lateral brain surface
- However, they are at the ends of the main arteries
- Affected most by decreased perfusion and BP => Watershed infarct => Stroke
Bilateral weakness of upper and lower proximal limbs
Bilateral visual loss/stupor
Name the 3 deep cerebral arteries and where do they arise from
ACA => anterior choroidal artery
MCA => MCA deep branches
PCA => PCA deep branches
Where do the deep arteries come off the C of W and what do they supply
What happens when the deep artery of the MCA is occluded
ACA and MCA => internal capsule and basal ganglia
PCA => ventral midbrain
MCA via lenticulostriate arteries
Embolus here => lacunar infarcts in end artery
Describe the distribution of the vertebral and basilar arteries
What happens if blood flow is occluded here
Basilar supplies cerebellum and pons
Vertebral supplies medulla
Occlusions
-Instantly fatal => coma due to damage to reticular formation/loss of resp control (damage in resp nuclei)
Cerebellar defects
Cranial nerve defects
Deafness if labyrinthine affected
Infarction of ventral pons => locked in syndrome, loss of all voluntary movements
What are the pros and cons of anastamoses
Pros
-If 1 artery occluded, affected region will still have a blood supply
Cons
-If part of C of W wall weakens => berry aneurysm => subarachnoid haemorrhage
How would you treat a berry aneurysm
Coiled ball of wire inserted into aneurysm to prevent blood from making it bigger
Describe the venous cranial drainage
Intercranial veins in subarachnoid space, flow with cerebral arteries
Pierce arachnoid and meningeal layer => pools into the dural superior sagittal sinus => jugular foramen in post cranial fossa => int jugular
Describe how the structure of the superior sagittal sinus is unique
Between the periosteal and meningeal layers of the dura and lined by endothelium
No valves here
What can happen in a subdural haemorrhage
Slow accumulation of venous blood between dural layers
Often found in the elderly after a fall
Describe the route of dural sinus drainage back into the heart
Sup sagittal sinus => L and R transverse sinus
Inf sagittal sinus => straight sinus => L and R transverse sinus
L and R transverse sinus, cavernous sinus => sigmoid sinus leaves skull via jugular foramen => sup jugular bulb of int jugular => brachiocephalic
Describe the pathway of the middle meningeal artery
How would you locate the MMA in the skull
How would the MMA get damaged
Branch of the maxillary artery => foramen spinosum to supply bones of the vault
Pterion directly above MMA, damage here => burst MMA
What can happen in an epidural haemorrhage
Arterial high pressure bleed fills epidural space
Must be drained, otherwise brainstem compressed
Describe the 3 methods of arterial blood supply to the spinal cord
1 ant spinal artery from superior end of vertebral arteries => fuse to form 1 artery
2 post spinal artery from inferior end of vertebral arteries => no fusion here
Radicular arteries from segmental spinal arteries which branch from aorta in thoracic and lumbar regions and enter via intervertebral foramina
Describe the 4 methods of venous drainage from the spinal cord
1 ant spinal vein
2 posteriorlateral spinal veins
1 posterior spinal vein
Radicular ceins
All anastomose in internal vertebral venous plexus
