4. Blood supply to the CNS Flashcards
What percentage of the brain takes up the following: • body weight • cardiac output • oxygen consumption • liver glucose
- body weight - 2% (1.3kg)
- cardiac output - 10-20%
- oxygen consumption - 20%
- liver glucose - 66%
What are the 2 sources of blood supply to the brain?
- Internal carotid arteries (front)
* Vertebral arteries (back)
Describe the branching of the common carotid and vertebral arteries
• CC bifurcates into internal and external carotid at around level of laryngeal prominence
• EC supplies face and IC goes towards brain
• Vertebral arteries branch off the subclavian arteries
- travel through transverse foramina in the cervical vertebrae
- through foramen magnum into the brain
What is the ventral view of the brain?
- Not the front
* Underneath the brain (inferior view) - like in four-legged animals
Describe the path of the vertebral arteries in the brain
- 2 vertebral arteries run up the bottom (brain stem)
- Join to form the basilar artery
- Bifurcates to form posterior cerebral arteries which curve back
Describe the path of the internal carotid arteries in the brain
- Up to the Circle of Willis
- Middle cerebral arteries head laterally through fissures between frontal, parietal and temporal lobes
- Anterior cerebral arteries branch off heading between medial surfaces of hemispheres
Which arteries connect the main branches in the brain to actually form a Circle (of Willis)
- Anterior communicating artery - joins 2 anterior cerebral arteries
- Posterior communicating arteries (2) - joins internal carotid artery to the posterior cerebral artery
What is formed in the venous system at the point where the 2 layers of the dura mater separate?
Venous sinus
What venous structure runs along the top of the brain between the two folds of the dura?
• Superior sagittal sinus
CSF drained back into venous system here too
What venous structure runs along the bottom of the dural fold?
Inferior sagittal sinus
Where do all the venous sinuses come together?
Confluence of the sinuses
When the venous sinuses join together, where does blood then go?
- From confluence to a transverse sinus
- Sigmoid sinus
- Continuous with internal jugular vein (via jugular foramen)
Define a stroke
- Rapidly developing focal disturbance of brain function of presumed vascular origin
- Lasting more than 24 hours
What proportion of strokes are due to infarctions and haemorrhages?
- 85% infarction
* 15% haemorrhage
Define a transient ischaemic attack (TIA)
- Rapidly developing focal disturbance of brain function of presumed vascular origin
- Resolves completely within 24 hours
(usually resolve in a few minutes - was blockage but thrombosis has broken down)
What is an infarction?
Degenerative changes that occur in tissue following occlusion of an artery
What is cerebral ischaemia?
- Lack of sufficient blood supply (not just oxygen) to nervous tissue
- Permanent damage if blood flow is not restored quickly
- Due to hypoxia/anoxia
What is the difference between and embolism and thrombosis?
Thrombosis
• Formation of a blood clot (thrombus)
• Usually form at places of non-laminar flow
Embolism
• Plugging of a small vessel by material carried from larger vessel
• More proximal occlusion => more devastating
How common is a stroke a cause of death in the UK
3rd most common cause of death
How many survivors of a stroke are permanently disabled/show signs of neurological deficit?
- Disabled - 50%
* Neurological deficit - 70%
What are the risk factors of a stroke?
- Age
- Hypertension
- Cardiac disease
- Smoking
- Diabetes mellitus
Describe the perfusion fields of the brain
- ACA supplies the front 2/3 of the medial part of the hemisphere + superior edge to parietal-occipital sulcus
- MCA supplies the front 2/3 of the lateral part of the hemisphere
- PCA supplies the medial and lateral parts of the posterior part of the hemisphere (occipital lobe and inferior parts of the temporal lobe)
What symptoms can present if the anterior cerebral artery is disturbed?
- Paralysis of contralateral leg (part of motor cortex that controls the leg is more medial)
- Disturbance of intellect, executive function and judgement (abulia - absence of willpower)
- Loss of appropriate social behaviour - aggression, hypersexuality
What symptoms can present if the middle cerebral artery is disturbed?
Classic stroke
• Contralateral hemiplegia (more arms than legs as more lateral part of brain is affected)
• Contralateral hemisensory deficits
• Hemianopia
• Aphasia - left-sided lesion and language centres are more on the left side than the right
