Blood supply to the CNS Flashcards
how much of CO does the brain use despite only being 2% of TBW?
10-20%
what is the glucose consumption of the brain?
66%
what is the oxygen consumption of the brain?
20%
what are the two sources of blood to the brain?
1) internal carotid arteries
2) vertebral arteries
what is the route of the internal carotid arteries (ICA)?
internal branch of the common carotid
goes through the carotid canal into the base of the skull
what is the route of the vertebral arteries (VA)?
branch of the subclavian artery, goes through the vertebral transverse foramina and into the foramen magnum to fuse and become the basilar artery
what arteries does the Circle of Willis consist of?
strictly speaking:
- anterior cerebral arteries
- anterior communicating artery
- middle cerebral arteries
- posterior cerebral arteries
- posterior communicating arteries
how is venous drainage mediated in the brain?
- cerebral veins
- venous sinuses
- dura mater
- internal jugular
what is the definition of stroke ?
rapidly developing focal disturbance of brain function of vascular origin
lasts > 24hrs
what are the main 2 causes of stroke?
haemorrhage (15%)
infarction (85%)
how does an infarction lead to stroke?
the occlusion of an artery leads to degenerative changes to the tissues
can be due to thrombosis (solid clot) or embolism (plugging of small debris)
what is cerebral ischaemia (infarction cause)?
lack of sufficient blood supply to nervous tissue
leads to permanent damage if not restored promptly
n.b. different to anoxia/hypoxia
epidemiology of stroke?
3rd most common cause of death in the UK
half are left with a permanent disability, most have an obvious neurological deficit
the risk factors of stroke
- age
- hypertension
- cardiac disease
- smoking
- diabetes mellitus
what is a Transient Ischaemic Attack (ITA)?
rapidly developing focal disturbance of brain function of vascular origin
however resolves in < 24 hrs (completely in even minutes)
there is a temporary blockage
the precursor to a full-blown stroke
stroke pathology
loss of differentiation of grey and white matter in brain
what are the three main arteries that supply the cortex?
anterior, middle and posterior cerebral artery
anterior cerebral artery (ACA)
supple the top anterior part unto the parieto-occipital fissure, going in medially into the centre above the diencephalon
posterior cerebral artery (PCA)
consequence of stroke, infarct, haemorrhage
supplies the posterior part of the cortex i.e. occipital lobe
therefore stroke can cause:
- homonymous hemianopia contralateral side
middle cerebral artery (MCA)
consequence of stroke?
supplies the outer lateral portion of the cortex and some part under the diencephalon
i.e. lateral side of PMC and somatosensory cortex
stroke:
- Contralateral hemiplegia upper body, face and upper limbs (refer to homonculus)
- Contralateral hemisensory deficits
- Hemianopia
- Broca’s aphasia
what is the result of the occlusion of the cerebral arteries?
may cause loss of ability to use/feel the legs (paraplegia)
disturbance of the Anterior Cerebral Artery
- paralysis of the contralateral lower limb
- distrusted intellect, executive function and judgement (collectively: aboulia)
- loss of appropriate social behaviour
- loss of sensation
due to supply to PMC and PSC
disturbance of the MCA
“classic stroke”
- contralateral hemiplegia (arm>leg)
- contralateral hemisensory deficits
- hemianopia (blindness over half of field of vision)
- aphasia due to left sided lesion (inability to understand or produce speech depending on Broca (speech) and Wernicke (understanding) )
Left sided lesion on MCA consequence
Aphasia- Inability to understand or produce speech depending on Broca (speech) and Wernicke (understanding)
disturbance of Posterior Cerebral Artery
visual deficits
- homonymous hemianopia (loss of half of vision field on same side of both eyes)
- visual agnosia (inability to recognise things)
2 types of injuries in the brain
lacunar infarcts
haemorrhagic strokes
lacunar infarcts (lacuna= small cavity)
- appear in deep structures due to small vessel occlusion
- often occur in basal ganglia (but deficit depends on anatomical location)
- area that has been infracted is cleared by phagocytosis leaving the lacuna)
- associated with chronic hypertension
the types of haemorrhagic stroke
1) extradural- due to trauma with immediate effect
2) subdural- due to trauma with delayed effects
3) subarachnoid- due to ruptured aneurysms (congenitally weak vessels e.g. Berry aneurysm)
4) intracerebral- due to spontaneous hypertensive events/bleeding
what are the 3 layers of the meninges?
1) dura mater (outer most)
2) arachnoid mater
3) pia mater
what types of bleeds occur in the meninges?
1) extradural- arterial bleed (middle meningeal)
2) subdural- venous bleed (cerebral vein)
3) subarachnoid bleed (Berry aneurysms: ACA, AcomA, MCA i.e CoW arteries)
4) intracerebral (basal ganglia, thalamus, pons, cerebellum)
which is the biggest venous sinus?
superior sagittal sinus
what may cause drowsiness after a subdural haemorrhage (cerebral vein)?
damaged reticular activating system (responsible for regulation of consciousness)
what may cause weakness after a subdural haemorrhage?
squashed somatomotor areas.
