BLOOD SUPPLY TO THE CENTRAL NERVOUS SYSTEM Flashcards
what are the demands on the brain
brain makes up 2% body weight 10-20% of CO - very demanding 20% of body O2 consumption 66% of liver glucose brain is very vulnerable if its blood supply is impaired
what are the 2 sources of blood to the brain *
2 internal carotid arteries 2 vertebral arteries - at the back of the neck associated with the cervical vertebrae
describe the path of the carotid arteries *
carotid branches at the adams apple the external carotid is branched and supplies the face and the surface soft tissue the internal carotid goes up into the skull into the anterior part of the cranial cavity and then supplies the anterior part of the circulation
summarise the arterial supply of the brain *
the 2 vertebral arteries are asymmetrical in size they merge to form the Basilar artery which is in front of the pons this splits to form the 2 posterior cerebral arteries (L and R) these are connected to the respective internal carotid arteries via the posterior communicating arteries biggest branch of the internal carotid is the middle cerebral arteries the anterior cerebral artery which branches off the internal carotid artery goes into the longitudinal fissure between cerebral hemispheres - the anterior cerebral arteries are joined by the anterior communicating artery - this is the only artery that is unpaired this all forms the anastomotic - Circle of Willis
summarise the venous drainage of the brain *
the cerebral veins drain into the venous sinuses, the blood then drains down the back of the neck into the internal jugular veins
how are the venous sinuses formed *
the 2 layer dura mater opens up and forms venous sinuses
describe the branching of the subclavian artery *
1st branch is vertebral artery goes through transverse foramen of cervical vertebrae gets to base skull - through foramen magnum and joins the rest of the blood supply
describe the sequence of the pathway of the venous sinuses *
biggest sinus runs across the top of the head - superior sagittal sinus venous blood drains to the confluence of sinuses behind the occipital bone then drains into the sigmoid sinus and the jugular vein
definition of stroke *
rapidly developing focal disturbance of brain function of brain function of presumed vascular origin and of more than 24 hours duration
other name for stroke
cerebrovascular accident - CVA
2 causes of stroke *
infarction - blockage 85% haemorrhage - bleed - 15% (more trauma related)
define a transient ischemic attack - TIA *
rapidly developing focal disturbance of brain function of presumed vascular origin that resolves completely within 24 hours
DESCRIBE a TIA *
warning sign people describe it as ‘having a turn that resolved within 24hrs it indicative of a risk of stroke - blood clot/atherosclerotic material breaks up cause a temporary blockage of blood supply but cleared quickly so don’t have stroke ??
define an infarction *
degenerative changes which occur in tissue following occlusion of an artery
DESCRIBE an infarction *
area of dead tissue because of loss of blood supply - because of loss of nutrients and O2
define cerebral ischemia *
lack of sufficient blood supply to nervous tissue resulting in permenant damage if blood flow is not restored quickly because of lack of nutrients and oxygen
what is hypoxia/anoxia
lack or no oxygen
what are the 2 causes of occlusions *
thrombosis embolism
describe thrombosis and how it can cause a stroke *
formation of a blood clot (thrombus) static blood can start forming thrombi, and turbulent flow throws the clot to head causing stroke
describe embolism *
plugging of a small vessel by material carried by larger vessels - eg thrombi from the heart or atherosclerotic debris from the internal carotid (hardening of the artery/fatty deposits on lining of the artery breaks away and goes up to smaller vessels - stroke) can be air/fat
in a post mortem what do healthy and unhealthy vessels look like
healthy - brown unhealthy - yellow (atherosclerotic fatty deposits) - problem when it is where the vessels divide
what would a brain with a thromboembolitic blockage look like
asymmetry lost differentiation of colour infarction if to the origin of middle cerebral artery would take out most of the lateral part of the brain
epidemiology of stroke
3rd commonest cause of death 100000 deaths UK pa 50% survivors permanently disabled 70% show obvious neurological deficit
risk factors for stroke *
age
hypertension - cause haemorrhagic stroke, especially if weak vessel wall/aneurism
cardiac disease - static blood around valves increase chance of thrombi
smoking
DM - vascular component increase the risk of stroke
describe the perfusion field for anterior cerebral aterery *
frontal lobe lower limbs - with muscular control field is all the way back to the parietal occipital sulcus small strip of cortex along midline
describe the perfusion field for the middle cerebral artery *
lateral part of the brain including the primary motor cortex supplies torso, head and abdomen
describe the perfusion field for the posterior cerebral artery *
occipital and inferior of temporal lobe
explain the neurological deficit that arises from disruption of the anterior cerebral artery *
paralysis of contralateral side - legs more than arms and face disturbance of intellect, executive function and judgement (abulia) - overaggressive, hypersexual - because interferes with the frontal lobe lose appropriate social behaviour
what is abulia
an absence of willpower or an inability to act decisively
describe the neurological deficit that arises from disruption of the middle cerebral artery *
classic stroke contralateral hemiplegia - arm more than leg might get complete hemiplegia because it might affect the fibres that go down the neck rather than the surface of the motor cortex contralateral hemisensory deficits - sensory defects hemianopia - vision controlled at back of head so can easily be disturbed aphasia - L sided legion - difficulty in recall of appropriate words - expressive aphasia
describe the neurological deficit that arises from disruption of the posterior cerebral artery *
visual defects - occipital lobe homonymous hemianopia - loss of visual field, same side both eyes because only one side of the cortex has been affected visual agnosia - object and face recognition - unable to identify something
effect to damage to Wernicke’s area
loss ability to comprehend speech
describe lacunar infarcts *
lacune is a small cavity in the brain - found post mortem representing strokes in life deficit is dependant on anatomical location - no clinical representation of small bleeds necessarily caused by hypertension brain’s natural response gets rid off blood and dead tissue - leave hole
list the different types of haemorrhagic strokes *
extradural/epidural subdural subarachnoid intracerebral
casue of extradural stroke *
trauma - rupture bv supply to the meninges - push the dura from the skull, increase the intracranial pressure - push down on brainstem
timescale of effect of extradural stroke *
immediate effect - artery
describe a subdural haemorrhage *
trauma - delayed effects - bridging veins are ruptured slow bleed - no effects immediately therefore difficult to detect - leave A and E and die in 24 hours blood more widely spread - accumulate over surface of brain - blown lobe
describe subarachnoid haemorrhages *
all vessels in subarachnoid space - rupture of berry aneurisms everything covered by blood in the subarchnoid space difficult to treat because you need to get into the vessels
describe intracerebral haemorrhages *
bleed in brain tissue itself - because of spontaneous hypertensive
compare the effects of a CVA in the brainstem and the cortex *
CVA in cortex is focal and there is chance for recovery CVA in brainstem is catastrophic - pathways and nuclei are close together so loads of things are effected by a small legion etc
does a haematoma always cause a stroke
no
what is the effect of raising the intercranial pressure on the reticular activating system
would affect the sleep wake cycle- explain drowsiness
affect of haematoma in the frontal lobe
affects motor pathways
what symptoms would show that the cerebellum was affected
dizzy, couldn’t move hand, fine movement, ataxia
