BLOOD SUPPLY TO THE CENTRAL NERVOUS SYSTEM

Question 1

what are the demands on the brain

Answer 1

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

Question 2

what are the 2 sources of blood to the brain *

Answer 2

2 internal carotid arteries 2 vertebral arteries - at the back of the neck associated with the cervical vertebrae

Question 3

describe the path of the carotid arteries *

Answer 3

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

Question 4

summarise the arterial supply of the brain *

Answer 4

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

Question 5

summarise the venous drainage of the brain *

Answer 5

the cerebral veins drain into the venous sinuses, the blood then drains down the back of the neck into the internal jugular veins

Question 6

how are the venous sinuses formed *

Answer 6

the 2 layer dura mater opens up and forms venous sinuses

Question 7

describe the branching of the subclavian artery *

Answer 7

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

Question 8

describe the sequence of the pathway of the venous sinuses *

Answer 8

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

Question 9

definition of stroke *

Answer 9

rapidly developing focal disturbance of brain function of brain function of presumed vascular origin and of more than 24 hours duration

Question 10

other name for stroke

Answer 10

cerebrovascular accident - CVA

Question 11

2 causes of stroke *

Answer 11

infarction - blockage 85% haemorrhage - bleed - 15% (more trauma related)

Question 12

define a transient ischemic attack - TIA *

Answer 12

rapidly developing focal disturbance of brain function of presumed vascular origin that resolves completely within 24 hours

Question 13

DESCRIBE a TIA *

Answer 13

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 ??

Question 14

define an infarction *

Answer 14

degenerative changes which occur in tissue following occlusion of an artery

Question 15

DESCRIBE an infarction *

Answer 15

area of dead tissue because of loss of blood supply - because of loss of nutrients and O2

Question 16

define cerebral ischemia *

Answer 16

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

Question 17

what is hypoxia/anoxia

Answer 17

lack or no oxygen

Question 18

what are the 2 causes of occlusions *

Answer 18

thrombosis embolism

Question 19

describe thrombosis and how it can cause a stroke *

Answer 19

formation of a blood clot (thrombus) static blood can start forming thrombi, and turbulent flow throws the clot to head causing stroke

Question 20

describe embolism *

Answer 20

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

Question 21

in a post mortem what do healthy and unhealthy vessels look like

Answer 21

healthy - brown unhealthy - yellow (atherosclerotic fatty deposits) - problem when it is where the vessels divide

Question 22

what would a brain with a thromboembolitic blockage look like

Answer 22

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

Question 23

epidemiology of stroke

Answer 23

3rd commonest cause of death 100000 deaths UK pa 50% survivors permanently disabled 70% show obvious neurological deficit

Question 24

risk factors for stroke *

Answer 24

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

Question 25

describe the perfusion field for anterior cerebral aterery *

Answer 25

frontal lobe lower limbs - with muscular control field is all the way back to the parietal occipital sulcus small strip of cortex along midline

Question 26

describe the perfusion field for the middle cerebral artery *

Answer 26

lateral part of the brain including the primary motor cortex supplies torso, head and abdomen

Question 27

describe the perfusion field for the posterior cerebral artery *

Answer 27

occipital and inferior of temporal lobe

Question 28

explain the neurological deficit that arises from disruption of the anterior cerebral artery *

Answer 28

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

Question 29

what is abulia

Answer 29

an absence of willpower or an inability to act decisively

Question 30

describe the neurological deficit that arises from disruption of the middle cerebral artery *

Answer 30

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

Question 31

describe the neurological deficit that arises from disruption of the posterior cerebral artery *

Answer 31

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

Question 32

effect to damage to Wernicke’s area

Answer 32

loss ability to comprehend speech

Question 33

describe lacunar infarcts *

Answer 33

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

Question 34

list the different types of haemorrhagic strokes *

Answer 34

extradural/epidural subdural subarachnoid intracerebral

Question 35

casue of extradural stroke *

Answer 35

trauma - rupture bv supply to the meninges - push the dura from the skull, increase the intracranial pressure - push down on brainstem

Question 36

timescale of effect of extradural stroke *

Answer 36

immediate effect - artery

Question 37

describe a subdural haemorrhage *

Answer 37

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

Question 38

describe subarachnoid haemorrhages *

Answer 38

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

Question 39

describe intracerebral haemorrhages *

Answer 39

bleed in brain tissue itself - because of spontaneous hypertensive

Question 40

compare the effects of a CVA in the brainstem and the cortex *

Answer 40

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

Question 41

does a haematoma always cause a stroke

Answer 41

no

Question 42

what is the effect of raising the intercranial pressure on the reticular activating system

Answer 42

would affect the sleep wake cycle- explain drowsiness

Question 43

affect of haematoma in the frontal lobe

Answer 43

affects motor pathways

Question 44

what symptoms would show that the cerebellum was affected

Answer 44

dizzy, couldn’t move hand, fine movement, ataxia