Blood supply to the CNS

Question 1

how much of CO does the brain use despite only being 2% of TBW?

Answer 1

10-20%

Question 2

what is the glucose consumption of the brain?

Answer 2

66%

Question 3

what is the oxygen consumption of the brain?

Answer 3

20%

Question 4

what are the two sources of blood to the brain?

Answer 4

1) internal carotid arteries

2) vertebral arteries

Question 5

what is the route of the internal carotid arteries (ICA)?

Answer 5

internal branch of the common carotid

goes through the carotid canal into the base of the skull

Question 6

what is the route of the vertebral arteries (VA)?

Answer 6

branch of the subclavian artery, goes through the vertebral transverse foramina and into the foramen magnum to fuse and become the basilar artery

Question 7

what arteries does the Circle of Willis consist of?

Answer 7

strictly speaking:

• anterior cerebral arteries
• anterior communicating artery
• middle cerebral arteries
• posterior cerebral arteries
• posterior communicating arteries

Question 8

how is venous drainage mediated in the brain?

Answer 8

• cerebral veins
• venous sinuses
• dura mater
• internal jugular

Question 9

what is the definition of stroke ?

Answer 9

rapidly developing focal disturbance of brain function of vascular origin

lasts > 24hrs

Question 10

what are the main 2 causes of stroke?

Answer 10

haemorrhage (15%)

infarction (85%)

Question 11

how does an infarction lead to stroke?

Answer 11

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)

Question 12

what is cerebral ischaemia (infarction cause)?

Answer 12

lack of sufficient blood supply to nervous tissue
leads to permanent damage if not restored promptly

n.b. different to anoxia/hypoxia

Question 13

epidemiology of stroke?

Answer 13

3rd most common cause of death in the UK

half are left with a permanent disability, most have an obvious neurological deficit

Question 14

the risk factors of stroke

Answer 14

• age
• hypertension
• cardiac disease
• smoking
• diabetes mellitus

Question 15

what is a Transient Ischaemic Attack (ITA)?

Answer 15

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

Question 16

stroke pathology

Answer 16

loss of differentiation of grey and white matter in brain

Question 17

what are the three main arteries that supply the cortex?

Answer 17

anterior, middle and posterior cerebral artery

Question 18

anterior cerebral artery (ACA)

Answer 18

supple the top anterior part unto the parieto-occipital fissure, going in medially into the centre above the diencephalon

Question 19

posterior cerebral artery (PCA)

consequence of stroke, infarct, haemorrhage

Answer 19

supplies the posterior part of the cortex i.e. occipital lobe

therefore stroke can cause:
- homonymous hemianopia contralateral side

Question 20

middle cerebral artery (MCA)

consequence of stroke?

Answer 20

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

Question 21

what is the result of the occlusion of the cerebral arteries?

Answer 21

may cause loss of ability to use/feel the legs (paraplegia)

Question 22

disturbance of the Anterior Cerebral Artery

Answer 22

• 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

Question 23

disturbance of the MCA

Answer 23

“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) )

Question 24

Left sided lesion on MCA consequence

Answer 24

Aphasia- Inability to understand or produce speech depending on Broca (speech) and Wernicke (understanding)

Question 25

disturbance of Posterior Cerebral Artery

Answer 25

visual deficits

• homonymous hemianopia (loss of half of vision field on same side of both eyes)
• visual agnosia (inability to recognise things)

Question 26

2 types of injuries in the brain

Answer 26

lacunar infarcts

haemorrhagic strokes

Question 27

lacunar infarcts
(lacuna= small cavity)

Answer 27

• 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

Question 28

the types of haemorrhagic stroke

Answer 28

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

Question 29

what are the 3 layers of the meninges?

Answer 29

1) dura mater (outer most)
2) arachnoid mater
3) pia mater

Question 30

what types of bleeds occur in the meninges?

Answer 30

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)

Question 31

which is the biggest venous sinus?

Answer 31

superior sagittal sinus

Question 32

what may cause drowsiness after a subdural haemorrhage (cerebral vein)?

Answer 32

damaged reticular activating system (responsible for regulation of consciousness)

Question 33

what may cause weakness after a subdural haemorrhage?

Answer 33

squashed somatomotor areas.