blood supply to the brain

Question 1

how much of the body weight is the brain?

Answer 1

2%

Question 2

how much of cardiac output, body O2 and total glucose does the brain use?

Answer 2

15% of cardiac output, uses 20% of body O2 and 25% of total body glucose

Question 3

what is the average brain blood flow?

Answer 3

46mL/100g of brain/minute

Question 4

how long does it take for anoxia to lead to unconsciousness?

Answer 4

20 seconds

Question 5

how is blood flow to the brain regulated?

Answer 5

auto-regulation

the brain is more sensitive to high CO2 levels than low O2 levels through central chemoreceptors

Question 6

how are arteries in the brain different to those in the body?

Answer 6

more thin walled, easily blocked/distorted/ruptured

Question 7

how are veins in the brain different to those in the body?

Answer 7

no valves, thin walled, no muscles/elasticity to help return –> drainage relies on gravity

Question 8

how much of the total cerebral blood flow do the internal carotids make up?

Answer 8

80%

Question 9

how much of the total cerebral blood flow do the vertebral arteries make up?

Answer 9

20%

Question 10

explain the path of the subclavian arteries to the vertebral arteries?

Answer 10

subclavian arteries –> transverse foramen of cervical vertebrae –> foramen magnum –> join to form basilar artery

Question 11

what do the vertebral arteries supply?

Answer 11

most of brainstem and posterior 1/3 of cerebral hemispheres

Question 12

why are the anterior and posterior communicating arteries normally closed?

Answer 12

• Right and left internal carotid arteries supply their respective halves of the brain and keeps pressure the same
• Communicating arteries only open when there’s a difference in pressure in pathologies

Question 13

how much of the population is the normal circle of willis seen in?

Answer 13

34.5%

Question 14

name some variations of the circle of willis

Answer 14

• Missing posterior communicating artery – doesn’t affect blood flow. Only becomes problem if one artery is blocked.
• Missing/small anterior communicating/cerebral artery
• Abnormal origin of posterior cerebral arteries from ICA

Question 15

how much of the brain does the anterior circulation supply?

Answer 15

anterior 2/3

Question 16

what are the main branches of the internal carotid artery?

Answer 16

opthalmic
posterior communicating
middle cerebral artery
anterior cerebral artery

Question 17

what does the opthalmic artery supply?

Answer 17

supplies the orbit, retina, optic nerve, choroid. Connects to the external carotid artery

Question 18

what does the posterior communicating connect?

Answer 18

connects carotid and vertebral artery system.

Question 19

what does the middle cerebral artery supply?

Answer 19

supplies the basal ganglia (needed in coordination of movement) and internal capsule (made of white matter tracts - striate arteries), lateral 2/3rds of cerebral cortex (frontal, parietal and occipital lobes)

Question 20

what does the anterior cerebral artery supply?

Answer 20

Internal capsule, medial side of frontal and parietal lobes. Anastomose with MCA

Question 21

what parts of the cerebral cortex does the MCA supply?

Answer 21

the frontal, parietal and the top half of the temporal lobe

o Primary motor, primary somatosensory, speech, language and understanding

Question 22

what part of the cerebral cortex does the ACA supply?

Answer 22

supplies medial wall of the cerebral hemisphere

Question 23

where does the MCA travel?

Answer 23

between the parietal and temporal lobe

Question 24

what branches does the MCA give of and where do they go?

Answer 24

lenticulostriate branches (internal capsule, basal ganglia)

Question 25

what does the primary motor cortex do?

Answer 25

upper motoneurons found here

Question 26

what does the primary somatosensory cortex do?

Answer 26

integration centre for ascending tracts

Question 27

what does Broca's area do?

Answer 27

pre-motor cortex for speech (where speech is produced)

Question 28

what does Wernicke's area do?

Answer 28

integrating and understanding what has been spoken to

Question 29

what does the primary auditory centre do?

Answer 29

where sound is processed (temporal lobe)

Question 30

how much of the brain does the posterior circulation supply?

Answer 30

posterior 1/3 of the brain

Question 31

what are the branches of the posterior circulation?

Answer 31

vertebral, basilar and posterior cerebral artery

Question 32

what are the branches of the vertebral artery and what do they supply?

Answer 32

meningeal - falx cerebri anterior/posterior spinal arteries postrior inferior cerebellar arteries - cerebellum and dorsal medulla of brainstem

Question 33

what are the branches of the basilar artery and what do they supply?

Answer 33

o Anterior inferior cerebellar artery: cerebellum, lateral medulla. o Pontine arteries: supply the pons. o Superior cerebellar arteries: supplies superior cerebellum

Question 34

what does the posterior cerebral artery supply?

Answer 34

o Inferior and medial aspects of temporal and occipital cortex o Thalamus and posterior internal capsule o Midbrain

Question 35

what does the posterior cerebral artery anastomose with?

Answer 35

MCA

Question 36

why is PICA most likely to be blocked by an embolus/blood clot?

Answer 36

one of the first branches of the posterior circulation

Question 37

what spinal tract does PICA not affect?

Answer 37

corticospinal tract

Question 38

what cranial nerves are found near the arteries in the brain?

Answer 38

VI passes underneath the AICA and III comes out at the joint of the basilar and posterior cerebral arteries and SCA

Question 39

where do the superficial cerebral veins cross?

Answer 39

the subarachnoid space | pierce the dura as they enter the intercranial venous sinuses

Question 40

what are arachnoid granulations and what are they for?

Answer 40

allow CSF to drain into venous blood of sinuses but prevent backflow of blood into sub-arachnoid space

Question 41

how are dural sinuses made?

Answer 41

between the periosteal and meningeal layers

Question 42

what blood vessels supply the dural sinuses?

Answer 42

superficial cerebral veins

Question 43

which sinus does the majority of blood in the brain drain into?

Answer 43

superior saggital sinus

Question 44

where is the inferior saggital sinus found?

Answer 44

runs across length of head. Drains into confluence of sinuses into right transverse sinus.

Question 45

describe the venous drainage system in the brain

Answer 45

inferior saggital --> straight --> transverse --> sigmoid

Question 46

what is the cavernous sinus?

Answer 46

large collection of thin walled veins | where the ICA comes in - makes an acute bend so its seen twice

Question 47

why is the ICA seen twice?

Answer 47

makes an acute bend

Question 48

where is the cavernous sinus found?

Answer 48

either side of the pituitary gland

Question 49

what effect can a pituitary adenoma have on the cavernous sinus?

Answer 49

pituitary adenoma can push into the cavernous sinus and compress CN 3

Question 50

which cranial nerves pass through the cavernous sinus?

Answer 50

3, 4 and 6

Question 51

why do spinal arteries need reinforcement and what do they receive reinforcement from?

Answer 51

small so they need reinforcement from lumbar and intercostal arteries to meet metabolic demands radicular arteries from intercostal in the thoracic region lumbar arteries in the lumbar region

Question 52

what is the biggest reinforcing artery?

Answer 52

Great segmental medullary artery (artery of Adamkiewicz)

Question 53

what level is Great segmental medullary artery (artery of Adamkiewicz) found? where is it found?

Answer 53

T9 • Found on left in 65% of population reinforces circulation to 2/3rds of spinal cord

Question 54

what complication can arise during surgery for aortic aneurysm?

Answer 54

may lose all sensation and voluntary movement inferior to level of occlusion bc of blockage of the reinforcing arteries bc the spinal arteries aren’t sufficient

Question 55

what are the types of cerebrovascular incidents/accidents?

Answer 55

• 2 types; extradural or subdural – depends whether the bleed is in or out of the dura

Question 56

what are the major causes of stroke?

Answer 56

atherosclerosis, hypertension, aneurysm, elderly, head injury, alcholics, arteriovenous malformation

Question 57

what are the 3 types of cerebral aneurysms?

Answer 57

saccular fusiform berry

Question 58

how many people develop a brain aneurysm? who is more at risk?

Answer 58

* 1 in 15 people develop a brain aneurysm (not necessarily will rupture – then risk arises) * Women at higher risk 3:2

Question 59

why are cerebral arteries at risk of aneurysms?

Answer 59

• Arteries are so thin --> easy to distort, especially at junctions between arteries (e.g. posterior cerebral artery to basilar)

Question 60

what are symptoms of an MCA stroke?

Answer 60

 Global aphasia – inability to understand what’s being said and produce meaningful speech (not in grammatical order)  Sensorimotor loss on contralateral face, upper limb and trunk – not the legs (anterior cerebral) neglect syndrome

Question 61

what are symptoms of ACA stroke?

Answer 61

o Contralateral sensorimotor loss below waist (legs) o Urinary incontinence o Personality defects (frontal lobe is affected) o Split-brain syndrome (corpus callosum is affected – right brain and left brain don’t communicate with each other)

Question 62

what are symptoms fo PCA stroke?

Answer 62

o Contralateral homonymous hemianopsia o Reading and writing deficits o Impaired memory

Question 63

what is a transient ischaemic attack?

Answer 63

• Temporary loss of brain function (<30 mins) -Sudden onset but resolves within 24 hrs

Question 64

what are TIAs a warning sign of?

Answer 64

heart attack or stroke

Question 65

what are TIA symptoms of the anterior circulation?

Answer 65

 Motor weakness  Hemi-sensory loss  Dysarthria  Transient monocular blindness

Question 66

what are TIA symptoms of the posterior circulation?

Answer 66

Vertigo, Diplopia, Ataxia, Amnesia