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brs (phase 1b) > (neuro) cerebral vasculature > Flashcards

(neuro) cerebral vasculature Flashcards

1
Q

what are the perfusion demands of the brain?

A

10-20% of the cardiac output
20% of the body’s oxygen consumption
66% of the liver glucose

= requires a rich blood supply to keep up with the high metabolic demand

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2
Q

what percentage of the total body weight is the brain?

A

2%

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3
Q

why is the brain very vulnerable if the blood supply is impaired?

A

brain requires a rich blood supply to keep up with the high level of metabolic activity

(i.e. if supply impaired, metabolic activity also slows)

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4
Q

how much of the total cardiac output is directed towards the brain?

A

10-20%

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5
Q

how much of the total oxygen consumption is directed towards the brain?

A

20%

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6
Q

how much of the total liver glucose is directed towards the brain?

A

66%

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7
Q

why does the brain have such huge perfusion demands?

A

to keep up with the high metabolic demands

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8
Q

how heavy is the brain?

A

1.4 - 1.5kg

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9
Q

what are the two components that make up blood supply to the brain?

A

anterior supply and posterior supply

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10
Q

describe the anterior blood supply to the brain

A

the brachiocephalic artery gives rise to the common carotid artery

the CCA bifurcates at the level of the laryngeal prominence into the external and internal carotid arteries

the external carotid artery supplies the structures of the face

the internal carotid artery supplies the cranial cavity by travelling up into the cranium via the carotid canal

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11
Q

describe the posterior blood supply to the brain

A

the subclavian artery gives rise to the vertebral artery

the vertebral artery goes up posterior through the transverse foramen of the cervical vertebrae

the vertebral artery rise to the skull base and via the foramen magnum, enters the cranial cavity

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12
Q

what does the brachiocephalic artery give rise to?

A

common carotid artery

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13
Q

into what and when do the common carotid arteries bifurcate?

A

into the R+L internal and external carotid arteries

at the level of the laryngeal prominence (Adam’s apple)

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14
Q

what does the external carotid artery supply?

A

supplies structures of the face

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15
Q

what does the internal carotid artery supply?

A

structures within the cranial cavity

gives rise to part of the circle of Willis

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16
Q

what does the subclavian arteries give rise to?

A

vertebral arteries

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17
Q

how does the internal carotid artery enter the cranial cavity?

A

via the carotid canal

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18
Q

through which foramen does the vertebral artery travel?

A

transverse foramen of the cervical vertebrae

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19
Q

how does the vertebral artery enter the cranial cavity?

A

via the foramen magnum

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20
Q

which vertebral segment is the vertebral artery associated with?

A

cervical

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21
Q

why is it important that the vertebral arteries are associate with the vertebrae?

A

the bony processes protect the delicate artery

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22
Q

where is the circle of Willis found?

A

base of the brain

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23
Q

why is it important that the circle of Willis is an anastomotic circuit?

A

if there is a blockage anywhere in the circle, there is a chance of compensatory blood flow from the other side

= so blood supply to brain not completely impaired

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24
Q

what is an anastomotic circuit?

A

all the vessels are joined together in one circuit

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25
Q

what are the two main feed arteries of the circle of Willis?

A

internal carotid artery (anterior)

vertebral artery (posterior)

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26
Q

describe the structure of the posterior component of the circle of Willis

A

the two vertebral arteries join to foem the basilar artery

basilar artery gives rise to smaller, pontine arteries laterally

basilar artery also bifurcates into two posterior cerebral arteries

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27
Q

what do the posterior vertebral arteries fuse to form?

A

basilar artery

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28
Q

what does the basilar artery give rise to?

A

two posterior cerebral arteries

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29
Q

which cerebral structure is closely linked to the basilar artery?

A

pons

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30
Q

describe the structure of the anteior component of the circle of Willis

A

the internal carotid artery gives rise to the middle cerebral artery and the anterior cerebral artery

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31
Q

what are the two branches of the internal carotid artery?

A

main branch = middle cerebral artery

second branch = anterior cerebral artery

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32
Q

into which fissure does the anterior cerebral artery travel?

A

longitudinal fissure

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33
Q

from where are atherosclerotic plaques common in the circle of Willis?

A

from the point where the common carotid artery bifurcates

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34
Q

give one example of how vessels in the circle of Willis would get blocked

A

artherosclerotic plaques originate from the point where the common carotid artery bifurcates

commonly travel up the neck into the circle of Willis via the internal carotid artery obstructing blood flow

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35
Q

how does the structure of the circle of Willis provide efficient perfusion even when there is a blockage?

A

anastomotic circuit

in case of a blockage anywhere in the circle, the circuit will allow for compensatory blood flow through the intact, communicating arteries to supply the rest of the brain

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36
Q

describe the venous drainage of the brain

A

cerebral veins drain into to dural venous sinuses which in turn drain into the internal jugular veins that take the venous blood back to the right atrium of the heart

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37
Q

how do dural venous sinuses form?

A

the dura mater is made up of two layers (periosteal and meningeal)

both are closely adherent to each other

the periosteal layer is closely adherent to the cranial bone

if the periosteal and maningeal layer separate from each other, a dural venous sinus forms

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38
Q

describe the direction of venous drainage from the superior sagittal sinus

A

superior sagittal sinus - confluence of sinuses - transverse sinus - sigmoid sinus - internal jugular vein - right atrium

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39
Q

what is the falx cerebri?

A

the dural fold that separates the two cerebral hemispheres

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40
Q

what is the falx cerebelli?

A

the dural fold that separates the two cerebellar hemispheres

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41
Q

describe the direction of venous drainage from the great vein of Galen

A

great vein of Galen - straight sinus - confluence of sinuses - transverse sinus - sigmoid sinus - interior jugular vein - right atrium

42
Q

describe the structure of the meninges

A

dura mater (periosteal and then meningeal)
arachnoid mater
sub-arachnoid space
pia meter

43
Q

describe the adherence of the dura mater to the skull and each other

A

periosteal layer is closely adherent to the cranial bone - never separates

meningeal layer is adherent to the periosteal layer but separates to form dural venous sinuses

44
Q

what is extradural/epidural space?

A

space between the cranial bone (skull) and the periosteal dural mater

(closely adherent to cranium so this space does not naturally occur anywhere along the skull)

45
Q

what are the four types of haemorrhage?

A

extradural
subdural
subarachnoid
intracerebral

46
Q

what is the main cause of an extradural haemorrhage?

A

trauma

47
Q

how can an extradural haemorrhage result?

A

due to a sharp blow to the pterion (the point where four cranial bones - frontal, parietal, sphenoid and temporal - join) and subsequent rupturing of the nearby middle meningeal artery

haemorrhage of the artery causes the periosteal dural to strip away from the skull

48
Q

which bony cranial feature is commonly affected causing an extradural haemorrhage and why?

A

pterion

(blow to the pterion can cause the middle meningeal artery to rupture and create an extradural space into which it haemorrhages)

49
Q

which artery is most commonly affected in an extradural haemorrhage?

A

middle meningeal artery

50
Q

why do extradural haemorrhages have an acute onset of symptoms?

A

usually the result of an arterial bleed where the rupture causes rapid blood loss at high pressure

51
Q

how can one differentiate between extradural and subdural haemorrhages in terms of symptoms?

A

extradural - rapid, acute onset of symptoms

subdural - delayed, slow onset of symptoms

52
Q

why do subdural haemorrhages have a late onset of symptoms?

A

usually the result of a venous bleed where the rupture causes slow blood loss at low pressure

53
Q

where do extradural haemorrhages occur?

A

in a space between the periosteal dural layer and the skull

54
Q

where do subdural haemorrhages occur?

A

in the region between the dura and arachnoid mater

55
Q

what is the main cause of subdural haemorrhages?

A

trauma

56
Q

how is an extradural space created?

A

high-pressure arterial blood haemorrhage causes the periosteal dural to strip away from the skull creating an extradural space

57
Q

what happens to intercranial pressure during a haemorrhage and why?

A

increases due to the effect of accumulating blood

58
Q

what is a subarachnoid haemorrhage?

A

bleeding in the region between the arachnoid mater and the pia mater (i.e. subarachnoid space)

59
Q

where does a subarachnoid haemorrhage take place?

A

in the subarachnoid space

60
Q

what is the main cause of a subarachnoid haemorrhage?

A

ruptured aneurysms

61
Q

what is an aneurysm?

A

a bulge/ballooning in the blood vessel caused by a weakness in the vessel wall

62
Q

which individuals are at greatest risk of a subarachnoid aneurysm haemorrhage and why?

A

hypertensive patients as the increased blood pressure can cause the aneurysm to rupture and a subsequent bleed into the subarachnoid space

63
Q

what is a intracerebral haemorrhage?

A

a bleed within the brain tissue (i.e. inside the brain)

64
Q

what is the main cause of an intracerebral haemorrhage?

A

hypertension

65
Q

why is a raised ICP a problem?

A

only space for the brain in the cranial cavity SO if the ICP increases, compresses structures of the brainstem and can lead to cardiorespiratory centres shutting down

66
Q

what is a stroke?

A

rapidly developing

focal disturbance of brain function

of presumed vascular origin

of >24 hours duration

67
Q

what are the two types of stroke?

A

thromboembolic or haemorrhagic

68
Q

how common are thromboembolic strokes?

A

approx 85% of strokes are thromboembolic

69
Q

how common are haemorrhagic strokes?

A

approx 15% of strokes are haemorrhagic

70
Q

how quickly do stroke symptoms present?

A

rapid onset of symptoms

71
Q

what is a transient ischaemic attack (TIA)?

A

rapidly developing

focal disturbance of brain function

of presumed vascular origin

that resolves completely within 24 hours

72
Q

what is an infarction?

A

degenerative changes within tissue following (hypoxia caused by) occlusion of an artery

73
Q

what is cerebral ischaemia?

A

lack of sufficient blood supply to tissue resulting in permanent damage if blood supply is not restored quickly

74
Q

why is a transient ischaemia attack a cause for concern?

A

it is often a warning for a bigger stroke down the line

75
Q

differentiate between a TIA and a stroke

A

both are focal disturbances of brain function that are of presumed vascular origin
BUT
stroke = lasts longer than 24 hours whereas TIA = resolves completely within 24 hours

76
Q

differentiate between an infarction and ischaemia

A

ischaemia is diminished volume of blood perfusion (impaired blood supply)

infarction is the cellular response to that diminished perfusion

77
Q

differentiate between hypoxia/anoxia and ischaemia

A

while ischaemia is a lack of sufficient blood perfusing tissues, anoxia/hypoxia are a absence/lack of oxygen perfusing tissues

ischaemia - refers to all lack of all blood components
anoxia/hypoxia - lack of oxygen only

78
Q

what is a thromboembolic stroke?

A

a type of stroke that is caused by a thrombus (blood clot) in the blood vessels supplying the brain

79
Q

define thrombosis

A

formation of a blood clot (thrombus)

80
Q

define embolism

A

plugging of a small vessel by material carried from a larger vessel (e.g. thrombi from heart, atherosclerotic debris from the internal carotid artery)

81
Q

give examples of embolisms that can cause occlusion of an artery

A

thrombi from the heart

atherosclerotic debris from other blood vessels

fat

air (from injections)

82
Q

why is it important to remove all air bubbles before giving an injection?

A

air can act as an embolism and plug/block a small vessel, occluding the artery, increasing the risk of stroke

83
Q

why is stroke a major public health issue?

A

third most common cause of death

38,000 deaths per annum in the UK

can cause sever neurological deficit

can cause permanent disability

84
Q

what is the acronym for stroke symptoms?

A

F - face
A - arms
S - speech
T - time

85
Q

what are the risk factors for stroke?

A

age, hypertension, cardiac disease, smoking, diabetes mellitus

86
Q

how is cardiac disease a risk factor for stroke?

A

inefficient cardiac function can increase the risk of thrombi formation

87
Q

how is smoking a risk factor for stroke?

A

affects vasculature

88
Q

how is diabetes mellitus a risk factor for stroke?

A

affects vasculature

89
Q

name the three cerebral arteries

A

anterior cerebral artery
middle cerebral artery
posterior cerebral artery

90
Q

what is the perfusion field of the anterior cerebral artery?

A

approx 1cm lateral either side of the midline, along the longitudinal fissure all the way back to the parieto-occipital fissure
AND
much of the frontal lobes

91
Q

what is the perfusion field of the middle cerebral artery?

A

much of the lateral surface of the brain and deep, subcortical brain structures

92
Q

what is the perfusion field of the posterior cerebral artery?

A

the occipital lobe and the inferior portion of the temporal lobe

93
Q

if the anterior cerebral artery is occluded, what main symptoms does the patient present with?

A

paralysis of contralateral structures - contralateral hemiplegia (leg > arm, face)

loss of appropriate social behaviours

disturbance of executive functions (e.g. judgement, decision making, intellect) = abulia

94
Q

if the middle cerebral artery is occluded, what main symptoms does the patient present with?

A

‘classic stroke’

contralateral hemisensory deficits

contralateral hemiplegia (arm > leg)

hemianopia

aphasia (if lesion is on left side)

95
Q

if the posterior cerebral artery is occluded, what main symptoms does the patient present with?

A

visual deficits (i.e. homonymous hemianopia, visual agnosia)

96
Q

why does middle cerebral artery occlusion present with hemianopia?

A

this visual system runs all the way to the occipital lobe in the back from the frontal lobe and will be affected by a haemorrhage

97
Q

when and why does the middle cerebral artery lesion present with aphasia?

A

if there is a left sided lesion of the middle cerebral artery, the haemorrhage can affect Broca’s area causing expressive aphasia (impairing speech production)

98
Q

define homonymous hemianopia

A

visual field defect involving either the two right or the two left halves of the visual fields of both eyes

99
Q

differentiate between prosopagnosia and visual agnosia

A

visual agnosia refers to the inability to name or describe an object when it is placed in front of you

prosopagnosia refers to the inability specifically to recognise human faces

100
Q

how can blood vessels that increase the risk of stroke be identified physically?

A

yellow discolouration that is indicative of atherosclerotic plaque development, atheroma formation and hardening of the arteries

101
Q

how can blood vessels that increase the risk of stroke be identified physically?

A

yellow discolouration that is indicative of atherosclerotic plaque development, atheroma formation and hardening of the arteries

brs (phase 1b) (71 decks)

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