Blood Supply to the Central Nervous System

Question 1

What percentage of cardiac output goes to the brain?

Answer 1

10-20%

Question 2

What percentage of liver glucose does the brain use?

Answer 2

66%

Question 3

State the two main sources of blood supply to the brain?

Answer 3

Vertebral arteries (posteriorly) Internal carotid arteries (anteriorly)

Question 4

State the major artery that the vertebral arteries branch off and describe the path of the vertebral arteries to the brain.

Answer 4

Subclavian artery The vertebral arteries pass through the transverse foramina of the cervical vertebrae and through the foramen magnum into the brain

Question 5

Draw the circle of Willis.

Answer 5

DO NOT FORGET the superior cerebellar artery and the anterior inferior cerebellar arteries

Question 6

State the names of the venous sinuses that are at the top and bottom of the falx cerebri.

Answer 6

Superior sagittal sinus Inferior sagittal sinus

Question 7

What is the name given to the place where all the sinuses meet?

Answer 7

Confluence of sinuses

Question 8

What connects the inferior sagittal sinus to the confluence of sinuses?

Answer 8

Straight sinus

Question 9

What vessel does the inferior sagittal sinus join with to form thestraight sinus?

Answer 9

Great cerebral vein

Question 10

Which sinus ascends to join the confluence of sinuses?

Answer 10

Occipital sinus

Question 11

Which two sinuses run along the temporal bone?

Answer 11

Superior petrosal sinus Inferior petrosal sinus

Question 12

Which main sinus drains into the internal jugular vein through the jugular foramen?

Answer 12

Sigmoid sinus

Question 13

Which sinus connects the confluence of sinuses to the sigmoid and superior petrosal sinuses?

Answer 13

Transverse sinus

Question 14

Which sinus runs along the sphenoid and parietal bones?

Answer 14

Sphenoparietal sinus- it comes off the cavernous sinus

Question 15

Which sinuses run on either side of the pituitary stalk?

Answer 15

Anterior and posterior intercavernous sinuses

Question 16

Which extension of dura mater separates the cerebellum from the inferior portion of the occipital lobe?

Answer 16

Tentorium cerebelli

Question 17

Define Stroke.

Answer 17

a rapidly developing focal disturbance of brain function of presumed vascular origin and of >24 hours duration

—2 types: Infarction (85%) or haemorrhage(15%)

Focal =localised

Question 18

Define Transient Ischaemic Attack (TIA).

Answer 18

A rapidly developing focal disturbance of brain function of presumedvascular origin that resolves completely within 24 hours

Question 19

What percentage of strokes are caused by infarction and what percentage are caused by haemorrhage?

Answer 19

85% infarction 15% haemorrhage

Question 20

State two causes of occlusions.

Answer 20

—Thrombosis

formation of a blood clot (thrombus)

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—Embolism

plugging of small vessel by material carried from larger vessel e.g. thrombi from the heart or atherosclerotic debris from the internal carotid

Question 21

Describe the perfusion fields of the brain.

Answer 21

The anterior cerebral artery supplies the medial part of both hemispheres

The middle cerebral artery extends laterally and emerges through the lateral fissure between the frontal and temporal lobes – it supplies the front 2/3 of the lateral part of the hemisphere

The posterior cerebral artery supplies the medial and lateral parts of the posterior part of the hemisphere

slide 20

Question 22

Describe the location of the leg in the motor and sensory homunculus compared to the arm.

Answer 22

Leg is more MEDIAL

Question 23

Describe the features of a disturbance in the anterior cerebral artery.

Answer 23

Contralateral hemiplegia in the LEG more than the arm

—Disturbance of intellect, executive function and judgement(abulia)

—Loss of appropriate social behavior

—The above 2 bullet points are functions of frontal lobe too

Question 24

Describe the features of a disturbance in the middle cerebral artery.

Answer 24

—“Classic stroke” - affects the lateral parts of the primary motor and somatosensory cortices.

—Contralateral hemiplegia (paralysis of one side): affects arm more than leg (look at motor humunculus)

—Contralateral hemisensory deficits (this artery supplies part of the somatosensory cortex too)

—Hemianopia (loss of half of visual field)

—Aphasia- speech problem (if it is a L sided lesion, Brocasarea is on the left hemisphere)

Question 25

Describe the features of a disturbance in the posterior cerebral artery.

Answer 25

The posterior cerebral artery supplies the occipital lobe, which is where the primary visual cortex is located.

This causes visual defects such as

1. homonymous hemianopia (loss of field of vision on the same side of both eyes see slide 24) and
2. visual agnosia (unable to recognise what you are seeing)

Question 26

Which parts of the brain are involved in speech and understanding language?

Answer 26

Broca’s area – speech

Wernicke’s area – understanding language

both normally located on the left hemisphere as it is the dominant hemisphere (right handed)

Question 27

What are lacunar infarcts, what can cause them? What long term condition is associated with this

Answer 27

—Lacunar infarcts are small infarcts (2–20 mm in diameter) in the deep cerebral white matter, basal ganglia, or pons, presumed to result from the occlusion of a single small perforating artery supplying the subcortical areas of the brain.

ie infarction of subcortical areas as a result of blockage of small perforating arteries. Symptoms depend on which part is affected.

associated with hypertension

Question 28

State the four types of haemorrhagic stroke and their likely causes.

Answer 28

Extradural – rapid onset – caused by trauma affecting an artery

Subdural – slow onset – caused by trauma, often affecting a vein hence slower onset. (lucid interval etc)

Subarachnoid – usually caused by ruptures aneurysms (subarachnoid space contains veins and arteries)

Intracerebral – usually due to spontaneous hypertensive rupture of small vessels

Question 29

What is the difference between the dura in the vertebral column compared to the brain?

Answer 29

The dura in the vertebral column has ONE layer whereas the dura in the skull has TWO layers

Question 30

What are the two layers of dura in the skull called?

Answer 30

Periosteal and Meningeal

Question 31

What is the name given to the fold of dura that extends between the medial surfaces of the two hemispheres?

Answer 31

Falx Cerebri

Question 32

Why are extradural haemorrhages more rapid onset than subdural haemorrhages?

Answer 32

Extradural haemorrhages are caused by rupture of a meningeal ARTERY (high pressure) whereas subdural haemorrhages are caused by rupture of veins in the skull

Question 33

Main risk factors for stroke/TIA?

Answer 33

ØAge

ØHypertension

ØCardiac disease

ØSmoking

ØDiabetes mellitus