4: Blood supply to brain

Question 1

What percentage of body weight does brain make up?

Answer 1

2%

Question 2

What percentage of CO does brain use?

Answer 2

10-20%

Question 3

What percentage of body oxygen consumption does brain use?

Answer 3

20%

Question 4

What percentage of liver glucose does the brain use?

Answer 4

66%

Question 5

What are the main two sources of blood supply to the brain?

Answer 5

Internal carotid arteries

Vertebral arteries

Question 6

Circle of willis?

Answer 6

Anterior cerebral arteries
Anterior communicating artery (branches two anteriors together)
middle cerebral artery, medially internal carotid comes off it and then ophthalmic artery comes of the internal carotid
Posterior communicating artery
Posterior cerebral artery (comes out lateral)
(superior cerebellar artery)
basillar artery
(anterior inferior cerebellar arteries)
vertebral artery

Question 7

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

Answer 7

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

Question 8

What are the components of the venous drainage of the brain?

Answer 8

Cerebral veins
venous sinuses
dura mater
internal jugular vein

Question 9

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

Answer 9

Superior sagittal sinus

Inferior sagittal sinus

Question 10

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

Answer 10

Confluence of sinuses

Question 11

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

Answer 11

Straight sinus

Question 12

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

Answer 12

Great cerebral vein

Question 13

Which sinus ascends to join the confluence of sinuses?

Answer 13

Occipital sinus

Question 14

Which two sinuses run along the temporal bone?

Answer 14

Superior petrosal sinus

Inferior petrosal sinus

Question 15

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

Answer 15

Sigmoid sinus

Question 16

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

Answer 16

Transverse sinus

Question 17

Which sinus runs along the sphenoid and parietal bones?

Answer 17

Sphenoparietal sinus

Question 18

Which sinuses run on either side of the pituitary stalk?

Answer 18

Anterior and posterior intercavernous sinuses

Question 19

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

Answer 19

Tentorium cerebelli

Question 20

Define Stroke.

Answer 20

A rapidly developing focal disturbance of brain function of presumed vascular origin that lasts more than 24 hours

Question 21

What percentage of strokes are haemorrhagic or infarction

Answer 21

infarction 85%

haemorrhagic 15%

Question 22

Define transient ischaemic attack (TIA)

Answer 22

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

Question 23

Define infarction

Answer 23

Degenerative changes which occur in tissue as following occlusion of an artery

Question 24

Define cerebral ischaemia

Answer 24

Lack of sufficient blood supply to nervous tissue resulting in permanent damage if blood flow is not restored quickly
hypoxia/anoxia(absence of oxygen)

Question 25

What are causes of occlusion?

Answer 25

thrombosis(formation of clot) embolism(plugging of small vessel by material carried from larger vessels e.g. thrombi from heart and atherosclerotic debris from internal carotid)

Question 26

Describe the perfusion fields of the brain.

Answer 26

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

Question 27

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

Answer 27

Leg is more medial

Question 28

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

Answer 28

``` Contralateral hemiplegia(paralysis in one side) in the LEG more than the arm Disturbance of intellect and executive function Loss of appropriate social behaviour ```

Question 29

What are risk factors for stroke?

Answer 29

``` Age Hypertension Cardiac disease Smoking Diabetes mellitus ```

Question 30

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

Answer 30

This is a CLASSIC STROKE Contralateral hemiplegia in the ARM more than the leg Contralateral hemisensory deficits Hemianopia(blindness over half field of vision) Aphasia (can’t speak) – left-sided lesion of the middle cerebral artery will result in aphasia because the language centres are more on the left side than the right

Question 31

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

Answer 31

The posterior cerebral artery supplies the occipital lobe, which is where the primary visual cortex is located This causes visual defects such as homonymous hemianopia(only one side of visual field for each eye, same for both) and visual agnosia (unable to recognise what you are seeing)

Question 32

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

Answer 32

Broca’s area – speech (frontal) Wernicke’s area – understanding language posterior section of superficial temporal gyrus

Question 33

What are lacunar infarcts?

Answer 33

``` Small spaces (lacunae) that appear in the brain due to small vessel occlusion The clinical deficit is dependent on the location of the small vessel occlusion Hypertension can cause lacunar infarcts ```

Question 34

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

Answer 34

Extradural – rapid onset – caused by trauma Subdural – slow onset – caused by trauma Subarachnoid – usually caused by ruptures aneurysms Intracerebral – usually due to spontaneous hypertensive rupture of small vessels

Question 35

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

Answer 35

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

Question 36

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

Answer 36

Periosteal and Meningeal

Question 37

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

Answer 37

Falx Cerebri

Question 38

Why are extradural haemorrhages more rapid onset than subdural haemorrhages?

Answer 38

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