Blood Supply to the Central Nervous System

Question 1

What percentage of cardiac output goes to the brain? What percentage of oxygen consumption?

Answer 1

10-20%

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)

• Circle of willis and cerebral arteries

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 are the four main features of venous drainage in the brain?

Answer 8

• Cerebral veins
• Venous sinuses
• Dura mater
• Internal jugular vein

Question 9

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

Answer 9

Straight sinus

Question 10

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

Answer 10

Great cerebral vein

Question 11

Which sinus ascends to join the confluence of sinuses?

Answer 11

Occipital sinus

Question 12

Which two sinuses run along the temporal bone?

Answer 12

Superior petrosal sinus

Inferior petrosal sinus

Question 13

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

Answer 13

Sigmoid sinus

Question 14

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

Answer 14

Transverse sinus

Question 15

Which sinus runs along the sphenoid and parietal bones?

Answer 15

Sphenoparietal sinus

Question 16

Which sinuses run on either side of the pituitary stalk?

Answer 16

Anterior and posterior intercavernous sinuses

Question 17

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

Answer 17

Tentorium cerebelli

Question 18

Define Stroke.

Answer 18

=CVA - cerebrovascular accident

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

Question 19

Define Transient Ischaemic Attack (TIA).

Answer 19

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

Question 20

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

Answer 20

85% infarction

15% haemorrhage

Question 21

State two causes of occlusions.

Answer 21

Thrombus - blood clots

Embolus - plugging of small vessels by material from larger vessel e.g. atherosclerotic debris

Question 22

Describe the perfusion fields of the different cerebral arteries to the brain.

Answer 22

• 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 23

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

Answer 23

Leg is more MEDIAL

Question 24

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

Answer 24

• Contralateral hemiplegia in the LEG more than the arm
• Disturbance of intellect and executive function and judgement (abulia)
• Loss of appropriate social behaviour

Question 25

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

Answer 25

This is a CLASSIC STROKE: * Contralateral hemiplegia in the ARM more than the leg * Contralateral hemisensory deficits * Hemianopia * 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 26

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

Answer 26

Supplies the occipital lobe, which is where the primary visual cortex is located so: Visual defects such as - * - homonymous hemianopia * - visual agnosia (unable to recognise what you are seeing)

Question 27

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

Answer 27

Broca’s area – speech Wernicke’s area – understanding language

Question 28

What are lacunar infarcts?

Answer 28

* 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 29

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

Answer 29

1. Extradural – rapid onset – caused by trauma 2. Subdural – slow onset – caused by trauma 3. Subarachnoid – usually caused by ruptures aneurysms 4. Intracerebral – usually due to spontaneous hypertensive rupture of small vessels

Question 30

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

Answer 30

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

Question 31

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

Answer 31

Periosteal and Meningeal

Question 32

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

Answer 32

Falx Cerebri

Question 33

Why are extradural haemorrhages more rapid onset than subdural haemorrhages?

Answer 33

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 34

What is infarction?

Answer 34

Degenerative changes which occur in tissue following occlusion of an artery

Question 35

What is cerebral ischaemia?

Answer 35

Lack of sufficient blood supply to the nervous tissue resulting in permanent damage if the blood flow is not restored quickly ## Footnote *This is both a BLOOD and OXYGEN supply problem.*

Question 36

Which arteries have the largest perfusion fields in the brain?

Answer 36

Middle cerebral arteries

Question 37

Which cerebral artery supplies the frontal lobe?

Answer 37

Anterior cerebral artery