Blood supply to the CNS

Question 1

What percentages of the CO, 02 consumption and liver glucose does the brain take up?

Answer 1

CO: 10-20%
02 consumption: 20%
Liver glucose: 2/3rds

Question 2

What is the major blood supply to the brain?

Answer 2

Internal carotid artery supplies anterior part

Vertebral artery supplies posterior part

Question 3

Describe the route of the vertebral arteries?

Answer 3

Branch of the subclavian artery
Ascends through the transverse foramina of the vertebrae
Enters the cranial cavity via the foramen magnum

Question 4

Describe the circulation of blood for the posterior half of the brain

Answer 4

The two vertebral arteries join to form the basilar artery.

This then bifurcates into two posterior cerebral arteries

Question 5

What is the benefit of the anastomotic circuit (circle of willis)?

Answer 5

Allows for compensation in case of artery occlusion preventing impairment of blood supply.

Question 6

Describe the circulation of blood for the anterior half of the brain

Answer 6

The internal carotid artery splits laterally into the middle cerebral artery.
It also continues anteriorly as the anterior cerebral arteries travel in the medial longitudinal fissure of the brain and follow the corpus callosum backwards by 2/3rds (parieto-occipital sulcus).
It forms a circuit by the two posterior communicating arteries and one anterior comminicating artery.

Question 7

Where do the middle cerebral arteries run?

Answer 7

Sylvian fissure (lateral sulcus)

Question 8

At what level does the common carotid bifurcate?

Answer 8

C4; at the level of the thyroid cartilage/laryngeal prominence

Question 9

When the common carotid bifurcates describe what happens next…

Answer 9

The external carotid goes on to supply the face, it branches outside the cranial cavity.
The internal carotid enters the skull via the carotid canal and supplies the anterior part of the brain.

Question 10

What are the branches that the vertebral artery gives off before it turns into the basilar artery?

Answer 10

The anterior spinal artery -> supplies the spinal cord

The posterior inferior cerebellar artery (PICA)

Question 11

Where is the basilar artery located?

Answer 11

On the anterior surface of the pons

Question 12

What are the branches of the basilar artery?

Answer 12

Anterior inferior cerebellar artery
Labyrinthe
Pontine
Superior cerebellar

Question 13

What is the order of venous drainage in the brain?

Answer 13

Cerebral veins
Venous sinuses
Dura mater
Internal jugular vein

Question 14

What are dural venous sinuses?

Answer 14

Endothelial lined spaces between the periosteal and meningeal layer of dura mater.

Question 15

How can infection enter the cranial cavity?

Answer 15

Through emissary veins which pass from outside the cranial cavity to the dural venous sinuses, they have no valves.

Question 16

Describe the appearance of the dural venous sinuses?

Answer 16

The superior sagittal sinus runs along the superior border of the falx cerebri. This is how CSF is drained back into the ventricular system.
The inferior sagittal sinus runs along the inferior surface of the dural fold.
The confluence of sinuses is where the superior sagittal, straight and occipital sinuses join.

Question 17

What lies in the carotid sheath?

Answer 17

The internal jugular vein, carotid and vagus nerve.

Question 18

What is a stroke and what are they caused by?

Answer 18

Cerebrovascular accident;
Rapidly developing focal disturbance of brain function of presumed vascular origin, 24+ hours duration.
85% due to infarction, 15% haemorrhagic

Question 19

What is a transient ischaemic attack?

Answer 19

Rapidly developing focal disturbance of brain function of presumed vascular origin that resolves within 24hrs.

Question 20

What is a cerebral infarction?

Answer 20

Degenerative changes in a tissue following occlusion of an artery.

Question 21

What is cerebral ischaemia?

Answer 21

Lack of sufficient blood supply to nervous tissue which can result in permanent damage if blood flow is not quickly restored (note that hypoxia/anoxia is a component of ischaemia)

Question 22

What is a cerebral thrombus?

Answer 22

Formation of a blood clot

Question 23

What is a cerebral embolism?

Answer 23

Plugging of small vessel by material carried from larger vessel e.g. thrombi from the heart or atherosclerotic debris from the internal carotid. [The more proximal the occlusion is in the artery, the more devastating the result]

Question 24

What are risk factors for stroke, why this increases the risk and predominant it is in causing death?

Answer 24

3rd most common cause of death
Age
Hypertension; congenital vessel weaknesses may lead to vessel rupture
Cardiac disease; turbulent flow may cause clots
Smoking; increase atherosclerosis
Diabetes mellitus; vascular efffects

Question 25

Which areas of the brain does the middle cerebral artery supply?

Answer 25

Travels through the lateral fissure of the brain. It supplies the majority of the lateral parts of the brain and the anterior half of the temporal lobe.

Question 26

Which areas of the brain does the anterior cerebral artery supply?

Answer 26

Supplies the medial surface of the brain as well as a strip of the anterosuperior part of the brain.
Travels from the frontal lobe to the parieto-occipital lobe.

Question 27

Which areas of the brain does the posterior cerebral artery supply?

Answer 27

Supplies the occipital lobe and the lateral parts of the temporal lobe.

Question 28

What will be the presentation of damage to the anterior cerebral artery?

Answer 28

Paralysis of contralateral leg
Disturbance of intellect and executive judgement
Loss of appropriate social behaviours due to disinhibition from damage to the frontal lobe e.g. aggressive behaviour

Question 29

What will be the presentation of damage to the middle cerebral artery?

Answer 29

‘Classic stroke’
Contralateral hemiplegia (mostly arms), if damaged at the subcortical level, complete hemiparesis will occur as the projecting fibres below will have been affected
Hemisensory deficits (affects post central gyrus)
Hemionopia
Aphasia (from lesion on the left side as this is where the language centres are located).

Question 30

What will be the presentation of damage to the posterior cerebral artery?

Answer 30

Homonymous hemianopia

Visual agnosia

Question 31

What is Broca’s and Wernicke’s area?

Answer 31

Broca’s: involved in speech

Wernicke’s: involved in understanding language

Question 32

What is a lacunar infarct?

Answer 32

Strokes can cause small holes/cavities to appear in the brain tissue called lacunae due to these parts of brain tissue dying.
Appear in deep structures (e.g. subcortical structures) due to small vessel occlusion.
May not be symptomatic depending on anatomical location.
Hypertension is another possible cause of lacunae.

Question 33

What is arachnoid granulation?

Answer 33

Small burst of subarachnoid space that protrude into the superior sagittal sinus.

Question 34

What is dysarthria?

Answer 34

Motor speech disorder; involved motor components that make up speech

Question 35

Describe an extra/epidural haemorrhage

Answer 35

• Due to trauma, immediate effects
• Rupture of large arteries supplying the dura (meningeal arteries)
• High pressured arterial blood rips the dura from the skull
• Pressure is increased on the brain as there is no space (between the periosteal layer and skull is only a potential space) so cardiac and respiratory centres give up
• Unconscious patient, ipsilateral dilated pupil, contralateral hemiparesis

Question 36

Describe an subdural haemorrhage

Answer 36

• Due to trauma, delayed effects
• Venous bleed
• More common in elderly patients and those on anticoagulants
• Headache, drowsiness -> hemiparesis and sensory deficits develop

Question 37

Describe an subarachnoid haemorrhage

Answer 37

Quick arterial bleeds
Ruptured aneurysms of the basal vessels
(beri aneurysms are usually found in vessels of the circle of willis)

Question 38

Describe an intracerebral haemorrhage

Answer 38

Spontaneous hypertensive rupture of arteries in the deep cerebrum

Question 39

What will be the difference when looking at a ct scan of a new vs old haemorrhage?

Answer 39

Blood appears as white and when it starts to degenerate turns in to water (seen as black).
A new haemorrhagic stroke will appear white.