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

give a brief outline of how the brain’s venous system works (ie the which veins drain into which sinuses, and which veins take the blood out of the head)

Answer 8

.

Question 9

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

Answer 9

Great cerebral vein

Question 10

Which three sinuses drain into the sigmoid sinus ?

Answer 10

Superior petrosal sinus Inferior petrosal sinus transverse sinus

Question 11

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

Answer 11

Sigmoid sinus

Question 12

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

Answer 12

Transverse sinus

Question 13

Define Stroke.

Answer 13

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

Question 14

Define Transient Ischaemic Attack (TIA).

Answer 14

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

Question 15

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

Answer 15

85% infarction 15% haemorrhage

Question 16

State two causes of occlusions.

Answer 16

Thrombus Embolus

Question 17

Describe the perfusion fields of the brain.

Answer 17

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 18

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

Answer 18

Leg is more MEDIAL

Question 19

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

Answer 19

Contralateral hemiplegia in the LEG more than(>) the arm and >face )

Disturbance of intellect and executive function/judgement

Loss of appropriate social behaviour

Question 20

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

Answer 20

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 (broca’s area)

Question 21

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

Answer 21

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 (eg cant see on left side of each visual field)
• visual agnosia (unable to recognise what you are seeing)

Question 22

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

Answer 22

Broca’s area – speech- left

Wernicke’s area – understanding language-right side

Question 23

What are lacunar infarcts?

Answer 23

Small spaces/cavities (lacunae) that appear in the brain due to small vessel occlusion–>infarct–> clearance of infarct by phagocytosis

The clinical deficit is dependent on the location of the small vessel occlusion

chronic Hypertension can cause lacunar infarcts

Question 24

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

Answer 24

Extradural – rapid onset – caused by trauma

Subdural – slow onset – caused by trauma- lucid period

Subarachnoid – usually caused by ruptures aneurysms

Intracerebral – usually due to spontaneous hypertensive rupture of small vessels

Question 25

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

Answer 25

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

Question 26

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

Answer 26

Periosteal and Meningeal

Question 27

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

Answer 27

Falx Cerebri

Question 28

Why are extradural haemorrhages more rapid onset than subdural haemorrhages?

Answer 28

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 29

define cerebral ischemia

Answer 29

Lack of sufficient blood supply to nervous tissue - Results in permanent damage IF blood blow is not restored quickly

Question 30

define cerebral infarction

Answer 30

INFARCTION (effect) - degenerative changes which occur in tissue following occlusion of an artery

Question 31

what are the risk factors for stroke

Answer 31

age

hypertension

smoking

diabetes mellitus cardiac disease