Blood Supply to the CNS

Question 1

List the 3 main arteries travelling via the neck up to the head and mention which ones do and do not supply the brain, and for any that do not, what it supplies instead

Answer 1

1. External carotid arteries - supplies the face
2. Internal carotid arteries - supplies the brain
3. Vertebral arteries - supplies the brain

Question 2

What gives rise to the vertebral arteries and what is their route?

Answer 2

• Subclavian arteries give rise to vertebral arteries
• Vertebral arteries travel up through the neck via transverse foramina in the cervical vertebrae → through the foramen magnum → to the brain

Question 3

Qualitatively describe the major vessels in the Circle of Willis from back to front (there are some minor branches which are XS info)

Answer 3

• Vertebral arteries from each side merge into the basilar artery
• Basilar artery sprouts off into the posterior cerebral arteries
• Posterior communicating artery goes forward and the middle cerebral artery comes in at the middle from either side, the internal carotid is what gives rise to the middle cerebral artery
• Forward from this is the anterior cerebral arteries on each side
• The anterior communicating artery acts as a bridge between the anterior communicating arteries

Question 4

Label this diagram of the Circle of Willis - the minor branches have been crossed out - don’t need to know these really

Answer 4

Question 5

1) Where is the CSF drained back into the venous system?
2) How does CSF drain into here?

Answer 5

1)

• Superior sagittal sinus

2)

• In the gap between the dural layers - arachnoid granulation in bursts of subarachnoid space protrude into the superior sagittal sinus. CSF leaks through

Question 6

Describe how venous drainage of the brain occurs, and the different aspects

Answer 6

• Superficial and internal cerebral veins drain the outer and inner parts of the hemispheres and drain into the venous sinuses
• Superior sagittal sinus runs between the 2 dural folds along the top of the brain. Also where CSF is drained
• Inferior sagittal sinus - runs along the bottom of the dural folds
• The superior and inferior sagittal sinuses meet at the confluence of the sinuses
• The great cerebral vein also drains into the straight sinus and into the confluence of sinuses
• Eventually, all outflow is via the internal jugular veins

Question 7

Where is the superior sagittal sinus housed?

Answer 7

• Falx cerebri - a fold of dura extends between the medial surfaces of the 2 hemispheres
• Peeling apart of the 2 layers of dura at the top of the falx cerebri forms the superior sagittal sinus

Question 8

1) Define stroke
2) What are the 2 causes of stroke?

Answer 8

1)

• ‘Rapidly developing focal disturbance of brain function of presumed vascular origin of > 24 hours duration’

2)

• Infarction
• Haemorrhage

Question 9

Define Transient Ischaemic Attack (TIA)

Answer 9

• Rapidly developing focal disturbance of brain function of presumed vascular origin lasting < 24 hours’

Question 10

Define infarction

Answer 10

• Degenerative changes which occur in tissue following artery occlusion

Question 11

What is cerebral ischaemia?

Answer 11

• Lack of sufficient blood supply to nervous tissue resulting in permanent damage if blood flow is not restored quickly → hypoxia and anoxia

Question 12

Give 2 causes of occlusions and what they are, giving 2 examples for one of them

Answer 12

1. Thrombosis
2. Embolism - fatty, thrombotic, air

Question 13

Qualitatively describe the perfusion fields of the brain

Answer 13

• Anterior cerebral artery supplies front and runs superiorly back before it reaches posterior cerebral artery
• Middle cerebral artery supplies medial and lateral parts of front 2/3rds of the brain
• Posterior cerebral artery supplies the back of the brain

Question 14

1) Describe the limbs’ motor dysfunction in anterior cerebral artery disturbance - and are the legs or arms more affected and why?
2) List other non-motor dysfunctions that occur in disturbance of the anterior cerebral artery

Answer 14

1)

• Paralysis of contralateral leg (contralateral hemiplegia)
• LEG because motor homunculus shows the part of the motor cortex controlling the legs are more medial to the part controlling the arm

2)

• Disturbance of intellect, executive function and judgement
• Loss of appropriate social behaviour

Question 15

1) List dysfunctions that occur with disturbance of the middle cerebral artery, starting with motor dysfunction in limbs, and which limbs are more affected and why?
2) One of these dysfunctions occur in particular with left-sided lesion / disturbance of the middle cerebral artery, which one is it, and why?

Answer 15

1)

• Contralateral hemiplegia of ARMS due to motor homunculus of motor cortex representation of arms - more lateralised for arms
• Contralateral hemisensory deficits e.g. hemianopia
• Aphasia

2)

• Aphasia
• Because the language centres are left hemisphere lateralised and located here (Broca’s and Wernicke’s)

Question 16

1) List dysfunctions that occur with disturbances of the posterior cerebral artery
2) Considering the area perfused by the posterior cerebral artery, explain why these types of dysfunction are seen

Answer 16

1)

• Visual defects:
• Homologous hemianopia (hemianopic visual field loss on same side of each eye)
• Visual agnosia (don’t recognise things you see)

2)

• The posterior cerebral artery supplies the back 1/3 of the hemispheres laterally and medially, the occipital lobe and thus the primary visual cortex is contained within this perfusion field therefore disturbance here leads to visual defects

Question 17

1) What are lacunar infarcts?
2) What type of deficits do they cause?
3) Possible other cause of lacunar infarcts?

Answer 17

1)

• Small cavities in the brain that appear in deep structures as a result of small vessel occlusion

2)

• Deficit is dependent on anatomical location

3)

• HTN

Question 18

4 types of haemorrhagic stroke and for each, the causes + for 2 of them, mention the onset timeline of their effects

Answer 18

1. Extradural

• Trauma
• Immediate effects

2. Subdural

• Trauma
• Delayed effects

3. Subarachnoid
   * Usually caused by ruptured aneurysms
4. Intracerebral
   * Spontaneous HTN rupture of small vessels

Question 19

Difference between dura in the skull and vertebral column?

Answer 19

• In the skull: 2 layers of dura that are stuck together
• In the vertebral column: 1 layer of dura with fat between the bone and the dura (in the epidural space)

Question 20

What are the 2 layers of dura in the skull called?

Answer 20

1. Periosteal
2. Meningeal

Question 21

What will rupture of the middle meningeal artery lead to?

Answer 21

• Extradural haemorrhage

Question 22

Process of development of extradural haematoma?

Answer 22

• High pressure supply to brain leads to splitting of some of the arteries running between the meninges themselves (between the dura and skull)
• This leads to compression of the skull underneath
• The periosteal dura is stuck to the skull so it is only a potential space that’s there, which can be filled by blood in an extradural haemorrhage

Question 23

What causes subdural haemorrhage, and why is the onset of symptoms slower thatn in extradural haemorrhage?

Answer 23

• Rupture of veins in skull
• Slower as involvement of veins, not arteries, which operate at a much lower pressure