Cerebral Blood Flow

Question 0

What does posterior cerebral artery supply?

Answer 0

• supplies ventral surface of temporal lobe and whole of occipital lobe
• (ie visual cortex)

Question 1

What part of brain does anterior cerebral artery supply?

Answer 1

• supplies medial surface of frontal and parietal lobes and superior part of the cortex dorsally
• (motor and sensory cortex of the lower limb)

Question 2

What do internal carotid arteries give rise of?

Answer 2

• middle and anterior cerebral arteries

Question 3

What does middle cerebral artery supply?

Answer 3

• mostly lateral side of the brain, i.e. temporal lobe

- ( supplies motor and sensory cortex of upper limb, face and auditory cortex)

Question 4

What does posterior inferior cerebellar artery?

Answer 4

• supplies the lateral medulla

Question 5

What is watershed infarct?

Answer 5

• The terminal branches of the major arteries may have insufficient supply if the perfusion pressure is low because the pressure usually would drop anyway towards the end
• this watershed infarct may occur where territories of blood supply of brain overlaps

Question 6

Types of stroke (2)

Answer 6

• ischaemic= a clot blocks the brain arteries
• Haemorrphagic= blood vessels tear in brain so bleed into the brain and the pressure can build up. Results in a damage of brain tissues

Question 7

Which cerebral artery is the most common site for ischaemic stroke? And why?

Answer 7

• middle cerebral artery
• because there are lots of branches coming off middle cerebral artery= increases in turbulence of blood flow. So plagues in arteries can become dislodged and block the supply.

Question 8

What is cerebral aneurysm?

Answer 8

• Weakness in walls of cerebral artery or vein which causes ballooning of vessel= further weakening of the artery wall
• usually at a branching point of vessel as the wall is weaker there
• symptoms: usually asymptomatic until vessel bursts= nausea, weakened eyesight, severe headache,seizures, confusion
• if the cerebral aneurysm bursts, it can cause a clot in the skull and sudden death

Question 9

Characteristics of cerebral blood flow

Answer 9

• typically 50ml/min per 100g of brain weight
• around 15% of cardiac output
• kept reasonably constant

Question 10

How to calculate cerebral blood flow?

Answer 10

CBF= cerebral perfusion pressure/ cerebral vascular resistance

CPP= mean arterial pressure- intracranial pressure

(Normal vaules: MAP=60-150mmHg; ICP=10mmHg; CPP=70-90mmHg)

Question 11

What are the potential treatments for cerebral aneurysm?

Answer 11

• put a surgical clip on the aneurysm
• coil procedure where inserting a thin piece of foil from the femoral artery and feed up to the aneurysm so it can close off the aneurysm.

Question 12

How does the brain control its blood flow?

Answer 12

• by autoregulation= where cerebral flow is kept fairly constant even there is a variation in the cerebral blood pressure ( 50-200mmHg)
• Below limits, it can reduce cerebral blood flow and causes ischaemic damage
• Above limits, intracranial pressure increases so causing odema, crushing of brain tissues

Question 13

What are the elements in regulating cerebral blood flow?

Answer 13

1) Neural control
2) Metabolic control
3) Myogenic control

so these work together to maintain CBF

Question 14

How does neural control contribute to maintain CBF?

Answer 14

• sympathetic neurones: orginates in superior cervical ganglion. Travel with internal carotid and vertebral arteries into skull. Releasing NA and causes vasoconstriction
• parasympathetic neruones: from the branches of facial nerve. Releasing ACh and causes vasodilation
• sensory nerve fibres on blood vessls can release vasodilatory substances
• overall, neural control of blood flow is weak