Blood Supply to the Brain

Question 1

Explain the 2 arteriole routes into the brain.

Answer 1

Internal cartoid artery…enters cranium via carotid canal. Many branches off it….opthalmic artery which becomes the central artery of the retina, also the hypophyseal arteries and the anteriror choroidal arteries. The internal carotid finally splits in the middle and anterior cerebral arteries (anterior circulation)

The right and left vertebral arteries enter the cranium via the foramen magnum and the forms the posterior cerebral artery and the basilar artery (posterior circulation).

Question 2

Explain the circle of Willis

Answer 2

Starting from top.
Anterior cerebral arteries joined by the anterior communicating artery. Then MCA and internal carotid. Then posterior communicating arteries to join anterior and posterior circulation.
Then the posterior cerebral artery and then the superior cerebellar artery.
Labyrinthine artery.
Anterior inferior cerebellar artery
Posterior inferior cerebellar artery
Basilar artery splits to 2 vertebral arteries

Question 3

Are anamososies good?

Answer 3

Yes - allow alternative route if normal route is occluded.

No - anyeurisms, space filling…rupture and bleed into subarachnoid space.

Question 4

Explain the distribution of the middle cerebral artery and what happens if it is occluded.

Answer 4

Supplies the majority of the lateral surface of the brain. 9 or so branches come out between the frontal, temporal and parietal lobes.

Occlusion of MCA:

• contralateral paralysis of lower face and arm
• hemianopsia of contralateral visula field (loss of 1/2 visula firled in contralateral eye) as MCA supplies the thalamovisual cortical tract.
• aphasia (can’t understand or express speech) if dominant hemisphere

Question 5

Explain the distribution of the anterior cerebral artery and what happens if it is occluded.

Answer 5

Supplies majority of medial surface and top of lateral.

Occlusion;

• paralysis and sensory deficits of contralateral leg an perineum
• mental confusion and dysphasia
• sometime contralateral deficit in face tounge and upper limb due to ACA supplyin internal capsule

Question 6

Explain the distribution of the posterior cerebral artery and what happens if it is occluded.

Answer 6

Occlusion;

• blindness of contralteral visual field
• hippocampal memory may be affected - usually temporarily.

Question 7

What are the consequences of an occlusion in either the basilar and or the vertebral arteries?

Answer 7

• Instantly fatal due to coma and loss of respiratory function
• cerebellar defects
• deafness is labyrinthine artery is affected
• infarction of ventral pons - loss of voluntary movement (not eyes - senses spared)

Question 8

Explain the venous drainage of the blood.

Answer 8

Deep and superfical veins drain into the dural venous sinuses then into the internal jugular via the jugular foramen in the posterior cranial fossa.

Question 9

What is an extradural haemorrhage?

Answer 9

between skull and dura eg meningeal artery

Question 10

What is a subdural haemorrhage?

Answer 10

between dura and arachnoid eg from superior cerebral vein

Question 11

What is a subarachnoid haemorrhage?

Answer 11

between arachnoid and pia - ruptured aneurysim of circel of willis and bleed into subarachnoid space - stoke

Question 12

What is an intracerebral haemorrhage?

Answer 12

within brainstem itself - perforating areries - another cause of stroke.