blood supply to CNS

Question 1

blood supply of brain

Answer 1

two internal carotid and 2 vertebral arteries which join to form the circle of willis, which branches to form cerebral arteries common carotid branches at level of adams apple to form external (face and skin- is very branched) and internal (anterior part of circulation- not branched) subclavian artery also gives rise to vertebral arteries, going through transverse foramen of cervical vertebrae

Question 2

pathway of arteries and unpaired artery DIAGRAM

Answer 2

vertebral arteries join to form basilar artery (in front of pons) basilar arteries split to form posterior cerebral arteries internal carotid branches to form the main middle cerebral artery, anterior cerebral and posterior communicating, which joins to posterior cerebral, hence this is an anastamotic circuit in case carotid is blocked NB: pair of anterior cerebral arteries form anterior communicating, which is UNPAIRED

Question 3

venous drainage of brain DIAGRAM

Answer 3

cerebral veins drain into venous sinuses (many present in brain), which are made from folds of dura mater (outer layer of brain), as dura mater is 2 layer structure (periosteal sticks to skull, meningeal forms the troughts), wiith sinus in between - sinuses only form at brain SULCI

sinuses drain at confluence of sinuses and form TRANSVERSE sinuses, then into internal jugular veins

Question 4

define stroke and its 2 causes, and other name

Answer 4

rapidly developing disturbance of brain function of vascular origin above 24 hours also known as cerebrovascular accident (CVA), with 85% due to infarction, and 15% due to haemorrhage

Question 5

define transient ischaemic attack

Answer 5

rapidly developing disturbance of brain function of vascular origin WITHIN 24 hours it’s a temporary blockage of blood supply suggestive of a future stroke

Question 6

define infarction vs cerebral ischaemia

Answer 6

degenerative tissue due to blockage of an artery vs insufficient blood supply which may damage nervous tissue if not restored quickly NB: not just to do with oxygen, also glucose and nutrients

Question 7

picture of brain thats suffered stroke DIAGRAM

Answer 7

there is asymmetry of grey and white matter

Question 8

epi of stroke

Answer 8

3rd most common cause of death (100 K per yr in UK) half of survivor permanantly disable, 70% with neurological deficit

Question 9

stroke risk factors

Answer 9

age, hypertension (aneurysm can burst), cardiac disease (static blood), smoking and diabetes mellitus

Question 10

santerior cerebral artery and associated problems

Answer 10

supplies motor cortex (in frontal lobes) of lower limb, so problems can cause paralysis of a contralateral leg (depending which side affected) frontal lobe also where judgement and intellect controlled, so this impaired as well as social behaviour

Question 11

middle cerebral artery and associated problems

Answer 11

'’classic stroke’’, leads to contralateral hemisensory deficits (lose of sensation down one side), as supplies sensory cortex (located in postcentral gyrus) also can lead to hemiplegia (paralysis on one side, usually arm rather than leg)

also aphasia (either inability to understand sth or express yourself), as supplies brochas/wernickers area, and FACIAL DROOP

Question 12

posterior cerebral artery

Answer 12

mainly occipital, so leads to visual problems- homonymous hemianopia (loss of visual field on same side on both eyes, as only one side of cortex affected) agnosia (unable to identify)

Question 13

lacunar infarcts

Answer 13

small cavities DEEP in brain after death due to small strokes often associated with hypertension, as brain gets rid of bits of tissue with blood, leaving lacunes

Question 14

haemorrhagic stroke- types

Answer 14

extradural- artery supplying meninges pushes dura away from skull and putting pressure on brain, raising cranial pressure with IMMEDIATE effects, so blood must be removed- occurs after damage to pterion

subdural is also due to trauma but has delayed effects as there is venous bleeding between dura subarachnoid due to blood vessels in subarachnoid space bleeding, due to ruptured aneurysms (weakness in vessel wall)- occurs when elderly fall

intracerebral- bleed within tissue itself, due to hypertension

Question 15

cavernous sinus- where is it, structures inside, and clinical significance

Answer 15

sinus right next to pituitary gland

nerves 3, 4, and first 2 of nerve 5 travel laterally, internal carotid and abducens in centre

infections of eye/skin can enter CNS through this sinus