4: Blood supply to brain Flashcards
What percentage of body weight does brain make up?
2%
What percentage of CO does brain use?
10-20%
What percentage of body oxygen consumption does brain use?
20%
What percentage of liver glucose does the brain use?
66%
What are the main two sources of blood supply to the brain?
Internal carotid arteries
Vertebral arteries
Circle of willis?
Anterior cerebral arteries
Anterior communicating artery (branches two anteriors together)
middle cerebral artery, medially internal carotid comes off it and then ophthalmic artery comes of the internal carotid
Posterior communicating artery
Posterior cerebral artery (comes out lateral)
(superior cerebellar artery)
basillar artery
(anterior inferior cerebellar arteries)
vertebral artery
State the major artery that the vertebral arteries branch off and describe the path of the vertebral arteries to the brain
Subclavian artery
The vertebral arteries pass through the transverse foramina of the cervical vertebrae and through the foramen magnum into the brain
What are the components of the venous drainage of the brain?
Cerebral veins
venous sinuses
dura mater
internal jugular vein
State the names of the venous sinuses that are at the top and bottom of the falx cerebri
Superior sagittal sinus
Inferior sagittal sinus
What is the name given to the place where all the sinuses meet?
Confluence of sinuses
What connects the inferior sagittal sinus to the confluence of sinuses?
Straight sinus
What vessel does the inferior sagittal sinus join with to form the straight sinus?
Great cerebral vein
Which sinus ascends to join the confluence of sinuses?
Occipital sinus
Which two sinuses run along the temporal bone?
Superior petrosal sinus
Inferior petrosal sinus
Which main sinus drains into the internal jugular vein through the jugular foramen?
Sigmoid sinus
Which sinus connects the confluence of sinuses to the sigmoid and superior petrosal sinuses?
Transverse sinus
Which sinus runs along the sphenoid and parietal bones?
Sphenoparietal sinus
Which sinuses run on either side of the pituitary stalk?
Anterior and posterior intercavernous sinuses
Which extension of dura mater separates the cerebellum from the inferior portion of the occipital lobe?
Tentorium cerebelli
Define Stroke.
A rapidly developing focal disturbance of brain function of presumed vascular origin that lasts more than 24 hours
What percentage of strokes are haemorrhagic or infarction
infarction 85%
haemorrhagic 15%
Define transient ischaemic attack (TIA)
A rapidly developing focal disturbance of brain function of presumed vascular origin that resolves completely within 24 hours
Define infarction
Degenerative changes which occur in tissue as following occlusion of an artery
Define cerebral ischaemia
Lack of sufficient blood supply to nervous tissue resulting in permanent damage if blood flow is not restored quickly
hypoxia/anoxia(absence of oxygen)
What are causes of occlusion?
thrombosis(formation of clot)
embolism(plugging of small vessel by material carried from larger vessels e.g. thrombi from heart and atherosclerotic debris from internal carotid)
Describe the perfusion fields of the brain.
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
Describe the location of the leg in the motor and sensory homunculus compared to the arm.
Leg is more medial
Describe the features of a disturbance in the anterior cerebral artery.
Contralateral hemiplegia(paralysis in one side) in the LEG more than the arm Disturbance of intellect and executive function Loss of appropriate social behaviour
What are risk factors for stroke?
Age Hypertension Cardiac disease Smoking Diabetes mellitus
Describe the features of a disturbance in the middle cerebral artery.
This is a CLASSIC STROKE
Contralateral hemiplegia in the ARM more than the leg
Contralateral hemisensory deficits
Hemianopia(blindness over half field of vision)
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
Describe the features of a disturbance in the posterior cerebral artery.
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(only one side of visual field for each eye, same for both) and visual agnosia (unable to recognise what you are seeing)
Which parts of the brain are involved in speech and understanding language?
Broca’s area – speech (frontal)
Wernicke’s area – understanding language
posterior section of superficial temporal gyrus
What are lacunar infarcts?
Small spaces (lacunae) that appear in the brain due to small vessel occlusion The clinical deficit is dependent on the location of the small vessel occlusion Hypertension can cause lacunar infarcts
State the four types of haemorrhagic stroke and their likely causes.
Extradural – rapid onset – caused by trauma
Subdural – slow onset – caused by trauma
Subarachnoid – usually caused by ruptures aneurysms
Intracerebral – usually due to spontaneous hypertensive rupture of small vessels
What is the difference between the dura in the vertebral column compared to the brain?
The dura in the vertebral column has ONE layer whereas the dura in the skull has TWO layers
What are the two layers of dura in the skull called?
Periosteal and Meningeal
What is the name given to the fold of dura that extends between the medial surfaces of the two hemispheres?
Falx Cerebri
Why are extradural haemorrhages more rapid onset than subdural haemorrhages?
Extradural haemorrhages are caused by rupture of a meningeal ARTERY (high pressure) whereas subdural haemorrhages are caused by rupture of veins in the skull
