Blood Supply to the Central Nervous System Flashcards
What percentage of cardiac output goes to the brain?
10-20%
What percentage of liver glucose does the brain use?
66%
State the two main sources of blood supply to the brain?
Vertebral arteries (posteriorly) Internal carotid arteries (anteriorly)
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
Draw the circle of Willis.
DO NOT FORGET the superior cerebellar artery and the anterior inferior cerebellar arteries
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
give a brief outline of how the brain’s venous system works (ie the which veins drain into which sinuses, and which veins take the blood out of the head)
.
What vessel does the inferior sagittal sinus join with to form the straight sinus?
Great cerebral vein
Which three sinuses drain into the sigmoid sinus ?
Superior petrosal sinus Inferior petrosal sinus transverse 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
Define Stroke.
A rapidly developing focal disturbance of brain function of presumed vascular origin that lasts more than 24 hours
Define Transient Ischaemic Attack (TIA).
A rapidly developing focal disturbance of brain function of presumedvascular origin that resolves completely within 24 hours
What percentage of strokes are caused by infarction and what percentage are caused by haemorrhage?
85% infarction 15% haemorrhage
State two causes of occlusions.
Thrombus Embolus
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 in the LEG more than(>) the arm and >face )
Disturbance of intellect and executive function/judgement
Loss of appropriate social behaviour
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
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 (broca’s area)
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 (eg cant see on left side of each visual field)
- 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- left
Wernicke’s area – understanding language-right side
What are lacunar infarcts?
Small spaces/cavities (lacunae) that appear in the brain due to small vessel occlusion–>infarct–> clearance of infarct by phagocytosis
The clinical deficit is dependent on the location of the small vessel occlusion
chronic 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- lucid period
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
define cerebral ischemia
Lack of sufficient blood supply to nervous tissue - Results in permanent damage IF blood blow is not restored quickly
define cerebral infarction
INFARCTION (effect) - degenerative changes which occur in tissue following occlusion of an artery
what are the risk factors for stroke
age
hypertension
smoking
diabetes mellitus cardiac disease
