4 - Anatomy of Bloodflow in the CNS and Consequences of Disruption 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)
Generally, what do the external and internal carotids supply?
external carotid - supplies the face
internal - Ames its way up tot the skull and supplies the cerebral hemispheres
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
(cerebral arteries are the main feed arteries to the brain)
What are the 2 arteries that enter at the the brain posteriorly?
vertebral arteries
from the foramen magnum
What artery is formed from the joining o the 2 vertebral arteries?
What does this artery then go to form when it bifurcates?
basilar artery
bifurcates to form the posterior cerebral artery
Give the order of venous drainage of blood in the brain?
cerebral veins
venous sinuses
dura mater
internal jugular veins
State the names of the venous sinuses that are at the top and bottom of the falx cerebri.
Superior sagittal sinus
Inferior sagittal sinus
Which sinus runs along the top between 2 folds of dura?
superior 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
Define Transient Ischaemic Attack (TIA).
A rapidly developing focal disturbance of brain function of presumed vascular 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
Disturbance of intellect and executive function
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
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 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
Wernicke’s area – understanding language
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 are the arachnoid granulations?
projections of the arachnoid membrane into the dural sinuses that allow CSF entrance from the subarachnoid space into the venous system
What are emissary veins?
Why are they important?
veins that connect the extracranial venous system with the intracranial venous sinuses
They connect the veins outside the cranium to the venous sinuses inside the cranium.
i.e. they pass through the top of the skull
they are important because they are another route of infection. infection of the scalp can spread through these veins and cause meningitis
Does subdural and extradural space exist?
extradural space does not exist
subdural scape does exist
CSF is in subarachnoid space
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
