Blood Supply to the Central Nervous System Flashcards
What percentage of cardiac output goes to the brain? What percentage of oxygen consumption?
10-20%
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)
- Circle of willis and cerebral arteries
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
What are the four main features of venous drainage in the brain?
- Cerebral veins
- Venous sinuses
- Dura mater
- Internal jugular vein
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.
=CVA - cerebrovascular accident
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 - blood clots
Embolus - plugging of small vessels by material from larger vessel e.g. atherosclerotic debris
Describe the perfusion fields of the different cerebral arteries to 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 and judgement (abulia)
- 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.
Supplies the occipital lobe, which is where the primary visual cortex is located so:
Visual defects such as -
- homonymous hemianopia
- 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 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
What is infarction?
Degenerative changes which occur in tissue following occlusion of an artery
What is cerebral ischaemia?
Lack of sufficient blood supply to the nervous tissue resulting in permanent damage if the blood flow is not restored quickly
This is both a BLOOD and OXYGEN supply problem.
Which arteries have the largest perfusion fields in the brain?
Middle cerebral arteries
Which cerebral artery supplies the frontal lobe?
Anterior cerebral artery
