Blood supply to the central nervous system Flashcards
What percentage of body weight is the brain?
2%
What percentage of cardiac output goes to the brain?
10-20%
What percentage of the body’s oxygen consumption is the brain responsible for?
20%
What percentage of liver glucose is used by brain?
66%
What do all these statistics mean?
Brain is very vulnerable if blood supply is damaged
What are the two sources of blood to the brain?
Internal carotid arteries (front) and vertebral arteries (back)
What does the external carotid artery supply?
The face
What does the internal carotid supply?
Cerebral hemispheres
Where do the vertebral arteries originate from?
They branch off the subclavian arteries
Describe the vertebral arteries journey from the subclavian to the brain?
They go through the transverse foramina in the cervical vertebrae and through the foramen magnum into the brain
What do the vertebral arteries go onto form
Circle of Willis
What do the vertebral arteries join together to form?
Basilar artery
What does the basilar then bifurcate to form?
Posterior cerebral arteries
Where do the middle cerebral arteries originate from?
The internal carotid arteries travel superiorly and then laterally to form the middle cerebral arteries that emerge through the fissure between the frontal, parietal and temporal lobes
What do the internal carotid arteries also branch to form?
Anterior cerebral arteries that go up in between the two medial surfaces of the hemispheres and they follow the corpus callosum back about 2/3 of the way
This arrangement is made into the circle of Willis by how many posterior and anterior communicating arteries
Two posterior and one anterior
What are the four components of the brain involved in venous drainage
Cerebral veins
Venous sinuses
Dura mater
Internal jugular vein
Where is the superior sagittal sinus?
It runs along the top and is housed between the two folds of dura
What happens at the superior sagittal sinus?
It is the point where CSF drains back into the venous system
Where is the inferior sagittal sinus?
Running along the bottom of the dural fold
What is the confluence of sinuses?
Where all the sinuses come together at the back of the head- A bleed here is fatal
What is a stroke?
Rapidly developing focal disturbance of brain function of presumed vascular origin lasting more than 24 hours
What is a transient ischaemic attack?
Rapidly developing focal disturbance of brain function of presumed vascular origin lasting less than 24 hours
What is an infarction?
Degenerative charges that occur in tissue after occlusion of an artery
What is cerebral ischameia?
Lack of blood supply to nervous tissue resulting in permanent damage if blood flow isn’t restored quickly due to hypoxia/anoxia
What is a thrombosis?
Formation of a blood clot
What is an embolism?
Plugging of small vessels by material carried from a larger vessel, the more proximal the occlusion is, the more damaging it is
Which part of the brain do the middle cerebral arteries supply?
Front 2/3 of the lateral parts of the hemispheres
What does the posterior cerebral artery supply?
Medial and lateral parts of posterior parts of the hemispheres
What are the effects of disturbance to the anterior cerebral artery?
Paralysis of contralateral leg more so than arm - Motor homunculus shows that the part of the cortex that controls the leg is more medial
Disturbance of intellect, executive function and judgement
What are the effects of disturbance to the middle cerebral artery?
Typical stroke
Contralateral hemiplegia- more likely arm than leg
Contralateral hemisensory deficits
Hemianopia
Aphasia (Can’t speak)- if on left side as language centres are more on left than right
What function is Broca’s area involved with?
Speech
What function is Wernicke’s area involved with?
Understanding language
What are the effects of disturbance to the posterior cerebral artery?
The posterior cerebral artery supplies the occipital lobe where you find the primary visual cortex- this leads to visual defects- homonymous hemianopia, visual agnosia -not being able to recognise what you see
What are lacunae
Small holes that appear in brain tissue due to strokes. They appear in deep structures as a result of small vessel occlusion. Symptoms are dependent on location of small vessels
What is the difference between an extradural and a subdural haemorrhagic stroke?
Extradural is due to trauma and has immediate effects
Subdural is also due to trauma but has delayed effects
What is a subarachnoid haemorrhage usually caused by?
Ruptured aneurysms
What is the difference between the dura in the skull and in the vertebral column?
The vertebral column has a single layer of dura with fat between the bone and the dura
In the skull there are two layers of dura that are mostly stuck together
What are the two layers of dura in the skull called?
Periosteal and meningeal
What is the falx cerebri
A fold of dura that extends between the medial surfaces of the two hemispheres.
The superior sagittal sinus is where the two layers of dura peel apart at the top of the falx cerebri
What do you find within the gap in the dural layers
Arachnoid granulation- bursts of subarachnoid space that protrude into the superior sagittal sinus
Why do extradural haemorrhages have a rapid onset?
Usually due to rupture of meningeal artery
What does a rupture of a meningeal artery cause?
Compression of the skull underneath
Why is a subdural haemorrhage slower?
Caused by the rupture of veins in the skull as this is at much lower pressure, the onset of symptoms is much lower
