Blood Supply of the Brain Flashcards
What are the 2 pairs of arteries that supply the brain?
- left and right internal carotid arteries
- left and right vertebral arteries
What is the pathway of the vertebral artery?
it originates from the subclavian artery in the neck then enters the skull through the foramen magnum then gives off branches for blood supply
What does the vertebral artery supply?
spinal cord, medulla oblongata and cerebellum
What are 3 the branches of the vertebral artery?
- anterior spinal artery
- posterior spinal artery
- posterior inferior cerebellar artery
What forms the basilar artery?
the 2 vertebral arteries joining at the pons
What does the basilar artery supply?
the hindbrain
What are 4 the branches of the basilar artery?
- anterior inferior cerebellar artery
- pontine branches
- labyrinthine artery
- superior cerebellar artery
How does the basilar artery end?
by dividing into the two posterior cerebral arteries
What do the posterior cerebral arteries supply?
- midbrain
- medial aspect of the occipital lobe
- base of the temporal and occipital lobes
What is the pathway of the carotid artery?
originates from the common carotid artery in the neck and enters the skull through the carotid canals situated within the cavernous sinus
How does the internal carotid artery end?
by dividing into the anterior and and the middle cerebral arteries
What is the pathway of the anterior cerebral artery?
it passes forward into the medial longitudinal fissure and then sweeps back to the parieto-occipital sulcus
What does the anterior cerebral artery supply?
most of the medial surface of the hemisphere (except the medial aspect of the occipital lobe)
What is the pathway of the medial cerebral artery?
it passes laterally between the temporal and frontal lobes then emerges at the lateral fissure and fans out
What does the middle cerebral artery supply?
the 4 lobes
What does the middle cerebral artery do between the temporal and frontal lobes?
give off the lenticulostriate arteries, which supply the internal capsule
What can a block in the lenticulostriate arteries cause?
motor defects in the limbs depending on which part of the striatum is affected
What is the circle of Willis?
an anastomosis between the vertebral and internal carotid arteries
What does the circle of Willis do?
supply blood to the opposite side of the brain in cases of slow occlusion of an artery in one side
What does the posterior communicating artery do?
connect the middle cerebral artery with the posterior cerebral artery
Why should the main arteries be present outside of the nervous tissue and where are they instead?
blood is cytotoxic; they sit in the arachnoid spaces between the pia and dura mater
Why is the circle of Willis clinically important?
if one of the arteries becomes slowly occluded, blood can still pass around the other way to reach the affected area i.e. collateral circulation
What causes an ischemic stroke?
the arteries of the brain becoming occluded by a thrombus or embolus
What is an embolus?
moving clot within the artery
What is the most common cause of stroke?
occlusion of the lenticulostriate arteries
What does a stroke result in?
motor deficits, sensory deficits and cognitive dysfunction
Where is a frequent site of aneurysms?
the circle of Willis
What is an aneurysm?
abnormal out-
pocketing of the wall of a blood vessel
What can cause visual disturbances?
an aneurysm pressing on adjacent structures, such as the optic chiasm
What causes a subarachnoid haemorrhage?
rupture of a berry aneurysm in the base of the circle of Willis
Which neurons are the most sensitive?
those in the cerebral cortex
Why can someone be impaired for life after a short interruption in the cerebral blood flow?
the neurons of the higher centres, such as personality, memory, have died, whereas the lower, life-sustaining ones might still be viable
How much of the CO does the brain use?
15-20%
What happens to blood from the brain?
it drains into venous sinuses, which eventually empty into the internal jugular vein
Where does blood from the superficial part of the superior aspect of the brain drain?
into the superior sagittal sinus
Where does blood from the inferior part of the brain drain?
into the transverse sinus as well as the superficial middle cerebral vein
Where does the superficial middle cerebral vein drain?
into the cavernous sinus
What is the cavernous sinus closely related to?
- cranial nerves III, IV, V and VI
- part of the internal carotid artery
Where does blood from the centre of the brain drain?
into the deep cerebral veins, which drain into the straight venous sinus
What is the pathway of blood from the superficial and deep parts of the brain?
venous sinuses → internal jugular vein → heart
Where do superior sagittal and straight sinuses flow?
into the transverse sinus → sigmoid sinus → internal jugular vein of the neck
Where can rupture of a cerebral vein occur?
between one of the superior cerebral veins as it drains into the superior sagittal sinus
What does rupturing of a cerebral vein lead to?
a subdural haemorrhage
What are symptoms of a subdural haemorrhage?
dizziness, headaches, apathy, falling, confusion, and drowsiness due to the slowly expanding haematoma pressing on the brain
What do capillaries of the brain do?
form the blood brain barrier
What does the blood-brain barrier do?
prevent the random entry of water-soluble substances into the brain parenchyma
What does the middle meningeal artery supply?
the dura matter (meninges) and the skull bone
Where does the middle meningeal artery lie?
between the dura mater and the skull
How can the middle meningeal artery be injured?
due to bone splinters from a head trauma cutting the artery
What are the 3 phases of injury to the middle meningeal artery?
- brief concussion
- lucid interval
- gradual loss of consciousness and death
What causes unconsciousness and coma after a head injury?
arterial blood flowing out rapidly between the dura and the bone forms an extradural haemorrhage that presses on the underlying brain and brain stem containing the cardiac and respiratory centres
What is the immediate surgical intervention to head trauma victims?
clamping of the cut artery and draining of the accumulated blood
What is CSF?
a clear fluid that acts as a protective “liquid cushion” around the brain and spinal cord by absorbing shock waves from blows and falls
What does the CSF do and why?
remove metabolites from the brain since the brain has no lymphatic channels
What is CSF produced by?
the choroid plexus in the cerebral ventricles
Where does CSF flow?
- from the lateral ventricle to 3rd ventricle
- via the cerebral aqueduct to the 4th ventricle
- flows out of the 4th ventricle to bathe the whole brain and spinal cord
How is CSF absorbed into the superior sagittal sinus?
by arachnoid granulations
