blood supply to the brain Flashcards
how much of the body weight is the brain?
2%
how much of cardiac output, body O2 and total glucose does the brain use?
15% of cardiac output, uses 20% of body O2 and 25% of total body glucose
what is the average brain blood flow?
46mL/100g of brain/minute
how long does it take for anoxia to lead to unconsciousness?
20 seconds
how is blood flow to the brain regulated?
auto-regulation
the brain is more sensitive to high CO2 levels than low O2 levels through central chemoreceptors
how are arteries in the brain different to those in the body?
more thin walled, easily blocked/distorted/ruptured
how are veins in the brain different to those in the body?
no valves, thin walled, no muscles/elasticity to help return –> drainage relies on gravity
how much of the total cerebral blood flow do the internal carotids make up?
80%
how much of the total cerebral blood flow do the vertebral arteries make up?
20%
explain the path of the subclavian arteries to the vertebral arteries?
subclavian arteries –> transverse foramen of cervical vertebrae –> foramen magnum –> join to form basilar artery
what do the vertebral arteries supply?
most of brainstem and posterior 1/3 of cerebral hemispheres
why are the anterior and posterior communicating arteries normally closed?
- Right and left internal carotid arteries supply their respective halves of the brain and keeps pressure the same
- Communicating arteries only open when there’s a difference in pressure in pathologies
how much of the population is the normal circle of willis seen in?
34.5%
name some variations of the circle of willis
- Missing posterior communicating artery – doesn’t affect blood flow. Only becomes problem if one artery is blocked.
- Missing/small anterior communicating/cerebral artery
- Abnormal origin of posterior cerebral arteries from ICA
how much of the brain does the anterior circulation supply?
anterior 2/3
what are the main branches of the internal carotid artery?
opthalmic
posterior communicating
middle cerebral artery
anterior cerebral artery
what does the opthalmic artery supply?
supplies the orbit, retina, optic nerve, choroid. Connects to the external carotid artery
what does the posterior communicating connect?
connects carotid and vertebral artery system.
what does the middle cerebral artery supply?
supplies the basal ganglia (needed in coordination of movement) and internal capsule (made of white matter tracts - striate arteries), lateral 2/3rds of cerebral cortex (frontal, parietal and occipital lobes)
what does the anterior cerebral artery supply?
Internal capsule, medial side of frontal and parietal lobes. Anastomose with MCA
what parts of the cerebral cortex does the MCA supply?
the frontal, parietal and the top half of the temporal lobe
o Primary motor, primary somatosensory, speech, language and understanding
what part of the cerebral cortex does the ACA supply?
supplies medial wall of the cerebral hemisphere
where does the MCA travel?
between the parietal and temporal lobe
what branches does the MCA give of and where do they go?
lenticulostriate branches (internal capsule, basal ganglia)
what does the primary motor cortex do?
upper motoneurons found here
what does the primary somatosensory cortex do?
integration centre for ascending tracts
what does Broca’s area do?
pre-motor cortex for speech (where speech is produced)
what does Wernicke’s area do?
integrating and understanding what has been spoken to
what does the primary auditory centre do?
where sound is processed (temporal lobe)
how much of the brain does the posterior circulation supply?
posterior 1/3 of the brain
what are the branches of the posterior circulation?
vertebral, basilar and posterior cerebral artery
what are the branches of the vertebral artery and what do they supply?
meningeal - falx cerebri
anterior/posterior spinal arteries
postrior inferior cerebellar arteries - cerebellum and dorsal medulla of brainstem
what are the branches of the basilar artery and what do they supply?
o Anterior inferior cerebellar artery: cerebellum, lateral medulla.
o Pontine arteries: supply the pons.
o Superior cerebellar arteries: supplies superior cerebellum
what does the posterior cerebral artery supply?
o Inferior and medial aspects of temporal and occipital cortex
o Thalamus and posterior internal capsule
o Midbrain
what does the posterior cerebral artery anastomose with?
MCA
why is PICA most likely to be blocked by an embolus/blood clot?
one of the first branches of the posterior circulation
what spinal tract does PICA not affect?
corticospinal tract
what cranial nerves are found near the arteries in the brain?
VI passes underneath the AICA and III comes out at the joint of the basilar and posterior cerebral arteries and SCA
where do the superficial cerebral veins cross?
the subarachnoid space
pierce the dura as they enter the intercranial venous sinuses
what are arachnoid granulations and what are they for?
allow CSF to drain into venous blood of sinuses but prevent backflow of blood into sub-arachnoid space
how are dural sinuses made?
between the periosteal and meningeal layers
what blood vessels supply the dural sinuses?
superficial cerebral veins
which sinus does the majority of blood in the brain drain into?
superior saggital sinus
where is the inferior saggital sinus found?
runs across length of head. Drains into confluence of sinuses into right transverse sinus.
describe the venous drainage system in the brain
inferior saggital –> straight –> transverse –> sigmoid
what is the cavernous sinus?
large collection of thin walled veins
where the ICA comes in - makes an acute bend so its seen twice
why is the ICA seen twice?
makes an acute bend
where is the cavernous sinus found?
either side of the pituitary gland
what effect can a pituitary adenoma have on the cavernous sinus?
pituitary adenoma can push into the cavernous sinus and compress CN 3
which cranial nerves pass through the cavernous sinus?
3, 4 and 6
why do spinal arteries need reinforcement and what do they receive reinforcement from?
small so they need reinforcement from lumbar and intercostal arteries to meet metabolic demands
radicular arteries from intercostal in the thoracic region
lumbar arteries in the lumbar region
what is the biggest reinforcing artery?
Great segmental medullary artery (artery of Adamkiewicz)
what level is Great segmental medullary artery (artery of Adamkiewicz) found? where is it found?
T9
• Found on left in 65% of population reinforces circulation to 2/3rds of spinal cord
what complication can arise during surgery for aortic aneurysm?
may lose all sensation and voluntary movement inferior to level of occlusion bc of blockage of the reinforcing arteries bc the spinal arteries aren’t sufficient
what are the types of cerebrovascular incidents/accidents?
• 2 types; extradural or subdural – depends whether the bleed is in or out of the dura
what are the major causes of stroke?
atherosclerosis, hypertension, aneurysm, elderly, head injury, alcholics, arteriovenous malformation
what are the 3 types of cerebral aneurysms?
saccular
fusiform
berry
how many people develop a brain aneurysm? who is more at risk?
- 1 in 15 people develop a brain aneurysm (not necessarily will rupture – then risk arises)
- Women at higher risk 3:2
why are cerebral arteries at risk of aneurysms?
• Arteries are so thin –> easy to distort, especially at junctions between arteries (e.g. posterior cerebral artery to basilar)
what are symptoms of an MCA stroke?
Global aphasia – inability to understand what’s being said and produce meaningful speech (not in grammatical order)
Sensorimotor loss on contralateral face, upper limb and trunk – not the legs (anterior cerebral)
neglect syndrome
what are symptoms of ACA stroke?
o Contralateral sensorimotor loss below waist (legs)
o Urinary incontinence
o Personality defects (frontal lobe is affected)
o Split-brain syndrome (corpus callosum is affected – right brain and left brain don’t communicate with each other)
what are symptoms fo PCA stroke?
o Contralateral homonymous hemianopsia
o Reading and writing deficits
o Impaired memory
what is a transient ischaemic attack?
• Temporary loss of brain function (<30 mins) -Sudden onset but resolves within 24 hrs
what are TIAs a warning sign of?
heart attack or stroke
what are TIA symptoms of the anterior circulation?
Motor weakness
Hemi-sensory loss
Dysarthria
Transient monocular blindness
what are TIA symptoms of the posterior circulation?
Vertigo, Diplopia, Ataxia, Amnesia
