Blood supply to the brain Flashcards
How much of the body weight is brain
- Brain is 2% of body weight
what is the glucose, cardiac and oxygen input into the brain
- Receives 15% of cardiac output and uses 20% of total body oxygen and 25% of total body glucose
how much time of anoxia leads to unconsciousness int he brain
- 20 seconds of anoxia leads to unconsciousness
- 5 minutes and greater leads to permanent unconsciousness
describe the blood vessels in the brain
- Arteries – these are thin walled, easily blocked, disorted or ruptured
- Veins, no valves, thin walled, no muscles of elasticity to help return
Flow regulation by auto-regulation
describe normotensive cerebral blood flow
- In Normotensive cerebral blood flow – 50ml per 100g of brain tissue per min if cerebral perfusion pressure between 60-160mmHg
- This causes lower oxygen and higher carbon dioxide which leads to increased flow, only a small amount of increase carbon dioxide causes an increase in flow – relies on gravity to drain venous return out of the skull
what are the two blood supplies to the brain
these are the internal carotid (80%) and vertebral arteries (20%)
what is the anterior circulation of the brain and what does it supply
- 80% of the total cerebral blood flow is done by the internal carotids –
- they carry out the anterior circulation
- they go through the cavernous sinus
- provides most of the blood supply to the cerebral cortex
what is the posterior circulation of the Brian
- 20% comes from the vertebral arteries
- this supplies the brainstem, cerebellum and a little part of the cerebral cortex
what is the name of the blood supply to the brain
circle of willis
what makes the circle of willis the circle of willis
- They have communicating arteries that communicate between the anterior and posterior system and this creates the circle of willis
normally the collateral..
circulation is not open and you do not need it between the two systems
- therefore the anterior and posterior communicating are closed
why is blood from the right side not go into the left side of the brain and vis versa
- It does not transimit across from the right to the left side, this is because the pressure is the same from the right and left side,
when is the anterior communicating artery involved
- when there is a problem with either the right and left cerebral arteries
describe the collateral circulation to the brainstem
- The blood flow already has kind of a collateral circulation, this is because there are right and left vertebral arteries that merge to form the basilar
- if one vertebral artery is blocked the whole of the brainstems still has a blood stem as it only needs one vertebral artery to supply it (expect the medulla)
how much of the population is the classic circle of willis seen in
34.5%
when is collateral circulation open
Collateral circulation should only open when there is a pressure difference
what are the things that can go wrong with the blood supply to the brain
- Missing posterior communicating artery – doesn’t affect under normal circulations, only becomes a problem if you are blocking one of the blood supplies
- Missing or small anterior communicating or anterior cerebral artery
- Abnormal origin of posterior cerebral arteries from ICA
describe the blood supply to the brain
- you have two vertebral arteries
- these join together and form a basilar artery
- the vernetral arteries also give of the posterior spinal and anterior spinal artery
- they also give of the posterior inferior cerebellar artery (PICA)
- The basilar artery gives of the anterior inferior cerebellar artery (AICA)
- The basilar artery gives of the superior cerebellar artery as well
- the last part of the basilar is the posterior cerebral artery
(there are three cerebral arteries these are the posterior, middle and anterior) - there is a posterior communicating artery between the posterior cerebral artery and middle cerebral artery
- the internal carotid artery leads into the middle cerebral artery
- the anterior cerbreral artery branches of these
- anterior communicating artery connects the two anterior cerebral arteries
what are the four main branches of the ICA internal carotid artery
- ophthalmic
- posterior communicating
- middle cerebral artery
- anterior cerebral artery
what does the ophthalmic artery do
- it supplies the orbit and retina and optic nerve
- it connects to the external carotid artery
- it is seen in the ophthalmoscope
what does the posterior communicating artery do
– Connects carotid and vertebral artery system
the middle cerebral artery is a continuation of…
the ICA
what does the middle cerebral artery do
– it supplies Basal ganglia and internal capsule (striate arteries), lateral 2/3rds of cortex, lateral wall of the cerebral cortex, internal nucleus frontal, lateral and parietal
what does the anterior cerebral artery do and what does it anatomise with
– it supplies Internal capsule, medial wall side of frontal and parietal lobes
- supplies the corpus callous .
– Anastomose with MCA
– Anatomise at the top of the lateral wall of the cerebral cortex with the MCA
what does the middle cerebral artery give of
- it goes from the partial and temporal and gives of lenticulostraite vessels
what do the lenticulostriate vessels supply
- they are the blood supply to nuclei that are involved in movement and coordination, such as the the internal capsule
what is the blood supply of the internal capsule
lenticulostriate vessels of the MCA
what are these areas supplied with
- primary motor cortex
- primary somatosensory
MCA
what does the vertebral arteries supply
– Supplied by Dorsal medulla of brainstem – PICA- posterior inferior cerberallar artery
when do the vertebral arteries merge into the basilar artery
– Merge into the basilar at the medullarypons junction
what does the basilar supply
– Goes over the Pons and supplies it
– cerebellum
where does the basilar artery divide into the posterior cerebral artery
at midbrain level
what does the posterior cereal artery supply
– Inferior and medial aspects of temporal and occipital cortex
– Thalamus and posterior internal capsule supplied by it
– Midbrain
describe the superficial venous drainage that happens in the brain
- Superficial cerebral veins cross the subarachnoid space
- Bridging veins pierce dura as they enter intracranial Dural venous sinuses – mainly superior sagittal sinus they also cross into other Dural sinuses
- CSF drains back into these
what is the main venous drainage in to
superior saggiata sinus
what are dural sinuses made up of
the dura mater
what allows the flow of the CSF into the dural sinuses
- Arachnoid granulations allow CSF to flow into venous blood of sinuses but prevent back-flow of blood into sub-arachnoid space
what artery goes through the cavernous sinus
internal carotid artery
what does the cavernous sinus drain
- the base of the skull
what happens if the pituitary tumour continues to grow
- Above it is the optic chiasm
- Between it is the pituitary gland, therefore if you have a pituitary adenoma it pushes out and compresses the optic chiasm, if it continues to grow it will push into the cavernus sinus
- this can compressor cranial nerve III
what helps supply the spinal cord
- there is reinforcing blood vessels that help supply the spinal cord arteries (anterior and posterior spinal arteries)
- Great segmental medullary artery (artery of Adamkiewicz) on left in 65% of population reinforces circulation to 2/3rds of spinal cord, this happens at around T9-T11, it is the largest of the reinforcing arteries,
what is the largest reinforcing artery in the Spinal cord
Great segmental medullary artery (artery of Adamkiewicz)
what happens during an aortic aneurysm
- Patients undergoing surgery for an aortic aneurysm may lose all sensation and voluntary movement inferior to level of occlusion – due to the reinforcing arteries
- Severe drop in BP for 3-6 mins may be reduce or stop blood flow from the segmental medullary to anterior spinal artery
what are the two types of haemotoma
extradura - middle meneigneal artery
subdrua - venous bridging veins
what are the major causes of stroke
– Atherosclerosis – Hypertension – Aneurysm – Elderly – Head injury (trauma) – Alcoholics – Arteriovenous malformation
what are the 3 types of cerebral aneurysm
– saccular, fusiform, berry
describe the statistics of cerebral aneurysm
- Can get subarachnoid
- 1 in 15 will develop a brain aneurysm
- Women are at higher risk 3:2
what happens if you get a stroke in the anterior cerebral artery
- Contralateral sensorimotor loss below the waist
- Urinary incontinence
- Personality defects
- Split brain syndrome
what happens if you get a stroke in the posterior cerebral artery
- Contralateral homonymous hemianopsia
- Reading and writing deficits
- Impaired memory
what is wallenbrug syndrome
- it is a syndrome that is effected by the lateral medullary PICA
describe the symptoms of Wallenberg syndrome
– Vertigo, nystagmus, nausea and vomiting, dysarthia, dysphonia, loss of pain and temp in body (contralateral), loss of pain and temp in face (ipsilateral), loss of gag reflex (nucleus ambiguus)
– Horner syndrome (ipsilateral)
what are TIAs
Transiet ischemic attacks
• Temporary loss of brain function (<30 mins)
• Sudden onset but resolves within 24 hrs
what are the warning signs of heart attack or stroke
number of TIAs
– 4-8% in 1st month
– 12-13% in 1st year
– 24-29% in 5 years
what are the symptoms of TIAs
– Anterior circulation • Motor weakness • Hemi-sensory loss • Dysarthria • Transient monocular blindness – Posterior circulation • Vertigo • Diplopia • Ataxia
- amnesias
