Blood Supply & Venous Drainage Flashcards
what are the main 2 sources of blood supply to the brain? where do they are from?
- vertebral arteries
- internal carotid arteries
- arise in the neck
what is the anastomotic circle of vessels in the cranial vault known as?
Circle of Willis
where do the internal carotid arteries originate from?
at the bifurcation on the left & right common carotid arteries at the level of the fourth cervical vertebrae (C4)
where does the internal carotid artery enter the brain?
via the carotid canal of the temporal bone
- pass anteriorly through the cavernous sinus
Distal to the cavernous sinus, what does each ICA give rise to?
- ophthalmic artery
- posterior communicating artery
- anterior chordial artery
- anterior cerebral
where do the vertebral arteries arise from?
from the subclavian arteries (medial to anterior scalene muscle)
what do the vertebral arteries travel through in order to ascent through the neck?
foramen transversarium (found in the transverse processes of the cervical vertebrae)
where do the vertebral arteries enter the cranial cavity?
via the foramen magnum
what are the branches given off from the vertebral arteries once in the cranial vault?
- meningeal branch
- anterior & posterior spinal arteries
- posterior inferior cerebella artery
what do the two vertebral arteries converge to form?
the basilar artery
what are the constituents of the Circle of Willis?
- anterior cerebral arteries
- internal carotid arteries
- posterior cerebral arteries
- anterior communicating artery
- posterior communicating artery
what arteries located in the Circle of Willis are considered ‘connecting vessels’?
- anterior communicating arteries
- posterior communicating arteries
what two arteries does the anterior communicating artery connect?
connects the two anterior cerebral arteries
what two arteries does the posterior communicating artery connect?
connects the ICA to the posterior cerebral artery
- the posterior communicating artery is a branch of the internal carotid
where does the posterior cerebral artery branch from?
branches off of the basilar artery to supply blood to posterior of brain
where is the Circle of Willis located?
forms around the optic chiasm’s & pituitary stalk
where does the Basilar artery lie?
lies over area of the pons
What is the function of posterior cerebral arteries?
branch off to the side from the Circle of Willis to supply the posterior part of brain
What is the function of the posterior communicating arteries?
communicate with the middle & arterial parts of circle of willis
what arteries supply the internal capsule?
Lenticulostriate arteries (branches of middle cerebral)
where does the middle cerebral artery travel to?
travels off to side into lateral fissure
why is it clinically relevant that different arteries supply different areas of the brain?
- different lobes of the brain have specialised functions
- a stroke in a specific lobe of brain will present differently compared to having a stroke in another lobe
if a patient has a stroke affecting the middle cerebral artery of the left hemisphere, what may the presentation look like?
Affected speech (aphasia)
- due to the middle cerebral artery going on to supply Broca’s area
- contralateral weakness affecting the face & arm
what will a stroke affecting the anterior cerebral artery present as?
- weakness in the lower limbs (leg & foot)
- personality changes
if a patient is having a stroke in the posterior cerebral artery, how may this present?
- visual agnosia
- memory impairment
what are the dural venous sinuses?
spaces between the periosteal & meningeal layers of the dura
why do the dural venous sinuses appear soon on the inside?
lined with epithelium
what is the function of dural venous sinuses?
- venous drainage of brain
- CSF resorption via the arachnoid granulations (these extend into the dural venous sinuses)
what are the main dural venous sinuses?
- superior sagittal sinus
- straight sinus
- sigmoid sinus
- petrosal sinuses
where does the sigmoid sinus drain into?
the internal jugular vein
where is the superior sagittal sinus?
runs along the Falx Cerebri
what can be said about the blood flow in the cavernous sinus?
blood supply is slow here
where does venous drainage of the upper part of the face go to?
the cavernous sinus
why is the danger triangle of the face named so?
any infection here can travel into the cavernous sinus
- slow blood movement results in bacteria multiplication
what type of haemorrhage may occur as a result of rupturing of the middle meningeal artery?
extradural/epidural haematoma
A person has a fall and bangs their head, they appear to lose consciousness very quickly… what may have occurred?
extradural/epidural haematoma
what type of haemorrhage is associated with old age? why?
subdural haematoma
- little veins pass through the tough dura, as age increases the tissues become less sturdy/vein walls thinner & any shock may cause rupture of vein
where is a subdural haemorrhage located?
bleed in between the dura & subarachnoid
how many cranial nerves are there?
12 bilateral pairs
where do the cranial nerves arise from?
Mainly in the brainstem (medulla)
- exceptions are Olfactory & optic nerve which arise in the forebrain
what do somatic motor axons innervate?
voluntary (striated) muscle
what do visceral motor axons innervate?
involuntary (smooth) muscles or glands
