1.2 Bloody supply Flashcards
Occlusion to BV in the brain for 10 seconds results in what?
unconsciousness
How much O2 does brain use?
What % of CO does brain receive?
Brain uses 20% Oxygen
Brain receives 17% Cardiac output
Define stroke
Persistent neurological deficit of vascular origin
What are the 4 major arteries that supply the brain?
2 Internal Carotid Arteries (80%)
2 Vertebral Arteries (20%)
Where do the vertebral arteries arise from and what do they supply?
Describe their pathway and include other arteries they give rise to
Branches of subclavian artery. Supply brainstem and spinal cord, cerebellum, inferior parts of cerebral hemispheres and parts of temporal and occipital lobes
1) ascend through transverse foramina for upper 6 cervical vertebrae
2) enter cranial cavity via foramen magnum
3) unite at lower pons to form Basilar Artery
4) Basilar artery divides into posterior cerebral arteries
Where do the Internal Carotid arteries arise from and what does it supply?
Describe their pathway and include other arteries they give rise too
Arises in the neck from common carotid arteries (at C3-C4) and supplies the majority of cerebral hemispheres and eye. (anterior part of brain)
1) enters cranial cavity via carotid canal and then foramen laserum
2) travels through cavernous venous sinus (related closely to CN III,IV, VI)
3) terminates into anterior and middle cerebral arteries (ACA, MCA)
List the 5 branches off the Internal carotid artery
1) Ophthalmic
2) Posterior Communicating
3) Anterior Choroidal
4) Anterior Cerebral Artery (ACA)
5) Middle Cerebral Artery (MCA) is direct continuation of ICA
How do the vertebral and carotid circulations link each other?
What is this known as?
The Internal carotid (anterior) links to vertebral (posterior) circulation via posterior communicating arteries
Connections between the VA and ICA form the circle of Willis (located on the base of brain)
Label the arteries shown on the Circle of Willis below
List the exact arteries that comprise the circle of willis and state how they connect
Internal Carotid arteries
- ACA: connect via anterior communicating artery
- MCA: connect to PCA via posterior communicating artery
Vertebral Arteries —> form Basilar Artery
- PCA connect to MCA via posterior communicating artery
Where in the brain do the anterior vs posterior circulations primarily supply?
Anterior circulation (ICA, ACA, MCA) supplies the Cerebrum Posterior circulation (VA) supplies the meningies and cerebellum
Before the vertebral arteries join to form the Basilar Artery, what 3 branch do they give off and what do these supply?
1) Posterior inferior cerebellar arteries (PICA) –> supply parts of the cerebellum
2) Posterior spinal
3) Anterior spinal (only ONE single AS created from a branch from each vertebral artery)
The 1 anterior and 2 posterior arteries supply the spinal cord
What branches does the Basilar artery give off? (5)
1) Posterior Cerebral Arteries (PCA)
2) posterior communicating
3) superior cerebellar arteries
4) pontine arteries
5) Anterior inferior cerebellar arteries (AICA)
What are the main territories of the brain supplied by the ICA and VB?
State and indicate on the image below (inclue main branches)
Internal carotid: supplies the anterior surface of the brain
- ACA supplies the superior strip
- MCA supplies the superolateral surface
Vertebral branches: supplies occipital part of brain
The PCA passes over what structure? What is the clinical revelance of this?
PCA passes over tentorium –> Prone to stretching and compression in raised ICP
State which teritory belongs to which artery in this coronal section of the brain
What is the V shape structure in middle and what is its function?
V shape structure in middle is known as the internal capsule This is the place where all the different axons from various regions of the brain come together in tight clusters
What arteries supply the spinal cord?
The anterior spinal artery supplies the anterior 2/3
The 2 posterior spinal arteries supply the posterior 1/3
List 3 ways arterial supply to the brain can be comprimised
1) Vessel occlusion: embolus or thrombus
2) Haemorrhage: burst aneurysm, degeneration of vessel wall
3) Aneurysm: abnormal dilatation of vessel wall often at sites of branching
Compare occlusion of an artery at the surface of the brain to occlusion in the Internal capsule (deeper) in the brain, explain why and the consequences
Chances of oclusion is unlikely in the arteries at the surface of the brain because of collateral circulation.
Size of arteries in the Internal capsule decreases, until we reach end arteries (terminal branches) which are extremely small and have no collateral circulation.
An occlusion here will lead to infarction of that part of the brain, which can subsequently lead to:
- Ischemic Stroke (87%)
- Hemorrhagic stroke (13%)
Compare an Ischemic vs Haemorrhagic stroke?
Which produces ‘focal’ vs ‘diffuse’ brain disfunction?
Ischemic: Occlusion to end artery (by clot/thrombus) comprises that region of the brain and causes it to become ischemic ➞ Focal brain disfunction
Hemorrhagic: weakness in vessel wall may cause vessel to rupture leading to a brain bleed which will compress the smaller vessels ➞ Focal brain disfunction
If a Hemorrhagic stroke is large it may leak into the subarachnoid space. This will cause a subarachnoid haemorrhage and increased ICP ➞ Diffuse brain disfunction
What is FAST?
What does specific stroke presentation depend on?
Signs of a stroke
- Face: one side of face drooping
- Arm: arm weakness
- Speech: speech difficulties
- Time: time to call for an ambulance
Specific stroke presentation (sign & symptoms) depend on part of brain affected
Give 4 consequences of a stroke
1) Hemiplegia, monoplegia, paraplegia (sensory loss and/or motor loss)
2) cranial nerve dysfunction
3) aphasia
4) Memory loss
Why will strokes/ neuron damage lead to permanent damage
because neurons are unable to regenerate, hence damage is irreversible
An image that represents the body over the surface of the brain is known as a what?
What does it show?
Homunculus: helps link symptom presentation to area of the brain affected
Describe the venous drainage of the brain incl structures involved
1) veins run in the subarachnoid space (do NOT follow arterial supply like other parts of the body)
2) drain into dural venous sinuses
* endothelial-lined spaces between periosteal and meningeal layers of dura
3) blood in dural sinuses ultimately drains into internal jugular veins
4) IJV > BCV > RA
What are the 2 layers of the Dura Mater and what is found between layers?
1) The menial layer
2) The periosteal layer
The dural venous sinus is located between these layers
Where do the dural sinuses join?
Join through the ‘straight sinus’ at the ‘confluence of sinuses’
Describe the superficial venous drainage of the brain
Superior cerebral Veins
⬇
Superior Sagittal sinuses
⬇
Straight sinus ➞ confluence ➞ transverse ➞ sigmoid
⬇
Internal jugular veins
Describe the venous drainage of the middle and inferior cerebral veins
middle and inferior cerebral veins (deeper part of cerebral hemisphere)
⬇
cavernous sinus (red arrow on image)
⬇
superior and Inferior pertrosal sinuses
⬇
sigmoid sinus
What structures do the deep cerebral veins drain and describe the pathway of drainage
Deep cerebral veins = Thalamus, Basal nuclei (deep subcortical structures)
⬇
Cavernous/cerebral venous sinuses
⬇
Petrosal sinuses ➞ sigmoid
⬇
Internal jugular veins
Where do the Internal cerebral veins drain?
Internal cerebral veins (under corpus callosum, splenium)
⬇
Unite with opposite side to form the great cerebral vein of Galen (GCV)
⬇
GCV joins with the inferior sagital sinus to form the straight sinus
⬇
confluence ➞ transverse ➞ sigmoid
⬇
Internal jugular
Do the dural venous sinuses have valves?
No
What cell type lines the ventricular system?
What are the contents of this system and where does this drain?
Cell type: Ependymal cells
Contents: CSF secreted from the choroid plexus
Pathway: CSF drains ➞ subarachnoid space ➞ through arachnoid granulations ➞ dural sinuses
How does the ventricular system communicate with the subarachnoid space?
Via 3 foramina in roof of 4th ventricle
What is the largest ventricle in the brain?
What horns does this contain?
R and L lateral ventricles which partly extend into:
- frontal lobe as the ‘frontal horn
- occipital lobe as the ‘occipital horn’
- temporal lobe as the ‘temporal horn’
What are the 4 ventricles of the brain? Include how each connects to the next and their locations
R and L lateral ventricles located in the R and L cerebral hemispheres
communicate with the third ventricle located down the midline between two thalami via the interventricular foramen (of Monro)
Third ventricle connects the fourth ventricle located in the brainstem at the cerebral aqueduct
What structure separates the R and L lateral ventricles?
The septum pellucidum
Arrangement of ependymal cells covering arterial loops form what structure?
label it below
Choroid plexus
Label CT
Describe the pathway of CSF flow in the brain, begin at lateral ventricles
List the 5 subarachnoid cisterns and indicate them on the image below
1) superior
2) cerebellomedullary
3) pontine
4) interpeduncular
5) chiasmatic
What is the function of the BBB?
BBB separates brain + cerebrospinal fluid (CSF) from blood AND tightly regulates movement of ions, molecules, cells between blood & brain
Describe the organisation (3 layers) of the BBB
1) layer of endothelial cells interconnected through tight junctions, NO fenestrations
2) basement membrane consisting of ➞ basal lamina of astrocytes and basal lamina of endothelial cells
3) protrusions of astrocytes ➞ pedicles, going onto the basal membrane
List 3 important functions of the BBB
1) maintains homeostasis in CNS (levels of hormones, nutrients and water)
2) protects brain from endogenous & exogenous toxins (pathogens in blood)
3) prevents escape of neurotransmitters into general circulation
Describe the organisation (3 layers) of the Blood-CSF barrier
1) choroidal epithelial cells ➞ secrete CSF, have microvilli Interconnected by tight junctions (which are more permeable than junctions b/w in BBB capillaries)
2) Basement membrane
3) Endothelium of pia mater capillaries containing fenestrations
Give one way in which we can get chemicals across the BBB (ie. medicines)
drugs structured to trick the BBB to and allow their passage across the BBB ➞ ‘trojan horse approach’
(drugs fused with chemicals that are able to cross BBB)
Compare capillaries in the BBB vs the Blood-CSF Barrier
BBB: non-fenestrated capillaries with tight junctions b/w endothelial cells
Blood-CSF Barrier: fenestrated capillaries in choroid plexus
List 4 substances that can freely cross the BBB and one substance that can cross via transport
Freely cross: CO2, O2, water and free forms of steroid hormones
Transport: glucose
What are circumventricular areas /organs (CVOs) of brain?
List 4 of these?
Structures of the brain that do NOT have a BBB
1) posterior pituitary (Neurohypophysis)
2) median eminence
3) area prostrema
4) lamina Terminalis
