IC1 Blood supply to the brain Flashcards
Why is blood supply to the brain so important?
- Nerve cells need a constant, adequate blood supply
- Any interruption of blood supply can quickly lead to irreparable damage or death
- The damage is irreversible as neurons are post-mitotic cells → no active cell division to form new neurons
What are the 2 main types of artery that supplies blood to the brain?
Two pairs of arteries
1. Left and right internal carotid arteries
2. Left and right vertebral arteries
The vertebral artery originates from _____ & enters ______
- Vertebrobasilar arterial system
- Originates from subclavian artery in the neck
- Enters skull through foramen magnum (hole at base of skull)
Arteries that branch off from the vertebral artery supply blood to?
- Spinal cord
- Medulla oblongata
- Cerebellum
The left and right vertebral arteries join to form ______ and ends by ______
- A single artery in the midline
- Called the basilar artery
- Ends by dividing into the 2 posterior cerebral arteries
Arteries that branch off from the basilar artery supply blood to?
- Pons
- Cerebellum
- Inner ear
The posterior cerebral artery supplies blood to?
- Midbrain
- Medial aspect of the occipital lobe
- Base of the temporal and occipital lobes
The _____ carotid artery originates from _____
- Internal
- Common carotid artery in the neck
The carotid artery enters the skull through _____ and is located in _____
- Carotid canals
- And is situated within the cavernous sinus (a massive vein)
This is the only artery present in a vein
The internal carotid artery ends by?
Dividing into the anterior cerebral artery and the middle cerebral artery
What is the path of the anterior cerebral artery?
Passes forward into the medial longitudinal fissure and then sweeps back to the parieto-occipital sulcus
The anterior cerebral artery supples blood to?
Most of the medial surface of the hemisphere, except the medial aspect of the occipital lobe
What is the path of the middle cerebral artery?
Pass laterally between the temporal and frontal lobes
The middle cerebral artery emerges at the _____ & fans out to supply ______
- Lateral fissure
- Most of the lateral surface of the hemisphere – frontal, parietal, temporal and occipital lobes
What is the Circle of Willis?
- An anastomotic (connection) ring between the vertebral and internal carotid arteries
- This arterial ring is located at the base of the brain
Explain the purpose of the Circle of Willis
- Allows for collateral circulation
- In cases of slow occlusion of an artery on one side, blood can still pass around the other way to reach the affected area (communicating arteries have time to enlarge, to accommodate the ↑ blood flow)
- But ineffective if occlusion is sudden
Which artery connects the left & right cerebral arteries?
Anterior communicating artery
Which artery connects the middle & posterior cerebral arteries?
Posterior communicating artery
What is the difference between Ischemic & Haemorrhagic stroke?
Ischemic
Arteries of the brain occluded by a thrombus or embolus → ischemic stroke (87% of strokes) where brain tissue dies
Haemororhagic
Circle of Willis is a frequent site for aneurysms
Blood from the ______ brain drains into?
- Superficial and deep parts of the brain
- Venous sinuses (superficial to deep sinuses)
- Which eventually empty into the internal jugular vein and the heart
Blood from the superficial part of the ______ drains into ______. How is the speed of blood flow like?
- Superior aspect of the brain
- Superior sagittal sinus (largest of the venous sinuses)
- So blood flow out of the brain is much slower due to the greater expansion capacity
Blood from the inferior part of the brain drains into (A) and (B), and (B) further drains into (C)
A) Transverse sinus
B) Superficial middle cerebral vein
C) Cavernous sinus, into Sigmoid sinus, then jugular
The Cavernous sinus is closely related to?
- Cranial nerves III, IV, V, VI and
- A part of the internal carotid artery
Blood from the centre of the brain drains into (A) which then drain into (B)
A) Deep cerebral veins
B) Venous sinus (the straight sinus)
(A) and (B) flow into the transverse sinus, which continues into the (C) before draining into the internal jugular vein of the neck
A) Superior sagittal
B) Straight sinuses
C) Sigmoid sinus
How does a subdural haemorrhage occur?
Rupture of a cerebral vein between one of the superior cerebral veins as drains into the superior sagittal sinus
Suggest why the clinical manifestation of subdural haemorrhage may be delayed
- Venous pressure is low so seepage is slow
- Weeks later, after the blow has been forgotten, the slowly expanding hematoma presses on the brain → symptoms like dizziness, headaches, apathy, falling, confusion and drowsiness
Describe the characteristic of capillaries of the brain
- Tight junctions between endothelial cells which form the BBB
- BBB prevents random entry of water soluble substances into the brain parenchyma
(especially important as brain lacks immune cells except Microglial cells)
What is the function of the cerebrospinal fluid, CSF?
CSF is a clear fluid that
1. Acts as a protective “liquid cushion” around the brain and spinal cord by absorbing shock waves from blows and falls
2. Helps to remove metabolites from the brain as the brain has no lymphatic channels
How is CSF produced?
By the choroid plexus in the cerebral ventricles (a delicate, lace-like structure)
What is the pathway of CSF flow?
Lateral ventricle → 3rd ventricle → 4th ventricle via the cerebral aqueduct → it then flows out of the 4th ventricle to bathe the whole brain and spinal cord
How is the CSF absorbed?
Absorbed into superior sagittal sinus by arachnoid granulations
