Blood Supply Flashcards
What are the metabolic demands of the brain like?
Very high:
- Only 2% of body weight
- 20% O2 consumption
How sensitive is the brain to O2 deprivation?
Very sensitive - with ischemic cell death resulting within minutes.
The skull is very rigid and cannot be expanded. What is the pathological effect of this?
If there is anything in the brain that there shouldn’t be, this will act as a mass and cause compressions or herniations (e.g. tumour)
What is a lesion?
an area of tissue that has been damaged through injury or disease
What can cause focal cerebral lesions?
- Vascular (most common)
- Tumours (1ary or 2ary)
- Abscess
- Hydrocephalus
What are examples of vascular cerebral lesions?
- Transient Ischaemic Attack (TIA)
- Stroke
What is a stroke?
A neurological deficit of vascular origin, lasting more than 24 hours (may be due to infarction or haemorrhage)
Which 2 main arteries supply the brain?
There are two paired arteries which are responsible for the blood supply to the brain:
- Vertebral arteries
- Internal carotid arteries
Where are the vertebral arteries and the internal carotid arteries connected?
The terminal branches of these arteries form an anastomotic circle at the base of the brain –> the Circle of Willis
The vertebral artery is a major artery in the neck. Where does it arise from?
Branch of the subclavian artery
What is the transverse foramen? What is it specific to?
Specific to the cervical vertebra is the transverse foramen (also known as foramen transversarium). This is an opening on each of the transverse processes which gives passage to the vertebral artery and vein and a sympathetic nerve plexus.
How does the vertebral artery ascend in the neck?
Ascends through the transverse foramina of the cervical vertebrae until they reach the foramen magnum
how do the vertebral arteries enter the skull?
Via the foramen magnum
After passing through the foramen magnum and entering the skull, what happens to the 2 vertebral arteries (one each side)?
They fuse at the base of the brainstem to form the basilar artery
Where do the internal carotid arteries (one each side) arise from?
At the bifurcation of the left and right common carotid arteries
What vertebral level is the bifurcation of the left and right common carotid arteries?
C4
As the interal carotid arteries move superiorly, what are the enclosed in?
The carotid sheath
How do the internal carotid arteries enter the skull?
Via the carotid canal of the temporal bone
What does the external carotid artery supply?
Gives off many branches that supply blood to the face and neck
Does the internal carotid artery give off any branches in the neck?
No - straight to brain
Once in the cranial cavity, the internal carotid artery has a series of characteristic bends inside which region?
The cavernous sinus
After the cavernous sinus, where does the ICA emerge?
Either side of the optic chiasm
Inferior view of skull and foramen
Before converging to form the basilar artery, what 3 branches does each vertebral artery give off?
- Meningeal branc
- Anterior and posterior spinal arteries
- Posterior inferior cerebellar artery (PICA)
Labelled diagram of PICA
What does the PICA supply?
The posterior and inferior portion of the cerebellum
Labelled diagram of anterior spinal artery
How many PICAs are there?
2 (paired)
How many anterior spinal arteries are there?
Only 1 (unpaired)
How is the anterior spinal artery formed?
Contribution from each vertebral artery which fuse to form the single anterior spinal artery
Where does the anterior spinal artery travel? What does it supply?
All the way down the length of the spinal cord to supply its anterior aspect
Labelled diagram of posterior spinal artery
How many posterior spinal arteries are there?
2 (paired)
How is the posterior spinal artery formed?
Origin is variable:
- In some people they come straight off the vertebral arteries
- In others they come from the PICA (seen in this image)
Where does the posterior spinal artery travel? What does it supply?
All the way down the length of the spinal cord to supply its posterior aspect
There is also an anterior inferior cerebellar artery (AICA). Where does this arise from?
Most commonly arises from the basilar artery (after the 2 vertebral arteries have fused)
How many AICAs are there?
2 (paired)
What does the AICA supply?
The anterior inferior portion of the cerebellum
Several branches arise from the basilar artery. What are these called? What do they supply?
(Transverse) pontine branches - supply the pons
Distal to these pontine branches arising, which branch arises from the distal basilar artery near the termination of the basilar artery?
The superior cerebellar artery (paired)
What does the superior cerebellar artery supply?
The superior aspect of the cerebellum
How does the basilar artery terminate?
by bifurcating into the posterior cerebral arteries (PCA)
What do the posterior cerebral arteries supply?
The posterior aspect of the cerebrum
How many posterior cerebral arteries are there?
2 (paired)
How many pairs of cerebellar arteries are there?
3: PICA, AICA, SCA
Cerebrum vs cerebellum?
Cerebrum: is the largest part of the brain and is composed of right and left hemispheres.
Cerebellum: is located under the cerebrum.
Diagram of ICA emerging
Either side of optic chiasmus
Distal to the cavernous sinus, what branches does the ICA give rise to?
- Middle cerebral artery (N.B. this can be viewed as the continuation of the ICA)
- Ophthalmic artery
- Posterior communicating artery
- Anterior choroidal artery
- Anterior cerebral artery
Diagram of middle cerebral artery
What does the middle cerebral artery supply?
The lateral portions of the cerebrum