24 - Blood Supply II Flashcards
There are three arteries that provide blood to the brain. What are they?
1 - Internal carotid
2 - Vertebral-basilar system
3 - Circle of Willis
Which artery provides 80% of the blood supply to the cortex?
Internal carotid artery
Which region does the internal artery primarily supply?
The internal carotid provides anterior circulation for the cortex
There are seven branches off of the internal carotid. What are they?
1 - Opthalmic artery 2 - Posterior communicating artery 3 - Anterior choroidal artery 4 - Anterior cerebral artery 5 - Middle cerebral artery 6 - Ganglionic (penetrating) arteries 7 - Watershed zones
Why is the ophthalmic artery important?
It is the main blood supply to the retina
Why is the posterior communicating artery important?
Part of the Circle of Willis
Each posterior communicating artery connects the three cerebral arteries of the same side
Remember - there are TWO of these… One on each side
What does the anterior choroidal artery supply?
- Optic tract
- Choroid plexus
- Cerebral peduncles
- Posterior limb of the internal capsule
- Globus pallidus
- Putamen
- Thalamus
Where can you see the anterior choroidal artery?
When there is a cross-section taken through the midbrain (you can see the “mickey mouse” face)
You can see both the substantia nigra and the cerebral aqueduct when looking at the cross-section of the midbrain
The anterior choroidal artery is a direct branch from the internal carotid
What does the anterior cerebral artery supply?
Anterior cerebral artery
- Medial aspect of the frontal and parietal lobes
- Medial sensorimotor cortex
The anterior cerebral artery gives off a branches while it is supplying the medial aspect of the frontal and parietal lobes. What is it called?
Pericallosal artery
Describe the pericallosal artery
Continuation of the Anterior Cerebral Artery as it arches superiorly and posteriorly.
Supplies the medial surface of the cerebral hemispheres and corpus callosum.
What is the name of the largest branch of the pericallosal artery
The callosomarginal artery is the largest branch of the pericallosal artery
What happens if there is an occlusion in the anterior cerebral artery?
Motor and somatosensory deficits will be evident on the CONTRALATERAL leg and foot
This is BA 1, 2, 3, 4
Think about the homonculus
Describe the anterior communicating artery
Anterior Communicating Artery connects the right and left anterior cerebral arteries.
Common location for cerebral aneurysms.
There is just ONE - this is different from the posterior communicating artery (there are two of those)
What is the recurrent artery of Heubner?
A branch of the anterior cerebral artery at the level of the optic chiasm
Supplies…
- portions of the caudate nucleus
- anterior putamen
- globus pallidus
- internal capsule
What does the middle cerebral artery supply?
Its another branch directly off the internal carotid artery
Supplies virtually the entire lateral surface of the cerebral hemispheres
There are two divisions of the middle cerebral artery. What are they?
The superior and inferior divisions
Describe the superior division of the middle cerebral artery
Superior division
- Located in the cortex ABOVE the lateral fissure
- Supplies the lateral frontal cortex, including the precentral and post central gyri (that would be the primary motor and primary somatosensory areas)
Describe the inferior division of the middle cerebral artery
Inferior division
- Located in the cortex BELOW the lateral fissure
- Supplies the lateral temporal lobe and parts of the parietal lobe
What are the lateral striate (lenticulostriate) arteries?
Branches of the middle cerebral artery
- Note that these arteries branch off before the middle cerebral artery enters the lateral fissure
- They supply the basal ganglia and the internal capsule
- They are PRONE TO NARROWING in patients with hypertension
Why do we call the lateral striate (lenticulostriate) arteries “stroke city”?
There is potential for something to go wrong when you go from a large vessel to a small vessel
Middle cerebral = BIG artery
Lateral striate = SMALL artery
The corticospinal tract is found in the area supplied by the lateral striate branches of the middle cerebral artery - This means there is potential for major deficits from a lesion in the corticospinal tract
What are the ganglionic (penetrating) arteries or anterior/posterior perforating substance?
These are direct branches of the internal carotid artery that penetrate into the area of the hypothalamus to supply with oxygenated blood
What is the last branch off of the internal carotid artery?
The Watershed Zones
What are the watershed zones?
The regions of the cortex between the two cerebral vessels
Why is the watershed zone clinically relevant?
Infarcts in these areas can occur with a severe drop in systemic blood pressure
Loss of blood = Loss of function ***
Explain this “watershed” thing a little more
During times of blockage of one of the arteries that supply the watershed area, such as in atherosclerosis, these regions are spared from ischemia by virtue of their dual supply. However, during times of systemic hypoperfusion, such as in disseminated intravascular coagulation or heart failure, these regions are particularly vulnerable to ischemia by virtue of the fact that they are supplied by the most distal branches of their arteries, and thus the least likely to receive sufficient blood.
(thanks wikipedia)
Okay, so now we have gone through the first of three arteries that supply the brain. What are the other two?
- Vertebral-basilar system
- Circle of Willis
There are seven branches off of the vertebral-basilar system. What are they? What percent of the cortex blood supply to they provide?
1 - Posterior spinal artery
2 - Anterior spinal artery
3 - Posterior inferior cerebellar artery (PICA)
4 - Anterior inferior cerebellar artery (AICA)
5 - Superior cerebellar artery
6 - Pontine arteries
7 - Posterior cerebral artery
20% of blood supply
Which artery does the posterior spinal artery branch from?
Vertebral artery
Where does the posterior spinal artery run?
Caudally on the dorsolateral aspect of the spinal cord
Remember that there are TWO of these, so they don’t run midline in the back of the spinal cord, but they both run a little off to the side on the dorsal brainstem
What does the posterior spinal supply?
The dorsal region of the caudal (lower) medulla (3)
What does the anterior spinal artery branch from?
Vertebral artery
Describe the path of the anterior spinal artery
It joins its mate from the opposite side, forming ONE single artery
This artery runs along the ventral midline of the spinal cord
Remember that cross section image of the spinal cord where it looked like a tripod of arteries around it… Two on the back of the spinal cord (2 posterior), one on the front (one anterior)
What does the anterior spinal artery supply?
The anterior spinal artery gives off paramedian branches which supply the medial regions of the caudal (lower) medulla (3)
What does the posterior inferior cerebellar artery (PICA) branch from?
Vertebral artery
Describe the course of the posterior inferior cerebellar artery (PICA)
It is a long, circumferential branch
This just means that it wraps around the circumference of the spinal cord to supply the opposite side it branches from
Remember that the vertebral-basilar system and the circle of willis is all located on the ANTERIOR surface of the spinal cord and brainstem - PICA supplies the cerebellum, so it makes sense that it has to wrap around to the back side of the brainstem where the cerebellum is located
What does PICA supply?
The inferior surface of the cerebellum, choroid plexus and the lateral regions of the caudal medulla
What does the anterior inferior cerebellar artery (AICA) branch from?
The basilar artery
This is DIFFERENT from PICA, which branches from the vertebral artery
Recall that the two vertebral arteries join together at the level of the caudal (lower) pons to form the basilar artery
Describe the path of the anterior inferior cerebellar artery (AICA)
It is also a long circumferential branch (same as PICA) because it wraps around to supply the cerebellum
What does AICA supply?
Supplies the anterior inferior surface of the cerebellum, the rostral (upper) regions of the medulla and the caudal (lower) regions of the lateral pons
What does the superior cerebellar artery branch from?
The basilar artery
Describe the path of the superior cerebellar artery
It is a long circumferential branch as well because it wraps around to the back side to supply the cerebellum
What does the superior cerebellar artery supply?
Superior surface of the cerebellum, caudal midbrain and rostral pons
What branches does the superior cerebellar artery give off?
It may give off a quadrigeminal artery to the corpora quadrigemina of the midbrain (2 superior colliculi, 2 inferior colliculi)
What do the pontine arteries branch from?
The basilar artery
There are two groups of branches on each side. What are they?
- Paramedian branches
- Short circumferential branches
What do the paramedian branches of the pontine arteries supply?
The medial regions of the pons (the area closest to the basilar artery)
What do the short circumferential branches of the pontine arteries supply?
The intermediate regions of the pons (the area a little further away from the basilar artery)
What is the last branch off of the vertebral-basilar system?
The posterior cerebral artery
Where can you find the posterior cerebral artery?
It arises from the bifurcation of the basilar artery at the level of the midbrain
What do the posterior cerebral arteries supply?
The midbrain, most of the thalamus and the medial and inferior surfaces of the occipital and temporal lobes
Does the posterior cerebral artery give off any branches?
- May give off a quadrigeminal artery to the corpora quadrigemina of the midbrain (2 superior colliculi, 2 inferior colliculi)
- Thalamoperforator arteries
- Posterior choroidal artery
What do the thalamoperforator arteries supply?
The thalamus and a portion of the posterior limb of the internal capsule
What does the posterior choroidal artery supply?
Supplies a portion of the thalamus
What is really important to keep in mind when thinking about obstructions in the vertebral-basilar system?
The rule of 4s
If an artery supplies the midbrain, you need to know that CN I, II, III, IV may be affected by an obstruction
If an artery supplies the pons, you need to know that CN V, VI, VII, VIII may be affected by an obstruction
If an artery supplies the medulla, you need to know that CN IX, X, XI, XII may be affected by an obstruction
There is one last arterial system to learn about…
Circle of Willis
What is the Circle of Willis?
The communication of the anterior and posterior circulations to the cerebrum and the brainstem
Is the Circle of Willis a true anastomoses?
No - it is not a true anastomotic cirlce, but instead these connections develop over time
What is the Wada test?
A test to determine which hemisphere of the brain is the dominant one
How do you perform the Wada test?
- First give a patient some reading material and instruct them to continue reading as long as they can
- Then you cannulate (insert a small tube) the internal carotid artery on one side of the body and infuse barbituates
- Barbituates are a pharmacological agent which will put the cortex to sleep
How do you determine which hemisphere is dominant?
It depends on the speech before the individual becomes unconscious
- If the speech continues fluently and accurately before the individual loses consciousness, we did not inject barbituates into the dominant hemisphere and the OPPOSITE side of the injection is the dominant side
- If the individual stops reading and is no longer capable of producing speech for a period of time before they pass out, we have injected barbituates into the dominant hemisphere and the SAME side of the injection is the dominant side
When would you conduct this test?
Primarily on left-handed individuals because it is unknown which hemisphere is dominant
There are two communicating arteries of the Circle of Willis. What are they?
Anterior communicating artery and posterior communicating artery
What is the function of the anterior communicating artery?
Joins the anterior cerebral arteries
There’s just ONE
What is the function of the posterior communicating artery?
Joins the internal carotid arteries with the posterior cerebral arteries
There are TWO
