0902 - Blood Supply of the Brain

Question 1

1.Describe the contributions of the vertebral and carotid arteries to the blood supply of the brain.

Answer 1

The vertebral and carotid arteries are the two major arteries supplying blood to the brain. Vertebral arteries supply cerebellar, basilar, and posterior cerebral arteries. Carotid arteries supply middle and anterior cerebral arteries. They are anastomosed by 2x posterior communicating arteries, which, together with an anterior communicating artery, form the Circle of Willis surrounding the optic chiasm.

Question 2

Draw the blood supply of the brain

Answer 2

Google Circle of Willis

Question 3

2. Explain the segmental nature of blood supply to the lower brainstem

Answer 3

At closed medulla, Anterior spinal supplies central wedge running anteriorly. Vertebral supplies lateral wedge and posterior spinal supplies most dorsal aspect.
At open medulla - anterior spinal supplies similar wedge, vertebral supplies wedge next to it running 1/2 way back , PICA supplies a spot next to that and posterior spinal supplies most dorsal.
At pons - Basilar artery (paramedian br) supplies the anterior wedge, short circumferential br supply the next lateral area, and long circumferential supplies between those two and the ventricle (draw it out). Superior cerebellar artery supplies the roof of the 4th ventricle and the most lateral aspects.

Question 4

What are the arteries that comprise the Circle of Willis? Where does it sit?

Answer 4

Encircles the hypothalamus, Optic chiasm, pituitary stalk, and mamillary bodies.
Comprised of posterior cerebral (base), posterior communicating (to carotids), anterior cerebral (to point where they run parallel), and anterior communicating between the two.

Question 5

What are the key branches of the vertebral arteries?

Answer 5

Posterior spinal arteries in postolateral sulcus.
Anterior spinal arteries - Unite to form the anterior spinal artery in spinal cord (tributaries come in at every level).
Posterior inferior cerebellar artery (PICA) - supplies lateral medulla, choroid plexus of 4th ventricle, and postero-inferior cerebellum (cerebrocerebellum).

Question 6

What does the PICA supply?

Answer 6

Supplies much of medulla and cerebellum including lateral medulla and choroid plexus of 4th ventricle. And postero-inferior surface of cerebellum.
Specifically - vestibular nuclei, olivocerebellar fibres, spinal V nucleus and tract, NTS, N ambiguus, spinothalamic tract, descending SY fibres.

Question 7

What happens in vascular accident in the PICA?

Answer 7

Lesion leads to Lateral Medullary Syndrome - (loss of N. Ambiguus)
I/L loss of pain and temp to face (Spinal V)
Vertigo, nausea, vomiting, nystagmus (Vestibular Nn)
Horner’s Syndrome (descending SY)
I/L limb and gait ataxia (dorsal spinocerebellar tracts, ICP, and olivocerebellar fibres)
C/L loss of pain and temperature sensation.

Question 8

What do the branches of the Basilar artery supply? How does it end?

Answer 8

Bifurcates to form the 2 posterior cerebral Aa.
AICA - Anterior inferior cerebellum and caudal pons
Superior Cerebellar - Superior cerebellum, caudal midbrain, and rostral pons.
Pontine Brs - Supplies pons and inner ear.

Question 9

What would occur with accident in Anterior spinal A at medulla?

Answer 9

Medial medullary syndrome - C/L hemiparesis (pyramid), C/L impairment of fine touch and proprioception (medial lemniscus), I/L paralysis of tongue muscles (XII nerve and nucleus)

Question 10

What medullary areas do the vertebral and spinal Aa supply?

Answer 10

Closed medulla
Branches of anterior spinal and direct branches of vertebral supply - Lower, spinal V nucleus and tract, Arcuate fibres and medial lemniscus, spinothalamic tracts, pyramids.
Posterior spinal artery supplies gracile and cunate nuclei
Open medulla
Anterior spinal supplies pyramids (corticospinal), medial lemniscus (dorsal columns), tecospinal tract and hypoglossal nucleus?

Question 11

What would a lesion of anterior spinal artery at open medulla affect?

Answer 11

Pyramid, medial lemniscus, tectospinal tract, MLF, XII nucleus.
Medial medullary syndrome - Contralateral hemiparesis (pyramid), C/L impairment of tactile discrimination, proprioception and movement (medial lemniscus), I/L paralysis of tongue (XII nucleus).

Question 12

What would a lesion of PICA at open medulla affect?

Answer 12

Vestiular nuclei, olivocerebellar fibes, spinal V nucleus and tract, Splitary nucleus and tract, N ambiguus, Spinothalamic tract, descending SY fibres, inferior cerebellar peduncle.
Lateral medullary syndrome - I/L loss of pain and temp sensation to face (Spinal V), dysphagia (N. Ambiguus), Vertigo, nausea, vomiting, nystagmus (Vestibular Nn), Horner’s Syndrome (descending SY), I/L limb and gait ataxia (dorsal spinocerebellar tracts, ICP and olivocerebellar fibres, C/L loss of pain and temp sensation (spinothalamic tracts).

Question 13

What would be affected in accident in basilar artery?

Answer 13

Entire pons is supplied by it. Gives locked in syndrome.
Apparently comatose - ischaemia affects descending/ascending pathways - and most/all pontine and medullary cranial nerves. Horner’s Syndrome due to descending SY affected.
Retain oculomotor and trochlear function (nuclei in midbrain) and hearing (cochlear and sup olivary fibres are lateral in pons).

Question 14

Affected in posterior communicating artery accident?

Answer 14

Most medial aspect of cerebral peduncle, and some of superior cerebral peduncle.

Question 15

What is supplied by the Anterior cerebral artery?

Answer 15

Passes medially into inter-hemispheric fissure. Medial aspects of frontal lobe and parietal lobe. Also runs over and supplies corpus callosum.Supplies olfactory bulbs and tracts, anterior hypothalamus. Also supplies paracentral-lobule (medial aspect near central sulcus) - leg and foot in M1 and S1.

Question 16

What is supplied by the Middle cerebral artery?

Answer 16

Runs laterally between frontal and temporal lobes into lateral fissure. Subdivides into 2 branches - frontal and anterior parietal lobes and temporal and posterior parietal lobes.
Supplies much of motor and sensory homunculus (contralateral hemiplegia and somatosensory loss, mainly affecting upper limb and head), sensory and motor aphasia, multiple sensory losses, and Wernicke’s area.

Question 17

What is supplied by the posterior cerebral artery?

Answer 17

Above tentum cerebelli. Wraps around brainstem at the midbrain.
Supplies tectum, cerebral peduncle (except most medial part), oculomotor (III) nucleus and Edinger Westphal.
Also supplies (central brs) - Thalamus, pineal, midbrain, and posterior aprts of putamen and globus pallidus. (Cortical brs) - entire inferior surface of temporal lobe, lateral and medial surfaces of occipital lobe.

Question 18

What would be affected by a lesion in the posterior cerebral artery?

Answer 18

Big one - Occipital cortex - contralateral hemianopsia - damage to V1-V3.
Weber’s Syndrome - necrosis of peduncle and CNIII I/L Ophthalmoplegia and ptosis, dilation of
pupil, no light response and no accommodation (CNIII nuclei/fibres); C/L paralysis of arm and leg (corticospinal fibres); C/L paralysis of lower face and tongue.
Benedikt’s syndrome - necrosis of the lemnisci and red nucleus - C/L involuntary limb movements (red nucleus, ascending SCP fibres), C/L loss of sensation (ascending sensory - spinal and medial lemnisci).

Question 19

What would be affected by a lesion in the middle cerebral artery?

Answer 19

Contralateral hemiplegia and somatosensory loss mainly affecting the upper limb and head (think homunculus layout), aphasia (sensory and motor). Multiple sensory losses.

Question 20

What would be affected by a lesion in the anterior cerebral artery?

Answer 20

Contralateral hemiplegia and somatosensory loss affecting the leg and foot.
Personality and executive function impairments too.

Question 21

6. Describe the system of venous dural sinuses, and the drainage of blood from the brain

Answer 21

Dural sinuses are contained between 2 layers of dura - virtually all outflow from cranium is via sigmoid sinus to internal jugular vein. Veins are only there to get blood to the sinuses.
Doesn’t follow arterial system so as to avoid heat transfer with arterial system.
Superior sagittal sinus runs above falx cerebri. Almost all blood leaves via the sigmoid sinus and then jugular vein.

Question 22

7. Discuss the anatomy of the cavernous sinus and explain its significance in the distribution of sympathetic fibres to the head.

Answer 22

It is where SY’s wrapped around carotid transfer to their CN friends. Carotid travels through bathed in venous blood.
Drains from deep structures of brain, the orbit, and central triangle of face. Thus infection in face/orbit was/is significant meningitis risk.

Question 23

Perforating branches of which artery supply some parts of the caudate and internal capsule

Answer 23

ACA (anterior limb)

Question 24

Perforating branches of which artery supply parts of the tnalamus, pineal gland, midbrain, cerebral peduncles, and posterior putamen and globus pallidus?

Answer 24

PCA