Blood supply to brain and spinal cord

Question 1

What are the main arteries supplying the brain?

Answer 1

• Aorta
• Common carotid arteries divide into internal and external carotid arteries (Internal carotid artery through carotid canal)
• The sub-clavian arteries give off the other arteries which supply the brain - vertebral arteries
• These arteries travel up through the cervical vertebrae and the skull through the foramen magnum

Question 2

How does the vertebral artery run up the neck?

Answer 2

• Through bony tunnels in the first six vertebrae
• popping your neck can cause a small tear in the internal vertebral artery causing an ischemic stroke

Question 3

Why is the blood supply to the brain important?

Answer 3

• Brain consusmes ~ 20% of the oxygen of the body
• Ischeamic stokes, are the most common cause of stroke (85%)m 15% haemorrhagic

Question 4

What happens to the arteries once they enter the skull?

Answer 4

• Vertebral and internal carotid arteries connect (anastamose) to form the circle of Willis.
• Smaller arterial branches from this circle span off to supply the different parts of the brain

Question 5

Explain the Circle of Willis

Answer 5

• Internal carotid arteries enter the skull through the carotid canal and then through the cavernous sinus in the brain ( venous sinus that drains venous blood from the brain)
• The inerncal CAS end by dividing into the anterior and middle cerebral artries
• The posterior communicating arteries complete the arterial circle
• The basillar artery ends by dividing into the two posterior cerebral arteries
• The basillar artery gives off branches to the cerebellum ( posterior inferior cerebellar, anterior inferior cerebellar and superior cerebellar arteries) + numerous branches to the pons itself
• The intracranial parts of the vertebral arteries unite at the pons to fomr the basillar artery

Question 6

What areas of the brain do the vertebral arteries supply?

Answer 6

• Cranial meninges
• Upper part of the spinal cord and medulla of the brainstem

Question 7

What areas of the brain do the basillar arteries supply?

Answer 7

• The pons
• Internal parts of ear
• The cerebellum and midbrain

Question 8

What are of the brain do the internal carotid arteries?

Answer 8

• Supply the majortiy of the forebrain

Question 10

What areas of the brain do the anterior, middle and posterior cerebral arteries supply?

Answer 10

• Anterior cerebral arteries = supply most of the medial and superior surfaces of the brain and frontal pole
• The middle cerebral arteries - supply the lateral surface of the brain and the temporal pole
• The posterior cerebral arteries - supply the inferior surface of the brain and occiptial pole

Question 11

What happens when a major artery is blocked?

Answer 11

• Branches of the cerebral arteries anastomose with each other on the surface of the brain
• These anastamoses are not capable of providint (or enough blood for the area of brain tissue supplied if a cerebral artery is obstructed by a blood clot (or other embolus)
• Cerebral ischemia - (loss of blood and oxygen supply to an area of brain tissue) -occurs
• Necrosis - death of tissue
• Large cerberal clots , occluding major cerebral vessels, may cause severe neurologic problems and even death

Question 12

What happens when there is a blockage to the anterior cerebral artery?

Answer 12

• leads to ischaemia of the pre-central gyrus in the frontal lobe
• The pre-central gyrus - where the primary motor areas of the cortex are situated
  Signs and symptoms :
• Paralysis of the opposite side of the body (contralateral) to the arterial blockage ( right ACA blockage results in left sided weakness) - descending corticospinal tract decussates (ccrosses over) in the medulla
• Results in hemiplegia maninly of the lower limb
• If postcentral gyrus is also affected, there will be a contralateral opposite side impaired sensation , mainly of the leg

Question 13

What happens when there is a blockage to the middle cerebral artery?

Answer 13

• supplies the lateral aspect of the brain
• ischaemia to lateral part of the parietal lobe
• Patient will have paralyis on the contralateral side of the body especially of the upper limb and face.
• If postcentral gyrus is also affected then there willl also be impaired sensation of the contralateral side
• Patients ignore the contralateral side of their bodues and all objects in space on that side, as their brain no longer receives sensory information from this area
• If the left hemisphere is involved, aphasia (Speech disturbances) may occur because the speech centres are located laterally in this hemisphere

Question 14

What happens if there is a blockage to the posterior verenral artery?

Answer 14

• Posterior cerebral artery supplies the occipital lobe
• Blockage will result in ischaemia to the visual cortex in the occipital lobe
• Patient will experience a loss of half of their vision in both eyes = homonymous hemianopia with sparing of macular vision

Question 15

Where do the arteries which supply the spinal cord come from?

Answer 15

• The sub-clavian arteries give off the vertebral arteries
• Anterior spinal artery and 2 posterior spinal arteries
• They travel down the spinal cord to end around the conus medullaris

Question 16

Explain the structure of the longitudinal spinal arteries

Answer 16

• Two posterior spinal arteries run down the posterior aspect of the cord
• Anterior spinal artery runs down the anterior aspect of the cord
• The anteripr and posterior spinal arteries anastomose and form an arterial spinal plexus around the spinal cord

Question 17

What is the function of the segmental arteries>

Answer 17

• provide additional supply to the spinal cord
• A segmental spinal artery from a posterior intercosatal artery communicate with the anterior and posterior longitudinal arteries
• given off from a number of arteries e.g. the ddep cervical artery , lumbar arteries

Question 18

What is anterior spinal artery syndrome?

Answer 18

• most common form of spinal infarction
• antero-lateral area of the spinal cord will lose its blodo supply

Signs and symptoms :
- Bilateral loss of motor function and pain/temperature sensation (both descending corticospinal and ascending spinothalamic tracts are affected)
- Flaacid paralysis to start wirh
- Spastic paralysis later on ( because it is an upper motor neuron lesion)
- Relative sparing of proprioception and vibratory senses below the level of the lesion ( dorsal column tracts are unaffected)
- Autonomic nervous system dysfunction may be present and manifest as hypotension, sexual dysfunction and/ or bowel and bladder dysfunction

Question 19

What is posterior spinal artery syndrome ?

Answer 19

An infarct of the posterior spinal artery which results in a samller area do imjury to the spinal cord which is located posteriorly
Signs and symptoms :
- Loss of proprioreception and vibratory senses below the level of injury due to loss of dorsal column tracts
- No significant muscle weakness as the posterior spinal cord carries mainly sensory information