S4) Blood Supply to the Brain Flashcards
There are two paired arteries which are responsible for the blood supply to the brain.
What are they?
- Vertebral arteries
- Internal carotid arteries
What is the Circle of Willis?
- The Circle of Willis is the anastomotic circle formed from the terminal branches of the ICA and vertebral arterie
- From this circle, branches arise which supply the majority of the cerebrum
Describe the anatomical course of the internal carotid artery
⇒ Originates at the bifurcation of the common carotid artery (C4)
⇒ Move superiorly within the carotid sheath
⇒ Enter the brain via the carotid canal of the temporal bone
⇒ Pass anteriorly through the cavernous sinus
Distal to the cavernous sinus, the internal carotid artery gives rise to four branches.
Identify these branches as well as the respective region they supply
- Ophthalmic artery – supplies structures of the orbit
- Posterior communicating artery – acts as an anastamotic connecting vessel in the CoW
- Anterior cerebral artery – supplies part of the cerebrum
- Middle cerebral artery – supplies the lateral portions of the cerebrum
Describe the anatomical course of the vertebral arteries
⇒ Originates from the subclavian artery (medial to anterior scalene muscle)
⇒ Ascends up the posterior side of the neck, through the foramen transversarium
⇒ Enters the cranial cavity via the foramen magnum
⇒ Gives off branches, then converge to form the basilar artery
Within the cranial vault, the vertebral artery gives rise to three branches.
Identify these branches as well as the respective region they supply
- Meningeal branch – supplies the falx cerebelli
- Anterior and posterior spinal arteries – supplies the spinal cord, spanning its entire length
- Posterior inferior cerebellar artery – supplies the cerebellum
There are three main paired constituents of the Circle of Willis.
Identify them as well as their origins
- Anterior cerebral arteries – terminal branches of the internal carotid arteries
- Internal carotid arteries – immediately proximal to the origin of the middle cerebral arteries
- Posterior cerebral arteries – terminal branches of the vertebral arteries
To complete the circle, there are two connecting vessels present.
Identify these as well as their role
- Anterior communicating artery: connects the two anterior cerebral arteries
- Posterior communicating artery: connects the ICA to the posterior cerebral artery
There are three cerebral arteries.
Identify them as well as the respective portion of the cerebrum that they supply
- Anterior cerebral arteries – supply the anteromedial portion of the cerebrum
- Middle cerebral arteries – supply the majority of the lateral part of the brain, travels across the lateral fissure (Sylvian fissure) into deep structures of hemisphere
- Posterior cerebral arteries – supply both the medial and lateral parts of the posterior cerebrum arise from bifurcation of basilar artery
The spinal cord is primarily supplied by three longitudinal arteries, as it descends from the brainstem to the conus medullaris.
Identify them as well as their origins
- Anterior spinal artery – formed from branches of the vertebral arteries and travel in the anterior median fissure, terminating as sulcal arteries
- Two posterior spinal arteries – originate from the vertebral artery / the posteroinferior cerebellar artery, anastomosing in the pia mater
Below the cervical level, longitudinal arteries offer insufficient blood supply. There is support via anastomosis with the segmental medullary and radicular arteries.
Describe the location of the segmental medullary arteries
Anterior and posterior segmental medullary arteries originate from spinal branches of many of arteries, then enter the vertebrae through the intervertebral foramina
Below the cervical level, longitudinal arteries offer insufficient blood supply. There is support via anastomosis with the segmental medullary and radicular arteries.
Describe the regions supplied by the radicular arteries
- The radicular arteries supply the anterior and posterior nerve roots
- Some radicular arteries may also contribute to supplying the spinal cord
What is the great anterior segmental artery of Adamkiewicz?
The great anterior segmental artery of Adamkiewicz reinforces circulation to the inferior 2/3 of the spinal cord, and is found on the left in the majority of individuals
What is a stroke?
A stroke is an acute development of a neurological deficit, due to a disturbance in the blood supply of the brain
There are four main causes of a cerebrovascular accident.
Identify and describe them
- Thrombosis – obstruction of a blood vessel by a locally forming clot
- Embolism – obstruction of a blood vessel by an emboli formed elsewhere
- Hypoperfusion – lack of blood supply to the brain, due to systemically low blood pressure e.g shock
- Haemorrhage – an accumulation of blood within the cranial cavity
What is the most common cause of a cerebrovascular incident?
Embolism – in many patients, an atherosclerotic emboli will arise from the vessels of the neck
What is an aneurysm?
- An aneurysm is a dilation of an artery, which is greater than 50% of the normal diameter
- They are most likely to occur to occur in the vessels contributing to the Circle of Willis
What is a spinal cord infarction?
- A spinal cord infarction (aka spinal stroke) refers to the death of nervous tissue, which results from an interruption of the arterial supply
- Clinical signs include muscle weakness, paralysis and loss of reflexes
What are the lenticulostriate arteries?
The lenticulostriate arteries are small, deep penetrating arteries which branch from the middle cerebral artery - easily blocked (lacunae infarcts)
surrounds the primary motor and sensory cortex of the brain so a stroke in one can effect sensory or motor function
fibres in optic radiations can also be infected
circle of willis diagram
subfalcine herniation effect on anterior cerebral artery
it can put pressure on the artery → stroke
subfalcine herniation effect on anterior cerebral artery
calcarine sulcus used under falls cerebri it can put pressure on the artery → stroke
what is the course of the posterior cerebral arteries
- loop around midbrain and run along inferior surface of posterior hemisphere supplying occipital lobe and inferior aspect of temporal lobe
- some perforating branches going up to the thalamus
what does this diagram show
xray = blockage of small arteries from middle cerebral artery. lots lacunes // mini strokes
→ blockage where the red dot is (internal capsule) will create a pure motor stroke
what do the superior cerebellar arteries supply
superior aspect of cerebellum and the midbrain
what do the anterior cerebellar arteries supply
anterolateral cerebellum and the lateral pons
what are the two branches that form from the vertebral arteries
anterior spinal artery: supplies anterior ⅔ of the cord
posterior inferior cerebellar arteries: supplies posterior ⅓ of cord
