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Questions and Answers
What percentage of the total cerebral blood flow is supplied by the carotid arteries?
Where do the vertebral arteries join to form the basilar artery?
Which arteries are considered the major contributors to the anterior circulation of the brain?
What direct source does the left common carotid artery arise from?
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What structure is formed by the series of bends made by the internal carotid arteries as seen in a cerebral angiogram?
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Which of the following arteries is NOT a branch of the internal carotid artery?
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Which statement about the common carotid arteries is true?
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Which part of the brain is primarily supplied by the vertebral arteries and their branches?
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What does the hypophysial artery primarily supply?
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Which artery gives off branches that supply the optic tract, amygdala, and hippocampus?
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What is the consequence of occlusion of the anterior cerebral artery?
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Which structure does the posterior communicating artery primarily join?
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What is a common effect of occlusion in the branches of the middle cerebral artery?
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Which arteries contribute to the formation of the arterial circle of Willis?
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What type of artery is most frequently involved in producing lateral medullary syndrome when occluded?
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Which of the following is NOT a component of the blood-brain barrier?
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What is the function of the anterior inferior cerebellar artery (AICA)?
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What types of substances can pass through the blood-brain barrier without assistance?
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What is a transient ischemic attack?
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What is a cerebral aneurysm?
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Which sign is typically associated with anterior cerebral artery occlusion?
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What happens when blood flow is compromised in the circle of Willis?
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Study Notes
Blood Supply to the Brain
- The brain receives blood supply from two internal carotid arteries and two vertebral arteries.
- Vertebral arteries join at the ventral part of the pons, forming the basilar artery.
- The carotid arteries supply 80% of cerebral blood flow, while the vertebral arteries supply the remaining 20%.
- The anterior circulation (internal carotid system) supplies anterior and middle portions of the cerebral hemispheres and diencephalon.
- The posterior circulation (vertebral-basilar system) supplies the brainstem, cerebellum, and posterior portions of the cerebral hemispheres.
Anterior Circulation
- The internal carotid arteries course through the carotid canal in the base of the skull.
- The internal carotid arteries divide into the middle and anterior cerebral arteries.
- Branches of the internal carotid artery include superior and inferior hypophyseal arteries, ophthalmic artery, anterior choroidal artery, posterior communicating artery, anterior cerebral artery, and middle cerebral artery.
Branches of the Internal Carotid Arteries
- Hypophyseal arteries supply the infundibulum and median eminence of the hypothalamus.
- Ophthalmic artery enters the orbit through the optic canal and supplies the eye, orbit structures, scalp, frontal and ethmoid paranasal sinuses, and parts of the nose.
- Posterior communicating artery joins the proximal part of the posterior cerebral artery, forming part of the circle of Willis.
- Anterior choroidal artery supplies the choroid plexus, optic tract, uncus, amygdala, hippocampus, globus pallidus, lateral geniculate body, ventral portion of the thalamus, subthalamus, and ventral portion of the internal capsule.
- Middle cerebral artery ramifies over the lateral surface of the cerebral hemisphere, giving rise to frontal, parietal, and temporal branches.
- Anterior cerebral artery courses around the genu of the corpus callosum, supplying the medial aspect of the parietal and frontal cerebral cortex.
Posterior Circulation
- Vertebral arteries arise from the right and left subclavian arteries and ascend in the foramen of the transverse processes of the upper six cervical vertebrae.
- Vertebral arteries join at the caudal border of the pons to form the basilar artery.
- The basilar artery courses forward in the midline of the pons and divides into the posterior cerebral arteries.
Branches of the Vertebral Arteries
- The vertebral arteries supply the upper portion of the cervical spinal cord.
- Posterior inferior cerebellar arteries (PICA) supply the posterior part of the cerebellar hemisphere, inferior vermis, central nuclei of the cerebellum, choroid plexus of the fourth ventricle, and the lateral medulla.
- Occlusion of PICA results in lateral medullary syndrome (Wallenberg's syndrome).
Branches of the Basilar Artery
- Anterior inferior cerebellar artery (AICA) supplies the cortex of the inferior surface of the cerebellum, underlying white matter, deep nuclei of the cerebellum, upper medulla, and lower pons.
- Labyrinthine artery supplies the labyrinth of the internal ear.
- Pontine arteries supply the ventral portion of the pons and pontine tegmentum.
- Superior cerebellar artery supplies the dorsal surface of the cerebellum, medullary core, and central nuclei of the cerebellum, as well as the pons, superior cerebellar peduncle, and inferior colliculus of the midbrain.
- Posterior cerebral arteries supply the medial and inferior surfaces of the occipital and temporal lobes, rostral part of the midbrain, and caudal part of the diencephalon.
Medullary Syndromes
- Medial medullary syndrome results from infarct of paramedian penetrating branches, generally arising from the vertebral, anterior spinal, or basilar artery.
- Lateral medullary syndrome (Wallenberg's syndrome) generally results from occlusion of the direct branches of the vertebral artery supplying the lateral part of the medulla, or the vertebral or PICA artery.
Arterial Circle of Willis
- Major arteries supplying the cerebral hemispheres join at the base of the brain to form the arterial circle of Willis.
- The circle of Willis includes the anterior communicating artery, anterior cerebral artery, internal carotid artery (or middle cerebral artery), posterior communicating artery, and posterior cerebral artery.
- The anterior and posterior communicating arteries provide alternate routes for blood flow if one of the major arteries is compromised by occlusion.
Blood Brain Barrier
- Blood-brain barrier is a physical barrier between the central nervous system and blood vessels in the central nervous system.
- The barrier is formed by the wall of blood capillaries in the brain.
- The blood-brain barrier protects the brain from common infections.
- Tight junctions between the endothelial cells, a continuous basal membrane, and astrocyte processes contribute to the blood-brain barrier.
- Endothelial cells in the brain are packed more tightly, limiting transport.
- Glucose, ions, and oxygen readily pass through.
- Small fat-soluble molecules, such as ethanol, pass through.
- Water-soluble molecules require protein carriers for transport.
- The barrier is impermeable to high-size molecules, such as plasma proteins and large organic molecules.
- Cerebrospinal fluid (CSF) perfuses the central nervous system, and a barrier exists between the blood in the capillaries of the choroid plexus and CSF.
Clinical Notes
- Cerebrovascular accident (stroke) can be caused by occlusion (ischemic attack) or rupture of a vessel (hemorrhagic attack).
- Most strokes are ischemic attacks.
- Hemorrhagic attacks result from rupture of a weakened vessel, causing bleeding.
- Transient ischemic attack is short-term vascular occlusion which resolves without causing damage.
- Cerebral aneurysm is an abnormal dilation or ballooning of a brain artery.
- Unruptured aneurysms may cause neurological symptoms depending on the location and size.
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Description
This quiz covers the essential aspects of the blood supply to the brain, focusing on the internal carotid and vertebral arteries. It discusses their roles in supplying different parts of the brain, including anterior and posterior circulation. Test your knowledge on the anatomy and significance of these critical blood vessels.
