Blood Supply

The supply of blood to the brain can be divided into arterial territories. Blood travels from the heart through the aortic arch and into the carotid and vertebrobasilar arterial systems. All of the arteries supplying blood to the brain arise from the aortic arch. These arterial systems join at the base of the brain to form the circle of Willis. The circle of Willis gives rise to branches that travel to the surface of the cerebral cortex, interior of the brain, cerebellum and brainstem

A blockage or leak in an artery or arteriole will cause an interruption of blood flow and damage the area of the brain supplied by that vessel. Minor occlusions may occur in the intracranial or extracranial vessels without causing neurological signs and symptoms due to extensive collateral connections exist between the arterial systems of the brain. The brain accounts for just 2% of our body weight but receives 15% of resting cardiac output and consumes 20% of the oxygen produced by the cardiovascular system

Anterior Circulation — The Carotid Arterial System

The anterior or the carotid arterial circulation includes the external and internal carotid arteries that branch off of the common carotid arteries. The carotid arterial system supplies blood to most of the cerebral hemispheres via the middle and anterior cerebral arteries. Deep branches of the carotid arterial system supply blood to the subcortical regions of the brain such as the basal ganglia and the thalamus. Lesions in the carotid arterial system may cause damage to structures supplied by any or all of its three clinically important branches

• The ophthalmic artery
• The anterior cerebral artery
• The middle cerebral artery

Symptoms associated with damage to the carotid arterial system involve three main arteries

• Ophthalmic artery
• Anterior cerebral artery (ACA)
• Middle cerebral artery (MCA)

Damage to the ophthalmic artery causes ipsilateral monocular loss of vision, homonymous hemianopsia and amaurosis fugax (fleeting blindness). Damage to the anterior cerebral artery causes contralateral weakness and sensory loss primarily in the leg. Damage to the middle cerebral artery causes contralateral weakness and sensory loss in the face, neck and arm and to a lesser degree in the leg. If the damage is in the left (dominant) hemisphere, aphasia may occur

The most common artery involved in stroke is the middle cerebral artery (MCA) which supplies blood to lateral surface of the frontal, temporal and parietal lobes. Deep penetrating branches of the MCA perfuse the subcortical regions of the brain including the basal ganglia, internal capsule and the corona radiate

The second most common artery damaged in stroke is the anterior cerebral artery (ACA) which perfuses the anterior surface of the frontal lobe and the medial surfaces of the frontal and parietal lobes

Posterior Circulation — The Vertebrobasilar Arterial System

The posterior or vertebrobasilar arterial circulation includes the two vertebral arteries that join to form the basilar artery. The vertebrobasilar system supplies blood to the posterior part of the cerebral hemispheres including the occipital lobes and the posterior portions of the temporal lobes, the cerebellum and the brainstem. Lesions in the vertebral and basilar arteries may cause damage to any of the structures supplied by their clinically important branches including

• Brainstem
• Cerebellum
• Occipital lobe
• Temporal lobe

Interruption of blood supply to the brainstem causes loss of brainstem function, cranial nerve abnormalities with or without hemiparesis and hemisensory deficits. Brainstem damage may lead to dysphagia (difficulty swallowing due to paralysis of tongue and larynx) and dysarthria (inability to articulate clearly due to facial paralysis)

Loss of blood flow to the cerebellum causes ataxia (gross motor incoordination due to cerebellar damage), hypotonia, dysmetria, loss of equilibrium and vertigo. Loss of blood flow in the posterior cerebral artery will cause diplopia and bilateral hemianopsia

Information

• Blood supply to brain module for medical students by Stroke Association