Cerebral arteries

Arterial blood is delivered to the brain through four main arteries: the two internal carotid arteries and the two vertebral arteries. The internal carotid artery enters the skull through the carotid canal in the petrous temporal bone and then passes through the cavernous sinus to emerge through the dura close to the anterior clinoid process and as it does so it gives off the ophthalmic artery which supplies the structures off the orbit, including the central retinal artery. Thereafter the internal carotid artery forms part of the circle ofWillis.

The two vertebral arteries arise from the subclavian arteries. On each side the artery ascends to run through the foramina transversaria of the upper six cervical vertebrae, runs across the lateral mass of the atlas into the vertebral canal and through the foramen magnum. The anterior and posterior spinal arteries are given off as is the posterior inferior cerebellar artery before the two vertebral arteries join to form the basilar artery.

The circle of Willis is a ring of arteries at the base of the brain formed in the front by the internal carotid arteries bifurcating to give the middle cerebral arteries, and the anterior cerebral arteries which are joined by a channel,

Striate branch of anterior cerebral artery Anterior cerebral artery Internal carotid artery

Central branches

Superior cerebellar branches

Pontine branches

Anterior cerebral artery

Anterior • communicating artery

Middle cerebral artery

Posterior communicating artery

Anterior cerebral artery

Central branches

Middle cerebral artery

Posterior communicating artery

OTpt JlB

—si^-Basilar artery

Posterior cerebral artery

\3icr

Anterior inferior _ cerebral artery

Anterior spinal artery

OTpt JlB

—si^-Basilar artery

\3icr

Posterior inferior cerebral artery

Vertebral artery

Figure 21.2. Arteries on the base of the brain.

Posterior inferior cerebral artery

Vertebral artery

Figure 21.2. Arteries on the base of the brain.

the anterior communicating artery, which has very variable configurations (Fig. 21.2). The internal carotid arteries before their bifurcation give off the posterior communicating artery which runs backwards to join the posterior cerebral artery which is formed by the bifurcation of the basilar artery.

The middle cerebral artery through its branches supplies the lateral hemisphere above and below the Sylvian fissure (Fig. 21.3). The anterior cerebral artery supplies the medial aspect of the hemisphere as far back as the occipital lobe which is supplied by the posterior cerebral artery as is the medial aspect of the temporal lobe. Deep structures are supplied by perforating arteries from the circle of Willis. Although the arteries anastomose on the surface of the brain, once they enter the brain substance they become terminal (end arteries).

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