Circle of Willis

The Circle Of Willis ( cerebral ) (Latin arterial ring ( of the brain ) ) is an arterial ring in mammals and is one of the extracerebral anastomoses of the brain. In humans, it is supplied by three vessels with blood and is the midbrain to the base of the brain to the pituitary stalk and the chiasm of anterokaudal ( forward and down ). The idea of a ring, circulates through the blood, is not true as a rule. Rather, in most healthy individuals, it can be assumed that the three cerebral arteries split into terminal branches that are connected to each other. This connection is usually not so pronounced that a sudden, total occlusion of these vessels can be compensated before the ring by the other vessels. In chronic stenosis, however, reinforce the anastomosis, so that in extreme cases enough a single AC supply vessel to ensure the blood supply to the entire brain.

This arterial ring is called after the English anatomist Thomas Willis as vicious ( arteriosus ) Willis.

Supplying the brain vessels

Basilar artery

The basilar artery ( " for (brain ) basis belonging artery " ) draws from the spinal cord through the foramen magnum to the brain stem. It arises from the vertebral confluence of the left and right Endastes artery. Basilar go from the artery before it becomes a part of the arterial circle, yet different from most paired branches. For many people one of the two vertebral arteries is hypoplastic or not trained at all, without this having a disease value.

Internal carotid artery

The internal carotid artery ( internal carotid artery) is paired. The front part of the arterial circle is formed by itself and its branches.

External carotid artery ( animals only )

In some mammals ( Artiodactyla, cat, guinea pig) to ( obliterated ) closes the internal carotid artery after birth in the section outside the skull. However, the location within the skull (intracranial ) section is retained and receives secondary branches of the maxillary artery its inflow. In this initial section of the intracranial internal carotid artery in ruminants is a so-called " miracle power " ( rete mirabile ), a splitting into many small, intercommunicating arteries, which come together again to a large arterial vessel. In cats and other predators, a branch of the external carotid artery forms after passing through the sphenoidal artery anastomotica, over which runs the majority of the blood supply to the arterial circle. In humans, this is not the case. In guinea pigs, about 40 % of the amount of blood is transported through the ophthalmic artery to the internal circle of Willis.

Cerebral arteries ( cerebral arteries )

The cerebral arteries are branches of the basilar artery or either one of the two arteries. carotid internae:

Branches d Aa. carotid int:

• Anterior cerebral artery ( in animals: rostral cerebral artery ) supplies the anterior located towards the center sections of the cerebrum. The two front arteries are connected by a connecting branch ( anterior communicating artery ), which completes the ring in front.
• Middle cerebral artery: main vessel for the supply of the cerebrum

Branches d basilar artery:

• Posterior cerebral artery ( in animals: the caudal cerebral artery ) supplies the rear situated towards the middle sections of the cerebrum

Diseases

Disorders of the arterial blood supply can lead to a stroke. The laying of a vessel (eg by a thrombus ) or the injury to the vessel wall, such as may occur as a result of an aneurysm (see also subarachnoid hemorrhage ) are typical causes for this. In the moyamoya syndrome occurring mainly in Asians causes the blood vessels in the brain constrict slowly, leading to stroke and transitory ischemic attacks.