Our brain is a complex organ that governs and coordinates all the systems that make up our body. But this organ, and the nervous system in general, does not work from scratch: it needs a continuous supply of oxygen and nutrients in order to function. This supply will reach it through the blood supply, reaching the different structures through the cerebrovascular system. Within this system we have different veins and arteries, which converge in the Willis polygon .

The Willis Range: description, location and functions

We call a Willis polygon a heptagonal-shaped structure present in the brain. This structure is formed by the union of the different arteries that irrigate the brain, having an important role in the contribution of oxygen and nutrients of this one. It is considered an anastomosis, or interconnection in a network of parts or elements (in this case the arteries) differentiated from each other.ç

The Willis polygon can be found in the lower part of the brain , surrounding the heptagon which forms structures such as the optic chiasm, the hypothalamus and the pituitary. Its structure can vary greatly from one person to another, with more than half the population having a different structure of this polygon from what is considered classic or typical.

The functions carried out by the Willis polygon are of great importance for our survival, since through it flows the blood that irrigates much of the brain . In addition, this is the main auxiliary mechanism that allows blood to continue to reach the different regions of the brain even if there is an alteration or damage to the artery that in principle governs it. It also balances the blood supply received by both cerebral hemispheres, allowing blood that reaches one hemisphere to communicate with that of others.

Arteries that converge in this polygon

As we have said, the Willis polygon is the structure by which the different main arteries that irrigate the brain are interconnected. Among these arteries, the main ones and from which many others branch off are the following (although there are many other branches).

1. Internal carotid artery

The carotid arteries ascend through the body to the head, on both sides of the neck , to end up penetrating the skull (at which point they are called the internal carotids). Once inside it, they are responsible for supplying blood to the front part of the brain, taking charge of a large part of the supply of oxygen and nutrients to most of the brain (both cortex and subcortical structures), to form, together with its branches, the front part of the Willis polygon. Later it will be divided into anterior and middle cerebral arteries, among many others.

2. Basilar artery

Another of the main arteries supplying the brain, the basilar artery, appears after the junction in the brain stem of the vertebral arteries , which go into the base of the skull directly up around the vertebrae. This artery and its branches (the posterior cerebral arteries) are responsible for providing blood flow to the brain stem and the posterior regions of the brain (including the occipital lobe), forming the back of the Willis polygon.

3. Posterior communicating arteries

These are two very important arteries, since they allow communication between the internal carotid and the posterior cerebral artery in such a way that the main cerebral arteries on the same side of the brain are connected to each other.

4. Anterior communicating artery

The anterior communicating artery is a small artery that connects the right anterior cerebral artery and the left anterior cerebral artery, acting as a bridge between both hemispheres .

5. Anterior cerebral artery

Part of the bifurcation of the internal carotid artery, this artery is directly part of the circle or polygon of Willis. Its ramifications allow the irrigation of sensorimotor and orbitofrontal areas, among other areas of interest.

6. Middle cerebral artery

The largest branch of the carotid artery and the most vulnerable to occlusion, its blood supply tends to be directed into the interior of the brain. Its blood supply reaches the striatum, the insula , and the orbital, frontal, parietal and temporal regions. It follows Silvio’s fissure, which is why it is also called Silvio’s artery or silviana.

7. Posterior cerebral artery

Artery that arises from the connection between the basilar artery and the posterior communicating artery. Especially important for the irrigation of the lower and deep areas of the temporal and occipital lobes , since its action allows aspects related to vision

8. Cerebellar arteries

These are the arteries that help to irrigate the cerebellum, as well as other structures in the brain stem. We can find the superior, anteroinferior and posteroinferior cerebellum

9. Spinal arteries

The spinal artery is the artery that supplies blood to the spinal cord. It is of great importance to the autonomic nervous system and the transmission of information from the brain to the various organs.

When injuries occur

The Willis polygon is an area of great importance for the human being, emerging in its interconnections a large number of branches that can accommodate up to 80% of the brain’s blood supply . But sometimes it can happen that this polygon is damaged after a trauma, that an aneurysm appears or that there is a cardiovascular accident in this region.

If any type of obstruction appears in the polygon, it is possible that the irrigated areas will run out of oxygen and die. The consequences can be multiple, from death (if for example the nuclei that regulate vital signs are lost) to loss of mental and physical functions, sensitivity or motor capacity .

Another problem that can occur is the fact that an aneurysm appears (in fact, the Willis area is one of the main places where problems of this type usually appear) and ends up producing a spill, which can have dire consequences for the affected subject. And even if the outcome is not fatal, it is possible that he will lose his vision due to the compression of the optic chiasm.

Bibliographic references:

  • Gómez García, ;.; Espejo-Saavedra, J.C.; Taravillo, B. (2012). Psychobiology. Manual CEDE de Preparación PIR, 12. CEDE, Madrid.
  • Gray, D.J. (1985). Willis Arterial Circle. In: Tratado de Anatomía Humana, Editorial Interamericana. 1st Edition: 760-3.
  • Kandel, E.R.; Schwartz, J.H. & Jessell, T.M. (2001). Principles of neuroscience. Fourth edition. McGraw-Hill Interamerican. Madrid.
  • Quintero-Oliveros, S.T.; Ballesteros-Acuña, L.E.; Ayala-Pimentel, J.O. and Forero-Porras, P.L. (2009). Morphological characteristics of brain aneurysms in the Willis industrial area: direct anatomical study. Neurosurgery, 20 (2): 110-116.