Polygon of Willis: parts and arteries that form it.

This is a place where most of the arteries that nourish the brain join at the base of the brain.

Our brain is a complex organ that governs and coordinates the totality of the systems that form our organism. But this organ, and the nervous system in general, does not function from nothing: it needs a continuous supply of oxygen and nutrients to be able to function. This supply will arrive through the Blood irrigation, reaching the different structures through the cerebrovascular system. Within this system we have different veins and arteries different veins and arteries, which converge in the polygon of Willis..

The polygon of Willis: description, location, and functions.

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

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

The functions carried out by the polygon of Willis are of great importance for our survival, since the blood flows through it. through it flows the blood that irrigates a large part of the encephalon.. 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 the blood that reaches one hemisphere to communicate with the other.

Arteries that converge in this polygon

As we have said, the polygon of Willis is the structure through which the different main arteries that supply 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 up to the head, through both sides of the neck, and finally penetrate into the crusand finally penetrate the skull (at which point they are called internal carotid arteries). Once inside it, they will be in charge of supplying blood to the anterior part of the brain, being in charge of supplying oxygen and nutrients to most of the brain (both cortex and subcortical structures), to form, together with its branches, the anterior part of the polygon of Willis. It will later 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 enter the base of the brain.which enter the base of the skull directly ascending around the vertebrae. This artery and its branches (the posterior cerebral arteries) are responsible for providing blood flow to the brainstem and posterior regions of the brain (including the occipital lobe), forming the posterior part of the polygon of Willis.

3. Posterior communicating arteries

These are two arteries of great importance, since they allow communication between the internal carotid artery 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 the two 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 branches irrigate sensorimotor areas and the orbitofrontal, 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 towards the interior of the brain. Its blood supply reaches the striatum, the insula, and orbital, frontal, parietal, and parietal regions of the brain.and to orbital, frontal, parietal and temporal regions. It follows the fissure of Sylvius, which is why it is also called the artery of Sylvius or Sylvian.

7. Posterior cerebral artery

Artery arising from the connection between the basilar artery and the posterior communicating artery. Particularly important for the irrigation of the inferior and deep areas of the temporal and occipital lobes.Its action allows aspects related to vision.

8. Cerebellar arteries

These are the arteries that contribute to irrigate the cerebellum, as well as other structures of the brainstem. We can find the superior cerebellar, anteroinferior and posteroinferior cerebellar arteries.

9. Spinal arteries

The spinal artery is the artery that supplies blood to the spinal cord, being of great importance for the autonomic nervous system and the transmission of information from the brain to the different organs.

When lesions appear

The polygon of Willis is an area of great importance for the human being, arising in its interconnections a large number of branches that can host up to 80% of the blood vessels. can host up to 80% of the cerebral blood supply.. But sometimes this polygon can be damaged after a trauma, an aneurysm or a cardiovascular accident in this region.

If some kind of obstruction appears in the polygon, it is possible that the irrigated areas are deprived of oxygen and die. The consequences can be manifold, ranging from death (if, for example, the nuclei that regulate vital signs are lost) to the loss of mental and physical functions, sensibility or motor capacity..

Another problem that can occur is the appearance of an aneurysm (in fact, the polygon of Willis is one of the main places where problems of this type tend to appear), which can have dire consequences for the affected subject. And even if the outcome is not fatal, it is possible to lose vision due to 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). Arterial circle of Willis. In: Tratado de Anatomía Humana, Editorial Interamericana. 1st Edition: 760-3.
• Kandel, E.R.; Schwartz, J.H. & Jessell, T.M. (2001). Principles of neuroscience. 4th Edition. McGraw-Hill Interamericana. Madrid.
• Quintero-Oliveros, S.T.; Ballesteros-Acuña, L.E.; Ayala-Pimentel, J.O.; and Forero-Porras, P.L. (2009). Morphological characteristics of cerebral aneurysms of the polygon of Willis: direct anatomical study. Neurosurgery, 20 (2): 110-116.