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Polygon of Willis: parts and arteries that form it

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Our brain is a complex organ that governs and coordinates all of 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 contribution will reach you through the blood supply, reaching the different structures through the cerebrovascular system. Within this system we have different veins and arteries, which converge at the circle of Willis.

  • Related article: "Parts of the human brain (and functions)"

The polygon of Willis: description, location and functions

We call a polygon of Willis 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 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

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, surrounding the heptagon that forms structures such as the optic chiasm, the hypothalamus and the hypophysis. Its structure can vary enormously from one person to another, finding that more than half of the population has a structure of this polygon different from what is considered classic or typical.

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

Arteries that converge in this polygon

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

1. Internal carotid artery

The carotid arteries up the body to the head, on both sides of the neck, to end up penetrating the skull (at which time they are called internal carotids). Once inside it, they will be in charge of supplying blood to the front part of the brain, taking care of a large part of the supply of oxygen and nutrients to the most of the brain (both cortex and subcortical structures), to form together with its ramifications the anterior part of the polygon of Willis. 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 union in the brainstem of the vertebral arteries, 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 Brain stem and to the posterior regions of the brain (including the occipital lobe), forming the posterior part of the circle of Willis.

3. Posterior communicating arteries

We are facing two arteries of great importance, since they allow communication between the internal carotid artery and posterior cerebral arteries in such a way that the main cerebral arteries on the same side of the brain are connected each.

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 forms part of the circle or polygon of Willis directly. Its ramifications allow to irrigate sensorimotor areas and the orbitofrontal, among other areas of interest.

6. Middle cerebral artery

The largest branch of the carotid and the most vulnerable to occlusions, its blood supply tends to be directed towards the interior of the brain. His blood supply reaches the striatum, the insula, and to orbital, frontal, parietal and temporal regions. Follow the Silvio fissure, which is why it is also called the Silvio or Silvian artery.

7. Posterior cerebral artery

Artery arising from the connection between the basilar artery and the posterior communicating artery. Especially important for 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 supply the cerebellum, as well as other structures of the brain stem. We can find the superior, anteroinferior and posteroinferior cerebellar

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 Willis polygon is an area of ​​great importance for humans, with a large number of ramifications arising in its interconnections that can host up to 80% of the cerebral 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 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 death. loss of mental and physical functions, sensation or motor ability.

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

Bibliographic references:

  • Gómez García,;.; Espejo-Saavedra, J.C.; Taravillo, B. (2012). Psychobiology. CEDE PIR Preparation Manual, 12. CEDE, Madrid.
  • Gray, D.J. (1985). Arterial circle of Willis. In: Treaty of Human Anatomy, Editorial Interamericana. 1st Edition: 760-3.
  • Kandel, E.R.; Schwartz, J.H. & Jessell, T.M. (2001). Principles of neuroscience. Fourth 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 brain aneurysms of the circle of Willis: direct anatomical study. Neurosurgery, 20 (2): 110-116.
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