New Muscle Layer Discovered on Jaw

The recently found muscle layer ranges from the back of the cheekbone to the anterior muscular procedure of the lower jaw. (S=shallow layer, D=deep layer, C=coronoid layer). Credit: Jens. C. Türp, University of Basel/ UZB

Human anatomy still has a couple of surprises in shop for us: scientists at the University of Basel have actually found a formerly neglected area of our jaw muscles and explained this layer in information for the very first time.

The masseter muscle is the most popular of the jaw muscles. If you position your fingers on the back of your cheeks and push your teeth together, you’ll feel the muscle tighten up. Anatomy books usually explain the masseter as including one shallow and one deep part.

Now, scientists led by Dr. Szilvia Mezey from the Department of Biomedicine at the University of Basel and Professor Jens Christoph Türp from the University Center for Dental Medicine Basel (UZB) have actually explained the structure of the masseter muscle as including an extra 3rd, even much deeper layer. In the clinical journal Annals of Anatomy, they propose that this layer be offered the name Musculus masseter pars coronidea— to put it simply, the coronoid area of the masseter– since the freshly explained layer of muscle is connected to the muscular (or “coronoid”) procedure of the lower jaw.

The physiological research study was based upon in-depth assessment of formalin-fixed jaw musculature, computer system tomographic scans and the analysis of stained tissue areas from departed people who had actually contributed their bodies to science. This remained in addition to MRI information from a living individual.

As if a brand-new animal types had actually been found

” This deep area of the masseter muscle is plainly appreciable from the 2 other layers in regards to its course and function,” discusses Mezey. The plan of the muscle fibers, she states, recommends that this layer is associated with the stabilization of the lower jaw. It likewise seems the only part of the masseter that can pull the lower jaw in reverse– that is, towards the ear.

A take a look at historic anatomy research studies and books exposes that the structure of the masseter muscle has actually currently raised concerns in the past. In a previous edition of Gray’s Anatomy, from the year 1995, the editors likewise explain the masseter muscle as having 3 layers, although the mentioned research studies were based upon the jaw musculature of other types and partially opposed one another.

Other specific research studies from the early 2000 s likewise reported 3 layers, however they divided the shallow area of the masseter into 2 layers and concurred with basic operate in their description of the much deeper area.

” In view of these inconsistent descriptions, we wished to analyze the structure of the masseter muscle once again thoroughly,” states Türp. “Although it’s usually presumed that physiological research study in the last 100 years has actually left no stone unturned, our finding is a bit like zoologists finding a brand-new types of vertebrate.”

Reference: “The human masseter muscle reviewed: First description of its coronoid part” by Szilvia E. Mezey, Magdalena Müller-Gerbl, Mireille Toranelli and Jens Christoph Türp, 2 December 2021, Annals of Anatomy– Anatomischer Anzeiger
DOI: 10.1016/ j.aanat.2021151879

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