Chew on This: Muscles of the Jaw

There are a LOT of muscles in your face that work while you are singing and speaking. Some of them are mostly about expression, some are focused on function, and some have a mix of both. For this week, I'm going to focus on only seven of those muscles that are connected to the jaw. These muscles act while we're chewing, opening our mouths, and articulating. Because of their role in chewing, they are really powerful, but also can execute incredible nuance and precision work. Let's learn about our jaw muscles and show them a bit of love!


Your mandible, or jaw bone, is the only bone in your skull that moves while chewing, speaking, breathing, yawning, or singing. Every other bone (except the three teeny tiny bones in your middle ear) are fixed and offer an anchor point for the other muscles to work against. It seems obvious, but until I really thought about it, I hadn't explicitly realized how static most of my head was, and how much motion the jaw uses to operate. Pretty neat.

The jaw can move in multiple planes: forward and backward, swinging up and down, and side to side. We can combine those planes of movement so that the jaw can move in a dizzying number of ways. Each side can move somewhat independently of the other, though the range of motion is somewhat reduced compared to when the two sides move together. This is also illustrative of some really complex neurological control of these muscles, because it appears that the brain can send signals and activate parts of a particular muscle to execute certain movements, as well as activating the entire muscle for larger movements. In other words, the fine motor control of your jaw muscles is rather intricate and precise.


A little side note here before we go any further, there are numerous issues that can come up with the jaw, such as TMJD and muscle tension that can happen with dental or orthodontic work, for example. I'm not going to get into that in this blog post today, but there are some resources out there for voice teachers who need more information on those topics. However, it might be beneficial to book a coffee chat with your dentist or orthodontist and ask some specific questions if you have a student with difficulties in their jaw movement.


There are seven main muscles that move the jaw: four of them are closers and three are openers. (Note that different textbooks and authors differ on how many muscles are really involved in the jaw, but that is usually a matter of whether we're talking about only chewing, or whether we're discussing speech and swallowing, too.)


Masseter


The masseter is a muscle that is only found in mammals and is the most powerful muscle attached to the mandible. It originates underneath the cheek bone and travels down to attach to the back angle of the jaw, just below the ear. This is a powerful closer, and exerts a huge amount of force for chewing.


Temporalis

You might guess from the name that this muscle runs along your temple. It is a fan-shaped muscle that originates along the parietal bone of your skull, and it travels under your cheek bone (zygomatic arch) and attaches to the two coronoid (crown-like) arches of the mandible, shown in red in the photo to the right. This muscle is another closer and pulls the jaw up and back.


Internal Pterygoid


This muscle generally follows the same track as the masseter, but on the inside of the jaw instead of the outside. It is another closer. Because of it's relation to the masseter, these two muscles in essence tie the jaw to the skull.


External Pterygoid


This small muscle originates from the sphenoid bone beside the eye and travels back to attach to the bony neck of the jaw (the two end points in the picture above). When this muscle contracts, it pulls the jaw forward. If each side operates independently, it will result in wagging the chin back and forth.


Digastric


Like the name suggests, this muscle has two bellies (literally named two-belly in Latin). It originates on the hyoid bone and attaches to the back of the chin. When the front part of this muscle contracts, it pulls the chin down and opens the mouth.


Mylohyoid


This small muscle runs along the floor of the mouth, under the tongue and it has some really neat super powers. While most muscles generally pull in one direction, this muscle can either pull the hyoid bone up, or the jaw down, or both. If the hyoid bone is stabilized by other muscles, then generally the muscle will pull the jaw down and open the mouth.


Geniohyoid


Lying above the mylohyoid, the geniohyoid follows along the same general track as the digastric. It also has the dual capabilities of pulling up on the hyoid or down on the jaw, depending on how stable the hyoid bone is fixed by other muscles.


These muscles are relatively small compared to other muscles of comparable strength in the body. Anyone who's ever accidentally had their finger bitten by a small child can attest just how powerful those muscles are! Sometimes these muscles can hold tension, and as we are looking to identify where a client might be holding excess tension, examining how these jaw muscles are working and collaborating together can be an important part of the puzzle.


As you're chewing on these anatomical facts (sorry, I couldn't help myself), take some time to explore how your muscles are working and get to know them each by name. I think you'll be amazed at just how incredibly powerful and intricate they are!


References:


Hixon, T. J., Weismer, G., and Hoit, J. (2014). Preclinical Speech Science: Anatomy, Physiology, Acoustics, Perception, Second Edition. Plural Publishing.


Facial muscles drawing by Patrick J. Lynch, medical illustrator - Patrick J. Lynch, medical illustrator, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=1498151


Coronoid process drawing by Polygon data is from BodyParts3D - Polygon data is from BodyParts3D, CC BY-SA 2.1 jp, https://commons.wikimedia.org/w/index.php?curid=24834691

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