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The Jaw Muscles

Jaw Muscles

In my last two articles, we’ve gone into the layers of muscles that stabilize and move the head and neck. In this article, we’ll continue up that chain and go into the jaw muscles. There are many small muscles that are important for complex functions like chewing, swallowing, and speaking. However, don’t get overwhelmed by the list of names. My intention here is to give a general overview of these muscles, their locations, and actions so that you can dive deeper when it’s relevant to you.

Muscle names

The jaw muscles that I’ll go over in this article include:

  • Masseter
  • Temporalis
  • Medial pterygoids
  • Lateral pterygoids
  • Suprahyoid muscle group
    • Digastric
    • Stylohyoid
    • Mylohyoid
    • Geniohyoid
  • Infrahyoid muscle group
    • Sternohyoid
    • Sternothyroid
    • Thyrohyoid
    • Omohyoid

Attachments

Bones to know

There are several relevant bones to know to understand where the jaw muscles attach. The mandible is the technical name for the bone that makes up the lower part of our jaw. The temporal bone is a large bone at the side of our skull. We have one on the right and one on the left side of our skull. Where these bones meet is called the temporomandibular joint. 

The temporomandibular joint is the joint that moves every time we open and close our mouth. We also have a pair (a right and left side) of zygomatic bones. These bones form the lower part of our eye socket and “cheekbones.” The hyoid bone is a small U-shaped bone that floats in a sea of myofascial tissue about halfway down our neck and at the front. A number of muscles attach to it.

Masseter and temporalis muscles

The masseter is the most superficial of the jaw muscles, however, it has two sections, a superficial portion, and a deeper part. At its superior end, it attaches to the maxillary process (projection of bone) and the zygomatic arch of the zygomatic bone. At its inferior end, both sets of fibers converge to attach onto the ramus (branch of bone) and the coronoid process (projection of bone) of the mandible. The temporalis attaches at its superior end to the temporal fossa of our skull. All the fibers then come together to attach at the inferior end to the coronoid process of the mandible.

Medial pterygoids and lateral pterygoids

The medial and lateral pterygoids are some of our jaw muscles that are found a little deeper. The medial pterygoid has two heads, a deep head and a superficial head. At one end the sets of fibers of the medial pterygoid attach to several bones in our face: the pterygoid plate of the sphenoid bone, the palatine bone, and the maxilla. The fibers then come together to attach to the ramus and angle of the mandible.

The lateral pterygoid muscle also has two heads, a superior and inferior portion.  At one end the multiple sets of fibers of the lateral pterygoid attach to the greater wing and lateral pterygoid plate of the sphenoid bone. The fibers come together to attach to the condyle of the mandible, and sometimes also part of the the articular disc and capsule of the temporal-mandibular joint.

Suprahyoid muscle group

The word supra means above. Hyoid, of course, refers to the small, but very important bone midway down the front of our neck that I described earlier. So based on breaking down the name, you could guess that the suprahyoid muscles are a group of jaw muscles that attach to the superior, or top part, of the hyoid bone. These four muscles connect the mandible, the lower part of our jaw, to the superior part of the hyoid bone.

Infrahyoid muscle group

Infra means below. So you can probably guess that the infrahyoid muscles are a group of jaw muscles that attach to the inferior, or lower part, of the hyoid bone. Like the suprahyoid muscles, the infrahyoid muscles are all muscles that as a group are found on the anterior, or front side, of the cervical spine.

While each of the four jaw muscles in this group has a specific attachment at each end, it’s enough for our purposes here to understand that the infrahyoid muscles are found on the lower part of the front of the cervical spine. With the exception of the sternothyroid, they all attach to the lower aspect of the hyoid bone in various places. The sternothyroid muscle in this group attaches to the thyroid cartilage at its superior end and the manubrium of the sternum at its inferior end.

Actions

Masseter and temporalis muscles

As a group, all of the jaw muscles below are involved in the series of actions we call chewing, technically called mastication. That includes the opening, closing, and side-to-side actions of our jaw. Specifically, the masseter muscle does elevation of the mandible (closes the mouth) and does protrusion and retraction of the mandible which aids chewing. The temporalis is engaged in elevation of the mandible (closing the mouth) and retracting the mandible (pulling the lower jaw in).

Lateral pterygoids and medial pterygoids

The two heads of each lateral pterygoid can function bilaterally or unilaterally. When the two heads are acting bilaterally, they work to depress and protrude the mandible. Unilaterally, they can create a side-to-side movement of the mandible (lower jaw). The medial pterygoid acts to elevate the mandible (close the jaw) and protrude the jaw. Additionally, it works with the lateral pterygoid to create side-to-side movement of the jaw. 

Suprahyoid muscle group

While there are additional actions specific to each of the individual muscles, generally, the suprahyoid muscle group acts primarily to elevate and position the hyoid bone either anteriorly or posteriorly, as needed. Two muscles in this group also assist with depressing the mandible. These actions together help support the complex actions of swallowing and speaking.

Infrahyoid muscle group

As with the suprahyoid group, there are additional actions specific to each of the individual infrahyoid muscles. However, generally, the infrahyoid muscle group acts primarily to depress the larynx (voice box) and hyoid bone. Those actions happen when we are swallowing and speaking. Because this muscle group is located on the inferior side of the hyoid bone, this muscle group is also important in balancing the tension with the suprahyoid muscle group on the superior side of the hyoid bone. The balance of tension between these two groups helps support maintaining the important hyoid bone in the right position.

Why learn the jaw muscles?

While the details about the jaw muscles and their locations may not necessarily be relevant to you, their functions certainly are. These are the muscles involved in chewing, swallowing, and speaking. These are definitely activities that we all engage in. And if there is dysfunction in these muscles and their actions, then we can experience some very serious issues in essential daily functions. 

For example, teeth grinding, jaw pain, some types of headaches, and one common dysfunction that I will cover in a separate article, temporomandibular joint disorder (TMJ disorder) can all result if there is dysfunction in this group of muscles. (Temporomandibular joint disorder is not one single issue, but actually the name for a collection of symptoms that occur when there is pain and dysfunction at this joint.) You can imagine the challenges that any of those problems would present to daily function. Hopefully, you can see why understanding the healthy function of the jaw muscles can help us better understand what happens when there is dysfunction.

References

Basit H., M.A.Tariq, M.A. Siccardi. 2024. Anatomy, Head and Neck, Mastication Muscles. [Updated 2023 Jun 5]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. Available from: https://www.ncbi.nlm.nih.gov/books/NBK541027/

Chaitow, L. and J. DeLany. 2011. Chapter 12: The Cranium. In Clinical Application of Neuromuscular Techniques. Volume 1 (Second Edition). New York, NY: Churchill Livingstone Publishing.

Jung, B., A.C. Black, B.S. Bhutta. 2024. Anatomy, Head and Neck, Neck Movements. [Updated 2023 Nov 9]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. Available from: https://www.ncbi.nlm.nih.gov/books/NBK557555/

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