The lateral pterygoid is the primary muscle responsible for pulling your lower jaw forward and helping open your mouth. It sits deep on each side of your face, behind the cheekbone and in front of your ear, and plays a central role in chewing, talking, and yawning. Unlike the larger jaw muscles you can feel clenching at your temples or along your jawline, the lateral pterygoid works mostly out of reach, which makes it both easy to overlook and surprisingly important when something goes wrong.
Where the Muscle Sits
The lateral pterygoid is a short, thick muscle tucked inside the infratemporal fossa, a small pocket of space behind your cheekbone. It has two distinct sections called heads. The upper (superior) head originates from the underside of the skull near the base of the eye socket. The lower (inferior) head originates from a bony plate that hangs down behind your upper molars. Both heads angle backward and outward to attach near the jaw joint, specifically on the neck of the mandibular condyle, the rounded knob at the top of your lower jawbone that fits into the socket of your temporomandibular joint (TMJ).
The superior head has an especially important relationship with the TMJ. Some of its fibers attach to the joint capsule, which is firmly connected to the articular disc, the small pad of cartilage that cushions the joint. Anatomical studies using serial tissue sections have shown that the superior head does not insert directly into the disc itself, but rather connects through the capsule. This indirect attachment still gives the muscle significant influence over how the disc moves during jaw function.
The Three Main Actions
The lateral pterygoid performs three distinct movements of the lower jaw, each critical to everyday activities like eating and speaking.
- Protrusion: When both lateral pterygoids contract together, they pull the lower jaw straight forward. You use this motion when you jut your chin out or when your jaw slides forward during the early phase of opening wide.
- Mouth opening: The lateral pterygoid works alongside the muscles under your chin to depress the jaw and open your mouth. It does this by pulling the condyle and disc forward and downward along the slope of the joint socket.
- Side-to-side movement: When only the lateral pterygoid on one side contracts, it swings the jaw toward the opposite side. This lateral excursion is the grinding motion you use to break down food between your back teeth.
How the Two Heads Divide the Work
The superior and inferior heads of the lateral pterygoid do not fire at the same time. Research using electromyography, which measures electrical activity in muscles, has consistently shown that the two heads take turns during different phases of chewing. The inferior head is most active during jaw opening, protrusion, and movement toward the opposite side. The superior head is most active during jaw closing, retrusion (pulling the jaw back), and movement toward the same side.
This division of labor means the muscle essentially has two jobs happening in alternation. While the inferior head helps pull the jaw open and forward, the superior head helps stabilize and guide the disc as the jaw closes back down. Some newer research suggests there may be even more complexity within the superior head itself, with different bundles of fibers activating in different patterns depending on the exact direction of jaw movement. This functional variety within a single small muscle is unusual and helps explain why problems here can produce such a wide range of symptoms.
Its Role in the TMJ
Because the superior head connects to the joint capsule and influences disc position, the lateral pterygoid is deeply involved in how smoothly your TMJ operates. During normal chewing, the disc glides forward with the condyle as you open and slides back as you close. The lateral pterygoid’s pull on the capsule helps coordinate this movement.
When the muscle is overworked, in spasm, or chronically tight, it can pull the disc out of its normal position. This is called disc displacement, and it is the most common structural problem inside the TMJ. In the early stages, the disc slips forward when your mouth is closed but snaps back into place when you open, producing a clicking, popping, or snapping sound. Over time, if the disc stays displaced and fails to snap back, you may notice your jaw locking or your mouth opening becoming restricted. This progression from “displacement with reduction” (the click) to “displacement without reduction” (the lock) is a well-recognized pattern in TMJ disorders.
Connections to Jaw Pain and Bruxism
The lateral pterygoid is one of four muscles of mastication commonly involved in temporomandibular disorders (TMD). Stress, teeth grinding (bruxism), jaw clenching, poor posture, and psychological conditions like anxiety and depression can all drive these muscles into dysfunction. Because the lateral pterygoid is so closely tied to the joint itself, problems here tend to produce symptoms that feel like they’re coming from the joint rather than a muscle: deep aching near the ear, pain when chewing, or difficulty opening the mouth fully.
Bruxism is a particularly common aggravator. Chronic grinding forces the lateral pterygoid to work overtime, especially during sleep when you have no conscious control over jaw tension. This sustained overuse can create painful trigger points within the muscle. Botulinum toxin injections have been used to treat both chronic bruxism and painful trigger points in the jaw muscles, though a Cochrane review found the evidence for pain relief specifically in myofascial cases remains inconclusive.
How It’s Examined
The lateral pterygoid’s deep position makes it one of the harder muscles to assess. It cannot be felt from the outside of the face. Clinicians examine it through intraoral palpation, reaching a gloved finger along the inside of the cheek behind the upper molars toward the back of the mouth. A cadaver study confirmed that direct digital contact with the muscle is possible using this approach, but success depends heavily on the examiner knowing the exact anatomy and palpation pathway.
During the exam, the muscle is easiest to feel when the jaw moves toward the same side (which relaxes the muscle on that side) and when opening and closing the mouth (which contracts it). Tenderness during palpation, especially if it reproduces your familiar pain, points toward the lateral pterygoid as a source. Imaging such as MRI can also reveal disc displacement or inflammation in the joint area when the clinical picture is unclear.
Nerve Supply
The lateral pterygoid is controlled by a dedicated nerve branch that comes off the mandibular division of the trigeminal nerve, the fifth cranial nerve responsible for sensation in your face and motor control of your chewing muscles. The nerve to the lateral pterygoid is actually a paired nerve, with one branch supplying each head independently. This separate wiring aligns with the fact that the two heads activate at different times during the chewing cycle. Damage or irritation to this nerve branch, whether from trauma, surgery, or compression, can impair the muscle’s ability to coordinate jaw movement properly.