Mac Lee

Mac Lee

Muscles of the arm are easy to understand. When the triceps in the back of the arm contract, the arm is extended. To bend the arm, the biceps kick in and the triceps relax. Both bicep and triceps work in harmony via an antagonistic relationship. One set of muscles closes or flexes the forearm while the other opens or extends the forearm. When one muscle is working, the other is relaxing. Body builders work very hard in balancing the strength and size of each antagonistic muscle.

The opening and closing of the jaw is no different from the arm. It, too, is extended (opened) and flexed (closed) by muscles. Unlike the muscles of a weightlifter, there is a gigantic difference in the size and power of the muscles that operate the opening and closing of the jaw.

Plus, the muscles of the head and neck are vastly complicated. The arm muscles create movement to and from the body. The muscles of the head and neck create chewing, swallowing, talking and breathing. Imagine how complicated those movements are.

All muscles of the head and neck must work in perfect harmony to make these movements happen. When you add the intricacies of the tongue, things really get complicated.

Closing muscles

The major muscles used to close the jaw are the temporalis and the masseters. Put your fingers on the sides of your cheeks and bite down. Feel the movement? Those are the masseters.

Now, put your finger on your temples and bite down. Those or the temporalis.

Average biting pressure for a human is close to 200 psi compared to an alligator with a bite of more than 2,000 psi.

The masseter muscles mostly fire at the same time, causing the jaw to bite straight down.

The temporalis muscle, in conjunction with other muscles, are the ones that guide the jaw left and right. Most people chew sideways like a cow. When chewing on the right, the jaw opens, goes to the right, begins to close on the food in a scissor like fashion from right to left. If chewing on left side, it is a left to right movement on closing. Just imagine the amount of coordination between the opening, positioning, and closing muscles. This action occurs hundreds if not thousands of time a day without the slightest thought.

Opening muscles

The muscles that open the jaw are tiny in comparison. Same with an alligator. One wrapping of duct tape overpowers the opening muscles in the alligator.

People who cannot open their mouth easily are having a battle between the opening and closing muscles and the closing muscles are winning. If one has a problem eating a hamburger, your closing muscles are winning (sometimes, it is the joint preventing opening).

A normal opening is 50 millimeters. That is about three fingers wide. If you can only open wide enough for two fingers, you have a battle between the muscles. Those of you who cannot easily eat a hamburger know what I am talking about.

The lateral pterygoid is the major opening muscle and is located on the joint right in front of the ear canal. When it contracts, the joint is pulled forward, which opens the jaw. If you or someone you know has a pop or click on opening, the lateral pterygoid is involved.

The purpose of this article is to express the miracle of the workings of the muscles of the head and neck. Next month’s article will explain what happens when the muscles are not in harmony.

It is extremely rare for a muscle to not have an antagonistic partner, yet there are two in the head. They just fire and relax.

One, the tensor tympani is a tiny muscle in the inner ear that has the single job of tightening the ear drum when it perceives loud noises.

The ear drum is a thin membrane that is vibrated by sound. Via the special bones in the inner ear, the vibrations are turned into sound signals to the brain.

When certain sounds are unwanted, like chewing, yawning, talking, etc., the tensor tympani flex, which tightens the ear drum, which diminishes sound to the brain.

Animals in the wild do not chew when on high alert because they want to hear and do not want the tiny muscle to contract.


Dr. Mac Lee practices in Edna. He is an international speaker and trainer to dentists. He is dedicated to educate the public about dental disease. To learn more about dentistry, visit or call 361-782-7191.

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