The Jaw, Mouth, and Throat

The skeleton part of the head, called the skull, functions like a box made of bones. It holds and protects all of the important organs and anatomic structures located in the head. These include the brain, ears, eyes, nose, and mouth. The human head weighs, on average, 8.8 pounds (4 kg). Strong bones and muscles in the neck hold up the head.

While the skull looks like one big bone, it actually consists of twenty-nine separate bones. The section of bone encasing the brain is called the cranium, which is made up of eight connected bones. Fourteen interlocking bones frame the nose, the mouth, and the eyes.

The Jaw

The jaw has an upper and lower section. The upper jaw, called the maxilla, consists of two bones. The lower jaw, referred to as the mandible, is hinged where it meets the upper jaw. This enables the mandible to move up and down, while the top part of the jaw stays relatively still.

Muscles stretching from the neck to the top of the head help to close the lower jaw. These muscles are incredibly strong. They allow the jaw to close with a force of 200 pounds (90.7 kg). Such strength gives the jaw the power to crush hard foods like nuts and raw vegetables. It is even possible to feel the strong muscles controlling the jaw. To do this, clench your teeth together tightly. Next, hold a hand near the lower jaw and then near your temple above the eyes. What you feel are just a few of the muscles that give the jaw its impressive strength.

The jaw, along with the skeleton, grows from birth until an individual is about twenty years old. A newborn infant has a very small jaw. That is one reason why babies have such soft features and must consume special baby food, which is often pureed or finely chopped. By the time a person is six years old, the lower jaw has greatly increased in size. At twenty, both the upper and lower jaws have fully developed.

The Mouth

Mouth View Larger Image © Articulate Graphics/Custom Medical Stock Photo

Set in between the upper and lower jaws is the mouth, with the lips forming an entrance to the mouth’s interior. Glancing in a mirror reveals that the lips are covered with a different type of tissue than the kind of skin that surrounds the rest of the body. The orbicularis oris is the major muscle that forms the lips (its action allows you to purse your lips). The epithelial lining of the lips is comprised of non-keratinized stratified squamous epithelium whereas the rest of the face and the vast majority of the body are comprised of keratinized stratified squamous epithelium. Keratin is a protein that makes up the skin, hair, and nails. Unlike most skin, the lips have no hairs or sweat and oil glands. Glands are organs that secrete, or produce, certain substances like hormones and saliva.

Given its extraordinary flexibility, the mouth is one of the most expressive features of the face. Frowning actually requires a lot more energy and effort than smiling. Forty-three muscles are activated with a frown, but only seventeen are required to produce a smile. Smiling, therefore, promotes relaxation and helps to prevent certain wrinkles.

Teeth

Teeth may seem like hard, lifeless objects, but they are very much alive. These bonelike structures are attached to the jaws as though they were plants growing out of soil. Teeth have two main jobs. First, they bite into food and chop it into pieces that can be managed in the mouth. Second, teeth crush, munch, and pulverize food into a mashed-up pulp that can be swallowed.

When a child begins to lose their baby teeth, this marks the development of permanent teeth. Before that time, individuals have what are known as milk teeth. Milk teeth cells begin to form in the womb, before a baby is born. At birth, infants possess thick gum pads, which contain the cells necessary for teeth to develop. When the baby reaches about six months of age, teeth begin to emerge. Their emergence continues until about the age of two, when the child usually has a full set of twenty milk teeth. After the age of six, the milk teeth begin to fall out and are replaced by permanent teeth. By the age of twenty, most people should have a set of thirty-two teeth, if wisdom teeth or other teeth are not removed or accidentally knocked out.

There are four types of permanent teeth: incisors, canines (also called eyeteeth), premolars, and molars. Incise means to cut, and that is what incisors do. These have a narrow edge shaped like a knife blade. Incisors cut or bite into food and chop it into small pieces.

Canine teeth are located to the sides of the incisors. They rip and tear food apart. Think of biting into a chewy piece of bread or meat. The mouth opens wider to expose the canines so they can tear off bite-sized morsels. While incisors have a flat edge on the bottom, canines are pointed. This can be felt by running the tongue over them.

Premolars are like a cross between a canine and a molar. They have slightly more jagged edges than canines. The main job of premolars is to cut and chew. Usually this action is done to pieces of food bitten off by the incisors and canines.

Molars have a wide exposed surface area that enables them to chew and crush. Given their shape and location at the back of the gum line, molars are not effective at cutting and biting. They grind food that has already been cut up by the other teeth.

Wisdom teeth are molars that emerge in 75 percent of people by the time they reach the age of eighteen. A throwback to earlier stages in human evolutionary development, wisdom teeth often do not fit properly in the jaw, which has gotten smaller over time. In such cases, the wisdom teeth must be extracted.

Inside a Tooth

Each tooth consists of two main parts: the crown and the root. The crown is the portion of the tooth that is visible in the mouth. The root is the part that is embedded within the jaw. When a tooth falls out or is extracted, the root can be seen as a pointy, hard tip on the bottom of the tooth.

A cross-section diagram reveals that teeth are composed of layers. The outer layer consists of enamel, a hard substance that protects the tooth. Underneath the enamel is dentin, a softer material that makes up the bulk of the tooth. In the center of every tooth, there is a pulp cavity containing nerves and blood vessels. Finally, a material called cementum glues the tooth in place within the jawbone.

With all of their nooks and crannies, teeth can be a breeding ground for bacteria from food. Over time, this leads to plaque, a combination of rotting food, bacteria, and other tooth-decaying substances. If the bacteria are not removed by brushing, they can produce acids that may eat through the enamel and into the dentin. The resulting damage can create cavities. Dentists fill cavities because the infection could spread to the pulp, then into the jawbone, where it could lead to serious health problems. It is, therefore, very important to floss and brush your teeth after every meal, and to visit a dentist regularly.

Flossing

Toothbrushes often miss the tight areas between teeth, so it is important to floss daily. Waxed and unwaxed dental flosses are available. Both work well when used properly, ideally before you brush.

To floss, wind an eighteen-inch piece of floss around the middle fingers of each hand. Using the thumbs and forefingers, slide the floss between each tooth, gently scraping any plaque off the tooth sides. Repeat with a clean section of floss for each area in your mouth. After flossing, rinse your mouth thoroughly with water or mouthwash.

The Hard and Soft Palates and Tonsils

Taking a look inside the mouth, the top is bound by a part of the upper jaw known as the hard palate. It is hard because the tongue and lower jaw need something to push up against in order to crush food. Resting alongside the hard palate is the soft palate, which extends back into the throat. This tissue, more tender than the hard palate, moves upward when food is swallowed. Without the soft palate, food would shoot up and out of the nose.

A U-shaped piece of tissue hangs in the back center of the mouth, attached to the soft palate. This tissue is called the uvula. Its function in the mouth isn’t entirely clear, although it may help to close off air passages coming from the nose, lessening the chances of choking on food. It also produces a thin saliva used in swallowing and has a function in certain languages as well.

Underneath the hard and soft palates are the tonsils. These two organs help to remove microbes that may enter the throat from food and air. Sometimes the tonsils become infected—most often in children—and must be removed.

The Throat

Leading from the back of the mouth and down into the neck is the throat. It is the area that directs air from the nose to the lungs, and food and liquids from the mouth into the stomach. The throat is divided into two main parts: the pharynx and the larynx.

The pharynx is a muscular passage that extends from the nose to the esophagus, the tubelike structure that sends food to the stomach. About 5 inches (12.7 cm) long, the pharynx is the common passage for movement of air, food, and liquids. Not everything goes down to the stomach, however. Like trains switching tracks, air can be diverted down through the trachea into the lungs.

The trachea, or windpipe, looks a bit like a vacuum-cleaner hose. Just as a hose has plastic for flexibility and support, the trachea has rings of cartilage surrounding it. The cartilage rings prevent the trachea from collapsing and allow for intake of different levels of air. Tiny hairlike appendages called cilia stick out of a slimy membrane lining the trachea. They help to keep the throat clean and ensure that food and water move smoothly.

The trachea has a flap of cartilage above it called the epiglottis. Like a lid, the epiglottis closes the entrance to the windpipe when food is swallowed. Without it, food and liquid could wind up in the lungs instead of the stomach.

Above the trachea is the thyroid gland. This gland has two lobes, which together look like a bow tie in the throat. The thyroid gland controls energy use in the body, calcium levels, and growth. It is protected by the thyroid cartilage (commonly called the Adam’s apple), which is the largest of nine sections of cartilage in the larynx, or voice box. This cartilage sticks out like a bump in the throat. The bump is particularly noticeable in men, because they generally have larger larynxes than women.

The Larynx

Before air travels from the nose to the trachea, it must first move across the larynx, a triangular box about 1.6 inches (4.1 cm) long that opens behind the tongue in the throat. The inside looks like a tube with a slit in the middle and lined on both sides with white, reedy material. This material forms the vocal cords.

When breathing, the vocal cords open to allow air to flow freely down the trachea. When speaking, the cords draw closer together. Airflow makes the cords vibrate, which produces sound waves. The tightness of the cords determines the rate of vibration and pitch. Larynx size also affects the sound. People with small voice boxes generally have high-pitched voices, while large larynxes produce lower tones. That is why men tend to have deeper voices than women.

Mouth and Throat Cancer

The mouth and throat are susceptible to specific types of cancer, especially for people who use tobacco, drink excessive amounts of alcohol, or both. Mouth (oral) cancer includes abnormal, uncontrolled growth of cells in the lips, mouth, tongue, gums, and salivary glands. Throat cancer involves abnormal cell growth in the part of the throat right behind the mouth, in the pharynx, or in the larynx. According to the Oral Cancer Foundation, about fifty-three thousand new cases of mouth cancer are diagnosed in the U.S. every year, while the American Cancer Society reports that over twelve thousand new cases of throat cancer are diagnosed annually.

Over 90 percent of people who develop mouth or throat cancer use tobacco in some form, either by smoking, vaping, or chewing. Moreover, people who use chewing tobacco are at a higher risk of cancers involving the inner surfaces of the cheeks and lips. In addition, nearly 80 percent of people with oral and upper throat cancers drink large amounts of alcohol. Other risk factors include habitually chewing on your lips and cheeks and prolonged, unprotected exposure of the lips to harsh sunlight.

Symptoms of mouth and throat cancer include lumps inside the mouth or on the throat; discolored patches inside the mouth; trouble chewing or swallowing food; changes in the voice; and a painful, swollen jaw. Many mouth and throat cancers aren’t detected until they’re already advanced, but when detected early these types of cancers can almost always be treated successfully. The best ways to avoid getting mouth or throat cancer is to abstain from using tobacco and alcohol, and to apply sun protection to your lips before going outside.