Oral Cavity

Oral Cavity Definition

Also known as the mouth, the oral cavity is the oval-shaped opening through which air, food, and liquid enter the human body. The cavity starts at the lips and ends at the throat. It contains many structures, including the lips, the hard and soft palate, the tongue, teeth, gums, and salivary glands.

Fig. 1 - The oral cavity plays a critical role in speech production.

Structure of Oral Cavity

Many structures make up the oral cavity. These structures help play a role in the functions of the oral cavity, especially speech. They work together to shape speech sounds and allow for intelligible communication between people.

Lips

The lips are muscular folds that encircle the oral cavity and shape speech sounds. For instance, they close when an English speaker pronounces the letter /m/, but they are rounded when a speaker pronounces the letter /o/. These sounds made with the lips are called labial sounds.

Hard Palate

The roof of the mouth is called the palate. There are two parts of the palate's surface, the hard and soft palate. The hard palate is the anterior, bony part. When the body of the tongue comes up close to the hard palate in speech, the sounds produced are called palatal sounds, such as /j/.

Soft Palate

Also called the velum, the soft palate is the posterior part of the palate and the gatekeeper of the nasal cavity. It generally prevents airflow through the nose, but there are some nasal sounds, such as /n/, which it lowers to allow nasal airflow. The body of the tongue also touches the velum to make the sounds /k/ /g/ and /ŋ/.

Alveolar Ridge

The alveolar ridge is a small, thick protuberance separating the upper teeth and the hard palate. The tongue touches the ridge to form consonant sounds, and this helps people articulate when they speak. Sounds like /z/ and /s/ are heavily reliant on this area.

Fig. 2 - The lips shape the sounds that exit the oral cavity.

Salivary Glands

The salivary glands in the oral cavity produce an extracellular fluid called saliva. These enzymes help people digest food and help speech production by lubricating the oral cavity.

Tongue

The tongue is a soft, muscular part of the floor of the mouth. It is covered by sensory organs called taste buds that help people taste food. It is also used in speaking, as the movement of the tongue and lips shape the sounds a person makes.

Teeth

Teeth are hard, enamel-coded structures that help break down food. The teeth also support speech because they control the airflow from the oral cavity. The tongue also brushes against the teeth in different ways to help form a variety of sounds. For instance, when the tongue brushes up against the upper row of teeth, people can produce the "TH" sound.

Oral Cavity Diagram

The diagram below depicts the location of all of the structures in the oral cavity.

Fig. 2 - Oral Cavity diagram

Oral Cavity Function

The oral cavity plays a role in speech production, digestion, and respiration.

Speech Production

An oral sound is a name for any sound that passes through the oral cavity. When people speak, air pressure rises from their lungs into their larynx (also called the voice box), making the vocal folds vibrate. From there, the sound travels through the pharynx to the oral cavity. Here, the various movements of structures like the tongue and lips shape the sound into articulate speech.

When the air flows through all these structures without obstruction, humans can produce vowels, or open sounds. The airflow must be obstructed to produce one of the twenty-four phonetic consonants in English. The following chart demonstrates how the structures of the oral cavity come together to produce each sound.

Voiced/Voiceless Consonants

There are two types of phonetic consonants: voiced and voiceless. Voiced consonants are consonant sounds produced through the vibration of the vocal cords in the larynx. Once air moves up through the larynx, the oral cavity modifies it into one of the following voiced consonants and blends: B, D, G, J, L, M, N, V, W, Y, Z, Ng, R, Sz, and Th.

Voiceless consonants are consonant sounds that do not require the vibration of the vocal cords. In these cases, air flows freely from the lungs to the oral cavity, and the structures of the oral cavity control the sound that is produced. The voiceless consonants are Ch, F, K, P, S, Sh, T, and TH.

Under the umbrella of voiced and voiceless, phonetic consonants are also either plosives or fricatives.

Plosives

Sometimes the nasal and oral cavities are both closed and the flow of air is blocked. Pressure builds up in the oral cavity and is abruptly released in aspiration. The resulting sounds are called plosives. For example, //b/, /d/, and /g/ are voiced plosives, and /p/, /t/, and /k/ are voiceless plosives.

Fricatives

Fricatives are produced when two articulators come close together, but a small opening allows for steady airflow. The resulting friction noise is called a fricative.

There are two types of fricatives: slit fricatives, in which the tongue is flat, and groove fricatives, in which the tongue forms a groove. For instance, /f/ is a voiceless fricative, and /v/ is a voiced fricative. Meanwhile, /s/ is a voiceless fricative, and /z/ is a voiced fricative.

Fig. 3 - The oral cavity is the final resonating chamber.

Digestion

The oral cavity is the first organ in the process of digestion, facilitating the first stage, called ingestion. People put food into their oral cavity and break it down by chewing it. As they chew the food into tiny pieces, the salivary glands produce saliva that adds enzymes, which kicks off the process of chemical digestion. Meanwhile, the tongue creates a small mass called a bolus out of the chewed food. This tongue moves the bolus down, so it can travel through the pharynx and down into the esophagus.

Respiration

The oral cavity is the second opening in the respiratory tract. Air typically enters the nasal cavity, where it is warmed, moisturized, and filtered. When air passes through the oral cavity, these processes do not occur, but the air has a shorter distance to travel to enter the lungs.

Difference Between Oral and Buccal Cavity

Sometimes, people use the terms oral cavity and buccal cavity interchangeably. However, the oral cavity technically refers to the entire mouth and all the aforementioned structures. The buccal cavity is the name for the section of the oral cavity on the inside of the cheeks to the beginning of the teeth. It is also called the buccal vestibule.