When you eat, breathe, or speak, you rely on your oral cavity to help you. The oral cavity, also known as the mouth, is the opening through which food and air enter the human body.
The oral cavity plays a role in many biological processes, such as digestion and respiration. It also plays a critical role in speech because it controls the airflow and shape of the sounds humans produce. Understanding the structure of the oral cavity and the oral cavity's functions can help one better understand phonetics.
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.
The oral cavity is the orifice through which food, liquid, and air enter the human body.
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/.
When the velum lowers to direct air through the nasal cavity, the resulting sound is called a nasal sound. Sometimes the velum directs air there, but the air still goes through the mouth. This sound is then called a nasalized sound.
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.
A whole subfield of phonetics called articulatory phonetics focuses on how humans articulate!
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.
The most mobile parts of the tongue are the blades and the tip (also called the apex). These are what consistently move to articulate speech sounds. Sounds made with the blade of the tongue are called laminal sounds, while sounds made with the tip are called apical sounds. Some sounds are also made with the back of the tongue, which lies below the velum. These sounds are called dorsal sounds.
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.
Most adult humans have 32 teeth.
Oral Cavity Diagram
The diagram below depicts the location of all of the structures in the oral cavity.
Fig. 2 - Oral Cavity diagram
The structures in this diagram are lined with a mucous membrane called the oral mucosa. This membrane consists of a type of tissue called the stratified squamous epithelium. This type of tissue has many protective functions, like preventing microorganisms and toxic materials from entering.
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.
| Place of Articulation | Explanation | Consonants |
| Alveolar ridge | The tip of the tongue on the alveolar ridge | t, d, n, z, s, r/l |
| Bilabial | Upper and lower lips come together | p, b, m, w |
| Dental | Tongue touches teeth | th |
| Glottal | Sound is produced by air expelled through the glottis | h |
| Labio-dental | Lips come together with teeth | f, v, |
| Palatal | Tongue moves toward the palate | y |
| Post alveolar | The tip of the tongue is behind the alveolar ridge | sh, zh, ch, j |
| Velar | The back of the tongue moves toward the velum | k, g, ng |
The phonetic consonants belong to the phonetic alphabet. The International Phonetic Alphabet (IPA) is a phonetic notation system representing human speech sounds in written form. The IPA has 107 letters that represent vowel and consonant sounds. It also includes 52 diacritics, which are signs that indicate differences in pronunciation. It also consists of 17 signs that denote suprasegmental attributes like tone and intonation.
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.
The oral cavity is also the final resonating chamber in the human body. Resonance refers to the intensity and tone of produced sound. When vocal cords in the pharynx vibrate, sound waves travel through resonating areas like the larynx, pharynx, nasal cavity, and oral cavity.
The oral cavity is the resonating chamber that alters the tone of the produced sound. Humans can control the movement of the structures within it, and different choices lead to different tones. For instance, the tongue is higher when a singer sings "ee" than when they sing "ah."
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.
Oral Cavity - Key takeaways
- The oral cavity is the orifice that air, food, and liquid pass through to keep the human body functioning properly.
- The oral cavity contains structures that work together in speech production, including the tongue, teeth, salivary glands, palate, alveolar ridge, and lips.
- The oral cavity helps control the amount of air that exits during speech and how much air is let into the nasal cavity.
- The oral cavity helps shape the sounds humans produce and ensures articulate speech.
- The oral cavity is different from the buccal cavity because the buccal cavity is the name for the section of the oral cavity between the cheeks and the start of the teeth.
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