The mouth opens to the outside at the lips and empties into the throat at the rear; its boundaries are defined by the lips, cheeks, hard and soft palates, and glottis. It is divided into two sections: the vestibule, the area between the cheeks and the teeth, and the oral cavity proper. The latter section is mostly filled by the tongue, a large muscle firmly anchored to the floor of the mouth by the frenulum linguae. In addition to its primary role in the intake and initial digestion of food, the mouth and its structures are essential in humans to the formation of speech.
The chief structures of the mouth are the teeth, which tear and grind ingested food into small pieces that are suitable for digestion; the tongue, which positions and mixes food and also carries sensory receptors for taste; and the palate, which separates the mouth from the nasal cavity, allowing separate passages for air and for food. All these structures, along with the lips, are involved in the formation of speech sounds by modifying the passage of air through the mouth.
Anatomy of the mouth.
Floor of the mouth with Lingual frenum and sublingual fold
The mouth consists of two regions: the vestibule and the oral cavity proper. The vestibule is the area between the teeth, lips and cheeks. The oral cavity is bounded at the sides and in front by the alveolar process (containing the teeth) and at the back by the isthmus of the fauces. Its roof is formed by the hard palate at the front, and the soft palate at the back. The uvula projects downwards from the middle of the soft palate at its back. The floor is formed by the mylohyoid muscles and is occupied mainly by the tongue. A mucous membrane – the oral mucosa, lines the sides and under surface of the tongue to the gums, and lines the inner aspect of the jaw (mandible). It receives secretions from the submandibular and sublingual salivary glands.
A closed human mouth.
The lips come together to close the opening of the mouth, forming a line between the upper and lower lip. In facial expression, this mouth line is iconically shaped like an up-open parabola in a smile, and like a down-open parabola in a frown. A down-turned mouth means a mouth line forming a down-turned parabola, and when permanent can be normal. Also, a down-turned mouth can be part of the presentation of Prader-Willi syndrome.
The teeth and the periodontium (the tissues that support the teeth) are innervated by the maxillary and mandibular nerves – divisions of the trigeminal nerve. Maxillary (upper) teeth and their associated periodontal ligament are innervated by the superior alveolar nerves, branches of the maxillary division, termed the posterior superior alveolar nerve, anterior superior alveolar nerve, and the variably present middle superior alveolar nerve. These nerves form the superior dental plexus above the maxillary teeth. The mandibular (lower) teeth and their associated periodontal ligament are innervated by the inferior alveolar nerve, a branch of the mandibular division. This nerve runs inside the mandible, within the inferior alveolar canal below the mandibular teeth, giving off branches to all the lower teeth (inferior dental plexus). The oral mucosa of the gingiva (gums) on the facial (labial) aspect of the maxillary incisors, canines and premolar teeth is innervated by the superior labial branches of the infraorbital nerve. The posterior superior alveolar nerve supplies the gingiva on the facial aspect of the maxillary molar teeth. The gingiva on the palatal aspect of the maxillary teeth is innervated by the greater palatine nerve apart from in the incisor region, where it is the nasopalatine nerve (long sphenopalatine nerve). The gingiva of the lingual aspect of the mandibular teeth is innervated by the sublingual nerve, a branch of the lingual nerve. The gingiva on the facial aspect of the mandibular incisors and canines is innervated by the mental nerve, the continuation of the inferior alveolar nerve emerging from the mental foramen. The gingiva of the buccal (cheek) aspect of the mandibular molar teeth is innervated by the buccal nerve (long buccal nerve).
The mouth plays an important role in eating, drinking, and speaking. Mouth breathing refers to the act of breathing through the mouth (as a temporary backup system) if there is an obstruction to breathing through the nose, which is the designated breathing organ for the human body.
Infants are born with a sucking reflex, by which they instinctively know to suck for nourishment using their lips and jaw. The mouth also helps in chewing and biting food.
For some disabled people, especially many disabled artists, who through illness, accident or congenital disability have lost dexterity, their mouths take the place of their hands, when typing, texting, writing, making drawings, paintings and other works of art by maneuvering brushes and other tools, in addition to the basic oral functions. Mouth painters hold the brush in their mouth or between their teeth and maneuver it with their tongue and cheek muscles, but mouth painting can be strenuous for neck and jaw muscles since the head has to perform the same back and forth movement as a hand does when painting.
A male mouth can hold, on average, 71.2 ml (2.51 imp fl oz; 2.41 US fl oz), while a female mouth holds 55.4 ml (1.95 imp fl oz; 1.87 US fl oz).
- AnatomyBranch of biology and medicine that considers the structure of living things
- TongueThe tongue is a muscular organ in the mouth of a typical tetrapod. It manipulates food for mastication and swallowing as part of the digestive process, and is the primary organ of taste.
- Organ (anatomy)Collection of tissues joined as a structural unit that serves a common function
- LiverThe liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth.
- BoneRigid organs that constitute part of the endoskeleton of vertebrates
- Skeletal muscleOne of three major muscle types
- Cell (biology)The basic structural and functional unit of all organisms. includes the plasma membrane and any external encapsulating structures such as the cell wall and cell envelope.