Anatomy of oral cavity. The oral cavity extends from the lips to the oropharyngeal isthmus, which is defined by the anterior tonsillar pillars. These pillars are a key anatomical landmark, as they mark the boundary between the oral cavity and the oropharynx. We can divide the oral cavity into two main parts:
- Oral Vestibule: The space between the lips and cheeks externally and the teeth and gums (alveolus) internally.
- Oral Cavity Proper: The space inside the arches of the teeth.
Oral cavity encompasses several distinct anatomical structures, each with unique features and functions. Structures included in it are:
- Lips
- Buccal mucosa.
- Gums and teeth.
- Hard palate.
- Anterior two-thirds of the tongue.
- Floor of mouth.
- Retromolar trigone.
1. Lips
The lips form the anterior boundary of the oral vestibule. They consist of fleshy folds primarily made up of the orbicularis oris muscle, which is externally lined by skin and internally by mucous membrane. The inner surface of each lip is supported by a frenulum, a small fold of tissue that connects it to the gum. A unique feature of human lips is the vermilion border, the red zone where the highly keratinised external skin transitions to the less keratinised internal mucosa. Notably, the upper lip has a median vertical groove on its outer surface called the philtrum.
Lymphatic drainage of the central part of the lower lip is directed to the submental lymph nodes, while the remainder of the lower lip drains into the submandibular lymph nodes.
2. Buccal (Cheek) Mucosa
The buccal mucosa lines the inner surfaces of the cheeks and lips, extending posteriorly to the pterygomandibular raphe (ascending ramus of the mandible). Anteriorly, the buccal mucosa extends to the junction of the lips. It primarily comprises the buccinator muscle, which is penetrated by the parotid duct (Stenson’s duct). The duct opens on a small papilla opposite the upper (maxillary) second molar tooth. Fordyce granules, which are ectopic sebaceous glands, can appear as small yellow spots on the buccal mucosa.
The buccinator muscle receives innervation from the buccal branch of the facial nerve (cranial nerve VII), while general sensory input from the skin and oral mucosa of the cheeks is carried by the buccal branch of the mandibular nerve (V3). Lymphatic drainage from the cheek primarily flows to the submandibular and preauricular lymph nodes, with additional contributions to the buccal and submandibular nodes.
3. Gums (Gingivae)
The gums, or gingivae, are the tissues that surround the teeth and cover the upper and lower alveolar ridges, providing support and protection to the teeth.
4. Hard Palate
The hard palate forms the roof of the oral cavity and serves as a partition between the nasal and oral cavities. It is composed of two parts: the anterior two-thirds, formed by the palatine process of the maxilla, and the posterior one-third, formed by the horizontal plate of the palatine bones. Lymphatic drainage from the hard palate is primarily directed to the upper deep cervical nodes, with some drainage to the retropharyngeal nodes.
5. Oral Tongue
The oral tongue is defined as the freely mobile anterior two-thirds of the tongue and is demarcated from the base of the tongue by the circumvallate papillae located posteriorly. It is subdivided into several parts: the tip, dorsum, lateral borders, and ventral surface. At the apex of the sulcus terminalis lies the foramen caecum, a small depression that marks the origin of the embryonic thyroid diverticulum. This is a crucial embryological point for NEET PG.
Papillae of the Tongue. The dorsal surface of the tongue is covered with tiny projections called papillae.
- Circumvallate Papillae: Large, round papillae (8-12 in number) arranged in a V-shape just in front of the sulcus terminalis. They contain taste buds.
- Fungiform Papillae: Mushroom-shaped papillae interspersed among the filiform papillae. They also contain taste buds.
- Foliate Papillae: Present on the posterolateral aspects of the tongue. They contain taste buds.
- Filiform Papillae: The most numerous papillae, giving the tongue its velvety appearance. They do NOT contain taste buds.
Mnemonics:
- Filiform = For Friction, not For Flavour. (Helps remember they don’t have taste buds)
- Circumvallate = Circle of Checkers. (Helps visualise their shape and arrangement)
The ventral and lateral surfaces connect with the floor of the mouth and are lined with nonkeratinizing stratified squamous epithelium. In contrast, the dorsum and tip of the tongue are covered by specialised gustatory mucosa, characterised by thick, primarily keratinised epithelium. Beneath the mucosal lining, the intrinsic muscles of the tongue, along with four pairs of extrinsic muscles (genioglossus, hyoglossus, styloglossus, and palatoglossus), provide functional support.
- Motor innervation to the tongue muscles, with the exception of the palatoglossus muscle, is provided by the hypoglossal nerve (cranial nerve XII). The palatoglossus muscle is innervated by the vagus nerve (cranial nerve X).
- Sensory innervation of the anterior two-thirds of the tongue is divided into general sensation, carried by the lingual nerve (a branch of the mandibular nerve, V3), and special sensation (taste), carried by the chorda tympani (a branch of the facial nerve). The posterior one-third of the tongue receives both general and special sensory innervation from the glossopharyngeal nerve (cranial nerve IX).
- The major blood supply to the tongue is through the lingual artery, and venous drainage occurs via the dorsal and deep lingual veins.
- Lymphatic drainage from the tip of the tongue is directed to the submental and jugulomohyoid nodes, while the lateral portions drain into the ipsilateral submandibular and deep cervical nodes. The central portion and base of the tongue drain into the deep cervical nodes on both sides.
6. Floor of the Mouth
The floor of the mouth is a crescent-shaped area situated between the gingivae and the undersurface of the tongue. The anterior portion of the floor is best visualized when the patient elevates the tip of the tongue towards the hard palate. Prominent structures in this area include the frenulum and the sublingual papillae, where the openings of the submandibular ducts (Wharton’s ducts) are located. The lateral portion of the floor of the mouth can be examined by gently displacing the tongue medially with a tongue depressor. The floor of the mouth is supported by paired muscles of the mylohyoid and geniohyoid muscles.
Sensory innervation to the area is by the lingual branch of the mandibular division of the trigeminal nerve. Lymphatic drainage of the lateral floor of the mouth is via the ipsilateral submandibular nodes to the deep cervical chain and from anterior floor of mouth is via the submental nodes to both the left and right deep cervical chains.
7. Retromolar Trigone
The retromolar trigone is a small triangular area located immediately posterior to the last molar tooth on the medial upper surface of the body of the mandible. It covers the anterior surface of the ascending ramus of the mandible. The base of the retromolar trigone lies posterior to the last molar, and its apex is situated adjacent to the tuberosity of the maxilla. This area is bordered by the buccal mucosa on the outside and the anterior tonsillar pillar on the inside. Since the retromolar mucosa is not subjected to the pressures of chewing, it is covered by a lining mucosa with nonkeratinizing stratified squamous epithelium, similar to the tissue found in the buccal mucosa. The buccal branch of the mandibular division of the trigeminal nerve supplies the sensory nerves in this area. Lymph from this region drains into the submandibular and deep cervical lymph nodes on the same side.
The Taste Pathway
Taste buds, located on papillae, detect five basic taste sensations: salty, sweet, sour, bitter, and umami. The taste pathway is a common NEET PG question.
Pathway Flowchart:
- Taste Receptors: In the taste buds of the tongue, palate, and epiglottis.
- Cranial Nerves:
- Chorda tympani (VII) from the anterior 2/3 of the tongue.
- Glossopharyngeal nerve (IX) from the posterior 1/3 of the tongue.
- Vagus nerve (X) from the palate and epiglottis.
- Nucleus of the Tractus Solitarius: All three nerves relay here in the brainstem.
- Thalamus: Second-order neurons synapse in the ventral posterior nucleus of the thalamus.
- Cortex: Fibers project to the primary gustatory cortex, including the frontal operculum and insular cortex.
———— End of the chapter ————
Download the full PDF Link:
Anatomy of Oral Cavity Best Lecture Notes Dr Rahul Bagla ENT Textbook
Reference Textbooks.
- Scott-Brown, Textbook of Otorhinolaryngology-Head and Neck Surgery.
- Cummings, Otolaryngology-Head and Neck Surgery.
- Stell and Maran’s, Textbook of Head and Neck Surgery and Oncology.
- Ballenger’s, Otorhinolaryngology Head And Neck Surgery
- Susan Standring, Gray’s Anatomy.
- Frank H. Netter, Atlas of Human Anatomy.
- B.D. Chaurasiya, Human Anatomy.
- P L Dhingra, Textbook of Diseases of Ear, Nose and Throat.
- Hazarika P, Textbook of Ear Nose Throat And Head Neck Surgery Clinical Practical.
- Mohan Bansal, Textbook of Diseases of Ear, Nose and Throat Head and Neck Surgery.
- Hans Behrbohm, Textbook of Ear, Nose, and Throat Diseases With Head and Neck Surgery.
- Logan Turner, Textbook of Diseases of The Nose, Throat and Ear Head And Neck Surgery.
- Arnold, U. Ganzer, Textbook of Otorhinolaryngology, Head and Neck Surgery.
- Ganong’s Review of Medical Physiology.
- Guyton & Hall Textbook of Medical Physiology.
Author:
Dr. Rahul Bagla
MBBS (MAMC, Delhi) MS ENT (UCMS, Delhi)
Fellow Rhinoplasty & Facial Plastic Surgery.
Renowned Teaching Faculty
Mail: msrahulbagla@gmail.com
India
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