Anatomy of the Oral Cavity
Objectives
§ Describe the boundaries of the oral cavity and oropharynx, and their relationships to the soft and hard palate.
§ Describe the muscular organization of the tongue in terms of extrinsic and intrinsic muscles.
§ Describe the relations of the hyoglossus muscle.
§ Describe the sensory and motor innervation to the tongue and structures of the oropharynx.
§ Describe the location and component parts of Waldeyer’s (Tonsillar) Ring.
§ Describe the arterial supply to the tongue and oropharynx, especially in relation to the floor of the mouth.
§ Describe the formation of the hard and soft palate.
§ Describe the basic organization of the adult teeth and venous drainage.
Boundaries and the inferior surface of the tongue
§ The oral cavity is divided into a vestibule, between the teeth and gums, and the oral cavity proper.
§ The oral cavity proper has the hard palate for its roof. It is also bounded by the cheeks, lips, floor of the mouth, and posteriorly – the oropharynx.
§ The undersurface of the tongue has some interesting anatomical features.
§ In particular, there is a prominent frenulum that serves to anchor the tongue to the floor of the mouth.
§ When the frenulum limits the excursion of the tongue during speech, the person is said to be ‘tongue-tied.’
§ The mucosa of the tongue’s undersurface is thin, so deep lingual veins are usually apparent.
§ Because of their proximity to the surface, drugs may be administered in a sublingual manner for a more rapid absorption that through the GI tract.
§ Also, at the base of the tongue, there is a sublingual fold that contains, near the midline, the openings for the submandibular glands.
§ Lateral to the sublingual papillae are numerous openings for the sublingual glands.
§ The last of the major salivary glands are the parotid glands which empty into the vestibule through the parotid papilla opposite the second upper molar.
Dorsum of the tongue
§ The dorsum of the tongue is generally discussed in terms of an anterior two-thirds and a posterior one-third.
§ The line of separation is the sulcus limitans, which features the foramen cecum at the midline.
§ These portions have differing embryonic origins.
§ The dorsum of the anterior two-third is characterized by its rough appearance.
§ There are several varieties of papillae, some of which contain ‘taste buds.’
§ The types of papillae are: (1) fungiform, (2) filiform, (3) vallate papillae, and (4) foliate.
§ Abundant taste buds are found in the vallate and fungiform papillae, but taste buds, which are specialized nerve endings, are more widely distributed than the papillae.
§ In fact, they are generally spread across the whole dorsum of the tongue and also the lingual surface of the soft palate.
Muscles
a. Intrinsic:
§ The intrinsic musculature of the tongue is organized as a 3-dimensional matrix.
§ These muscles are responsible for shaping the tongue for swallowing and phonation.
| Intrinsic Muscle | Action | Innervation |
| Longitudinal | XII | |
| Transverse | XII | |
| Vertical | XII |
b. Extrinsic:
§ The extrinsic muscles of the tongue are those that insert into the matrix of intrinsic muscles to grossly position the tongue.
§ The extrinsic muscles of the tongue are listed in the Table below,
§ note that the palatoglossus is probably best grouped with the muscles of the palate because of innervation and functional considerations.
| Extrinsic Muscle | Action | Innervation |
| Palatoglossus | Questionable function with respect to tongue movements | X |
| Styloglossus | Retracts and elevates | XII |
| Hyoglossus | Flattens the tongue | XII |
| Genioglossus | Protrudes the tongue | XII |
Nerve Supply
§ The hypoglossal nerve (CN XII) supplies all the muscles of the tongue, both intrinsic and extrinsic.
§ The lingual nerve, which is a major branch off of V3 is distributed to the dorsum of the tongue in front of the vallate papillae; to most of the anterior two-thirds.
§ Fibers distributed by the lingual nerve mediate special sensory (i.e., taste) and general sensory (touch, temperature, and pain) functions.
§ Remember, the taste fibers of the lingual nerve are donated by the chorda tympani nerve.
§ The surface of the posterior one-third is largely innervated by CN IX.
§ CN X, however, appears to have some distribution to regions about the epiglottis.
Blood Supply
§ The bulk of the arterial supply to the tongue arises from the lingual artery, but there are contributions from the tonsillar artery and also from the ascending pharyngeal.
§ The relationship between the lingual artery and the lingual nerve and hyoglossal muscle should be well appreciated.
Clinical correlates
§ Since the tongue can be protruded only to the midline if the genioglossus muscle is functioning bilaterally, the integrity of CN XII can be conveniently tested by asking the patient to stick their tongue out as far as possible.
§ In a hypoglossal nerve paralysis, only the unaffected side operates and the tongue is projected to the side of the lesioned nerve.
§ With respect to taste sensation, damage to the lingual nerve can lead to an ipsilateral impairment of taste in the anterior two-thirds of the tongue, but rarely does such a lesion obliterate taste sensation because the vallate papillae, which contains an abundance of taste buds, is innervated by CN IX.
§ In any event, when a patient presents with a complaint of a change in taste, always investigate olfaction since much of our appreciation of taste is really tied to our sense of smell.
Tags: dorsum of the tongue, genioglossus muscle, hard palate, hyoglossal muscle, hypoglossal nerve, ipsilateral impairment of taste, lingual nerve, oral cavity, palatoglossus, papillae, parotid glands, prominent frenulum, sense of smell, soft palate, sublingual papillae, sulcus limitans, swallowing and phonation, tonsillar artery hypoglossal nerve paralysis, vallate papillae
