Oral Cavity: Lips and Tongue

The lips are the soft and movable most external parts of the oral cavity. The tongue, on the other hand, is a complex muscular structure that permits tasting and facilitates the process of mastication and communication. Together, these structures play an important role in each of these vital processes. The blood supply of the lips and tongue originates from the external carotid artery, and the innervation is through cranial nerves.

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Gross Anatomy of the Lips

Characteristics

  • Philtrum: vertical indentation in the middle area of the upper lip
  • Oral commissures: lateral borders of the oral cavity where upper and lower lips join
  • Vermilion lip: pink portion of external lip
  • Contain fewer melanocytes than the rest of the skin
  • Do not contain sweat glands
  • Lips are attached to the gums by the upper and lower labial frenula (frenulum labii).

Movement

Numerous muscles are responsible for movement of the lips.

  • Lip elevation:
    • Levator labii superioris
    • Levator labii superioris alaeque nasi
    • Levator anguli oris
    • Zygomaticus minor
    • Zygomaticus major
  • Lip depression:
    • Risorius
    • Depressor anguli oris
    • Depressor labii inferioris
    • Mentalis

Neurovasculature

  • Blood supply:
    • Supplied by branches of the facial artery (external carotid artery origin)
    • Superior labial artery: supplies upper lip
    • Inferior labial artery: supplies lower lip
  • Innervation:
    • Supplied by branches of the trigeminal nerve
    • Infraorbital nerve (V2): innervates upper lip
    • Mental nerve (V3): innervates lower lip

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Gross Anatomy of the Tongue

The tongue is a muscular projection that assists with chewing, speech, and taste. The tongue has variable innervation depending on which section is of interest and is supplied by a branch of the external carotid artery.

Characteristics

  • Made up of 3 parts:
    • Root (radix linguae)
    • Body (corpus linguae)
    • Tip (apex linguae)
  • Consists of skeletal muscle, which allows for flexibility.

Movement

The tongue is moved by extrinsic and intrinsic muscles. Extrinsic muscles connect the tongue to surrounding structures, while intrinsic muscles do not have a bony origin or insertion.

  • Extrinsic tongue muscles:
    • Genioglossus
    • Hyoglossus 
    • Styloglossus 
    • Palatoglossus 
  • Intrinsic tongue muscles:
    • Verticalis linguae
    • Superior longitudinal
    • Inferior longitudinal
    • Transverse lingual
Table: Muscles of the tongue
MuscleOriginInsertionFunction
GenioglossusMental spine of mandibleBody of hyoid
  • Protrusion of the tongue
  • Depression of the tongue
  • Draws the tip of the tongue back and down
HyoglossusHyoid boneSide of the tongue
  • Depression of the tongue
  • Retraction of the tongue
StyloglossusStyloid process of temporal boneTip and sides of tongue
  • Retraction of the tongue
  • Elevation of the tongue
PalatoglossusPalatine aponeurosisTongueRaises the posterior part of the tongue

Neurovasculature

  • Blood supply:
    • Supplied by branches of the external carotid artery
    • The lingual artery branches directly off of the external carotid artery to supply the tongue.
  • Motor innervation:
    • Hypoglossal nerve: all tongue muscles except for the palatoglossus
    • Vagus nerve: palatoglossus muscle
  • Innervation of taste and sensation:
    • Anterior ⅔ of the tongue:
      • Taste: chorda tympani (cranial nerve (CN) VII)
      • Sensation: lingual nerve (CN V3)
    • Glossopharyngeal nerve: posterior ⅓ of the tongue
    • Internal branch of superior laryngeal nerve: base of the tongue
Geographic innervation of the tongue

Geographic innervation of the tongue
CN: cranial nerve

Image by Lecturio.

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Microscopic Anatomy of the Lips

The microscopic anatomy of the lips consists primarily of 3 layers: the pars cutanea, pars intermedia, and pars mucosa. The pars cutanea is the outer layer of skin, the pars intermedia is the pink portion of the lip, and the pars mucosa is inside the lip. These layers contain varying amounts of skeletal muscle.

  • Pars cutanea:
    • Skin (stratified squamous epithelium)
    • Hair follicles
    • Sebaceous glands
    • Sweat glands
  • Pars intermedia:
    • Stratified squamous epithelium
    • No sebaceous glands or hair follicles
  • Pars mucosa:
    • Nonkeratinized stratified squamous epithelium
    • Labial glands
    • Small salivary glands
  • Muscles contained in all layers: 
    • Orbicularis oris
    • Depressor labii inferioris
    • Levator labii
Histologic cross section of the lip

Histologic cross section of the lower lip

Image by Lecturio and Geoffrey Meyer.

Microscopic Anatomy of the Tongue

The microscopic anatomy of the tongue comprises squamous epithelium and nerve cells, which assist in the highly variable functions of the organ. 

  • Stratified squamous epithelium:
    • Dorsal surface: keratinized
    • Ventral surface: nonkeratinized
  • The tongue contains:
    • Papillae
    • Taste buds:
      • Taste receptor cells
      • Sustentacular cells → opens onto the surface → taste pore
  • Glands: serous glands
Table: Papillae of the tongue
PapillaeCharacteristics
Filiform papillae (thread-like)
  • Tactile: cover the surface of the tongue
  • Most common
  • Do not possess taste buds
  • Help to drag food
Conic papillae (cone-shaped)Similar to the filiform papillae
Fungiform papillae (mushroom-shaped)
  • Highly vascularized
  • A few gustatory papillae and taste buds
Foliate papillae (leaf-shaped)Large amount of gustatory papillae and taste buds
Circumvallate papillae (dome-shaped)
  • Only 7–12 gustatory papillae in total
  • Taste buds in the medial walls
  • Von Ebner’s glands (serous glands) open into the cleft

Clinical Relevance

  • Cleft tongue or lips: due to a lack of fusion of the lateral lingual swellings or lips. A cleft lip usually presents as an opening in the upper lip that may extend into the nose. Along with cosmetic disfigurement, these disorders can result in feeding problems that may be severe. The treatment is usually surgical.
  • Microglossia: small or rudimentary tongue. Microglossia is a rare congenital condition that presents with difficulty in eating and swallowing. Relative microglossia is when the tongue is smaller in structure than the jaw bones. There is no treatment for microglossia.
  • Macroglossia: enlarged tongue. Macroglossia can be either congenital or acquired. Macroglossia is often associated with Down syndrome and Hunter syndrome. Acquired macroglossia may be seen in lingual tumors, myxedema, amyloidosis, and angioedema.
  • Ankyloglossia: condition characterized by fixation of the tongue to the floor of the mouth. Partial ankyloglossia is also known as tongue-tie. Patients have difficulty with speaking and swallowing. Ankyloglossia may be resolved by surgical intervention.

References

  1. Tolarová, M.M., Cervenka, J. (1998). Classification and birth prevalence of orofacial clefts. Am J Med Genet 75:126–137. https://pubmed.ncbi.nlm.nih.gov/9450872/
  2. Mai, C.T., Cassell, C.H., Meyer, R.E., et al. (2014). Birth defects data from population-based birth defects surveillance programs in the United States, 2007 to 2011: highlighting orofacial clefts. Birth Defects Res A Clin Mol Teratol 100:895–904. https://pubmed.ncbi.nlm.nih.gov/25399767/
  3. Shkoukani, M.A., Chen, M., Vong, A. (2013). Cleft lip—a comprehensive review. Front Pediatr 1:53. https://pubmed.ncbi.nlm.nih.gov/24400297/
  4. Centers for Disease Control and Prevention (CDC). (2020). Facts about Down syndrome. Retrieved January 30, 2021, from https://www.cdc.gov/ncbddd/birthdefects/DownSyndrome.html

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