Anatomy of the Oral Cavity and Pharynx

Oral Cavity - Entry Essentials

• Definition: Extends from lips (cutaneous-vermilion junction) to palatoglossal arches.
• Boundaries:
  • Anterior: Lips (orbicularis oris m.).
  • Posterior: Palatoglossal arches (anterior tonsillar pillars).
  • Superior: Hard palate (bony anterior 2/3), Soft palate (muscular posterior 1/3).
  • Inferior: Floor of mouth (mylohyoid m.), tongue.
  • Lateral: Cheeks (buccinator m.).
• Subdivisions:
  • Vestibule: Between lips/cheeks and teeth/gingivae.
    • Parotid (Stensen's) duct opens opposite upper 2nd molar.
  • Oral Cavity Proper: Space internal to dental arches.
    • Contents: Tongue, teeth, gingivae.
    • Ducts: Wharton's (submandibular) at sublingual caruncle; Rivinus' (sublingual) on sublingual fold.
• Lining: Stratified squamous epithelium (non-keratinized; keratinized on hard palate, tongue dorsum, gingiva).

⭐ Stensen's duct (parotid) opens into vestibule opposite maxillary 2nd molar; a key landmark.

Tongue & Salivary Glands - Taste & Moisten

• Tongue: Muscular organ for taste, speech, mastication, deglutition.
  • Parts: Oral (ant. 2/3), Pharyngeal (post. 1/3); separated by sulcus terminalis.
  • Muscles:
    • Intrinsic: Alter shape.
    • Extrinsic: Alter position (Genioglossus, Hyoglossus, Styloglossus, Palatoglossus). 📌 Mnemonic: Good Hygienic Students Practice.
  • Innervation (Motor): CN XII (Hypoglossal) to all except Palatoglossus (CN X - Vagus).
  • Innervation (Sensory):
    • Ant. 2/3: General - Lingual (V3); Taste - Chorda Tympani (VII).
    • Post. 1/3: General & Taste - CN IX (Glossopharyngeal).
    • Root/Epiglottis: CN X (Vagus).
  • Papillae: Filiform (touch, no taste), Fungiform (taste), Foliate (taste), Circumvallate (taste, Von Ebner's glands).
• Salivary Glands: Produce saliva (~1-1.5 L/day).
  • Major Glands:
    • Parotid: Serous. Stensen's duct. CN IX (parasymp).
    • Submandibular: Mixed (serous > mucous). Wharton's duct. CN VII (parasymp).
    • Sublingual: Mixed (mucous > serous). Ducts of Rivinus/Bartholin's. CN VII (parasymp).
  • Minor Glands: Scattered, mainly mucous. Von Ebner's (serous, associated with circumvallate papillae).
  • Functions: Lubrication, digestion (amylase), immunity (IgA), taste.

⭐ Frey's Syndrome: Post-parotidectomy gustatory sweating/flushing due to aberrant CN IX nerve regeneration to sweat glands over the parotid area.

Pharynx - The Crossroads

• Location & Extent: Musculomembranous tube (12-14 cm); base of skull to C6 (inferior border of cricoid).
• Subdivisions:
  • Nasopharynx: Skull base to soft palate.
    • Contents: Adenoids (pharyngeal tonsil), Eustachian tube opening, Fossa of Rosenmüller.
    • Epithelium: Ciliated columnar.
  • Oropharynx: Soft palate to hyoid/epiglottis.
    • Contents: Palatine tonsils, lingual tonsil.
    • Waldeyer's Lymphatic Ring: Pharyngeal (adenoids), tubal, palatine, & lingual tonsils. 📌 (P.T.P.L.)
    • Epithelium: Non-keratinized stratified squamous.
  • Laryngopharynx (Hypopharynx): Hyoid/epiglottis to C6.
    • Contents: Piriform fossae, postcricoid region.
    • Epithelium: Non-keratinized stratified squamous.
• Muscles:
  • Outer Circular (Constrictors): Superior, Middle, Inferior. Propel bolus.
    • Killian's Dehiscence: Weakness between thyropharyngeus & cricopharyngeus (inferior constrictor); site of Zenker's diverticulum.
  • Inner Longitudinal: Stylopharyngeus, Salpingopharyngeus, Palatopharyngeus. Elevate pharynx/larynx.
• Innervation:
  • Motor:
    • Most muscles: Pharyngeal plexus (CN X, cranial root of CN XI).
    • Stylopharyngeus: Exclusively CN IX.
  • Sensory: Nasopharynx (CN V2), Oropharynx (CN IX), Laryngopharynx (CN X - internal laryngeal n.).

  ⭐ The stylopharyngeus is the only muscle innervated by the glossopharyngeal nerve (CN IX).

• Oral cavity proper: Bounded by teeth/alveolar arches, palate, floor of mouth muscles.
• Waldeyer's ring: Lymphoid tissue: pharyngeal, tubal, palatine, lingual tonsils.
• Tongue motor: CN XII (not palatoglossus: CN X). Sensory: Ant 2/3rd Lingual (V3), Chorda tympani (VII); Post 1/3rd CN IX.
• Pharynx: Nasopharynx (Eustachian tube), Oropharynx (palatine tonsils), Laryngopharynx (to cricoid).
• Killian's dehiscence: Inferior constrictor weak spot for Zenker's diverticulum.
• Palatine tonsil artery: Mainly tonsillar branch of facial artery.
• Retropharyngeal space: Infection can spread to mediastinum.