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The Oral Cavity

The Oral Cavity

  • Also known as the mouth or buccal cavity.
  • Located in the lower part of the head, below the nasal cavities.
  • It is the beginning of the digestive tract.
  • Spans between the oral fissure (opening between the lips) anteriorly and the oropharyngeal isthmus (opening of the oropharynx) posteriorly.
  • Contains structures necessary for mastication and speech: teeth, tongue, and salivary glands.

Anatomical Framework and Primary Functions

  • The bony framework consists of paired maxillae, palatine and temporal bones, and unpaired mandible, sphenoid, and hyoid bones.
  • Major functions include:
    • Digestion
    • Communication
    • Breathing

Divisions of the Oral Cavity

  • Divided into 2 compartments by the upper and lower dental arches (formed by the teeth, alveolar bone, and gum).
    • Vestibule: outer, smaller portion.
    • Oral cavity proper: inner, larger part.
  • The two divisions are depicted as the vestibule and the oral cavity proper.

Hard Palate and Soft Palate; Roof and Soft Tissues

  • Hard palate:
    • A bony plate located anteriorly.
    • Separates the nasal cavity from the oral cavity.
    • Superior surface: respiratory mucosa (ciliated pseudostratified columnar epithelium).
    • Inferior surface: oral mucosa (stratified squamous epithelium).
  • Soft palate:
    • Posterior continuation of the hard palate.
    • Muscular structure functioning as a valve: lowers to close the oropharyngeal isthmus and elevates to separate nasopharynx from oropharynx.
  • Posterior wall of the oral pharynx, isthmus of the fauces, uvula, soft palate, palatopharyngeal arch, palatine tonsil, palatoglossal arch, gingiva (gum), vestibule of the mouth, and teeth are key surface landmarks.
  • The diagrammatic arrangement shows teeth types (incisors, canines, premolars, molars) and the relation of the hard palate, soft palate, tongue, and vestibule.

The Vestibule

  • The vestibule is horseshoe-shaped, situated anteriorly.
  • It lies between the lips/cheeks and the gums/teeth.
  • Communicates with the mouth proper via the space behind the third molar tooth (behind the 3^{
    rd}
    molar).
  • Communicates with the exterior via the oral fissure.
  • Diameter of the oral fissure is controlled by muscles of facial expression, principally the orbicularis oris.
  • The parotid duct opens into the vestibule opposite the upper 2^{ ext{nd}} molar tooth, secreting salivary juice.

The Oral Cavity Proper

  • Lies posterior to the vestibule.
  • Bordered by a roof, a floor, and lateral walls (cheeks).
  • The tongue fills a large portion of the cavity proper.
  • The interior is continuously lubricated by salivary glands, which also start carbohydrate digestion.
  • Salivary glands include the parotid, submandibular, and sublingual glands.

The Roof: Hard and Soft Palates (Details)

  • Roof consists of:
    • Hard palate (as above): anterior, bony, nasal-oral separation; mucosal coverings as described.
    • Soft palate: muscular, acts as a valve to regulate nasopharynx/oropharynx communication.

Openings and Landmarks Within the Oral Cavity

  • Palato-glossal arch and palato-pharyngeal arch form the palatine arches.
  • The tongue, frenulum, uvula, and tonsillar structures (palatine tonsil) are key intra-oral landmarks.
  • Openings of sublingual and submandibular glands are present on the floor of the mouth.
  • The parotid duct opens in the vestibule of the mouth opposite the upper second molar.
  • The underside of the tongue and the sublingual fold are visible within the oral cavity.

Muscles of the Soft Palate

  • Muscles listed:
    • Tensor veli palatine
    • Levator veli palatini
    • Palatopharyngeus
    • Palatoglossus
    • Musculus uvulae
  • Note: Innervation is not specified in the transcript; consult detailed anatomy sources for pharyngeal plexus (CN X) and related branches.

The Floor of the Mouth

  • The floor comprises several structures:
    • Muscular diaphragm formed by paired mylohyoid muscles, providing structural support and aiding in laryngeal movement during swallowing.
    • Geniohyoid muscles, which help pull the larynx forward during swallowing.
    • Tongue connected to the floor via the frenulum (fold of oral mucosa).
    • Salivary glands and ducts located on the floor of the oral cavity.

The Cheeks

  • Formed by the buccinator muscle.
  • Internally lined by the oral mucous membrane.
  • The buccinator contracts to keep food between the teeth during chewing.
  • Innervation: buccal branches of the facial nerve (CN VII).

Gums (Gingivae)

  • Soft tissues enveloping the alveolar processes of the jaws and surrounding the necks of the teeth.
  • Composed of dense fibrous tissue covered by stratified squamous epithelium.
  • Two parts:
    • Free part: surrounds the neck of the tooth like a collar.
    • Attached part: firmly fixed to the alveolar arch (jaw alveolus).
  • The fibrous tissue of the gum is continuous with the periosteum lining the alveoli (periodontal membrane).

Innervation of the Oral Cavity

  • Sensory innervation: branches of the trigeminal nerve (CN V).
    • Upper parts (palate and upper teeth) supplied by the maxillary nerve (V2).
    • Lower parts supplied by the mandibular nerve (V3).
  • Parasympathetic fibers to salivary glands in the oral cavity arise from branches of the facial nerve (CN VII) and are distributed through trigeminal branches.
  • Tongue taste (special sensory) fibers come from the chorda tympani, a branch of the facial nerve (CN VII).
  • Sympathetic fibers originate from the T1 spinal cord segment, synapse in the superior cervical sympathetic ganglion, and distribute to the oral cavity along branches of the trigeminal nerve or directly with blood vessels.

Clinical Relevance: The Gag/Pharyngeal Reflex

  • The gag reflex protects the airway from foreign bodies.
  • Triggered by stimulation of the posterior aspects of the oral cavity, which are mainly innervated by the glossopharyngeal nerve (CN IX).
  • Reflex arc results in:
    • Contraction of pharyngeal muscles to expel the object.
    • Elevation of the soft palate to prevent object entry into the airway.
    • Closure of the glottis to block airway entry.
  • The gag reflex can be used to assess brainstem function, particularly the integrity of CN IX and CN X.
  • Absent or reduced gag reflex can be observed in stroke, brainstem injury, or neurodegenerative diseases.

Summary and Connections

  • The oral cavity is a structurally integrated system for ingestion, digestion initiation, speech, and respiration.
  • Coordination among the teeth, tongue, palate, salivary glands, and neural innervation enables mastication, lubrication, taste, and swallowing.
  • Innervation includes CN V (sensory), CN VII (parasympathetic to glands and taste via chorda tympani), CN IX and X (gag reflex and pharyngeal function), and sympathetic pathways via T1.
  • Clinically, reflexes such as the gag reflex provide insight into brainstem integrity and neurological health.