Sinuses, Nasal Cavity, and Oral Cavity

Sinuses and Nasal Cavity Openings

• There are three bilateral sinuses: frontal, sphenoid, and maxillary.
• The ethmoid sinuses are a single bilateral group that opens into each nasal cavity.
• Sinuses are named after the bone in which they are located.
• Frontal sinuses reside in the anteromedial aspects of the frontal bone.
• Maxillary sinuses are located inside the body of each maxilla.
• Sphenoid sinuses are situated in the body of the sphenoid bone.
• While most sinuses open into the middle meatus, the sphenoidal sinuses open into the spheno-ethmoidal recess, and the posterior ethmoidal air cells open into the superior meatus.
• Sinuses are air-filled cavities lined with a mucous membrane that reduces weight and warms and moistens incoming air.
• The nasolacrimal duct drains fluid from the medial aspect of the eye into the inferior meatus of the nasal cavity.

Oral Cavity

• It is located inferior to the nasal cavities and connects to the outside via the oral fissure.
• Posteriorly, it connects to the pharynx (oropharynx) through the oropharyngeal isthmus.
• Major functions include beginning the digestive process and manipulating sound from the larynx for speech.
• Walls consist of a roof, floor, and two lateral walls.

Roof

• The roof is divided into the hard palate and soft palate.
• Hard palate acts as the floor of the nasal cavities.
• Soft palate is posterior to the hard palate.
• Soft palate primarily consists of skeletal muscles covered in oral mucosa, including the uvula.
• The soft palate serves to depress, closing off the oropharyngeal isthmus, or elevate to close off the nasopharynx, preventing food or drink from entering the nasal cavity.

Lateral Walls

• Cheeks form the lateral walls with the buccinator muscle being the major muscle.

Floor

• The floor is composed of the tongue, some suprahyoid muscles, and many salivary glands.

Contents of the oral Cavity

• Key structures within the oral cavity: teeth, tongue, and salivary glands.
• Teeth receive innervation from the maxillary nerve for the upper teeth and the mandibular nerve for the lower teeth.

Tongue

• Consists mainly of muscular structure with a base and apex.
• The apex is the tip, while the base (pharyngal part) forms part of the oropharynx wall.
• The tongue has a root which joins the mandible anteriorly and the hyoid bone posteriorly, and a body which is superior to the root.
• The tongue's superior surface features papillae containing taste buds to increase surface area for taste.
• The inferior surface lacks papillae but has mucosal folds, including the midline frenulum.
• The tongue comprises mostly skeletal muscle and contains intrinsic and extrinsic muscles.

Tongue Musculature

• Intrinsic muscles attach and originate within the tongue, manipulating its width, length, and shape for precise movements during speech.
• Extrinsic muscles originate outside the tongue and insert into it, altering the tongues position.
• Most tongue muscles are innervated by the hypoglossal nerve, while one is innervated by the Vagus nerve.
• Somatic sensation for touch and pressure, as well as special sensation for taste, are present.
• Both general and special sensation to the posterior 1/3 is supplied by the hypoglossal nerve, while the facial nerve supplies the special sensation of taste to the anterior 2/3 and the mandibular nerve supplies the general sensation.

Salivary Glands

• Salivary glands synthesize and secrete saliva.
• Three large paired salivary glands: parotid, submandibular, and sublingual glands.
• Parotid glands receive visceral motor supply from CNIX (Vagus).
• Submandibular glands receive visceral motor supply from the facial nerve.
• Sublingual glands receive visceral motor suppletion from the facial nerve.

Pharynx

• The pharynx is a musculofascial tube shaped like a half-cylinder with its flat edge anteriorly, located posterior to the nasal and oral cavities and the larynx.
• The pharynx consists of three parts: nasopharynx, oropharynx, and laryngopharynx.

Pharyngeal Muscles

• The pharyngeal walls are constructed from fascia and two skeletal muscle groups: constrictor and longitudinal.
• Constrictor muscles have transverse fibres that originate from bone or cartilage, wrapping posteromedially to insert into the pharyngeal raphé.
• Constrictor muscles constrict the pharyngeal tube.
• Longitudinal muscles have vertical fibres that elevate the pharynx.
• All pharynx muscles, except one, are innervated by the Vagus nerve; one longitudinal muscle is innervated by the glossopharyngeal nerve.

Nasopharynx

• Anterior to the choanae, the nasopharynx connects to the nasal cavities.
• The soft palate marks the inferior aspect, while the sphenoid bone and basilar part of the occipital bone form the ceiling.
• Posterior to the bottom of the nasopharynx lies the anterior arch of C1 and the superior part of the dens of C2.
• Prominent features: the opening of the pharyngotympanic tube and the pharyngeal tonsils.

Oropharynx

• Located posterior to the oral cavity
• The palatoglossal arch and oropharyngeal isthmus marks the opening between two regions.
• Palatopharyngeal arch follows the opening.
• The palatine tonsils are palatine tonsils wither side of the oropharynx between the two aforementioned arches
• The soft palate, closely associated with the oropharynx, can depress to close of the oropharyngea isthmus and elevate to close off the nasopharynx from the rest of the pharynx.
• The soft palate marks the division between the nasopharynx and the oropharynx.
• The epiglottis marks the division between the oropharynx and the laryngopharynx.

Laryngopharynx

• Extends from the superior aspect of the epiglottis to the top of the oesophagus and connects the larynx via the laryngeal inlet.
• The Epiglottis closes the laryngeal inlet during swallowing to prevent food and drink from entering the airways.

Tonsils

• Lymphoid tissues surrounds the connections between the nasal and oral cavities and the pharynx given their role in protecting the body from foreign pathogens.
• Tonsils form in the mass tissue of the: phalangeal tonsils, the lingual tonsils, and the palatine tonsils.

Larynx

• Cartilage skeleton with musculoligamentous connections suspended from the hyoid bone.
• Begins at the laryngeal inlet and ends at the beginning of the trachea.
• Serves as a passageway for air and the organ of sound production.
• It also functions to shut off the lower respiratory tract during swallowing.
• Sensations to the larynx and motor supply to intrinsic muscles are carried out by the Vagus nerve.