Anatomy of Paranasal Sinuses

Paranasal Sinuses

• Each frontal sinus is roughly triangular in shape and extends upward above the medial end of the eyebrow and backward into the medial part of the roof of the orbit.
• Frontal sinuses open into the middle meatus of the nose through the infundibulum.
• Sphenoidal sinuses are located within the body of the sphenoid bone and open into the sphenoethmoidal recess above the superior concha.
• Ethmoidal sinuses are contained within the ethmoid bone, between the nose and the orbit, and are separated from the latter by a thin plate of bone.
• Anterior ethmoidal sinuses open into the infundibulum; middle ethmoidal sinuses open into the middle meatus on or above the bulla ethmoidalis; and posterior ethmoidal sinuses open into the superior meatus.

Drainage of Mucus and Functions of Paranasal Sinuses

• Mucus produced by the mucous membrane is moved into the nose by ciliary action of the columnar cells.
• Drainage of mucus is also achieved by the siphon action created during the blowing of the nose.
• The function of the sinuses is to act as resonators to the voice and to reduce the weight of the skull.
• When the apertures of the sinuses are blocked or they become filled with fluid, the quality of the voice is markedly changed.

Mandibular Nerve

• The mandibular nerve is a mixed nerve with both motor and sensory functions.
• The sensory root leaves the trigeminal ganglion and passes out of the skull through the foramen ovale to enter the infratemporal fossa.
• The motor root of the trigeminal nerve also leaves the skull through the foramen ovale and joins the sensory root to form the trunk of the mandibular nerve.
• The mandibular nerve divides into a small anterior and a large posterior division.
• Branches from the main trunk of the mandibular nerve include:
  • Meningeal branch
  • Nerve to the medial pterygoid muscle, which supplies the medial pterygoid muscle and the tensor veli palatini muscle
• Branches from the anterior division of the mandibular nerve include:
  • Masseteric nerve to the masseter muscle
  • Deep temporal nerves to the temporalis muscle
  • Nerve to the lateral pterygoid muscle
  • Buccal nerve to the skin and the mucous membrane of the cheek
• Branches from the posterior division of the mandibular nerve include:
  • Auriculotemporal nerve, which supplies the skin of the auricle, the external auditory meatus, the temporomandibular joint, and the scalp, and conveys postganglionic parasympathetic secretomotor fibers from the otic ganglion to the parotid salivary gland
  • Lingual nerve, which descends in front of the inferior alveolar nerve and enters the mouth to run forward on the side of the tongue and crosses the submandibular duct
  • Inferior alveolar nerve, which enters the mandibular canal to supply the teeth of the lower jaw and emerges through the mental foramen to supply the skin of the chin

Clinical Notes

• Injury to the lingual nerve may occur during clumsy extraction of an impacted third molar.
• The otic ganglion is a parasympathetic ganglion that is located medial to the mandibular nerve just below the skull, and it is adherent to the nerve to the medial pterygoid muscle.

Oral Cavity

• The lips are two fleshy folds that surround the oral orifice and are covered on the outside by skin and lined on the inside by mucous membrane.
• The substance of the lips is made up of the orbicularis oris muscle, the muscles that radiate from the lips into the face, labial blood vessels and nerves, connective tissue, and many small salivary glands.
• The philtrum is the shallow vertical groove seen in the midline on the outer surface of the upper lip.
• Median folds of mucous membrane (the labial frenulae) connect the inner surface of the lips to the gums.

Temporomandibular Joint

• The temporomandibular joint is composed of the condyle of the mandible and the articular fossa of the temporal bone.
• The joint is divided into upper and lower cavities by the articular disc.
• The superior retrodiscal layer of the TMJ joint is a lamina composed of connective tissue and elastic fibers that continues the posterior part of the articular disk and connects the disc to the tympanic plate of the temporal bone.
• The inferior retrodiscal layer of the TMJ joint is a lamina composed of collagen fibers that continues the posterior part of the articular disk and inserts into the condylar neck.
• The synovial membrane lines the capsule in the upper and lower cavities of the joint.
• The nerve supply of the TMJ is from the auriculotemporal and masseteric branches of the mandibular nerve.
• The vascular supply of the TMJ is mainly from the deep auricular artery, the superficial temporal artery, and the anterior tympanic artery.
• The venous drainage of the TMJ is via the superficial temporal vein and the maxillary vein.
• The movements of the TMJ include depression, elevation, protrusion, retraction, and rotation.
• In the position of rest, the teeth of the upper and lower jaws are slightly apart. On closure of the jaws, the teeth come into contact.

This quiz covers the anatomy and location of paranasal sinuses, including frontal, sphenoidal, and ethmoidal sinuses.