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Paranasal sinuses

The paranasal sinuses are paired and symmetrical, air-filled cavities situated around the nasal cavity. Paranasal sinuses are found in three bones of the neurocranium (braincase), the frontal bone, ethmoid bone, and sphenoid bone. The maxilla is the only facial bone (viscerocranium) that contains its own sinuses. 

The four pairs of sinuses are named by their corresponding bones and include:

  • The maxillary sinuses
  • The frontal sinuses
  • The sphenoidal sinuses
  • The ethmoidal cells (sinuses)

The prime function of the paranasal sinuses is to protect the organism, mostly by humidifying the inhaled air and facilitating the immune response of the respiratory system

This article will discuss the anatomy and function of the paranasal sinuses.

Key facts about the paranasal sinuses
Definition A collection of paired air-filled spaces that surround the nasal cavity
Types Frontal sinuses
Ethmoidal cells (sinuses)
Maxillary sinuses
Sphenoidal sinuses
Function Humidify inhaled air
Facilitate immune response of nasal cavity
Decreasing weight of the head
Impacts the resonance of human voice
Contents
  1. Frontal sinuses
  2. Sphenoidal sinuses
  3. Ethmoidal cells (sinuses)
  4. Maxillary sinuses
  5. Functions
  6. Clinical relations
    1. Sinusitis
  7. Sources
+ Show all

Frontal sinuses

The frontal sinuses are paired triangular-shaped cavities located in the frontal bones. They are the most superior paranasal sinuses, situated deep to the superciliary arches and the root of the nose. The frontal sinuses are drained via the frontonasal duct to the ethmoidal infundibulum. This infundibulum then opens into the middle nasal meatus via the semilunar hiatus. These sinuses are usually not detectable in children before the age of 7. 

The frontal sinuses are innervated by the supraorbital nerve, a branch of the ophthalmic nerve (CN V1). The blood supply is provided by the anterior ethmoidal artery, a branch of the ophthalmic artery.

Sphenoidal sinuses

The sphenoidal sinuses are situated within the body of the sphenoid bone. Sometimes they can be extended into the wings of the sphenoid bone. The sinuses are not symmetrical as they   are separated unevenly by the bony septa. The sinuses are drained into the area known as the sphenoethmoidal recess. This area is located supero-posterior to the superior nasal concha

The sphenoidal sinuses are closely related to the important structures of the brain including the optic nerves and optic chiasm, pituitary gland, internal carotid arteries, and cavernous sinuses.

The sphenoidal sinuses are mainly innervated by the posterior ethmoidal nerves, branches of the ophthalmic nerve (CN V1). They are vascularized by the posterior ethmoidal arteries, branches of the ophthalmic artery.

Ethmoidal cells (sinuses)

The ethmoidal sinuses, or commonly known as ethmoidal cells, are small spaces located in the ethmoid bone. More specifically, they are located between the nasal cavity and the orbit. 

These cells can be divided into three groups that include: 

  • The anterior ethmoidal cells are drained to the middle nasal meatus via the ethmoidal infundibulum. 
  • The middle ethmoidal cells are drained into the middle nasal meatus. The middle cells are also known as “bullar cells” from a bulge they form on the middle nasal meatus (ethmoidal bulla).
  • The posterior ethmoidal cells are drained into the superior nasal meatus. 

The ethmoidal cells are innervated by the anterior and posterior ethmoidal branches of the nasociliary nerve, the branches of the ophthalmic nerve (CN V1).  The blood supply is provided via the anterior and posterior ethmoidal arteries.

Maxillary sinuses

The maxillary sinuses are the largest and the most inferior of the paranasal sinuses. They are situated deep in the bodies of the maxillae. Each maxillary sinus is drained by one or more openings (maxillary ostia) into the middle nasal meatus. Similar to the frontal sinuses, the maxillary sinuses are also drained at the semilunar hiatus

The maxillary sinuses are innervated by the anterior, middle, and posterior superior alveolar nerves, branches of the maxillary nerve (CN V2). The blood supply comes from the superior alveolar branches of the maxillary artery.

Functions

The paranasal sinuses have a number of functions. The primary function is the protection of the organism which is achieved by different mechanisms. The sinuses humidify the inhaled air and contain cells that participate in the immune system response. In addition, the sinuses are air-filled spaces that significantly decrease the weight of the head and impact the resonance of the human voice.

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