The ethmoid bone is nestled within the human skull. This single, unpaired bone, whose name derives from the Greek word “ethmos” meaning “sieve,” plays a role in several bodily functions despite its hidden location. Its delicate, spongy construction contributes to its lightweight nature.
Its Place and Shape in the Skull
The ethmoid bone is positioned centrally in the skull, at the roof of the nasal cavity and between the orbital cavities. It contributes to the medial wall of the orbits and forms part of the anterior cranial fossa, effectively separating the nasal cavity from the brain. This bone articulates with numerous other bones, including the frontal, sphenoid, nasal, maxillary, lacrimal, palatine, and vomer bones.
The ethmoid bone is characterized by its lightweight, spongy, and somewhat cubical shape. It consists of three main parts: the cribriform plate, the perpendicular plate, and two ethmoidal labyrinths. The cribriform plate, a horizontal and perforated section, forms the roof of the nasal cavity. Projecting superiorly from this plate is the crista galli, a triangular process that serves as an attachment point for a membrane that separates the brain’s hemispheres.
Descending from the cribriform plate is the perpendicular plate, a thin, flattened structure that forms the upper two-thirds of the nasal septum, the wall dividing the nasal cavity. On either side of the perpendicular plate are the ethmoidal labyrinths, which are large, irregular masses containing the ethmoidal air cells, also known as ethmoidal sinuses. These labyrinths contribute to the medial wall of the orbit and the lateral wall of the nasal cavity, from which the superior and middle nasal conchae extend.
What It Does
The ethmoid bone performs several functions related to the sense of smell, respiration, and structural support. The cribriform plate, with its numerous small openings, acts as a crucial pathway for the olfactory nerves to pass from the nasal cavity to the brain, enabling the sense of smell. This sieve-like structure supports the olfactory bulb, which processes smell information.
The ethmoidal labyrinths, containing the ethmoidal air cells or sinuses, play a role in respiration. These air-filled cavities help to humidify and warm inhaled air, and their lining, equipped with tiny hairs called cilia, helps filter out dust and debris. Additionally, the ethmoid bone contributes to the overall structure of the nasal cavity and the eye orbits, providing support and influencing vocal resonance.
Why It Matters for Your Health
The ethmoid bone is susceptible to injury, particularly from facial trauma. Fractures of the ethmoid bone can occur from forces such as hitting a dashboard in a car collision or falls from height. Such fractures, especially those affecting the cribriform plate, can damage the olfactory nerves, leading to anosmia, or loss of the sense of smell. This can also affect the ability to taste, as taste is closely linked to smell.
A significant concern with cribriform plate fractures is the potential for a cerebrospinal fluid (CSF) leak. The cribriform plate acts as a barrier between the nasal cavity and the brain, and a breach can allow CSF to leak into the nasal cavity. This creates a pathway for bacteria from the nasal cavity to enter the sterile environment of the brain, increasing the risk of serious infections like meningitis.
The ethmoid sinuses are also prone to inflammation, a condition known as ethmoid sinusitis. Symptoms of ethmoid sinusitis can include pain between the eyes, headaches, nasal congestion, and a reduced sense of smell. If left untreated, severe ethmoid sinusitis can lead to complications such as eye pain, swelling, or even vision changes due to the sinuses’ proximity to the eyes.