Ethmoid bone
The ethmoid bone (from Greek ethmos, "sieve") is a bone in the skull that separates the nasal cavity from the brain. As such, it is located at the roof of the nose, between the two orbits. The cubical bone is lightweight due to a spongy construction.
Articulations
The ethmoid articulates with thirteen bones:
- two of the cranium—the frontal, and the sphenoid (at the sphenoidal body and at the sphenoidal conchae).
- eleven of the face—the two nasals, two maxillae, two lacrimals, two palatines, two inferior nasal conchae, and the vomer
Injuries
The ethmoid bone is very delicate and is easily injured by a sharp upward blow to the nose, such as a person might suffer by striking an automobile dashboard in a collision. The force of a blow can drive bone fragments through the cribriform plate into the meninges or brain tissue. Such injuries are often evidenced by leakage of cerebrospinal fluid into the nasal cavity, and may be followed from the nasal cavity to the brain.
Sagittal section of the skull. Ethmoid bone is labeled with white
Blows to the head can also shear off the olfactory nerves that pass though the ethmoid bone and cause anosmia, an irreversible loss of the sense of smell and a great reduction in the sense of taste (most of which depends on smell). This not only deprives life of some of its pleasures, but can also be dangerous, as when a person fails to smell smoke, gas, or spoiled food.
Fracture of the lamina papyracea, the lateral plate of the ethmoid labyrinth bone, permits communication between the nasal cavity and the ipsilateral orbit through the inferomedial orbital wall, resulting in orbital emphysema. Increased pressure within the nasal cavity, as seen during sneezing, for example, leads to temporary exophthalmos.
Role in magnetoception
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Main article: Magnetoception
Some birds and other migratory animals have deposits of biological magnetite in their ethmoid bones which allow them to sense the direction of the Earth's magnetic field. Humans have a similar magnetite deposit, but it is believed to be vestigial.
Additional images
See also
References
External links
This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained herein may be outdated. Please edit the article if this is the case, and feel free to remove this notice when it is no longer relevant.
The Bones which form the Orbit |
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Bones of head and neck: the cranium of the skull |
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Occipital |
Squama
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external (Inion/External occipital protuberance, Nuchal lines) - planes (Occipital, Nuchal) - internal (Cruciform eminence, Internal occipital protuberance, Sagittal sulcus, Internal occipital crest)
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Lateral parts
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Condyle (Condyloid fossa, Condylar canal) - Hypoglossal canal - jugular (Jugular process, Jugular tubercle)
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Basilar part
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Pharyngeal tubercle
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Other
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Foramen magnum
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Parietal |
Parietal eminence - Temporal line - Parietal foramen
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Frontal |
Squama
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Frontal suture - Frontal eminence - external (Superciliary arches, Glabella) - foramina (Supraorbital, Cecum) - Zygomatic process - internal (Sagittal sulcus, Frontal crest)
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Orbital part
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Ethmoidal notch - Lacrimal fossa - Trochlear fovea - Frontal sinus - Frontonasal duct
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Temporal |
Squama
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Articular tubercle - Suprameatal triangle - Mandibular fossa - Petrotympanic fissure - Zygomatic process
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Mastoid part
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Mastoid foramen - Mastoid process (Mastoid cells) - Mastoid notch - Occipital groove - Sigmoid sulcus - Mastoid antrum (Entrance)
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Petrous part
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Carotid canal - Facial canal (Hiatus) - Internal auditory meatus - Aqueduct of cochlea - Stylomastoid foramen
fossae (Subarcuate fossa, Jugular fossa) - canaliculi (Inferior tympanic, Mastoid) - Styloid process - Petrosquamous suture
(note: ossicles in petrous part, but not part of temporal bone)
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Tympanic part
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Suprameatal spine
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Sphenoid |
Surfaces
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Superior surface: Sella turcica (Dorsum sellae, Tuberculum sellae, Hypophysial fossa, Posterior clinoid processes) - Ethmoidal spine - Chiasmatic groove - Middle clinoid process - Petrosal process - Clivus
Lateral surface: Carotid groove - Sphenoidal lingula
Anterior surface: Sphenoidal sinuses
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Great wings
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foramina (Rotundum, Ovale, Vesalii, Spinosum) - Spine - Infratemporal crest - Sulcus for auditory tube
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Small wings
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Superior orbital fissure - Anterior clinoid process - Optic canal
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Pterygoid processes
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fossae (Pterygoid, Scaphoid) - pterygoid plates (Lateral, Medial) - Pterygoid canal - Hamulus
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Other
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Body - Sphenoidal conchae
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Ethmoid |
Plates
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Cribriform plate (Crista galli, Olfactory foramina) - Perpendicular plate
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Surfaces
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Lateral surface Orbital lamina - Uncinate process
Medial surface Superior nasal concha - Superior meatus - Middle nasal concha - Middle meatus
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Labyrinth
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Ethmoid sinus - ethmoidal foramina (Posterior, Anterior)
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