Ethmoid bone
Overview
The ethmoid bone is a bone
Bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...

 in the skull
Human skull
The human skull is a bony structure, skeleton, that is in the human head and which supports the structures of the face and forms a cavity for the brain.In humans, the adult skull is normally made up of 22 bones...

 that separates the nasal cavity
Nasal cavity
The nasal cavity is a large air filled space above and behind the nose in the middle of the face.- Function :The nasal cavity conditions the air to be received by the other areas of the respiratory tract...

 from the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...

. As such, it is located at the roof of the nose
Human nose
The visible part of the human nose is the protruding part of the face that bears the nostrils. The shape of the nose is determined by the ethmoid bone and the nasal septum, which consists mostly of cartilage and which separates the nostrils...

, between the two orbit
Orbit (anatomy)
In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents...

s. The cubical bone is lightweight due to a spongy construction. The ethmoid bone is one of the bones that makes up the orbit of the eye. The ethmoid has three parts: the cribriform plate, the ethmodial labyrinth, and the perpendicular plate
The ethmoid articulates with fifteen bones:
  • four of the neurocranium—the frontal
    Frontal bone
    The frontal bone is a bone in the human skull that resembles a cockleshell in form, and consists of two portions:* a vertical portion, the squama frontalis, corresponding with the region of the forehead....

    , and the sphenoid
    Sphenoid bone
    The sphenoid bone is an unpaired bone situated at the base of the skull in front of the temporal bone and basilar part of the occipital bone.The sphenoid bone is one of the seven bones that articulate to form the orbit...

     (at the sphenoidal body
    Body of sphenoid bone
    The body of the sphenoid bone, more or less cubical in shape, is hollowed out in its interior to form two large cavities, the sphenoidal air sinuses, which are separated from each other by a septum.- Superior surface :...

     and at the sphenoidal conchae
    Sphenoidal conchae
    The sphenoidal conchae are two thin, curved plates, situated at the anterior and lower part of the body of the sphenoid...

    ).
  • eleven of the viscerocranium—, two Nasal bones, two maxillae, two lacrimals, two palatines
    Palatine bone
    The palatine bone is a bone in many species of the animal kingdom, commonly termed the palatum .-Human anatomy:...

    , two inferior nasal conchae
    Inferior nasal conchae
    The inferior nasal concha is one of the turbinates in the nose. It extends horizontally along the lateral wall of the nasal cavity [Fig. 1] and consists of a lamina of spongy bone, curled upon itself like a scroll...

    , and the vomer
    Vomer
    The vomer is one of the unpaired facial bones of the skull. It is located in the midsagittal line, and articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right maxillary bones.-Biology:...


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.
Discussions
Encyclopedia
The ethmoid bone is a bone
Bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...

 in the skull
Human skull
The human skull is a bony structure, skeleton, that is in the human head and which supports the structures of the face and forms a cavity for the brain.In humans, the adult skull is normally made up of 22 bones...

 that separates the nasal cavity
Nasal cavity
The nasal cavity is a large air filled space above and behind the nose in the middle of the face.- Function :The nasal cavity conditions the air to be received by the other areas of the respiratory tract...

 from the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...

. As such, it is located at the roof of the nose
Human nose
The visible part of the human nose is the protruding part of the face that bears the nostrils. The shape of the nose is determined by the ethmoid bone and the nasal septum, which consists mostly of cartilage and which separates the nostrils...

, between the two orbit
Orbit (anatomy)
In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents...

s. The cubical bone is lightweight due to a spongy construction. The ethmoid bone is one of the bones that makes up the orbit of the eye. The ethmoid has three parts: the cribriform plate, the ethmodial labyrinth, and the perpendicular plate

Articulations

The ethmoid articulates with fifteen bones:
  • four of the neurocranium—the frontal
    Frontal bone
    The frontal bone is a bone in the human skull that resembles a cockleshell in form, and consists of two portions:* a vertical portion, the squama frontalis, corresponding with the region of the forehead....

    , and the sphenoid
    Sphenoid bone
    The sphenoid bone is an unpaired bone situated at the base of the skull in front of the temporal bone and basilar part of the occipital bone.The sphenoid bone is one of the seven bones that articulate to form the orbit...

     (at the sphenoidal body
    Body of sphenoid bone
    The body of the sphenoid bone, more or less cubical in shape, is hollowed out in its interior to form two large cavities, the sphenoidal air sinuses, which are separated from each other by a septum.- Superior surface :...

     and at the sphenoidal conchae
    Sphenoidal conchae
    The sphenoidal conchae are two thin, curved plates, situated at the anterior and lower part of the body of the sphenoid...

    ).
  • eleven of the viscerocranium—, two Nasal bones, two maxillae, two lacrimals, two palatines
    Palatine bone
    The palatine bone is a bone in many species of the animal kingdom, commonly termed the palatum .-Human anatomy:...

    , two inferior nasal conchae
    Inferior nasal conchae
    The inferior nasal concha is one of the turbinates in the nose. It extends horizontally along the lateral wall of the nasal cavity [Fig. 1] and consists of a lamina of spongy bone, curled upon itself like a scroll...

    , and the vomer
    Vomer
    The vomer is one of the unpaired facial bones of the skull. It is located in the midsagittal line, and articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right maxillary bones.-Biology:...


Injuries

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
Exophthalmos
Exophthalmos is a bulging of the eye anteriorly out of the orbit. Exophthalmos can be either bilateral or unilateral . Measurement of the degree of exophthalmos is performed using an exophthalmometer...

.

The porous, fragile nature of the ethmoid bone makes it particularly susceptible to fractures. The ethmoid is usually fractured from an upward force to the nose. This could occur by hitting the dashboard in a car crash or landing on the ground after a fall. The ethmoid fracture can produce bone fragments that penetrate the cribriform plate. This trauma can lead to a leak of cerebral spinal fluid into the nasal cavity. These openings allow for opportunistic bacteria in the nasal cavity to enter the sterile environment of the central nervous system (CNS). The CNS is usually protected by the blood brain barrier, but holes in the cribriform plate
Cribriform plate
The cribriform plate of the ethmoid bone is received into the ethmoidal notch of the frontal bone and roofs in the nasal cavities....

 allow bacteria to surpass the barrier. The blood brain barrier makes it extremely difficult to treat such infections because only certain drugs can cross in the CNS.

An ethmoid fracture can also sever the olfactory nerve. This injury results in anosmia, or the loss of smell. A reduction in the ability to taste is also a side effect because it is based so heavily on smell. This injury is not fatal.

Role in magnetoception

Some bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s and other migratory animals have deposits of biological magnetite
Magnetite
Magnetite is a ferrimagnetic mineral with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. The chemical IUPAC name is iron oxide and the common chemical name is ferrous-ferric oxide. The formula for magnetite may also be written as FeO·Fe2O3, which is one part...

 in their ethmoid bones which allow them to sense the direction of the Earth's magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

. Humans have a similar magnetite deposit, but it is believed to be vestigial
Vestigial structure
Vestigiality describes homologous characters of organisms that have seemingly lost all or most of their original function in a species through evolution. These may take various forms such as anatomical structures, behaviors and biochemical pathways. Some of these disappear early in embryonic...

.

See also

  • Ossification of ethmoid
    Ossification of ethmoid
    The ethmoid is ossified in the cartilage of the nasal capsule by three centers: one for the perpendicular plate, and one for each labyrinth.The labyrinths are first developed, ossific granules making their appearance in the region of the lamina papyracea between the fourth and fifth months of fetal...

  • Bone terminology
  • Terms for anatomical location

External links

  • http://www.theregister.com/2006/11/17/the_odd_body_nose_compass/
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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