mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...

ian anatomy, the cribriform plate (

Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...

for lit. ''

sieve A sieve, fine mesh strainer, or sift, is a device for separating wanted elements from unwanted material or for controlling the particle size distribution of a sample, using a screen such as a woven mesh or net or perforated sheet materia ...

-shaped''), horizontal lamina or lamina cribrosa is part of the ethmoid bone. It is received into the

ethmoidal notch The ethmoidal notch separates the two orbital plates; it is quadrilateral, and filled, in the articulated skull, by the cribriform plate of the ethmoid. The margins of the notch present several half-cells which, when united with corresponding hal ...

of the

frontal bone The frontal bone is a bone in the human skull. The bone consists of two portions.'' Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bony part of the forehead, ...

and roofs in the

nasal cavities The nasal cavity is a large, air-filled space above and behind the nose in the middle of the face. The nasal septum divides the cavity into two cavities, also known as fossae. Each cavity is the continuation of one of the two nostrils. The nasal c ...

. It supports the

olfactory bulb The olfactory bulb (Latin: ''bulbus olfactorius'') is a neural structure of the vertebrate forebrain involved in olfaction, the sense of smell. It sends olfactory information to be further processed in the amygdala, the orbitofrontal cortex ...

, and is perforated by

olfactory foramina The olfactory foramina, also known as the cribriform foramina (cribr- is "a sieve" in Greek), is the grouping of holes located on the cribriform plate. The cribriform plate forms the roof of the nasal cavity, and the olfactory foramina are in the t ...

for the passage of the

olfactory nerve The olfactory nerve, also known as the first cranial nerve, cranial nerve I, or simply CN I, is a cranial nerve that contains sensory nerve fibers relating to the sense of smell. The afferent nerve fibers of the olfactory receptor neurons t ...

s to the roof of the

nasal cavity The nasal cavity is a large, air-filled space above and behind the nose in the middle of the face. The nasal septum divides the cavity into two cavities, also known as fossae. Each cavity is the continuation of one of the two nostrils. The nasal ...

to convey smell to the brain. The foramina at the medial part of the groove allow the passage of the nerves to the upper part of the nasal septum while the foramina at the lateral part transmit the nerves to the superior nasal concha. A fractured cribriform plate can result in olfactory dysfunction, septal hematoma, cerebrospinal fluid rhinorrhoea (CSF rhinorrhoea), and possibly infection which can lead to

meningitis Meningitis is acute or chronic inflammation of the protective membranes covering the brain and spinal cord, collectively called the meninges. The most common symptoms are fever, headache, and neck stiffness. Other symptoms include confusion or ...

. CSF rhinorrhoea (clear fluid leaking from the nose) is very serious and considered a

medical emergency A medical emergency is an acute injury or illness that poses an immediate risk to a person's life or long-term health, sometimes referred to as a situation risking "life or limb". These emergencies may require assistance from another, qualified ...

. Aging can cause the openings in the cribriform plate to close, pinching olfactory nerve fibers. A reduction in olfactory receptors, loss of blood flow, and thick nasal mucus can also cause an impaired sense of smell.

Structure

The cribriform plate is part of the ethmoid bone, which has a low density, and is spongy. It is narrow, with deep grooves supporting the

. Its anterior border, short and thick, articulates with the

. It has two small projecting alae (wings), which are received into corresponding depressions in the frontal bone to complete the foramen cecum. Its sides are smooth, and sometimes bulging due to the presence of a small air sinus in the interior. The crista galli projects upwards from the middle line of the cribriform plate. The long thin posterior border of the crista galli serves for the attachment of the falx cerebri. On either side of the crista galli, the cribriform plate is narrow and deeply grooved. At the front part of the cribriform plate, on either side of the crista galli, is a small fissure that is occupied by a process of

dura mater In neuroanatomy, dura mater is a thick membrane made of dense irregular connective tissue that surrounds the brain and spinal cord. It is the outermost of the three layers of membrane called the meninges that protect the central nervous system. ...

. Lateral to this fissure is a notch or foramen which transmits the

nasociliary nerve The nasociliary nerve is a branch of the ophthalmic nerve, itself a branch of the trigeminal nerve (CN V). It is intermediate in size between the other two branches of the ophthalmic nerve, the frontal nerve and lacrimal nerve. Structure The na ...

; from this notch a groove extends backward to the anterior ethmoidal foramen.

Keros classification

The Keros classification is a method of classifying the depth of the olfactory fossa. The depth of the olfactory fossa is determined by the height of the lateral lamella of the cribriform plate.

Keros Keros ( el, Κέρος; anciently, Keria or Kereia ( grc, Κέρεια) is an uninhabited and unpopulated Greek island in the Cyclades about southeast of Naxos. Administratively it is part of the community of Koufonisia. It has an area of an ...

in 1962, classified the depth into three categories. * type 1: has a depth of 1–3 mm (26.3% of population) * type 2: has a depth of 4–7 mm (73.3% of population) * type 3: has a depth of 8–16 mm (0.5% of population) * type 4: has asymmetric depths (described by Stammberger)

Function

The cribriform plate is perforated by

, which allow for the passage of the

s to the roof of the

. This conveys information from smell receptors to the

brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...

. The foramina at the medial part of the groove allow the passage of the nerves to the upper part of the nasal septum while the foramina at the lateral part transmit the nerves to the superior nasal concha.

Clinical significance

A fractured cribriform plate (anterior skull trauma) can result in leaking of

cerebrospinal fluid Cerebrospinal fluid (CSF) is a clear, colorless body fluid found within the tissue that surrounds the brain and spinal cord of all vertebrates. CSF is produced by specialised ependymal cells in the choroid plexus of the ventricles of the ...

into the nose and loss of sense of smell. The tiny apertures of the plate transmitting the olfactory nerve become the route of ascent for a pathogen, '' Naegleria fowleri''. This

amoeba An amoeba (; less commonly spelled ameba or amœba; plural ''am(o)ebas'' or ''am(o)ebae'' ), often called an amoeboid, is a type of cell or unicellular organism with the ability to alter its shape, primarily by extending and retracting pseudop ...

tends to destroy the olfactory bulb and the adjacent inferior surface of the frontal lobe of the brain. This surface initially becomes the site of proliferation of the trophozoites of ''Naegleria fowleri'' and their subsequent spread to the rest of the brain and CSF. Because of its initial involvement and trophozoite presence in early phases of ''Naegleria fowleri'' infection, flushing of this region with saline using a device, to obtain ''Naegleria fowleri'' for diagnostic PCR and microscopic viewing, has been proposed for patients affected by

naegleriasis Naegleriasis (also known as primary amoebic meningoencephalitis; PAM) is an almost invariably fatal infection of the brain by the free-living unicellular eukaryote ''Naegleria fowleri''. Symptoms are meningitis-like and include headache, fever ...

, by (Baig AM., et al.) in a recent publication. Researchers have suggested the same route to administer drugs at an early phase of infection by using a "Transcribrial Device" that has been proposed to kill this pathogen at the place of its maximum proliferation. In 2017 the inventor of this device suggested that after slight modifications this method could be effective in delivery of stem cells to the brain as well. A recent Australian study has shown that the bacterium causing the tropical disease

melioidosis Melioidosis is an infectious disease caused by a gram-negative bacterium called ''Burkholderia pseudomallei''. Most people exposed to ''B. pseudomallei'' experience no symptoms; however, those who do experience symptoms have signs and symptoms ...

, '' Burkholderia pseudomallei'', can also invade the brain via the olfactory nerve within 24 h by traversing the cribriform plate.

Etymology

The cribriform plate is named after its resemblance to a sieve (from Latin ''cribrum'', "sieve" + -form). It is also known as the horizontal lamina, and the lamina cribrosa.

Other animals

The cribriform plate is found in every

that has been studied. It serves the same function of allowing passage of the

olfactory nerves The olfactory nerve, also known as the first cranial nerve, cranial nerve I, or simply CN I, is a cranial nerve that contains sensory nerve fibers relating to the sense of smell. The afferent nerve fibers of the olfactory receptor neurons tr ...

Additional images

File:Cribriform plate and Olfactory nerve - animation.gif, Animation. Cribriform plate (green) and

s (yellow) File:Cribriform plate and Olfactory nerve - superior view.svg, Human skull, superior view. The calvaria is removed. File:Base of skull 3.jpg, Cribriform plate File:Ethmoid crista galli.jpg, Cribriform plate File:Sobo 1909 69.png, Ethmoid bone (red) and

, seen from bottom.

Olfactory foramina The olfactory foramina, also known as the cribriform foramina (cribr- is "a sieve" in Greek), is the grouping of holes located on the cribriform plate. The cribriform plate forms the roof of the nasal cavity, and the olfactory foramina are in the t ...

are illustrated. File:Crista galli and cribriform plate.webm, Video (1 min 32 s). Demonstrating crista galli, cribriform plate, and

References

External links

* {{Authority control Bones of the head and neck de:Siebplatte