The last layer, the granule cell layer, lies internal to the mitral cell layer and contains the cell bodies of the granule cells (Simpson & Sweazey, 2013). The carotid canal extends upward and medially and provides passage to the internal carotid artery and carotid sympathetic nerves in their course to the cavernous sinus.

The perpendicular plate is a thin lamina which runs vertically from the cribriform plate. The olfactory nerves run through the perforations from the nasal cavity to the olfactory bulbs which, in man, lie above the cribriform plate. The ethmoid bone is a single midline facial bone that separates the nasal cavity from the brain and is located at the roof of the nose and between the orbits. G, The floor of the middle fossa has been removed to show the relationships below the floor.
23.1), at the rostral end of the olfactory sulcus (see Fig. The posterior trigeminal root reaches an impression on the upper surface of the petrous bone, where Meckel’s cave and the semilunar ganglion sit.
A thorough rhinologic examination includes visualization of the entire nasal cavity, typically using a combination of anterior rhinoscopy and formal nasal endoscopy.

F, Superior endocranial view of middle cranial base. Both Bartholdy and Grigorowsky reported branches of the anterior cerebral and the ethmoidal arteries to be critical for arterial supply to the olfactory nerves (Bartholdy, 1897; Grigorowsky, 1928). As such, it is located at the roof of the nose, between the two orbits.

Nuclei of the sustentacular cells are found near the surface of the epithelium. The posterior part of the cranial base is formed by the posterior aspect of the sphenoid body and the temporal and occipital bones. C, The orbital contents have been removed to expose the lateral wall and floor of the orbit. Start studying Ethmoid Bone.

Certain patients, however, note a worsening of olfactory function postoperatively. The temporalis muscle is exposed in the temporal fossa lateral to the greater sphenoid wing.

Developing by the process of endochondral ossification, the ethmoid bone is an important piece of your skull, especially due to the cribriform plate, which allows the olfactory fibers to pass through in order for you to smell things. The ethmoid bone is a singular porous bone that makes up the middle area of the viscerocranium and forms the midfacial region of the skull.It contributes to the moulding of the orbit, nasal cavity, nasal septum and the floor of the anterior cranial fossa.. A, Anterior view of the left maxilla, right palatine, and sphenoid bones. Additional CN dysfunction may suggest an intracranial mass. Rarely, more arterial pedicles formed by branches of the anterior cerebral artery and the posterior ethmoidal artery are present.

The meningohypophyseal trunk, with its tentorial, inferior hypophyseal, and dorsal meningeal branches, and the inferolateral trunk, also called the artery of the inferior cavernous sinus, arise from the intracavernous carotid artery. The optic canal transmits the optic nerve and the ophthalmic artery. Diagnostic assessment of patients with olfactory dysfunction includes CT scans, MRI, olfactory testing, and taste testing. The falciform dural fold extends across the optic nerve at the entrance into the optic canal.

Candace Wooten, in Nerves and Nerve Injuries, 2015. The anterior ethmoid cells are contiguous with the nose through an important anatomic region known as the ostiomeatal complex. The anatomy of the ethmoid sinuses is variable. L, Enlarged view with highlighting of the pre- (red) and poststyloid (yellow) compartments of the parapharyngeal space. The bone consists of a perpendicular plate and two ethmoidal labyrinths parts which are all superiorly attached to the cribriform plate.

The orbit opens through the superior orbital fissure into the middle fossa and through the inferior orbital fissure into the pterygopalatine and infratemporal fossae. The frontal and trochlear nerves can be seen through the periorbita. E, Posterior view of the frontal, ethmoid, and sphenoid bones forming the intracranial surface of the anterior cranial base. The serous secretions of the Bowman glands, combined with the secretions of the sustentacular cells, provide the mucus covering of the olfactory mucosa. The receptors responsible for transduction of odor molecules are found in the olfactory mucosa. The nasal bone is interposed above the anterior nasal aperture between the maxillae. Osseous structure of the nasal cavity and skull base.

• 23.3C, D). JOHN H. KROUSE MD, PHD, in Managing the Allergic Patient, 2008.

This portion of nasal mucosa is 1 to 2 cm2 in size and is located in the roof of the nasal cavity on the inferior surface of the cribriform plate and along the nasal septum and medial wall of the superior turbinate (Fig. A general appearance of fatigue with the presence of allergic shiners and a nasal crease may suggest an underlying allergic disorder. The ethmoid bone is one of the bones that make up the orbit of the eye.

Anatomic or inflammatory disorders of the nose or paranasal sinuses ultimately obstruct odorants from reaching the olfactory receptor cells. MRI may be used if better soft tissue resolution is required, especially if intracranial pathology is suspected in the olfactory bulbs or tracts.

Inferiorly: vomer and inferior nasal concha. The olfactory fila pass through the cribriform plate to terminate in the olfactory bulb. The blocks are joined, superiorly, by a perforated plate of bone: the cribriform plate (cribriform meaning a sieve).

The medial part, covering the upper nasal cavity and the sphenoid sinus, is formed by the crista galli and the cribriform plate of the ethmoid bone anteriorly, and the planum of the sphenoid body posteriorly. D, Anterior view of the sphenoid bone. The clinoidal segment of the internal carotid artery, located between the distal and proximal dural rings, is covered by a layer of dura, which forms a collar (the carotid collar) around the artery. One layer invests the nerves and forms the inner layer of the lateral wall, and the medial layer faces the body of the sphenoid bone and forms the medial wall of the sinus. The olfactory bulb lies on the cribriform plate of the ethmoid bone.

Because of its central location within the skull the ethmoid bone comes in contact with 15 other skull bones.

The nasal cavity opens onto the nasopharynx through two apertures called choanae, formed laterally by the pterygoid processes. Copyright © 2020 Elsevier B.V. or its licensors or contributors. Noniatrogenic causes of olfactory nerve injury include diseases of the nose and paranasal sinuses, recent upper respiratory tract infection, and head trauma. The afferent neural pathway then travels via the olfactory tracts to cortical regions. The upper part of the nasal cavity is separated from the orbits by the ethmoidal sinuses. The borders of the ethmoid sinuses include: anterior ethmoid (lateral): lamina papyracea of the orbit (medial); middle turbinate (superior): fovea ethmoidalis (cribriform plate); posterior ethmoid (lateral): lamina papyracea of the orbit (medial); superior turbinate (superior); fovea ethmoidalis (cribriform plate).

The optic nerves are enclosed within the optic sheath as they course through the optic canal.

B, The intraorbital fat has been removed and the levator and superior rectus muscles have been retracted laterally to expose both globes, ophthalmic arteries, superior ophthalmic veins, and nasociliary nerves. The temporalis muscle descends medial to the zygomatic arch in the temporal fossa to insert on the coronoid process of the mandible. The sella houses the pituitary gland and is partially closed above by the diaphragma sellae. Ethmoid bone: want to learn more about it? Periglomerular cells serve as mediators between certain mitral cells (Simpson & Sweazey, 2013). The greater wing forms part of the middle fossa floor. The carotid canal opens below the trigeminal ganglion near the distal end of the carotid canal, where the carotid artery becomes intracavernous (Figure 2.5). Here they synapse with the apical dendrites of granule cells, which serve to inhibit selected mitral cells (FitzGerald et al., 2012; Simpson & Sweazey, 2013). The maxillary and mandibular nerves pass through the foramen rotundum and ovale, respectively, both located in the greater wing of the sphenoid. The anterior boundary of the pituitary fossa is the tuberculum and the posterior boundary is the dorsum and posterior clinoids.

A more life-threatening issue in patients with olfactory dysfunction is the decreased ability to detect harmful smoke or a nearby fire. This article will examine the important aspects and features of the ethmoid bone, together with its borders.

The hard palate, the floor of the nasal cavity, is formed by the palatine process of the maxilla anteriorly and horizontal plate of the palatine bone posteriorly. Upper respiratory infections may cause direct viral induced neuronal injury and epithelial damage but primarily increase nasal secretions, once again blocking the passage of odorants. The abducens nerve passes below the petrosphenoid ligament and through Dorello’s canal.

It is very thin and infection in the ethmoid sinuses can extend into the orbits through this thin bone, resulting in orbital cellulitis or abscess formation. 23.3A, C, D). Copyright © Olfactory structures are especially vulnerable to facial trauma, particularly fractures involving the nasal bones, frontal bone, or concha of the nose.

When the ostiomeatal complex is narrowed or occluded, the ethmoid sinuses can easily become diseased, resulting in a higher incidence of acute and chronic rhinosinusitis. The crista galli is a perpendicular projection of the cribriform plate of the ethmoid into the endocranial cavity.

M, The right carotid canal has been drilled to show the petrous segment of the internal carotid artery, and the right half of the clivus has been drilled to show the sphenoid sinus and sella. The interior of each block is filled with air contained by the ethmoid sinuses. The space between the blocks forms the upper part of the nasal cavity and is divided, in the sagittal plane, by a plate of bone which contributes, below, to the nasal septum and rises through the cribriform plate to form the crista galli (Latin for cock’s comb) which projects into the anterior cranial fossa. The roof of the orbit is formed by the frontal and sphenoid bones, the lateral wall by the greater sphenoid wing and the zygomatic bone, the floor by the maxilla, except for a small part of the posterior floor formed by the palatine bone, and the medial wall of the orbit by the maxilla, and lacrimal and ethmoid bones. A variety of taste disturbances may also be attributed to a primary olfactory dysfunction. Individuals suffering from olfactory nerve dysfunction suffer from a decreased quality of life (Croy, Nordin, & Hummel, 2014; Svider et al., 2014).

The tensor tympani muscle and eustachian tube are layered, with the former above the latter, along and separated from the anterior surface of the petrous carotid by a thin layer of bone. 23.3B). These cells provide mechanical support for the olfactory receptor cells (Fig. The terminal sensory fibers of the olfactory nerve penetrate the cribriform plate of the ethmoid bone into the superior nasal cavity. The not infrequently occurring sphenoidal emissary foramen, located anteromedial to the foramen spinosum, gives passage to a vein connecting the cavernous sinus and the pterygoid venous plexus. The exocranial surface is formed by the maxilla, zygomatic, palatine, sphenoid, temporal, and occipital bones, and the vomer.

The lamina propria contains bundles of olfactory axons, blood vessels, fibrous tissue, and numerous Bowman glands (Fig. Next, a head and neck examination should be undertaken.

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