Sphenoid

The sphenoid bone is a large bone in the middle of the skull base and contains the sphenoid sinus. Learn more about the sphenoid

Sphenoid

The sphenoid or Os Sphenoidale lies in the middle of the base of the skull in front of the occipital bone (Os occipitale). It is a part of the brain's skull and is associated with all other skull bones and also with most of the bones of the facial skull. The body of the sphenoid bone is hollowed out (sphenoid sinus) and divided into two chambers, over which lies the pituitary gland. Read everything important about the anatomy and function of the sphenoid bone!

What is the sphenoid?

The sphenoid bone (sphenoid bones) is a central skull bone, which has approximately the shape of a flying wasp with outstretched wings and drooping legs: It consists of the body of the sphenoid (Corpus), two large alae majores, two small sphenoid wings (Alae minores) and the downward wing-like processes (pterygoid process).

The sphenoid body (corpus)

The sphenoidal body (corpus) has an approximately dice-like shape. Inside, there are two cavities separated by a septum, called sphenoid sinuses.

The posterior surface of the sphenoidal body forms a (initially cartilaginous, later bony) connection with the occipital bone.

The upper surface of the sphenoidal body forms in the rear of the so-called Turkish Saddle (Sella turcica), in which the hypophysis (pituitary gland) is located. In the front upper area there is a connection to the ethmoid via a bone spike. In addition, a small, flat piece of bone (jugum sphenoidale) connects the two small sphenoidal wings in front of the chiasmatic sulcus, in which the optic nerve intersection (chiasm opticum) lies. The paired optic nerve runs through a bone opening, along with its artery.

The anterior border of the sphenoidal body forms the posterior part of the eye socket (orbita). About a bone crest is a connection to the ethmoid, continues to connect to the forehead and the palate leg. Multiple openings lead into the sphenoid sinuses, which communicate with the nasal cavity.

The lower surface of the sphenoidal body has a beak-like bony crest, the Rostrum sphenoidale, which extends vertically downwards and which is encompassed by the wings of the ploughshare and passes into the nasal septum.

The Great Keilbein wings (Alae majores)

The large sphenoid wings are strong bony processes on the side of the sphenoidal body that are curved outwards and upwards. They have four faces, four edges and an angle.

The areas of the large sphenoid wings are called:

  • Facies cerebralis (pointing up to the brain)
  • Facies temporalis (on the outer surface of the skull and separated by a bone band from the underlying facies infratemporalis of the upper jaw)
  • Facies orbitalis (confined to the eye socket with a flat, smooth bone surface)
  • Facies maxillaris (just below the facies orbitalis, represents the border to the upper jaw)

In the maxillary facies lies the foramen rotundum - a round opening through which the second trigeminal branch (a facial nerve) passes.

The edges of the large sphenoid wings are called:

  • Margo frontalis (adjacent to the frontal bone)
  • Margo zygomaticus (adjacent to the zygomatic bone)
  • Margo parietalis (adjacent to the parietal bone)
  • Margo squamosus (adjacent to the temporal bone)

The back edge of the large sphenoid wing is pulled out like a spine. Here there is a passage for an artery and a nerve. The muscle, which tenses the soft palate and keeps the Eustachian tube open, has its origin here.

The small Keilbein wings (Alae minores)

The small sphenoid wings are thin, triangular bone plates that sit at the top of the sphenoid body. They form the optic canal through which the optic nerve passes from the cranial cavity into the eye socket. With the lower surface they limit the eye socket, with the upper the skull cavity. To the middle and to the rear they form short bony processes.

The wing-extension of the sphenoid

As the processus pterygoidus medical doctors call wing-like processes that go almost vertically downwards from the approach of the large Keilbeinflügel on the sphenoidal body. They consist of two bone plates, the median lamina (central plate) and the lateral lamina (lateral plate).

Between these two is a pit, the fossa pterygoidea (wing palatal pit). The posterior part of this pit is formed by the wing-extension of the sphenoid bone, the plate of the palatine bone is perpendicular, and the front side is formed by the upper jaw.

The approach of the wing processes is pierced by a vascular nerve channel, this pit is a central distribution point for vessels and nerves.

The medial lamella has a hook-shaped extension at the lower end. Here runs the tendon of that muscle that tenses the palate.

The sphenoid sinus

The sphenoid sinus belongs to the paranasal sinuses.It is very small, borders with the rear wall on the rear fossa and with the lower side of the pharyngeal wall. It belongs to the so-called Pneumatisationsräumen, which are connected to the nasal caves. The sphenoid sinus opens into the upper nasal passage, and there is also a connection to the eye sockets and the optic nerve. The sphenoid sinus is - like the nasal mucosa - lined with a ciliated epithelium.

What is the function of the sphenoid bone?

The sphenoid bone, like the other cranial bones, protects the brain and serves as a point of attachment for various muscles (such as the masticatory muscles). It forms the posterior portion of the eye socket and, along with other bones, the base of the skull.

The function of the sphenoid sinus and the other paranasal sinuses is not yet fully elucidated. Presumably, the air-filled cavities reduce the weight of the skull and serve as the resonance chamber of the voice.

Where is the sphenoid?

The sphenoidal bone lies as a central bone of the skull wedge-shaped between all other skull bones, in front of the occiput (occipitale) in the middle of the skull base. With the occipital bone, the sphenoid bone is only cartilaginous until adolescence, only in adults there is a bony connection here.

What problems can the sphenoid bone cause?

Inflammation of the sphenoid sinuses is relatively rare. Because they are associated with the upper turbinate, viruses and bacteria that cause sinusitis (sinusitis) can also lead to an infection here. There is a pressure-like pain in the back of the head and in the apex area, because in the cave secretion accumulates, which exerts pressure. In addition, runny nose and fever.

If the disease symptoms last longer than a quarter of a year, then one speaks of a chronic sinusitis - usually due to anatomical bottlenecks in the nose area.

Extensive inflammation sometimes results in abscess or empyema in the sphenoid sinus.

A sphenoidal meningoma is a benign tumor of the temporal brain that spreads to the small sphenoid wing. It can also extend into the eye socket or the palate and then leads to visual disturbances and nerve paralysis.

In a fracture of the occipital bone, the sphenoid be involved.


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