Sphenoid & Ethmoid Bones

What is the sphenoid bone?

irregular, wedge-shaped (or bat shaped) bone on the floor of the skull (middle cranial fossa)

What makes up the sphenoid bone?

• body

• 2 lesser wings

• 2 greater wings

• 2 pterygoid processes

What is the “keystone of the cranial floor?”

the sphenoid, because it articulates with all of the other cranial bones

The central part of the sphenoid is the ___

body

Explain the location and makeup of the body of the sphenoid

• location

  • anterior surface forms the posterior wall of the nasal cavity

  • ½” anterior and ½” superior to EAM

• made up of:

  • sella turcica (turkish saddle)

  • tuberculum sellae

  • dorsum sellae - posterior clinoid process

  • pituitary fossa

  • optic foramen/canal

The optic foramen/canal contains the ___

optic nerve and optic groove

(optic groove/chiasmatic groove extends across the anterior portion of the superior surface of the body

What are the greater wings of the sphenoid?

2 wing-like plates that originate from each lateral surface of the body

List the 3 foramen of the greater wings of the sphenoid

• foramen rotundum

  • transmits the maxillary nerve out of the cranium

  • anterior, perfectly round

• foramen ovale

  • transmits mandibular nerve out of the cranium

  • posterior to rotundum, oval shaped

• foramen spinosum

  • transmits the middle meningeal artery

  • posterior to ovale, tiny

Explain the location, shape, and function of the superior orbital fissure

• on the medial margin of the greater wing of the sphenoid

• “slit” shaped

• transmits 3rd, 4th, and 5th cranial nerves

Explain the location and function of the inferior orbital fissure

• between maxilla, zygoma, and greater wing of the sphenoid

• transmits maxillary branch of the 5th cranial nerve

What are the 2 points of the lesser wing?

What are the 2 points on the dorsum sellae?

wing: anterior clinoid processes

dorsum sellae: posterior clinoid processes

What are the pterygoid processes?

inferior projections at the junction of the body and greater wing

What are the names of the pterygoid processes?

lateral pterygoids

medial pterygoids (longer, thinner, and has hook/hamulus)

What is the function of the pterygoid processes?

attachment for pterygoid muscle (help move and protrude the mandible)

Where is the ethmoid bone located?

anterior floor between the orbits

The ethmoid bone forms the ___

orbits and nasal septum

The ethmoid bone consists of what?

• cribriform plate

• perpendicular plate

• ethmoidal labyrinths

Explain the cribriform/horizontal plate of the ethmoid

• received into the ethmoidal notch of the frontal bone

• perforated foramina (olfactory foramina) for transmission of the olfactory nerves

Explain the crista galli

projects superiorly off of the cribriform plate and serves as the attachment for the falx cerebri (a fold of dura mater that separates brain hemispheres)

Explain the perpendicular/vertical plate of the ethmoid

• makes up the nasal septum (with the vomer)

• thin, flat bone the projects inferiorly from the inferior surface of the cribriform plate

Explain the ethmoidal labyrinths/ethmoidal masses

• contain air cells divided into anterior, middle, and posterior air cells

• medial portion

  • makes up the lateral walls of the nasal cavity

• lateral portion

  • makes up the medial wall of the orbits

  • orbital plate

Explain the location and function of the superior and middle nasal conchae/turbinates

• project inferiorly form each medial wall are two thin scroll-shaped processes

• filter the air that we breathe