Anatomy of the Sphenoid and Ethmoid Bones

Anatomical Morphology of the Sphenoid Bone\n- General Appearance: The sphenoid bone is described metaphorically as appearing like a "giant bag" or a "bat." This bat-like comparison is used to categorize its primary regions.\n- Major Regions and Features:\n - Greater Wings: These are the large, lateral portions of the bone extending outward, similar to where a "bat would flap its wing."\n - Lesser Wings: These appear as ridges located along the anterior (front) portion of the bone.\n - Vampire "Fangs": Located downward from the lesser wing ridges, these projections are described as the "fangs" of the vampire bat.\n- Foramina and Neural Passageways:\n - Optic Foramen: There are $2$ holes located just inside the "fangs."\n - Function: These holes are the conduit for the optic nerve ($eye$ nerve), which carries visual information from the back of the eye into the brain.\n - Visual Identification: The optic foramen is a round hole. It must be distinguished from a nearby tear-shaped opening, which is a different structure not covered in this lesson. Students can test the location of the optic foramen by looking through the eye orbit of the skull; if the foramen is covered from the inside, the finger should be visible through the eye socket.\n- Internal Depressions:\n - Sella Turcica: This is a distinct "divot" or depression in the center of the sphenoid bone.\n - Function: The pituitary gland sits within the sella turcica. Because the pituitary gland hangs off the bottom of the brain, it is highly susceptible to breaking off (as seen in many classroom models). In the human body, the sella turcica cradles and protects it.\n - Mnemonic: The instructor associates the name "Sella Turcica" with the name of a Mexican town to aid memory.\n- Excluded Structures:\n - Pterygoid Process: Students are instructed to cross this out on their documentation. The name features a silent "$p$," similar to the word Pterodactyl. The instructor mentions a book titled "$P$ is for Pterodactyl" as a reference for silent letters.\n\n# The Ethmoid Bone and Olfactory Features\n- Location: The ethmoid bone is located deep within the nasal cavity. When looking down into the skull (top-down view), only a small portion is visible.\n- Cribriform Plate: This is the flat part of the ethmoid bone visible from the top-down perspective.\n - Structural Detail: It contains numerous microscopic holes, which may be difficult to see depending on the specific model used.\n - Function: These holes allow the nasal nerves or olfactory nerves to pass from the nose to the brain. Olfactory receptors project through the cribriform plate to transmit sensory data, bypassing the skull bone.\n- Crista Galli: This is the bony part that sticks up vertically from the cribriform plate, dividing the plate into $2$ halves.\n- Nasal Cavity Components:\n - Superior and Middle Nasal Conchae: These are parts of the ethmoid located inside the nose, though they are not currently a primary testing focus.\n - Perpendicular Plate of the Ethmoid: This structure is a central bone visible when looking into the front of the skull through the nasal cavity.\n - Nasal Division: The nasal cavity is divided into left and right sides. The perpendicular plate forms the top half of this dividing wall.\n - Vomer: This is the bone that forms the bottom half of the nasal cavity divider.\n\n# The Cranial Sinus System\n- The skull contains specific sinuses named after the bones they reside in:\n - Mastoid Sinus: Located within the temporal bone.\n - Frontal Sinus: Located within the frontal bone.\n - Sphenoid Sinus: Located within the sphenoid bone (color-coded blue on some models).\n - Ethmoid Sinus: Located within the ethmoid bone (color-coded green on some models). These are the specific sinuses people usually refer to when experiencing pressure "right here in the nose."\n- Identification: These sinuses are described as anatomically "tricky" to differentiate without specific model guidance.\n\n# Model Identification and Classroom Resources\n- Color Coding: Identification of bones on classroom models is aided by color:\n - Sphenoid: Typically brown on various models.\n - Ethmoid: Typically yellow (back of the room) or light green (front of the room).\n - Ethmoid Sinus: Highlighted in green.\n - Sphenoid Sinus: Highlighted in blue.\n- Course Materials: The instructor reminds students to check D2L (Desire2Learn) under "Course Content" for uploaded pictures of the sinuses for further study. The instructor concludes by performing a physical demonstration to point out the sphenoid and ethmoid components on individual student models.