#7 Ethmoid bone, Vomer bone, & Inferior Conchae A E LONG VERSION Detailed Explanation Read The Ethmoid is often considered the toughest bone by Me students. Part of the reason for this is that the images are misleading…look at the accompanying images “A” and “B”. Ethmoid How can the ethmoid be in the eye orbit AND inside the bone nose? The lower image “B” is pointing at the nasal septum. This is actually the “perpendicular plate of the ethmoid” …. Remember “perpendicular” from high school geometry? These lines are “perpendicular”: B The easiest way to understand the ethmoid is to remove the nose, which is mostly cartilage. This is what your nasal cavity would look like: Note: I do not need you to ID the bone in the eye socket. I test in the C nasal cavity or cranial cavity! I have a video Most of this bony that explains stuff is ethmoid. the ethmoid CLICK HERE Follow image “D” below, following the numbers in sequence (1, 2, 3, etc.): 1 2 5 D D 4 3 Note: I can do this with my demo skull. Remove the nasal bones! Call me over if you need it! more E Notice that the ethmoid also forms most of the “nasal conchae”. These are the bumps on the later side of the nasal cavity, seen in image “E”: Follow image “F” below, following the numbers in sequence (1, 2, 3, etc.): 1 F 4 2 3 Note: I can do this with my demo skull. Remove the nasal bones! Call me over if you need it! Time for some trivia: The ethmoid bone only makes up the superior 2 conchae. The inferior-most is made up by its own bone, called the inferior nasal conchae, or “inferior turbinate”. But that’s trivia! It won’t be on the exam. more One last thing: the ethmoid makes up the top of the nasal cavity …. Think “ceiling”. So on the other side of the ethmoid bone, from the nasal cavity, is the brain. And the nerves for smell have to go from the nasal cavity to the brain through the ethmoid! Follow image “G”, following the numbers in sequence (1, 2, 3, etc.): 1 G 3 2 4 The ethmoid has 2 adaptions for this: 1. The crista galli, which anchors the brain. The term “crista galli” means “Rooster’s Comb”…that thing that sits on a rooster’s head. In a second you’ll see why. 2. Two small plates that allow the nerves fibers to pass through called the “cribriform plates”. Follow image “H”, following the numbers in sequence (1, 2, 3, etc.): H Specifically, a 3 And next to that, 2 small flange of 4 on either side, bone called the are 2 flat plates We see here, in “crista galli”. front of the with a bunch of sphenoid bone, a little holes in small part of the them. These Ethmoid are the “cribriform plates”. If we take off 1 the skull cap and look down more I have a video that explains the So here are your Wordlists: vomer Ethmoid CLICK HERE Perpendicular Plate Forms superior majority of the nasal septum Nasal conchae (partially) Crista Galli Bony projection, to which the membranes surrounding the brain are attached, anchoring the brain in front. Cribriform Plate Allows olfactory nerves to pass through to brain Vomer Bone & Inferior nasal conchae IGNORE THE Inferior Nasal Conchae. Vomer - Single, right in the middle of nasal cavity. Lower 1/3 of nasal septum. This is a CT scan of a person’s ethmoid. Can you spot the perpendicular plate, nasal conchae, crista galli & cribriform plates?? How about the vomer? NOTE: cavities are black. The small image on the right is ethmoid sinusitis. more Sidelines (not on exam) Deviated septa: CSF rhinorrhea: Leaking through nose due to damage to cribriform plate If you look at the cribriform plate, you’ll notice it represents a weak point in the otherwise very thick cranial vault. Sometimes, if a person hits their forehead hard just at the glabella, they will crack this small plate. However, the cranial cavity is filled with Cerebrospinal fluid CSF, which nourishes the brain. The CSF can now leak out, passing through the nasal cavity. Unfortunately, the brain must have CF to survive. CT scans normal ethmoid, and cracked cribriform plate (red arrow) Damage that cracks this bone or suture, such as a sharp blow to the forehead, can lead to leaking of CSF into nasal cavity. .