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Bones, cartilages and mucosa of the medial wall of the nasal cavity.
Hello everyone! This is Megan from Kenhub, and welcome to another anatomy tutorial. Today, we're going to talk about the structures on the medial wall of the nasal cavity. But, before we begin, I'm just gonna give you a quick overview.
The nasal cavities actually made up of two nasal cavities that are separated by the nasal septum. We can see the nasal septum here. The nasal cavities are the most superior part of the respiratory tract and they are located above and behind the nose. They are elongated, wedge-shaped spaces and their base is wide and their apex narrow. The cavities are created by skeletal framework composed of bone and cartilage. In this tutorial, we're going to look at the medial wall of the nasal cavity, particularly looking at the bony structures, the cartilages and the soft tissues.
Let's begin with the cartilaginous and osseous structures. The cribriform plate is part of the ethmoid bone. It's an elongated, horizontal plate in the midline on the anterior floor of the anterior cranial fossa. As you can see in the next illustration, the cribriform plate is perforated. The olfactory nerve fibers and the mucosa of the upper parts of the nasal cavity pass through these perforations to reach the olfactory bulb. Another structure associated with the cribriform plate is the crista galli? (1:25) which divides the cribriform plate into two in the midline.
The next bony structure of the medial wall is the perpendicular plate of the ethmoid bone. It forms the superior part of the bony portion of the nasal septum. The perpendicular plate of the ethmoid bone articulates superiorly with the cribriform plate. This perpendicular plate extends downwards from the ethmoid bone, articulates with the sphenoidal crest superiorly and the vomer inferiorly. So, here in this diagram, we can see where the perpendicular plate articulates with the cribriform plate, the sphenoidal crest and the vomer here.
The vomer is a small bone that's found in the midline of the nasal cavity. It forms articulations with the perpendicular plate of the ethmoid bone, the maxillary bones and the palatine bones. This small, unpaired bone forms part of the nasal septum. We can see it highlighted in green here.
The most anterior part of the nasal septum is formed by the cartilage of the nasal septum or the quadrangular cartilage. It is composed of hyaline cartilage and is thicker at its margins. In this image here, we can see how the quadrangular cartilage articulates with the nasal bone superiorly, the perpendicular plate of the ethmoid bone posteriorly, and the vomer and palatine process inferiorly. It is also connected with the medial crura of the greater alar cartilages via fibrous tissue. This cartilage is continuous with the anterior margins of the lateral nasal cartilages. Here, we can see the posterior process of the cartilage of the nasal septum. This expansion is formed at the junction with the lateral nasal cartilages.
Another bony structure that we can see in the view with the medial wall of the nasal cavity is the palatine process of the maxilla. This is a horizontal plate that makes up three-quarters of the hard palate. It makes up the majority of the roof of the mouth and the floor of the nasal cavity. The incisive foramen – we can see here – transmits greater palatine vessels and the nasal palatine nerve. It is situated in the midline just posterior to the upper incisors.
Immediately posterior to the palatine process of the maxilla is the horizontal plate of the palatine bone. This makes up the posterior quarter of the hard palate. Its posterior border is free and this is where the soft palate attaches. Here, we can see where the superior part of the medial border articulates with the lower edge of the vomer. It also forms part of the inferior nasal meatus on its nasal surface. The posterior nasal spine is made up of two sharp projections from the palatine bones on either side. These projections are in the midline on the posterior border of the horizontal plate of the palatine bone. This is where the musculus uvulae attaches.
The structures that I have described so far in this tutorial form the nasal septum highlighted here in green. It divides the nasal cavity into two. It is composed of both bony and cartilaginous components. The bones are the perpendicular plate of the ethmoid bone posteriorly, the vomer posteriorly and inferiorly, the crest of the maxillary bone, and the crest of the palatine bones which is situated inferior to the vomer. The cartilaginous part of the septum is the quadrangular cartilage.
Now that we've discussed the bones and cartilage that make up the medial wall of the nasal cavity, let's look up other related structures. I'm going to start with the hard palate which is this structure here highlighted in green. The hard palate makes up the anterior two-thirds of the roof of the mouth. You can feel it with your tongue. Anteriorly and laterally, it's lined with the upper dentition or the maxillary teeth. The hard palate is formed by the palatine processes of the maxillae and the horizontal plates of the palatine bones. The hard palate separates the oral and nasal cavity. The importance of this can be seen particularly in infants with birth defects where their hard palate hasn't formed properly. When the palatine shelves of the maxillae do not fuse properly during embryonic development, this results in a cleft palate.
So immediately posteriorly to the hard palate, we see the soft palate. The soft palate has no bony components and is comprised of five muscles used in swallowing. They are tensor veli palatini which is innervated by the mandibular nerve (cranial nerve V), the palatoglossus muscle, the palatopharyngeus muscle, levator veli palatini, and musculus uvulae.
The next structure that we see in the mucosa is this opening highlighted in green. It's called the choana. The choanae are oval-shaped openings between the nasal cavities and the nasopharynx on either side. The nasopharynx is located here behind the choana and above the level of the soft palate. The choanae are rigid openings formed by bone and opens into the nasopharynx close to where the adenoids are situated. The two choanae are separated by the vomer.
Another structure in the nasopharynx is the pharyngeal opening of the auditory tube. The auditory tube has several names. It's often called the pharyngotympanic tube or the Eustachian tube. All these names refer to the same anatomical structure. It is a channel that connects the tympanic cavity and the nasopharynx.
At the pharyngeal end of the Eustachian tube is a structure called the torus tubarius or tubular tonsil. It is an elevation produced by the dorsal medial cartilage of the Eustachian tube. It lies directly under the mucous membrane and can be visualized from the nasopharynx. Two mucosal folds are seen posterior and anterior to the torus tubarius. They are known as the salpingopharyngeal fold and the salpingopalatine fold. So, here, we can see the torus tubarius surrounding the Eustachian tube on the upper surface.
The final structures I'm going to cover in this tutorial are the pharyngeal tonsils. They are also known as the adenoids. They are made up of a mass of lymphatic tissue located at the roof of the nasopharynx. Their structure degrades with age and they are almost entirely absent after puberty.
Now that you just completed this video tutorial, then it’s time for you to continue your learning experience by testing and also applying your knowledge. There are three ways you can do so here at Kenhub. The first one is by clicking on our “start training” button, the second one is by browsing through our related articles library, and the third one is by checking out our atlas.
Now, good luck everyone, and I will see you next time.