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Bones, cartilages and mucosa with focus on the lateral wall.
Hello everyone! This is Megan from Kenhub, and welcome to another anatomy tutorial. In today's tutorial, we will be looking at the structures seen on the lateral wall of the nasal cavity. But before we do that, I just want to describe what the nasal cavity is.
So, here, we can see the lateral wall of the nasal cavity and some of the structures we're going to be going covering today such as the nasal conchae and the meatuses between them. We can also see the sphenoidal sinus and the frontal sinus. The nasal cavity is part of the upper respiratory tract located above and behind the nose. The nasal cavities are elongated wedge-shaped spaces with a large inferior base and a narrow superior apex. They are held open by skeletal framework consisting mainly of bone and cartilage. The two cavities are separated by the nasal septum. The bony borders of the nasal cavity and their adjacent alar cartilages make up the center of the face. In this tutorial, we will look in more detail at the lateral wall of the nasal cavity, which is rather complex and formed by bone, cartilage and soft tissues.
Firstly, I will begin this tutorial by describing the bones and bony structures that make up the lateral nasal cavity. So, let's begin by looking at the anterior nasal aperture. This is a pear-shaped bony opening in the skull and is also sometimes referred to as the piriform aperture. Here, we can see a lateral view of the anterior nasal aperture and, in the next image, we have a frontal view. The anterior bony aspects of the maxilla and nasal bones terminate at the anterior nasal aperture and form an opening into the cartilaginous nasal vestibule.
The surface of the lateral wall of the nasal cavity is irregular in contour and is interrupted by three nasal conchae – the superior nasal concha, the middle nasal concha and the inferior nasal concha. These structures are long, narrow curled shelves of bone that protrude into the nasal cavity. They are covered by a mucus membrane and the epithelium that lines them is pseudostratified columnar ciliated respiratory epithelium. The concha are responsible for the majority of airflow direction, humidification, heating and filtering of the air inhaled through the nose. Now, let's look at each of the three individual nasal concha in more detail.
So, here, we see the first of the three nasal conchae found on the lateral wall of the nasal cavity – the superior nasal concha. Remember, all of the conchae are lined with mucous membrane. We can see the superior nasal concha covered in its mucus membrane here. The superior nasal concha arises from the perpendicular plate of the ethmoid bone. This bony shelf is situated above the middle nasal concha and the superior nasal meatus and below the sphenoethmoidal recess.
The second of the three nasal conchae found on the lateral wall of the nasal cavity is the middle nasal concha. Like the superior nasal concha, the middle nasal concha also arises from the perpendicular plate of the ethmoid bone. It is situated below the superior nasal meatus and above the middle nasal meatus. It plays a role in humidifying and clearing inspired air of micro particles. Here, we can see the middle nasal concha with its mucous membrane highlighted in green.
The third and final of the three nasal conchae is the inferior nasal concha. Unlike the superior and middle nasal conchae, this structure is an independent bone emerging laterally from the bony septum. We can see the inferior nasal concha with the mucous membrane highlighted in green. The inferior nasal meatus is situated below it here. The superior, middle and inferior conchae that we have just seen divide the nasal cavity into three groove-like air passages – the superior, middle and inferior nasal meatuses. So, let's look at these three meatuses in more detail.
The superior nasal meatus is a nasal passage situated below the superior nasal concha. It is the smallest and most superiorly located of the three nasal meatuses. The sphenoethmoidal recess opens into it and it drains the posterior ethmoidal air cells. The middle nasal meatus is situated between the middle nasal concha and the inferior nasal concha. This nasal passage drains the maxillary, frontal and anterior ethmoidal sinuses. Last, but not least, we have the inferior nasal meatus which lies below the inferior nasal concha. It is the largest of the three meatuses and extends most of the lateral wall of the nasal cavity. The anterior third of the inferior nasal meatus contains the termination of the nasolacrimal duct. Here, we can see the inferior nasal meatus coated in mucous membrane. There's a fourth air passage that we can see in the nasal cavity and that is the sphenoethmoidal recess. This recess opens into the sphenoidal sinus and is situated superiorly and posteriorly to the superior nasal concha. Again, the next image shows the lateral wall of the nasal cavity covered in mucous membrane. We can see the sphenoethmoidal recess highlighted in green here.
The next structure we are going to talk about is the agger nasi. This structure is visible in the upper and anterior end of the middle nasal meatus. The agger nasi, which is sometimes referred to as the nasal ridge or the nasoturbinal concha, is a small, round ridge found on the lateral side of the nasal cavity. Seen here in our illustration highlighted in green, it is situated midway along the anterior aspect of the middle nasal concha.
Next, let's have a look at the nasal bones which are the two bones situated between the right and left halves of maxilla. They make up the bridge of the nose. The nasal bones form many articulations. They form articulations with the frontal bone superiorly, the ethmoid bone and, of course, the frontal process of the maxilla laterally. Distally, the nasal bones form articulations with the lateral nasal cartilages and with the nasal septum inferiorly. On the inner surface of the nasal bones, there are grooves formed by the passage of the nasociliary nerve.
Another bone that participates in the formation of the nasal skeleton and can be seen from the lateral view is the maxilla. The nasal surface of the maxilla is a portion of the maxilla that helps to form the anterolateral part of the bony nasal cavity. It is located inferior to the nasal bone and gives rise in part to the inferior nasal concha. This part is the medial surface of the maxilla and an opening leading to the maxillary sinus can be found on this part of the maxilla.
Immediately posterior to the nasal surface of the maxilla, we see a small, thin bone called the lacrimal bone. The lacrimal bone is a paired bone situated in front of the orbital plate of the ethmoid bone. It is the smallest bone of the skull and borders the frontal process of the maxilla anteriorly, the orbital lamina of the anterior ethmoidal cells posteriorly, and the anterior part of the inferior nasal concha inferiorly. A groove that forms the fossa for the lacrimal sac is found in the lateral surface of the lacrimal bone. This is known as the lacrimal groove.
Posterior to the lacrimal bone, we find the ethmoid bone. The ethmoid bone is a lightweight, spongy bone situated on the roof of the nose between the two orbits. It is comprised of the cribriform plate which is pierced by fibers of the olfactory nerve. In the next image, we can see the olfactory nerve piercing the cribriform plate. It's highlighted in green here. Other components of the ethmoid bone include the ethmoidal labyrinth and the perpendicular plate, which forms part of the posterior nasal septum and gives rise to the superior and middle nasal conchae.
The frontal bone is one of the large bones of the skull which also contributes to the formation of the lateral wall of the nasal cavity. It consists of the squamous part, an orbital part and a nasal part. The squamous part of the frontal bone is the largest part of the bone which encompasses the area of the forehead. In the next illustration, we can see the cavities of the frontal bone known as the frontal sinuses. In this illustration, we can see that the frontal sinus is situated superior to the orbit. The frontal sinuses are asymmetrical and are separated by thin, bony intrasinus septa. The nasal part of the frontal bone borders the frontal process of the maxilla and the nasal bones.
Next here, we can see the sphenoid bone which has an irregular shape and forms the central portion of the skull. The sphenoid bone can be divided into a body with the sella turcica which houses the pituitary gland, the two greater and lesser wings extending from the side of the body, and the pterygoid processes which project inferiorly. It forms the floor of the middle cranial fossa and contains numerous foramina through which various cranial nerves and blood vessels pass. For more on the sphenoid bone, please check our tutorial on the superior view of the base of the skull on our website.
Inside the body of the sphenoid bone, we see the paired paranasal sinuses known as the sphenoidal sinuses. The sinuses are lined with mucous membrane that receives sensory innervation from the facial nerve, cranial nerve 7. As I mentioned earlier, the sphenoethmoidal recesses of the nasal cavity open into the sphenoidal sinuses. As we saw earlier, the sphenoid bone is divided into the body, the greater and lesser wings, and the pterygoid processes. The pterygoid processes consist of a lateral and medial plate. Here, you see the medial plate of the pterygoid process which course laterally at the lower extremity giving these hook-like structures known as the pterygoid hamulus. Here, we can see the pterygoid hamulus highlighted in green. Its lateral wall forms part of the pterygoid fossa and, medially, it contributes to the lateral boundary of the choana.
The final bone that contributes to the formation of the lateral wall of the nasal cavity is the palatine bone. The palatine bone is a paired bone situated between the maxilla and the sphenoid bone. It is comprised of a horizontal plate which forms the posterior portion of the hard palate, a perpendicular plate which contributes to the formation of the lateral wall of the nasal cavity, and a pyramidal process where the lesser palatine canals are found through which the lesser palatine nerves and vessels pass. Here, we can see the horizontal plate contributing to the hard palate and the perpendicular plate contributing to the lateral wall of the nasal cavity.
The perpendicular plate and the pyramidal process at the palatine bone form a deep notch which becomes the sphenopalatine foramen when it is crossed by the inferior surface of the sphenoid bone. This foramen connects the nasal cavity with the pterygopalatine fossa. The vessels passing through this foramen include the sphenopalatine artery and vein and the nasopalatine nerve.
So far, we have covered the bony structures that form the lateral wall of the nasal cavity. Now, let's look at the cartilages and the other soft tissues that we can see from this perspective, starting with the greater alar cartilages. The greater alar cartilages form the tip of the nose. These two hook-shaped cartilages also form the medial and lateral walls of the naris or nostrils. They have a medial crus that forms the anterior and inferior part of the nasal septum and the lateral crus which curves laterally around the naris. The lesser alar cartilages are small, individual plates of cartilage seen here. They supplement the greater alar cartilages and are situated at their posterior margin. They are suspended in fibrofatty tissue that forms the lateral aspect of the nostrils and lie free from other cartilages that provide stability and form to the nostrils.
The lateral nasal cartilage is a flattened, triangular-shaped cartilage that is partially fused to the nasal septum. In this image, we can see where it is connected to the inferior margin of the nasal bone and the frontal process of the maxilla. We can also see where it's connected to the greater alar cartilages by fibrous connective tissue. The lateral nasal cartilages form the cartilaginous part of the bridge of the nose and together with the greater alar cartilages, they form the major structural appearance of the nose. The limen nasi is a mucous ridge formed by the margin of the alar cartilage. It is situated at the edge of the vestibule and is the boundary between the nasal cavity proper and the vestibule. The limen nasi is approximately ten millimeters in length.
Finally, here, we can see the nasal vestibule. The nasal vestibule is the most anterior part of the nasal cavity extending up to the limen nasi. It is lined by stratified squamous keratinized epithelium unlike the nasal cavity proper which is lined with respiratory epithelium.
In ending this tutorial, I just want to say a few words about the occurrence of nasal fractures. Due to the prominence of the external nasal skeleton, nasal fractures are very common. They are actually the most common fracture in the region of the face. Fractures usually occur as a result of blunt trauma to the nose and they are frequently observed in vehicular or sporting accidents. A common complication of these nasal fractures is a permanent deformity of the nasal skeleton.