Video: Nerves of the nasal cavity

Hey everyone! It's Nicole from Kenhub, and welcome to our tutorial on the nerves of the nasal cavity. In this tutorial, we're going to be looking at all the nerves shown on this image of the nasal cavity, which as you can see, has a bit of the nasal septum turned upwards around here, the lateral wall of the nasal cavity just here, the sphenoidal sinus, and the maxilla with some of the upper teeth down here. And as we go through the nerves, we'll just point out a few other structures here and there. And, of course, after talking about these nerves at the end of the tutorial, we'll also go over some relevant clinical notes. But first before we get on to the nerves of the nasal cavity, we're just going to begin with a little bit of a chat about the nasal cavity's function.

So we're just going to begin with our image of our midsagittal section of the skull, and here we can see the nasal cavity as we soar above as well as the bones of the skull. And we might as well point them out while we're here so our frontal, parietal, temporal and occipital bones. And the nasal cavities are two paired cavities found on either side of the nasal septum and these cavities begin at the nares or the nostrils and end at the pharynx. And the nasal cavity has three main functions, the first of which being its ability to warm, humidify and filter air as it enters the nares. And this ability to warm and filter the air is due to the hair and the mucous lining of the internal walls of the nasal cavity which remove allergens from the air before it passes into the lungs.

The nasal cavity also holds the organ that holds the receptors for the sense of smell – the olfactory epithelium – contributing to its second function. And finally, the nasal cavity also produces mucus which as I just mentioned helps filter the air entering the nose.

So let's have a brief look at the anatomy of the nasal cavity. And as I mentioned earlier, we each have two nasal cavities each separated from each other by a nasal septum. And the nasal septum which is pointed out by the green arrow just here is made of septal cartilage as well as two bones of the skull. And these two bones which are the vomer and the ethmoid bone can't be seen in this image but they would be located behind the mucosa that appears to be covering the bones and the cartilage. And these two bones also descend and arise from the cribriform plate, the maxilla and the palatine bone which are bones of the skull. The nose as we can see in the image is separated from the mouth by the hard palate which is also formed by parts of the maxilla and palatine bone and is highlighted in green.

So in this image of the nasal cavity we can also see a foramen in the lateral wall in the cavity highlighted in green. And this hole in the skull is known as the sphenopalatine foramen. This foramen connects the nasal cavity with the pterygopalatine fossa. So though you can't see the pterygopalatine fossa, just behind the foramen is a small space bounded by parts of the sphenoid and palatine bone and this fossa is important to know as many major structures pass through here such as the neural branches of the pterygopalatine ganglion which innervate the nasal cavity and the branches of the maxillary artery. And we'll talk about these structures a little bit later on in the tutorial.

Since we brought it up, we might as well introduce you guys to the nerve supply of the nasal cavity which we'll do first by identifying some of the nerves of the nasal cavity in our image and talking a bit more about each of the nerves in more detail.

So as you can see in the image, there are three sources of innervation in the nasal cavity. And the first one we're going to talk about is the olfactory nerve which is highlighted in yellow up here. And the olfactory nerve is a special nerve in that it is a special sensory nerve that receives the sense of smell. On the left of our image here highlighted in green, we have branches of the ophthalmic nerve which itself is the first major branch of the trigeminal nerve and these branches convey general sensory information from the mucosa of the nasal septum, some of the sinuses of the nasal cavity.

And finally on our right here highlighted in pink we have the branches of the pterygopalatine ganglion. And mostly some of the branches are actually branches of the maxillary nerve which convey general sensory information and just pass through the ganglion without making any synapses while others are autonomic nerves which synapse in the ganglion.

So as we mentioned before, we're going to now look at some of these nerves in a bit more detail. And to start off, we're going to look at the nerve involved in olfaction – the olfactory nerve. And if I can think back to our tutorial on the olfactory nerve, we might be able to recall that the olfactory nerve is the first cranial nerve and is often denoted as CN I. And as we've mentioned before, this nerve is involved with our sense of smell and the fibers that arise from the olfactory nerve are afferent fibers.

So I just wanted to take the time to explain a little bit about how the olfactory process works. And as you can see in this image, we have some of the forebrain pulled back to reveal the olfactory bulb highlighted in green which is where the sense of smell is processed. And reaching through the cribriform plate just here are what are called the central processes of the olfactory receptor neurons which then connects to the olfactory epithelium as we can see in this breakout image on the right here. And of course the olfactory epithelium is at the apex of the nasal cavity which receives odors as they enter the human body through the nose.

And so if we're thinking about this in reverse or the way that the odors enter the body, the process that generally happens is that the odor is received by the olfactory receptor neurons in the olfactory epithelium which in turns sends an electric signal through the central processes of these neurons through the cribriform plate of the ethmoid bone which then in turn synapse on the olfactory bulb which then sends the signals it has processed to the olfactory tracts finally being received by the primary and other associated regions of the cerebral cortex.

So besides olfaction, the nerves of the nasal cavity also receive general sensation specifically touch, pain and temperature and in the nasal cavity these are mainly covered by branches of the ophthalmic and maxillary nerves. And as the ophthalmic and maxillary nerves are both branches of the trigeminal nerve, they are therefore also referred to as CN or cranial nerve V1 and CN or cranial nerve V2 respectively. And it's important to note that the ophthalmic nerve receives sensory information from the nasociliary nerve and its branches which are highlighted in green here while the maxillary nerve does not receive any direct branches in the nasal cavity. Instead, some of its fibers run along the branches of the pterygopalatine ganglion.

And of course the ophthalmic nerve and the other nerve branches can be further broken down into their own branches. And so the first branch coming off the ophthalmic nerve I wanted to look at is the nasociliary nerve and we can see it highlighted in green on this image running through the orbit between the two heads of the lateral rectus muscle. And the nasociliary nerve gives rise to several branches that mostly supply the mucous membrane and the skin of the nose as well as the conjunctiva. But mostly in this tutorial, we just want to stick to the branches that pass through the nasal cavity. And so the branches of the nasociliary nerve that give rise to the nerves that we're currently interested in are the posterior ethmoidal nerve as well as the anterior ethmoidal nerve.

And so we're going to begin with the first of these nerves – the posterior ethmoidal nerve. And the posterior ethmoidal nerve innervates the posterior ethmoidal cells and sphenoid sinus. And here on this transverse section of the orbit we can see the posterior ethmoidal nerve coming off the nasociliary nerve as it enters the posterior ethmoidal foramen between the frontal and the ethmoid bones where it's accompanied by the posterior ethmoidal artery. And in this slide, we can see the anterior ethmoidal nerve branching off the nasociliary nerve a bit more distally in the orbit. And the anterior ethmoidal nerve enters the nasal cavity through the anterior ethmoidal foramen, and on the next slide here, we can see the anterior ethmoidal nerve as it makes its way through the ethmoid bone. And as you can see here, it splits off into two branches – the one over here supplying the lateral wall and the one over here supplying the septum. And of course, we're going to now take a closer look at these branches.

So the branch running along the septum here is the external nasal branch of the anterior ethmoidal nerve and as you can see, this is a terminal branch innervating the skin of the lateral nose. And the other branch we can see here is the lateral internal nasal branch of the anterior ethmoidal nerve which is also a terminal branch and this branch innervates the lateral wall of the nasal cavity.

There's one more branch of the anterior ethmoidal nerve that I want to talk about and this nerve is the medial internal nasal branch of the anterior ethmoidal nerve which is flipped up here on the reflected nasal septum. And as you can see, this branch again is a terminal nerve and it supplies the medial wall or the nasal septum of the nasal cavity.

Before we move on to look at the nerves derived from the maxillary nerve, I just wanted to show you this little structure highlighted on this image – the pterygopalatine ganglion. And this ganglion is a fairly important ganglion within this region as it contains many different axons of the main branches of the maxillary nerve which innervates the nasal cavity. And it also contains the cell bodies of autonomic neurons regulated by parasympathetic and sympathetic neurons from the nerve of the pterygoid canal. The pterygopalatine ganglion gives off the following branches – the nasopalatine nerve, the posterior superior and posterior inferior lateral nasal nerves, and the greater and lesser palatine nerves. We'll now start discussing each of these branches in a little bit more detail.

So, the first two branches we're going to look at are the nasopalatine nerve and the posterior superior and posterior inferior lateral nasal nerves as they mostly cover the innervation of the lateral wall of the nasal cavity. But, first off, we're going to start with the nasopalatine nerve and the posterior superior lateral nasal nerve as they both come directly off the pterygopalatine ganglion. And the nasopalatine nerve travels from the pterygopalatine fossa through the sphenopalatine foramen which I talked about earlier to enter the nasal cavity. And on this image, we can see highlighted in green the branches that innervate the medial nasal septum up here and the branch that innervates the superior nasal concha just here as well as the superior aspect of the lateral wall. So all in all as we've mentioned, the nasopalatine nerve innervates the septum, the superior nasal concha and the superior lateral wall.

And the next nerve we're going to look at is the posterior superior lateral nasal nerve which we can see running along the middle nasal concha in our image highlighted in green. And like the nasopalatine nerve, it arises in the pterygopalatine ganglion in the pterygopalatine fossa to travel through the sphenopalatine foramen to enter the nasal cavity, and the posterior superior lateral nasal nerve innervates the upper posterior lateral wall of the nasal cavity.

And the last of the nerves that innervate the lateral wall of the nasal cavity is the posterior inferior lateral nasal nerve. And as you can see, it's highlighted in green on this image and passes along the inferior nasal concha. The posterior inferior lateral nasal nerve passes through the perpendicular plate of the palatine bone from the pterygopalatine fossa to enter the nasal cavity where it innervates the lower posterior lateral wall of the nasal cavity. And an important thing to know about this nerve is that it doesn't actually come off the pterygopalatine ganglion. Instead, it's a branch of the greater palatine nerve which we'll talk about in the next slide.

So as I just mentioned in this slide we're going to talk about the greater palatine nerve which is one of the two nerves that come off the pterygopalatine ganglion to innervate the hard and soft palate. And the root of the greater palatine nerve involves it passing through the greater palatine canal before emerging through the greater palatine foramen to enter the nasal cavity which we can see down the bottom of this image here – so this little hole over here is our greater palatine foramen and of course this in green is our greater palatine nerve. And as we can see in this image, the greater palatine nerve innervates the hard palate. And as we mentioned on the previous slide, the greater palatine nerve gives off the posterior inferior lateral nasal nerve which it does while traveling through the greater palatine canal.

And the final nerve that innervates the palate that arises from the pterygopalatine ganglion is the lesser palatine nerve. And like the greater palatine nerve, the lesser palatine nerve passes through the greater palatine canal from the pterygopalatine ganglion. However, it enters the nasal cavity through a different foramen – the lesser palatine foramen – and the lesser palatine nerve also innervates the soft palate as well as the uvula and the tonsil within the oral cavity. And in this image, we can see it emerging from the lesser palatine foramen to innervate the soft palate which is not pictured here.

And to finish off this tutorial, we're going to have a brief chat about some clinical notes relevant to the nerves of the nasal cavity. So firstly the location of the olfactory bulb and its associated nerves is important to note as damage to the anterior cranial fossa from a blow or another kind of traumatic injury can cause the separation of the olfactory bulb from the olfactory nerves or it can just damage the olfactory nerves themselves. And this can lead to a loss of the sense of smell which is known clinically as anosmia although other sensations such as pain and touch will still remain intact as these sensations as we've discussed during this tutorial are carried by different nerve fibers. And these kinds of incidents are often caused by traumatic brain injuries but it also can be caused by a range of other conditions such as a brain aneurysm, diabetes, multiple sclerosis or radiation. And it's often quite overlooked so clinicians will be best to ask about a person's sense of smell any time a patient has any kind of injury or nerve damage in this area.

And that concludes our tutorial on the nerves of the nasal cavity. Thanks for watching.

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