Hello, everyone! This is Joao from Kenhub, and welcome to another anatomy tutorial where, this time, we're going to be talking about the nerves of the parapharyngeal space. Now, this might seem a complicated topic but it is not. It’s a very short topic where we’re going to be describing some of these nerves that you see here or most of these nerves that you find on this image.
Now, we’re looking at the posterior view of the neck where we stripped a lot of structures. We even made a cut here on the skull as you can see, to then we, exposing the different pharyngeal muscles from a posterior view. You also see here a bit of the esophagus. Notice the thyroid gland, the sternocleidomastoid muscles. You even see here, as I mentioned, the skull with the 2 mastoid processes, and you also see here the red and blue structures which show the very important blood vessels of the neck for a bit of orientation here. Then all of these yellow structures are the different nerves that we’re going to be describing. And keep in mind that just for a bit of location, we see here the internal jugular veins and also the common carotid arteries. Notice the aortic arch here and how all these nerves are then related to the structures.
Now on this image, we’re going to be able to describe 4 cranial nerves including the glossopharyngeal, the vagus, the accessory, and the hypoglossal nerve. Let’s start highlighting a few structures here starting with this that you see now on the screen highlighted in green. We’re seeing one cranial nerve – the glossopharyngeal nerve – which is the 9th cranial nerve. This nerve leaves the skull through the central part of the jugular foramen. It provides sensory information from the skin of the external ear, the internal surface of the tympanic membrane, the upper pharynx, and also the posterior 1/3 of the tongue. It also provides voluntary control of the stylopharyngeus muscle which alleviates the pharynx during swallowing and speech.
Next structures we’re going to be highlighting one on each side - right now, we just turned the image to show the anterior view of the neck as you can see here. You still see the larynx, the hyoid bone, and the different muscles especially scalene muscles and other blood vessels as you can see from an anterior view where we can highlight and you can see clearly then the 2 vagus nerves. They’re well-known as the 10th cranial nerves. These nerves extend through the jugular foramen and then pass into the carotid sheet between the internal carotid artery and the internal jugular vein down to the neck, chest and then abdomen where it contributes to the innervation of the different organs.
Now, we’re going to see these images here back to the same image that I showed you in the beginning where we’re highlighting the vagus nerves as you can see with all the structures. And notice that on the image on the right side, we just cut open the different pharyngeal muscles to then still see a bit of - as you can still see highlighted here - of the vagus nerves. Now, these nerves provide parasympathetic innervation to glands of mucous membranes of the pharynx, larynx, organs of the neck, and also thorax and abdomen. The vagus nerves also will be responsible for innervation of skeletal muscles of the pharynx and larynx.
The next structures that we’re going to be talking about that now we’re seeing from an anterior view of the thorax, just turn to the anterior view again but now a bit further down where we see the open thorax, we just removed here the lungs, just a bit of location here and explanation of what we’re seeing here. You notice the thoracic aorta, a bit of the aortic arch and you still see the different vagus nerves. To then highlight these structures here in green which we will talk about. So on the left side, we’re looking at the right recurrent laryngeal nerve while on the right side, we’re looking at then the left recurrent laryngeal nerve. Keep in mind that we’re looking at the subject’s perspective.
As I mentioned, these are branches of the vagus nerve. Now, they emerged from the vagus nerve at the level of the arch of the aorta and then travel up to the side of the trachea to the larynx. There are 2 recurrent laryngeal nerves - right and left - as you can see here. And we’re going to add a bit of information that you see now a bit more clearly on these 2 images. A bit more information associated to these nerves. They are not symmetrical - that’s one of the important points to clearly make here from these images. The left nerve is looping around the arch as you can see here. So, it’s looping around the aortic arch, while the right nerve travels directly upwards looping around the subclavian artery.
Now, the recurrent laryngeal nerves, they control all intrinsic muscles of the larynx except for the cricothyroid muscle. Now, these muscles act to open and close the vocal cords and include the posterior cricoarytenoid muscles, the only muscles to open the vocal cords.
Now, the nerves will be also innervating muscles found on the respective side of the body with the exception of the interarytenoid muscle which is innervated from both sides. These nerves also will be carrying sensory information from the mucous membranes of the larynx below the lower surface of the vocal fold as well as sensory and secretory and motor fibers to the cervical segments of the esophagus and the trachea.
Next nerves that we’re going to be highlighting here are known as the superior laryngeal nerves. The superior laryngeal nerves are also branches of the vagus nerve which you can see here on the image now, they are not highlighted in green, the vagus nerves. Then now, the nerves that we’re going to be talking about, the superior laryngeal nerves. Now, they arise from the middle of the inferior ganglion of the vagus nerve and descend by the side of the pharynx and dividing into 2 branches – the external laryngeal nerve and the internal laryngeal nerve which we will talk about next.
Let’s start off with the very first one on the list that you see now highlighted in green - the external branch of the superior laryngeal nerve. Now, these are the smaller branches of the superior laryngeal nerve and they descend on the larynx. As you can see, we just removed half of the pharyngeal muscles so we can see what is happening. Now, these give branches to the pharyngeal plexus and the superior portion of the inferior pharyngeal constrictor. They are responsible for tensing the vocal cords by activating the cricothyroid muscle increasing then pitch.
Now on the next image, we’re opening the pharyngeal muscles as you can see here to expose the structure, the larynx, and then show you this highlights which are then the internal branches of the superior laryngeal nerve. Now, these will be descending to the thyrohyoid membrane. They pierced it, as you can see a little bit here, and they will be providing sensory branches to the mucous membrane of the larynx, the epiglottis, the base of the tongue, and the epiglottic glands. If we moved to this image, where we closed again the pharyngeal muscles, you can see the internal branch of the superior laryngeal nerve just branching off of the superior laryngeal nerve and, just below, you see then the branch that we talked about before, the external branch of the superior laryngeal nerve.
Now above the vocal folds, the sensory innervation of the larynx is via the internal laryngeal nerve. Below the vocal folds, it is then provided by branches of the recurrent laryngeal nerve. The vocal fold itself receives dual innervation from both nerves.
Next on our list that we’re going to be highlighting here, we’re seeing another cranial nerve. This is the accessory nerve, which is also known as the 11th cranial nerve. It’s coiled in appearance and it is divided into the spinal and cranial parts. Its cranial parts is often disregarded because it is rapidly joining the vagus nerve becoming an integral part of the vagus nerve. The accessory nerve provides innervation to these muscles that you see here, the sternocleidomastoid muscles, as well as the trapezius.
We’re moving onto another cranial nerve. These are the hypoglossal nerves. They are the 12th cranial nerves. Now, the name hypoglossus comes from the fact that the passage of this nerve is just below the tongue. Hypo- meaning “under” and glossus meaning “tongue” – both of which are from ancient Greek. The nerve is involved in controlling the tongue movements required for speech, food manipulation and swallowing.
Next on this tutorial, we’re going to be talking about a few structures that are known as ganglia. The quick list of the structures are then the inferior ganglion of the vagus nerve, the superior and middle cervical ganglia, and the stellate ganglion.
Let’s start with the very first one here on our list that you see now highlighted in green which is known as the inferior ganglion of the vagus nerve or inferior ganglia, because there are 2, as you can clearly see here on this image. The inferior ganglion of the vagus nerve is cylindrical in shape and also has a reddish color that’s about 2.5 cm in length. It is located at the height of the transverse process of the first cervical vertebra, the atlas. Provides sensation of the heart, larynx, and alimentary canal and the pharynx to the transverse colon.
We’re moving on now to these 2 ganglia which are known as the superior cervical ganglia – so ganglia plural, ganglion singular. The superior cervical ganglion is the only ganglion in the sympathetic nervous system that innervates the head and neck. It is the largest of the 3 cervical ganglia. The superior cervical ganglion innervates many organs, glands and parts of the carotid system in the head including the pharynx.
Next, we’re going to move on and a bit further down talking about these ganglia which are known as the middle cervical ganglia. Individually, the middle cervical ganglion is the smallest of the 3 cervical ganglia, displaced opposite to the 6th cervical vertebra. The middle cervical ganglion has 3 branches – the gray rami communicantes to the anterior rami of the 5th and 6th cervical nerves, the thyroid branches which pass along the inferior thyroid artery to the thyroid gland, the middle cardiac branch which descends in the neck and ends in the cardiac plexus in the thorax. So, these 3 branches. It also gives off the middle cardiac nerve.
Next on our list, we’re going to be highlighting the structures which are known as the stellate ganglia. We can also call it individually as the cervicothoracic ganglion. These are sympathetic ganglia formed by the fusion of the inferior cervical ganglion and the first thoracic ganglion. I like to add a bit of clinical significance associated to the stellate ganglion. Now, these ganglia may be caught to decrease the symptoms shown in Raynaud’s phenomenon and also hyperhidrosis of the hands or extreme sweating.
And, finally, on this tutorial, we’re going to be talking about these structures that you see here highlighted in green on this cut of the thorax. Keep in mind that this is your chest. This is your back and we just cut open here to a lateral view where you can see these highlights and notice here for a bit of location, this is the heart enclosed by the pericardium. We also see here the aortic arch and the thoracic aorta. So you see a bit of structures and the clavicle here.
Now, the highlighted structures are known as the sympathetic trunks or in this case we’re only seeing one, the sympathetic trunk. Now, these structures allow nerve fibers to travel to the spinal nerves that are superior and inferior to the one in which they originate from. Also a number of nerves such as most of the splanchnic nerves arise directly from these trunks.
We’re going to go back to the image of the posterior view of the pharynx where you can see the sympathetic trunks highlighted in green. Now, the sympathetic trunks are paired bundle of nerve fibers. They run from the base of the skull to the coccyx so a long travel. Sympathetic trunk T1 to L2 travels in a downward direction from the skull just lateral to the vertebral bodies, interact with the spinal nerves or their ventral rami through the rami communicantes. The superior end of the sympathetic trunk has continued upwards through the carotid canal into the skull and forms then a plexus on the internal carotid artery which you see partially here, and also see a little bit of the external carotid artery. If you remember from previous tutorials, we’re looking at the common carotid which then splits into the internal carotid and then the external carotid arteries.