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Overview of the intrinsic and extrinsic muscles of the tongue.
Hello everyone! This is Megan from Kenhub, and welcome to our tutorial on the muscles of the tongue. In today's tutorial, we'll have a look at the anatomy of these muscles including their actions, their vascular supply and their innervation.
So, here, we can see an anterior coronal view of the tongue. To give some context, we can see the hard palate here and the hyoid bone here. Now, the tongue consists of two groups of muscles. We have the intrinsic muscles and the extrinsic muscles. The intrinsic muscles consist of the superior longitudinal muscle, the vertical muscle, the transverse muscle, and the inferior longitudinal muscle. We then have the extrinsic muscles which consist of genioglossus, hyoglossus, styloglossus, and palatoglossus. After we discuss these muscles, we will be looking into some clinical notes relating to them. But before we do that, let me give you a bit of an introduction to the tongue and its muscles.
The tongue is a muscular organ that helps form the floor of the oral cavity. It has three main functions – deglutition or swallowing, gustation or taste, and phonation or speech. It consists of a root which is the posterior third of the tongue and a body which is the anterior two-thirds. The dorsum of the tongue is divided into two halves by the median sulcus which is located on the body of the tongue here.
So, in the next image, we can see the coronal view of the tongue and its muscles. Highlighted here is the lingual mucosa which is usually pink and moist. This is the part of the tongue that covers the dorsum of the tongue and contains papillae and nerve endings for the sense of taste. For more on the lingual papillae and how they perceive taste, please take a look on our website for a video on the lingual papillae.
So, in the next image, we can see all of the tongue highlighted in green. It is separated into left and right halves by the vertical lingual septum which underlies the median sulcus and continues down to attach to the hyoid bone. The tongue consists of eight pairs of muscles which are located bilaterally on either side of the lingual septum. Four of these muscles are intrinsic muscles which are located within the tongue itself and are highlighted here in this image. The other four muscles are located outside the tongue and are referred to as extrinsic muscles. The intrinsic muscles act to change the shape of the tongue whereas the extrinsic muscles are involved in the movement of the tongue.
So let's start off by looking at the extrinsic muscles of the tongue. The first extrinsic muscle we'll look at is the genioglossus muscle. As we can see in this image, it runs from the bottom of the tongue to the hyoid bone. The main actions of the genioglossus is to protrude or stick out the tongue. It also acts to depress the tongue. It is supplied by the sublingual branch of the lingual artery as well as the submental branch of the facial artery. Both the lingual and facial arteries are branches of the external carotid artery. The genioglossus is innervated by the hypoglossal nerve which is the twelfth cranial nerve. If we switch to a lateral view, you can see that the genioglossus is triangular in shape and arises from the hyoid bone superior to the geniohyoid muscle.
The next extrinsic muscle we will look at is the hyoglossus. The hyoglossus is a thin muscle that extends from the side of the tongue to the hyoid bone. The main action of this muscle is to depress the tongue. Like the genioglossus, it's supplied by the sublingual branch of the lingual artery as well as the submental branch of the facial artery. It is also innervated by the hypoglossal nerve. A great way to remember this muscle is by breaking down its name. So, hyo refers to its relationship with the hyoid bone and glossus relates to the fact that it's a muscle of the tongue. So, if we switch to a lateral view, we can see that it inserts into the side of the tongue between the inferior longitudinal muscle and the styloglossus muscle.
The next muscle we'll look at is the styloglossus, which is another extrinsic muscle of the tongue. The styloglossus inserts into each side of the tongue and extends around each side laterally to meet the styloid process of the skull. The main action of the styloglossus is to draw the tongue upwards but it also acts to retract the tongue backwards in the mouth. It's supplied by the sublingual branch of the lingual artery and is innervated by the hypoglossal nerve. Again, you can remember the name of this muscle due to its relationship with the styloid process. If we look at the lateral view of this muscle, we can see its attachment with the styloid process of the temporal bone. As it travels from this process towards the tongue, it divides into two parts – a longitudinal part which blends with the inferior longitudinal muscle and an oblique part which overlaps with the hyoglossus.
The fourth and final extrinsic muscle of the tongue is called the palatoglossus muscle. It is also considered to be a muscle of the soft palate. In this image, we can see the palatoglossus muscle originating from the soft palate and continuing downwards to insert into the side of the tongue. The palatoglossus elevates the root of the tongue and closes off the oral cavity from the oropharynx. It is supplied by the ascending pharyngeal artery which is a branch of the external carotid artery. It's also supplied by the ascending palatine branch of the facial artery.
The palatoglossus is the only muscle of the tongue that is not innervated by the hypoglossal nerve. Instead, it is innervated by the pharyngeal plexus. The pharyngeal plexus is derived from cranial nerves nine, ten and the cranial part of eleven. Like styloglossus and hyoglossus, the name of this muscle can also be remembered due to its relationship with the soft palate. From a lateral view, we can see that the palatoglossus arises from the soft palate and then passes anteriorly, laterally and inferiorly to insert onto the side of the tongue.
So, now, let's move on to the intrinsic muscles of the tongue. The first intrinsic muscle we'll look at is the superior longitudinal muscle. Individually, the superior longitudinal muscle turns the end and sides of the tongue upwards to make it concave. With the inferior longitudinal muscle, it acts to shorten the tongue. As we can see in this image, the superior longitudinal muscle is located beneath the lingual mucosa and extends from the lingual septum to the edge of the tongue on either side. If we look at this muscle from a lateral view, we can see that the superior longitudinal muscle extends backwards and is always located deep to the lingual mucosa.
The next intrinsic muscle we will look at is the inferior longitudinal muscle. The inferior longitudinal muscle is located below the inferior lingual surface. Acting alone, the inferior longitudinal muscle brings the end of the tongue down making the tongue a convex shape. As stated previously, when it works with the superior longitudinal muscle, it acts to shorten the tongue. From the lateral view, we can see that the inferior longitudinal muscle extends from the root of the tongue to the front where it blends with the styloglossus muscle.
Now, let's look at the next intrinsic muscle of the tongue, the vertical muscle of the tongue. This muscle extends from the dorsal side of the tongue to the ventral side. The vertical muscle acts to flatten and widen the tongue. The final intrinsic muscle we'll look at is the transverse muscle of the tongue. This muscle passes laterally from the lingual septum on either side. The function of this muscle is to narrow and elongate the tongue. All of the intrinsic muscles of the tongue are supplied by the lingual artery and they are innervated by the hypoglossal nerve which is the twelfth cranial nerve.
So, in summary, there are eight pairs of muscles of the tongue located on either side of the median lingual sulcus. Four of these muscles are extrinsic muscles which act to move the tongue. They are the genioglossus, the hyoglossus, the styloglossus and the palatoglossus. In addition, there are four intrinsic muscles which act to change the shape of the tongue. These are the superior longitudinal muscle, the inferior longitudinal muscle, the vertical muscle and the transverse muscle.
To finish off this tutorial, we'll go over some clinical notes related to the tongue. As seven out of eight of the muscles of the tongue are supplied by the hypoglossal nerve, damage to one of these nerves can cause weakening of the muscles on the same side of the lesion. It can also cause unilateral paralysis which is shown clinically as the tongue deviating to the same side of the lesion when the tongue is protruded. Damage to the hypoglossal nerve can be caused by strokes, multiple sclerosis or brainstem tumors.
So that concludes our tutorial on the muscles of the tongue. I hope you enjoyed it and thank you for listening.
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Now, good luck everyone, and I will see you next time.