Tongue

00:01 The next group of muscles we're going to talk about is a very special ball of muscles called the tongue.

00:08 We're gonna start by looking at a sagittal cross section in a lateral view.

00:15 Here we see, anteriorly, the mandible, and posteriorly, the hyoid bone.

00:22 And this is going to connect what we call the root of the tongue.

00:27 Here we see the inferior surface of the tongue as it comes to a point which we call the apex of the tongue.

00:35 The oral part of the tongue is this anterior two thirds or so of the tongue.

00:41 Then we have this pharyngeal part more posteriorly, which is the posterior one-third.

00:48 We look at a superior view, we can see the surface of the tongue.

00:53 And again, we see the oral part as opposed to the pharyngeal part.

00:58 And we see a little groove going right down the midline, which represents the embryologic formation of the tongue from two lateral swellings that fused in the midline.

01:09 There are all types of bumps or papilla on the surface of the tongue, they go by different names such as fungiform, filiform, foliate, circumvallate, and a lot of them are associated with tastebuds, although the filiform papillae are not.

01:25 Around the area, just behind the circumvallate papillae, there's sort of a V-shaped called the terminal sulcus which really represents the border between these oral and pharyngeal parts, and also represent again, the union of two different embryologic origins of the tongue.

01:42 Right in the middle, or the sort of tip of this terminal sulcus is something called the foramen cecum which is important landmark for a lot of reasons.

01:51 But again, developmentally, this is actually where the thyroid gland started, and actually descended down into the neck.

01:58 And in some cases, you might find a topic thyroid tissue in this area.

02:04 We also have tonsils on the tongue called lingual tonsils.

02:11 Moving more posteriorly, we see the beginnings of the larynx with this flap of tissue called the epiglottis, which serves to protect the airway during the act of swallowing.

02:22 We see a lateral glossoepiglottic fold and a median glossoepiglottic fold in the midline.

02:32 The space between the tongue and the epiglottis is this little valley called vallecula.

02:37 Pretty much means little valley.

02:39 It's a spot where saliva can collect before the act of swallowing.

02:43 And in some cases where some small objects like little popcorn kernels might actually become lodged.

02:50 Let's look at the inferior surface of the tongue.

02:55 In the midline, we see a little connection to the floor of the mouth, called the lingual frenulum.

03:01 We also see little folds called fimbriated folds.

03:05 We also find the opening of salivary glands such as the opening of the submandibular duct.

03:11 Now the tongue is largely a ball of muscle.

03:14 So let's start looking at some of the muscles of the tongue.

03:18 Again, going back to the bony attachments, we have the mandible anteriorly and the hyoid bone posteriorly.

03:25 And in between is the tone.

03:28 We see some of the superhyoid muscles, we already saw earlier, including the anterior belly of the digastric.

03:35 The wide flat muscle that we call the mylohyoid and then the more linear one called the geniohyoid.

03:44 So again, here we have the intrinsic muscles of the tongue, and they run in various orientations such as longitudinal, vertical and transverse, and therefore they can have a wide range of movements in terms of changing how the tongue looks.

04:02 The extrinsic muscles of the tongue, on the other hand, are really moving it around within the oral cavity.

04:09 And these muscles all have the term glossus in them.

04:12 Glossus has been another word for tongue.

04:14 So for example, we have genioglossus, hyoglossus, styloglossus and palatoglossus all of which gives you some idea of where these tongue muscles are attaching.

04:30 In terms of innervation, we're talking about the hypoglossal nerve or cranial nerve XII.

04:38 The one exception being palatal glossus that's innervated by vagus nerve or cranial nerve X.

04:44 When it comes to sensation, the innervation is actually a bit more complicated.

04:50 In the anterior two-thirds, there's actually dual innervation.

04:55 In terms of general sensation, that's stuff like texture, heat, pain, that's provided by the lingual nerve which is a branch of the mandibular nerve, or cranial nerve V3.

05:07 In terms of special sensation, in this case taste, it's provided by the facial nerve or cranial VII.

05:15 And that's how this little tiny thing called the chorda tympani comes into play.

05:19 It's a little tiny connection between cranial nerve VII and trigeminal so that these fibers can hitch a ride with the lingual nerve on its way to the anterior two-thirds of the tongue.

05:31 It's easier in the posterior one-third of the tongue because both general and taste sensation are provided by the same cranial nerve, cranial nerve IX or glossopharyngeal.

05:42 It is worth keeping in mind that even beyond the tongue posteriorly in the epiglottis, the vagus nerve or cranial nerve X also has the ability to carry out some degree of taste sensation.