Next, let's take a look at the tongue which
is a very complicated ball of muscles.
If we do a sagittal section here, we can see the mandible anteriorly
and the hyoid bone posteriorly and these serve as the most important bony anchors for the tongue.
And the tongue itself has many different types of muscles,
but we can kind of divide them into intrinsic versus extrinsic.
Intrinsic means they're really just sitting on the
tongue itself, not really attaching to anything else
and these intrinsic muscles are oriented at right
angles to each other, sort of like an x, y, z axis.
And what they really do rather than move the
tongue is change the shape of the tongue.
Extrinsic muscles, on the other hand, really do move the tongue
and they are anchored to things away from the ball of muscle that is the tongue itself.
So, some of those extrinsic muscles of the tongue are the
genioglossus, genio when you see that term around here
means referring to the chin so it's something
that attaches to the chin area of the mandible.
Hyoglossus which you can kind of guess we just said there's the hyoid bones so it's something that goes to the hyoid bone.
Styloglossus. If you remember we had that bony projection of the temporal bone
called the styloid process so it tells you where that's going.
And then palatoglossus for something
that's attaching to the palate.
Now, let's talk about the sensation of the tongue,
which is actually fairly complicated due to its complicated development during the embryology.
The anterior 2/3 are supplied by 2 different cranial nerves.
The general sensation is supplied by a branch of the trigeminal nerve.
And when we say general sensation we mean the things
that you probably think about all the time with skin,
things like pain, temperature, texture, that's general
sensation and that's carried out by the trigeminal nerve.
When it comes to what we call special sensation, in this case taste,
it's carried out by the facial nerve or cranial nerve VII
and it takes a ride on the lingual nerve branch of the trigeminal nerve
via a tiny little thing called the chorda tympani.
So they sort of travel together to the anterior 2/3 of the tongue
but they carry out different types of sensation once they're there.
The posterior 3rd of the tongue is a lot easier
because both general and special sensation,
in this case taste, are supplied by the same cranial
nerve, cranial nerve IX or glossopharyngeal nerve.
And further back, there actually is a little bit
more taste sensation that can be carried out
by various branches of the vagus nerve but most of
the taste is coming from these ones listed here.
Now let's take a look at the pharynx.
The nasal cavity ends at 2 little apertures at the end of the hard palate called the choana.
And those choana are the passageway
between nasal cavity into pharynx.
And this is also the area where the hard
palate gives rise to the soft palate.
And so in this region bordered by the choana and the soft
palate and the surrounding bone, we have the nasopharynx.
And the mucosa in this area is innervated by the
2nd branch of trigeminal or cranial nerve V2.
Between that soft palate area and further down towards
the hyoid bone is the area behind the oral cavity
and so we call this part of the pharynx the
oropharynx and it's innervated by cranial nerve IX.
Inferior to that until the pharynx becomes the
esophagus at about the level that the trachea begins,
we have the laryngopharynx or the hypopharynx and that's
innervated by the vagus nerve or cranial nerve X.
There are some important features in the pharynx, in the nasopharynx particularly,
this is where we have the opening for the Eustachian tube.
The Eustachian tube is that narrow passageway that
connects the pharynx with the middle ear cavity.
And that's how we have the ability to, when we say pop
our ears when we have a lot of pressure differences
and the pressure is building up, we can equalize
it through this passageway to the nasopharynx.
We also have one of the tonsils located in this area. These
are the pharyngeal tonsils also called the adenoid tonsils.
In the oropharynx, we have the palatine tonsils
sitting over in the area of the soft palate.
We also have this little tiny space
anterior to the epiglottis called the vallecula which is an important landmark
for the process of intubation and it's one of the things
that you aim for with certain types of intubation.
The laryngopharynx beginning around the
area of the larynx, as the name implies,
beyond the epiglottis which is protecting the
passageway to the larynx, we have the trachea.
And that transition from larynx to trachea is the same
landmark for the transition from hypopharynx to esophagus.
At that point, it's a dedicated food and water only passageway.