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.