Hi, this is Dr. Kingston,
and in this video, I'll be going
over the muscles of the tongue.
Our objective here is to name
the intrinsic and extrinsic muscles
of the tongue and discuss
their origins, insertions and innervation.
The muscles that make up the tongue can be divided
up into intrinsic and extrinsic.
The intrinsic muscles of the tongue are located
in and actually make up a lot of
the bulk of the body of the tongue.
They're going to function to
change the shape of the tongue
without moving it around in or out of the oral cavity.
These are all innervated by the hypoglossal nerve,
and they include the superior
and inferior longitudinal muscles,
which are going to shorten the length of
the tongue by pulling the sides in like so.
Vertical fibers which will flatten
the tongue by pulling the top down
and the bottom in like that.
And then transverse fibers which are going to
narrow the tongue from side to side.
The extrinsic tongue muscles are
the muscles that actually move the tongue around.
So they have connections to
both the base of the tongue and surrounding structures.
These are typically named for
the structures that they attach to.
So we have palatoglossus,
which is this little guy right up here.
Palatoglossus runs between the soft palate
and the tongue and functions to elevate the tongue.
We have styloglossus, which
is another elevator of the tongue.
And that is going to connect up to
the styloid process of the skull. Genioglossus-
I'm actually going to show you over
on the drawing over here.
Genioglossus is this fan-shaped muscle
that originates from the genial spines
on the anterior medial
mandible and fans out up into the body of the tongue.
When this fires, it's going to pull the tongue
forward or protrude it out of the mouth.
I want to note here that there
are two genioglossus muscles,
even though they're originating from
the medial point on the mandible,
sometimes it looks like there's just one.
If you fire one of them at it's at a time,
so you fire them unilaterally,
It will also deviate the tongue to
the contralateral or opposite side that it's fired on.
All right, and finally we have hyoglossus,
which I'm going back over to the photographic image here.
Hyoglossus is a depressor of the tongue,
so it attaches down to
the hyoid bone and will
pull the tongue downward toward it.
One of the nice things about this group of muscles is
that they almost all share the same innervation.
The hypoglossal nerve, cranial nerve number 12,
exits the cranium through
the hypoglossal canal and then it's going to travel
anteriorly and inferiorly through
that anterior cervical triangle.
It enters the oral cavity by slipping deep to mylohyoid.
So here's mylohyoid and
here's that hypoglossal nerve going just deep to
it to get into the oral cavity and then it's going
to approach the tongue from an inferior position.
This lets it supply motor innervation to hyoglossus,
genioglossus, and styloglossus or three
out of our four muscles.
That fourth muscle,
palatoglossus is the exception to this rule.
So because it originates from the soft palate,
it actually shares its innervation
with other soft palate muscles.
And because the soft palate is largely in the pharynx,
it has the pharyngeal innervation pattern.
So these are getting their somatic
motor innervation from vagus.
And those are all the muscles of the tongue.
So here's a practice question for you.
The correct answer here is B.
A motor deficit for
the right genioglossus muscle would produce a reaction
where your patient's tongue
deviates uncontrollably to the right
when they try to protrude it.
Alright, so let's take a look at
that genioglossus muscle to
understand it a little bit better,
we often see it depicted looking like this,
like a straight fan that comes
into the body of the tongue medially.
But in actuality,
the situation's a little more complicated.
If we look at genioglossus,
there's actually two of them
here right down the middle.
Over here on the picture on the right,
we can see that it is
not oriented just straight up and down,
but these fibers are directed superiorly and laterally.
All right, Let me erase that now for a second.
That means that when these muscles fire,
they're going to pull the tongue forward,
yes, but they are also going to pull
the tongue out toward the opposite side.
So if we have those fibers
attaching here on the left side of the tongue,
when they fire, they are going to pull this way.
That means that if
the left genioglossus muscle is functioning correctly,
it will pull the tongue
toward the right if it's fired just on the left side.
So if we have a motor deficit over here on the right,
that means that there is no counteracting force.
Okay, Usually the right would
pull the tongue toward the right and forward.
And the combination of those two actions would
end up pulling the tongue straightforward or protruding,
it's straight out of the mouth.
But because we don't have a functioning right side here,
that left or that rightward tilt that's
produced by the left side genioglossus muscle
is never corrected and we end up
with an uncontrollable write deviation.
Thank you guys for watching.