hi again everyone this is dr. o and in this video we're going to look at the muscles of the middle
ear specifically what are those two muscles and how are they innervated but the first muscle is
the tensor tympani muscle remember this one from the anterior wall of the middle ear it projects
from the anterior wall toward the malleus so it's attachments here approximately are on the pharyngo
tympanic tube cartilage as well as the greater wing of the sphenoid bone then it projects toward
the manubrium of the malleus so this will serve to dampen the vibrations of not only the malleus
but also the tympanic membrane and it does so by pulling on the malleus to literally tense
the tympanic membrane given its name a tensor tympani is innervated by the mandibular nerve
or v3 through the nerve - tensor tympani well remember this branch from when we were looking at
the trunk or the main trunk of v3 we saw branches going off - tensor tympani tensor veli palatini
medial pterygoid neck muscle and sometimes this nerve will come directly off of that medial
pterygoid nerve remember that these muscles all develop from the first pharyngeal arch so that
is why they're all innervated by branches of v3 which develops within that arch the second muscle
here is the stapedius muscle now just as a point of reference this muscle right here is tensor
tympani then we see the malleus the incus and then the stay piece here attached to the stapes is
that stapedius muscle now we're really looking from lateral toward the medial wall so this is
posterior and this is more anterior the stapedius muscle will project out within this pyramidal
eminence coming from the posterior wall of the middle ear its tendon will course through that
pyramidal eminence to then attach to the neck of the stapes this will dampen the vibrations of the
stapes slowing down those oscillations forward toward the oval window this is innervated by the
nerve to stapedius which is a branch of the facial nerve. Now stapedius is one of the muscles
that develops in the second pharyngeal arch so this muscle along with all the other muscles
innervated by facial nerve developed together with the facial nerve in the second pharyngeal arch
in the case of a facial nerve palsy also known as Bell's palsy the nerve to stapedius can also
be affected this would lead to lack of functioning of that stapedius muscle now this would present in
someone as hyperacusis or being overly sensitive to sound because when things are loud say you're
at a rock concert in a year and a half and then in the first few minutes you feel it you feel it's
a little bit painful a little bit loud but over time you adapt and you aren't noticing it being
as loud and that in part is some of these muscles slowing down those oscillations and vibrations
of the ossicles both through the tensor tympani in the stapedius so in someone with a stapedius
muscle that's not functioning properly sounds will sound louder and they'll be unable to compensate
for you know an extended loud noise and it will continue to sound loud and feel painful
now we're going to revisit an image we looked at previously looking from medial toward the
lateral wall of the middle ear here being the tympanic membrane the malleus being here we
can see kind of coming from that anterior portion is the tendon of the tensor tympani
muscle which would run in this direction here which attaches then to the malleus so also from
the anterior wall we see this opening and that opening there is the pharyngotympanic tube again part of
the anterior wall also running in this region we see nicely the chorda tympani nerve and the
incus kind of coursing over that we're going to take a look at this in the context of the bones
so the first thing I want you to note right here is this is the lesser wing of the sphenoid bone
superior orbital fissure foramen rotundum so as we rotate this is kind of the view you get
when you look into the middle cranial fossa and this is the petrous part of the temporal bone
now as we turn laterally we can see the structures here of the tympanic membrane
back behind here this bony structure is the mastoid process and then more anteriorly
we're seeing the lateral pterygoid plate so here you see the tympanic membrane and
we'll get a closer look now into the middle ear right away - I want to note here kind of
running in this region is the tensor tympani muscle and that is the pharyngo tympanic tube
cartilage now let's remove the tympanic membrane going a little bit closer now I
can see even better here that tensor tympani muscle and the cartilage here and then here
is the malleus so you can see where those where that attaches right along in there
the other thing to note in this view is right away you can see that pyramidal eminence coming
from the posterior wall toward the neck of the scabies so those are the two major muscles in
this view we also see nicely where that oval window will sit and this structure right here
is the promontory so you'll remember this from our first video it is the projection
of the first part of the cochlea into the middle ear also in the posterior aspect of
this region we can see this in purple is the lateral semicircular canal or the prominence
of that lateral semicircular canal here is the facial nerve within the facial canal and
then there is the pyramidal eminence so you see those three together and then this kind
of coming out toward us branching off and then coming toward us is the chorda tympani nerve
and just as a note here as where the facial nerve continues on toward the stylomastoid
foramen all right so let's test ourselves using this question here so from which wall of the
middle ear does the pyramidal eminence project is it from the anterior the lateral the medial or the
posterior wall so pause so you can take a moment to choose your answer and when you're ready what
are we looking at here so first off here is our tensor tympani muscle and the pharyngotympanic
tube here remember those are the anterior wall what about this region right here where we're
seeing the oval window and the promontory those are the medial wall so I'm going to cross those
out because they are not the correct answer do you remember there was a structure here that was
ghosted in the last video and that is our lateral wall that structure would be the tympanic membrane
that leaves us with posterior as the correct answer now you'll remember posteriorly is
right here this wall along here we see the pyramidal eminence the facial canal and the
prominence of the lateral semicircular canal all from that posterior wall of the middle ear
all right so hopefully those views make sense to you but of course as always if you have any
questions please feel free to ask enjoy the rest of your day and I'll catch you in the next video