hello welcome back this is dr. o in this video we're gonna talk about the auditory ossicles
now the word ossicles just means little bones and we have a whole video here to talk about
the tiniest bones in your body as well as being the smallest bones in the body that actually the
first ones to ossify during development so any newborn baby has almost entirely mature
auditory ossicles whereas many of our bones like the long bones of our limbs don't fully
ossified or become mature until we're 25 years old so they're pretty cool little bones so the
learning objectives here are what are those middle ear ossicles and how did the middle ear
ossicles function in hearing you'll remember the auditory ossicles from our discussion of
the middle ear now all three of these bones are found within the petrous part of the temporal
bone and they articulate with one another to lead from the tympanic membrane to the
oval window this will project forward the sound that was collected by the external ear through
vibrations between these bones you'll note as well that the tympanic membrane is a lot larger
than the oval window is over here so by the time that the vibrations get to the stapes the
stapes will be having about ten times the strength of vibration then we see at the tympanic membrane
now let's talk through these ossicles from the tympanic membrane over to the oval window our
first is the malleus I have two listed here so we have one on either side the malleus is a
hammer that's what it refers to we can see this portion right here is referred to as its handle
and you can imagine that being the part that you would try to hammer a nail into the wall with
potentially this is the largest of the bones and we can see its attachment there at the tympanic
membrane the incus is the second and it is an anvil shape and this is found between the two
ossicles and is intermediate in size the smallest of the ossicles is called the stapes and it's
the smallest bone in our body as well so this is a stirrup shape as you see right here and it sits
in the oval window so let's take a look at how these are related to one another in 3d space and
you'll note that everywhere they come together is at a synovial joint so there are some oval
joints connecting each of the three ossicles malleus the incus and then incus to stapes
so here we see our stapes heading toward the medial wall there's the foot plate there
here's the malleus and it's handle there and the intermediate incus between the two and
just represented here just so you're aware of it but we'll keep bringing it up that is the chorda
tympani nerve and this in green is the tympanic membrane all right so let's start here with our
malleus so this is a hammer shape so the parts of it the hammer portion is the head and the head is
what will articulate with incus you can kind of see incus posteriorly here i also see where they
come together around there and around here from this different view below the head is a narrowing
and anytime you have a head with a narrowing that structure is called the neck you now the manubrium
is the handle or the portion that is pushed up or articulating directly with that tympanic membrane
so the manubrium also serves as the attachment point for the tensor tympani muscle which can slow
the vibrations of the malleus and the tympanic membrane we also see this is where we find the
chorda tympani will pass over the malleus at the manubrium you now let's move on to Incus here
we can see Incas it's actually a body and then two limbs one here and one here if the body is
what will articulate with malleus so there is a facet there or a little indentation for where
incus articulates with malleus as we can see here on the right then we see the shorter and kind of
more blunt and short limb here and then the long limb running right around here and we'll note
in this image over on the right the long name of the incus runs parallel to the malleus and
specifically the manubrium of the malleus at the base or the end of the long limb is what we call
the lenticular process now the lenticular process you see sort of a little bend and that will then
articulate with the stapes so here you can see that articulation and there as well this is sort
of a feature of the long limb and you'll note as well kind of the chorda tympani doesn't have as
close of a relationship with the Incus but you do see it pass between the incus and the tympanic
membrane before then passing over the manubrium of the malleus final bone here is the stay piece
so here is that stirrup shape in purple and we're looking actually from a superior view
so standing above the middle ear looking down here's the cochlea of the vestibule here's the
tympanic membrane and you can kind of see the malleus and incus ghosted out here all right
so let's start with the stay piece at the head so the head of the stabies is right here and that is
what articulates with that lenticular process of the incus you can see those articulations along
the way then we see a bit of a narrowing and the narrowing the neck is where the stapedius muscle
will come to articulate so the stapedius muscle can also kind of slow down the vibrations of the
stay piece and then the oval window from the head and the neck we then lead to two legs or
limbs but a crus is the kind of the word for a leg so we have an anterior one and a posterior
one kind of these two split of the stirrup shape and finally we get to the base of the stapes
which is the footplate and that sits in the oval window which then leads toward the vestibule
all right so let's assess ourselves here and I want you to answer this question which part
of the malleus attaches to the tympanic membrane it needs the attachment point for tensor tympani
muscle is it the head the manubrium or the neck so choose your answer and then we'll talk about it
so remember our first over here in the image our first obstacle is the malleus it's head
is this portion here followed by the neck and then this portion that articulates with the
tympanic membrane or comes in contact with it is the manubrium so the correct answer
here is the manubrium so the muscle that attaches to Stapes does so where do you
remember so that muscle will project from the posterior wall toward the stay piece and that
attaches to the neck and that's the stapedius muscle awesome great job that's everything for
this video thank you for joining me and please let me know if you have any questions at all