hi let's talk about the ear so the ear as you recall has three divisions there's an outer ear
a middle ear and an inner ear the outer ear is the external acoustic meatus and all of the space
that's occupied lateral to the tympanic membrane or the eardrum so in this cartoon in the the lower
left-hand corner this is an anterior view of the middle ear we can see the tympanic membrane here
so that would be the outer ear this space is the middle ear and that space that is within
the middle ear is called the tympanic cavity and so the tympanic membrane or the eardrum is on the
lateral wall here is the roof or the Tagum timpani and then this is the medial wall and the medial
wall is going to be contiguous with the inner ear and sound is conducted through the middle
ear ossicles to the inner ear and I think that having this this cartoon is going to be helpful
for us as we look at the Kennebec images here so what we're looking at is a ladder or I'm sorry a
medial view of the lateral wall so we are looking from the medial wall towards the outer ear and so
here is the tympanic membrane and beyond that tympanic membrane would be the outer ear the
malleus is that the handle of the the malleus there is inserted on that tympanic membrane
such that when the tympanic membrane vibrates the malleus is going to vibrate the malleus connects
to the incus which we can see here and here's part of the head of the the malleus so this particular
temporal bone has been cut in half and the the remainder of that temporal bone has been removed
so the the stay piece has been removed now there are a couple of interesting features to to see
here so running anteriorly from this you can see along there that's part of the fringo tympanic
tube also known as the eustachian tube or the auditory tube so this this passageway is going
to lead from the middle ear to the nasopharynx and so this is a means by which pressure can
equilibrate between the nasopharynx and the middle ear now just superior to this and we can't see it
because it's somewhat obstructed but the canal is right about there there's a muscle called the
tensor tympani muscle and the belly of that muscle is within the canal that's running parallel to the
fringo tympanic coming out of this passageway is going to be the tendon for tensor tympani
and it's going to insert itself on the handle of the malleus and so having this tensor tympani here
is useful for helping to deaden any loud sounds so as to protect hearing tensor tympani is innervated
by branches of v3 and I always remember that v3 innervates tensor tympani because I feel like
people carry a lot of tension in their jaw in their in their mandible and so that's you know
the the area that is innervated both apparently and a lot of the the efferent muscles the muscles
of mastication and so anything with this tensor in in the name like tensor tympani is a v3 target
there's also a nerve here chorda tympani and this is a classic anatomical relationship that we see
here of chorda tympani and so what's going on is the facial nerve which we cannot see here
cranial nerve seven enters into the internal acoustic meatus with cranial nerve eight the
vestibular cochlear nerve and then it enters into the facial canal of the temporal bone this is the
longest osseous canal that contains a nerve in the skull and one of the branches that facial
nerve gives off is chorda tympani chorda tympani traverses the tympanic cavity and it runs between
the malleus and the incus and so you can find chorda tympani there now the interesting thing
about chorda tympani is then it leaves the skull through the Petra tympanic fissure and at that
point it's inside the infra temporal fossa now it joins up with the lingual nerve which is a branch
of v3 and so chorda tympani fibers are hitchhiking on the lingual nerve and these fibers are twofold
important one they're carrying preganglionic parasympathetic fibers so pre ganglionic
parasympathetic fibers to the submandibular ganglion that's submandibular ganglion if
you recall serves the submandibular gland and the sublingual glands chorda tympani is also
carrying special sensory fibers for taste that are bound for the anterior tongue so it's it's
making its its way through the the middle ear at this point and we should all see it here you know
we talked about chorda tympani and in the infra temporal fossa we talked about it when discussing
the salivary glands in the oral cavity and the submandibular triangle so we may as well also see
it here early on in its its journey so turning our attention to the the basic cranium so let's see
here is the mastoid process there's the styloid process just so we can orient ourselves and just
anterior medial to where that style of mastoid foramen would be if we kind of head that way we
can see the opening you can see that over here for the carotid canal it's difficult
to see here but we can also see the openings for the the internal jugular vein so the the jugular
foramen oh it might be best to look over here on this skull that somewhat canted so there's
foramen magnum there are the occipital condyles so that way is anterior that way is posterior and so
there is the carotid canal here is the jugular fossa and if we were to continue the jugular
foramen and between the two look at this tiny little thing that is the tympanic canaliculus
tympanic canaliculus and this is going to be an important osteological part of the journey of
preganglionic parasympathetic fibers on their way from the glossopharyngeal nerve cranial
nerve number nine through the middle ear through the skull out into the in four temporal fossa to
synapse in the otic ganglion so let's uh let's take a look here at the the medial wall also
called the labyrinthine wall and some of those structures so anterior is this direction posterior
is this direction and one thing that we can note posteriorly is that this is very cancellous lots
of lots of space here and the sum total of all of this space are the mastoid air cells so within
the mastoid process it's very cancellous all of these open spaces in those spaces are contiguous
with the middle ear we can actually get to them through the posterior wall here so again we're
looking at this wall and let's point out some of the structures that that we can see here so
anteriorly again we have part of this we've got a little bit of the pharyngotympanic tube so this
isn't really on the medial wall this would be more of an anterior wall but we can see part of
it because this has been sectioned we can also see this is this is pretty prominent here we could see
the tympanic nerve rising up onto the promontory here and then branching out into the tympanic
plexus and then it's going to continue so that tympanic nerve is a branch of glossopharyngeal
glossopharyngeal nerve as you recall is going to exit through the jugular foramen nine ten and
eleven glossopharyngeal vagus and accessory when glossopharyngeal exits this it's heading out the
tympanic nerve enters that tympanic canaliculus okay so now it's heading superiorly it goes over
the promontory that promontory remember the medial wall of the middle ear is going to be against the
inner ear so the promontory is actually a little out budding of bone formed by a portion of the
cochlea so coming out of that tympanic plexus is the lesser petrosal nerve that lesser petrosal
nerve is going through the the Tagum tympani the roof of the middle ear it's going across
the the basic cranium and it's going to dive down through foramen ovale where those preganglionic
parasympathetic fibers are going to meet the otic ganglion all right now just posterior
to the promontory we can see another ossicles so there is the stay piece the stay piece is
sitting with its foot plate in the oval window so it's conducting those vibrations those sound
vibrations to the oval window and then that is being conducted in the middle ear below the oval
window we have the round window that round window is a membranous part of the wall of the middle ear
the medial wall and that allows for some expansion of the auto lymph within the cochlea now there is
also a muscle attached from the posterior wall to the neck of the stay Peas and we we can't
see that muscle unfortunately here it's not it's not present in this particular image but we can
see here there's the stapedius muscle going out to the neck of the state bees stapedius muscle
is innervated by the facial nerve so within the canal in addition to the what's in in addition
to let's see the the greater petrosal nerve which is given off in the canal there's a pre
ganglionic parasympathetic fibers bound for the pterygopalantine ganglion and the chorda tympani
there's also a nerve to the stapedius muscle which is facial and sometimes with Bell's palsy
it's very rare but sometimes with Bell's palsy a person can suffer from hyperacusis
because the stapedius muscle has been denervated all right we have a another view of the medial
wall and this is just to reinforce the the round window for the footplate of the stay
Pease and I'm sorry the oval window and the round window that would be inferior to it so
promontory with tympanic plexus tympanic nerve going in lesser petrosal nerve coming out oval
window round window and then finally we come to the the inner ear so the inner ear pardon me is
surrounded by by bone and we can see that there are there are two large bony elements
here there's there's a third which is the the vestibule that we can see this the snail shaped
cochlea the cochlea is the is the site for our auditory sense for hearing and we also have three
semicircular canals and the semicircular canals partly are oriented in a posterior horizontal
and superior position and these correspond to pitch roll and yaw axes and so these are full
of endo limbs with hair cells and so as the as the head turns and there's there's motion
the endolymph moves into triggers hair cells and you can detect which way you're moving in these
pitch roll and yaw axis and these various rotary movements now the the special sensory fibers that
are innervating the inner ear are compliments of cranial nerve eight the vestibulocochlear nerve
and so vestibulocochlear nerve is entering in through the internal acoustic meatus the misses
of the petrous portion of the temporal bone so if we look here that's the petrous portion of
the temporal bone we've got a nice Ridge here and that Ridge has a face going down and that
internal acoustic meatus is on the lateral surface of that face so if we're here's the
Ridge looking at this from a different angle so there's anterior there's posterior so this
is a hot axis but right there is the internal acoustic meatus and it's through that that we
get the facial nerve and the vestibulocochlear nerve so 7 & 8 are going in through that space
so we've talked about the ear the outer ear the middle ear and the inner ear and
various features especially of the middle ear and inner ear I thank you for your time