Middle Ear

by Darren Salmi, MD, MS

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    00:01 As we move deeper, we reach the middle ear.

    00:06 And this is a small cavity, also called the tympanic cavity.

    00:12 That superiorly has a small little area called the epitympanic recess.

    00:18 The portion of the middle ear directly behind the tympanic membrane, we call the mesotympanum.

    00:27 Superiorly, we would have the epitympanum and inferiorly, the hypo tympanum, beyond which, we would have the Eustachian tube or or pharyngotympanic tube.

    00:41 Here's going to be a schematic representation of the middle ear to give some idea of the structures and relationships within this cavity.

    00:51 We can think of it as having a roof also called a tegmental wall, a floor also called a jugular wall because of the nearby location of the internal jugular vein.

    01:03 A posterior wall also called the mastoid wall.

    01:07 That has an opening or aditus to the mastoid antrum.

    01:14 It also has a little bony projection called the pyramidal eminence that a very tiny muscle called the stapedius will attach to.

    01:22 And this is where we're going to find part of that chorda tympani nerve we mentioned.

    01:28 We'll also have an anterior wall that's going to have an opening for another tiny muscle called the tensor tympani.

    01:36 As well as that opening for the for pharyngotympanic or Eustachian tube, that will lead down to the nasal pharynx.

    01:43 We'll also have the other side for the opening of the chorda tympani.

    01:49 Medially, we're going to have our labyrinth wall which is going towards our inner ear.

    01:56 And we're going to have these little what we call windows called the round window and the oval window and a little bump in between called the promontory.

    02:06 And that's basically where we're going to find something called the cochlea on the other side.

    02:12 We're also going to find some prominences for the facial canal or the facial nerves traveling.

    02:17 And for something called the lateral semicircular canal, something that's going to be part of the vestibular apparatus.

    02:24 Laterally, because we're looking from a lateral point of view, we would put on the membranous wall, which is actually the tympanic membrane.

    02:35 Now let's take a look at the middle ear cavity as if we were in it looking medially.

    02:39 Essentially towards the inner ear.

    02:44 We would see our connection to the pharynx, particularly the nasal pharynx called the for pharyngotympanic or auditory or Eustachian tube.

    02:54 And we would see a bump called the promontory and that bump is basically where something called the cochlea would sit on the other side.

    03:04 We would have these windows as we call them, called the oval window and the round window, which are structures related to the inner ear.

    03:14 We would have that prominence for the facial canal through which the facial nerves traveling.

    03:19 And again, prominence is for these vestibular apparatus called the lateral semicircular canal.

    03:27 We would also see part of that muscle called the tensor tympani, something that's going to act on our hearing apparatus.

    03:37 If we were in that middle ear cavity, looking laterally, what we would see is the backside of the tympanic membrane.

    03:48 We would again see our Eustachian tube or pharyngotympanic tube as well as that tensor tympani but now we would see those three middle ear bones, the malleus, incus and stapes.

    04:02 We would also see a very tiny muscle called the stapedius muscle.

    04:07 In fact, it's the tiniest skeletal muscle in the human body.

    04:12 And together the tensor tympani and stapedius act to serve as something like moderators in the act of hearing so that very loud sounds get their amplitude somewhat modified.

    04:23 For example, during chewing, it keeps the sound of chewing from being deafening to our ears.

    04:30 Then finally, we would see the passage of this chorda tympani behind the tympanic membrane.

    04:37 Again, giving this branch of the facial nerve its name.

    04:41 Now let's take a closer look at those middle ear bones or ossicles.

    04:46 We have the malleus, incus and stapes, going from external to internal.

    04:52 Sometimes you'll hear their old terms, hammer, anvil and stirrup.

    04:57 Despite being some of the smallest bones you'll ever see, they do have several unique features.

    05:03 So the malleus has a head, a neck, and various processes and anterior and a lateral process and then the long handle.

    05:11 Again, something we could see during an otoscopic examination.

    05:16 The incus has a facet for its interaction with the malleus.

    05:21 And in fact, these bones, as small as they are, do form true synovial joints with each other.

    05:29 There is then a body connecting to a long limb that ends in a lenticular process that forms yet another synovial joint with the stapes, which is going to end on our portion of the inner ear that will help us perceive sound.

    05:47 The stapes will have that tiny neck connecting the head to two crura or legs that will terminate in a base.

    05:55 This base is what's going to connect to the oval window of the inner ear.

    06:03 Now let's take a look at the vascular supply to the middle ear.

    06:07 Most of which is going to be coming off of the maxillary artery coming off of the external carotid.

    06:14 We have the superior branch of the anterior tympanic, the chronic tympanic, the inferior tympanic, and the superior tympanic.

    06:25 From a lateral point of view, we can again see the anterior tympanic, we can see the mallear branch, we can see the incudal branch and a branch actually coming from the posterior auricular artery, the style of mastoid branch and finally the deep auricular branch.

    06:44 In terms of innervation, most of it is going to come from the tympanic nerve, which is a branch of cranial nerve IX or glossopharyngeal nerve.

    06:55 It's going to have branches that have come from the internal carotid plexus and this tympanic nerve will end typically in a branch called the lesser petrosal nerve.

    About the Lecture

    The lecture Middle Ear by Darren Salmi, MD, MS is from the course Special Senses.

    Included Quiz Questions

    1. Mesotympanum
    2. Epitympanum
    3. Hypotympanum
    4. Eustachian tube
    1. Tegmental wall
    2. Jugular wall
    3. Mastoid wall
    4. Tensor wall
    5. Carotid wall
    1. Anterior wall
    2. Lateral wall
    3. Roof
    4. Floor
    5. Posterior wall
    1. Pharyngotympanic tube
    2. Mastoid antrum
    3. Pyramidal eminence
    4. Round window
    5. Oval window
    1. Stapedius
    2. Tensor tympani
    3. Auricular muscle
    4. Ossicles
    5. Incus

    Author of lecture Middle Ear

     Darren Salmi, MD, MS

    Darren Salmi, MD, MS

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