Middle Ear

by Craig Canby, PhD

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    00:01 Now, we can proceed to the middle ear.

    00:04 And again, this is also referred to as the tympanic cavity.

    00:08 There are three regions of the tympanic cavity.

    00:11 The first one is that area just immediately medial to the tympanic membrane.

    00:18 This is referred to as the mesotympanum.

    00:22 Above that is the epitympanic recess, and epi does mean above.

    00:32 And then, we also have an area just below the mesotympanum, and that's the hypotympanum.

    00:41 Hypo means below.

    00:43 When we're within the middle ear, the middle ear will have six walls.

    00:51 Two of these six walls can literally be referred to as a roof and a floor.

    00:56 So, these six walls would resemble the cube that we see in this particular orientation.

    01:03 So, we'll quickly identify the boundaries or the borders of these walls.

    01:07 The uppermost wall, the roof, is formed by the temporal bone.

    01:14 Specifically, the region of the temporal bone called the tegmen tympani.

    01:19 The floor or wall is the jugular wall.

    01:25 Posteriorly, we have the mastoid wall of the middle ear.

    01:32 Anterior wall is also referred to as the carotid wall.

    01:40 Here, we're looking at the medial wall between the middle ear and the internal ear, and this is referred to as a labyrinthine wall.

    01:55 And then, lastly, we have the lateral wall, which is also referred to as the membranous wall because of the presence of the tympanic membrane.

    02:06 The membranous wall, specifically in the tympanic membrane which we see here, is forming the lateral wall.

    02:16 We have some structures here that we'll point out because of their association within the middle ear cavity and in ear ossicles and the tympanic membrane.

    02:27 And specifically, we're looking at the chorda tympani.

    02:30 The chorda tympani is a nerve that arises from the mastoid segment of your facial nerve, and we see the facial nerve right in through here.

    02:39 The chorda tympani carries afferent special sensation from the anterior two-thirds of the tongue, and this is via the lingual nerve.

    02:48 And it also conveys afferent parasympathetic secretomotor fibers to the submandibular and sublingual glands.

    02:58 The medial wall or labyrinthine wall is shown in through here.

    03:09 Again, this separates the tympanic cavity from the internal or inner ear.

    03:14 The most prominent feature here is the promontory, and also the round window that we see in through here.

    03:24 And the oval window would be right where the stapes is located.

    03:33 And the bulge that we see here that forms the promontory is a bulge of the cochlea.

    03:44 That is a member of the inner ear.

    03:48 Some structures within the middle ear.

    03:52 First, there are some ligaments of the middle ear that are labeled here.

    03:56 These well anchor the ear ossicles in place and we see the three ear ossicles here.

    04:05 We'll identify them very, very shortly.

    04:08 Also associated with the middle ear is the eustachian tube, also known as auditory tube or the pharyngotympanic tube.

    04:19 This is of communication between the middle ear and the nasopharynx, and the eustachian tube functions to equalize the pressure within the middle ear with that of atmospheric pressure.

    04:34 Now, the ear ossicles, there are three.

    04:39 We'll go through them, and then we'll finish up with a mnemonic, and it's a can't miss mnemonic.

    04:46 First, we have the malleus that's shown here.

    04:50 The malleus would be associated with the tympanic membrane.

    04:55 The malleus will articulate with the second ear ossicle called the incus.

    05:00 And then, the incus will articulate with the stapes.

    05:06 And the mnemonic for that is M-I-S, MIS.

    05:13 M for malleus, I for incus, and then the S for stapes.

    05:19 We also have a couple muscles within the middle ear.

    05:27 These are very thin, delicate muscles as you might think that they would be in a very small, confined area.

    05:35 The first one is the stapedius muscle. You see it here.

    05:39 As the name implies, it has an insertion on the stapes.

    05:44 The nerve supply to the stapedius muscle is the stapedius branch from your facial nerve and this protects the ear from sudden loud noises.

    05:57 When the stapedius contracts, it will dampen the vibrations that are being transmitted into the cochlea.

    06:05 Through the oval window specifically.

    06:08 The other muscle is a larger muscle, but again, by muscle standards, it's still a small muscle, and this is referred to as the tensor tympani muscle.

    06:22 And the tensor tympani is attached to the malleus.

    06:25 Its innervation is from the medial pterygoid nerve, which is a branch of the mandibular nerve of the trigeminal.

    06:35 It too will dampen and protect the ear against sudden loud noises.

    06:43 All right. Now, we're looking at the blood supply of the middle ear.

    06:48 Here, we have the superior branch of the anterior tympanic artery that helps to supply the middle ear. This is a branch of the maxillary artery.

    06:59 We also have the caroticotympanic artery.

    07:03 This is a branch of the internal carotid artery.

    07:08 We also have the inferior tympanic artery, and this is a branch of the ascending pharyngeal artery.

    07:16 And then, we have the superior tympanic artery that is also feeding the middle ear.

    07:24 Some additional views to the blood supply to the middle ear are shown here.

    07:30 Here's another view of the anterior tympanic artery.

    07:34 As mentioned, this is a branch of the maxillary artery.

    07:38 The incudal branch from the anterior tympanic is shown in through here.

    07:45 Here is the stylomastoid branch of the posterior auricular artery that helps to supply the middle ear.

    07:53 We also have the deep auricular branch, and this is a branch of the maxillary artery.

    08:00 And the last branch to point out is this branch in through here.

    08:05 This is the mallear branch and it is from the anterior tympanic artery.

    08:11 Innervation of the middle ear is shown in through here.

    08:16 Again, we're looking at the promontory.

    08:18 And the two main nerves that we need to be focused about would be the tympanic nerve.

    08:26 We see it coming into play here.

    08:28 This is a branch from the glossopharyngeal nerve, cranial nerve number nine.

    08:34 It branches into anterior and posterior tympanic nerves. It also receives contributions.

    08:40 The plexus receives contributions from branches from the internal carotid plexus.

    08:46 These are sympathetic fibers.

    08:49 And then, leaving the plexus, the tympanic plexus, is the lesser petrosal nerve.

    08:56 This conveys parasympathetic fibers to the parotid gland.

    About the Lecture

    The lecture Middle Ear by Craig Canby, PhD is from the course Head and Neck Anatomy with Dr. Canby.

    Included Quiz Questions

    1. The floor of the middle ear is formed by the jugular wall.
    2. The mesotympanum is the middle ear region below the tympanic membrane.
    3. The epitympanic recess is lateral to the tympanic membrane.
    4. The membranous wall forms the medial border of the middle ear.
    5. The anterior border is formed by the mastoid wall.
    1. The oval window is found on the medial wall.
    2. The promontory is located on the inferior wall.
    3. The promontory is formed by the protrusion of a blood vessel.
    4. The round window is located on the posterior wall.
    5. The chorda tympani runs along the medial wall.
    1. The stapedius muscle prevents damage from loud noises.
    2. The tensor tympani muscle attaches to the stapes.
    3. The incus directly articulates with the tympanic membrane.
    4. The tensor tympani muscle is innervated by a branch of the facial nerve.
    5. The malleus directly articulates with the stapes.
    1. The tympanic nerve is a branch of the glossopharyngeal nerve.
    2. The anterior tympanic artery is a branch of the internal carotid.
    3. The caroticotympanic artery is a branch of the external carotid.
    4. The chorda tympani nerve carries sympathetic fibers through the middle ear.
    5. The superior tympanic artery branches from the maxillary artery.

    Author of lecture Middle Ear

     Craig Canby, PhD

    Craig Canby, PhD

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