Middle Ear

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.