Hearing (Nursing)

00:02 Now let's look at some special senses in relationship to the ear.

00:07 So when we think about the ear, we typically think about what's called the external ear.

00:12 Although, there are much deeper structures that are considered part of the ear as well.

00:17 For example, we have the middle ear, which is a small chamber here just beyond the eardrum.

00:24 And then, we have the internal ear, which is really embedded into the bone here of the portion of temporal bone that we're looking at.

00:34 The external ear, the part that you're most familiar with is this soft part called the auricle or pinna.

00:42 And it's soft, because that has a lot of cartilage in it.

00:45 And it's very easily deformable because it doesn't have any bone in it.

00:50 And then leads to the ear canal or auditory canal, and terminates in this thin membrane called the tympanic membrane or the eardrum.

01:04 And the eardrum is where we're going to start the middle ear.

01:10 So the middle ear is going to have three special bones called the malleus, the incus, and then the stapes.

01:21 And these three bones are going to span the cavity of the middle ear from eardrum all the way to the inner ear portion.

01:29 And it's going to connect to a very special tiny area that connects to the internal ear at the oval window.

01:40 There's also another window, that's called the round window.

01:44 But it's sort of a compensatory window.

01:47 And we'll make sense when we talk about how hearing works.

01:49 But it's not the one that the stapes is directly attaching to.

01:54 The other important thing about the middle ear is that the middle ear actually formed during development as part of the pharynx.

02:03 So there's this connection to the pharynx called the auditory or Eustachian tube.

02:08 You've probably heard of the Eustachian tube when you've heard about your ears popping.

02:12 So when you for example, go to high elevation and you change elevations, you might feel pressure that gets relieved by "popping." And that's when the pressure in the middle ear builds up until it's able to equilibrate with the surrounding pressure via this passageway into the pharynx.

02:30 So that's what the Eustachian tube is, and where it ends up.

02:34 It ends up in the pharynx.

02:38 Now, the inner ear is getting very small, and is really on the cusp of becoming microanatomy.

02:46 But in this very zoomed in view, we can see a little bit about the complicated structure.

02:52 And we again have the beginnings of the middle ear as the oval window.

02:58 And that's just this little tiny window if you will, in the surrounding temporal bone that the stapes attaches to, and essentially transmits these vibrations from the eardrum to the inner ear via this window.

03:14 The round window, essentially because there's this pressure and vibration that needs some sort of like outlet.

03:20 So the round window is sort of a compensatory window, So that the pressure doesn't get too high inside the internal ear.

03:29 We see there's this spiral shaped thing here called the cochlea.

03:33 That's going to be very important for hearing.

03:36 But on the other side, we're going to have things that are more related to balance our equilibrium.

03:41 And these are the semicircular canals, which are oriented at right angles to each other sort of like an XYZ axis.

03:50 And they're called the anterior, posterior, and lateral semicircular canals.

03:56 And those along with this structure in between the semicircular canals and cochlea called the vestibule, are really going to help the body know where it is in space.

04:09 So let's look at hearing first.

04:12 So hearing is really about vibrations, working their way from the external ear down to the tympanic membrane, through the middle ear to that oval window to stimulate the internal ear.

04:29 So sound waves will work their way to that eardrum, cause a vibration of those middle ear bones.

04:38 And that vibration will again in turn stimulate that oval window and produce a fluid wave that goes back into the cochlea, and will affect things at a very, very small level to essentially produce the effect of hearing.

04:58 So when it comes to deficits in hearing, there are two ways to categorize them.

05:05 So if the damage is to something further back in this process, if it's damaged to the auditory nerve, or cranial nerve VIII itself, or if it's damaged to that specialized tiny organ of hearing called the cochlea, that's called sensory neural deafness.

05:27 So it has something to do with the actual like, complicated neurologic acceptance of hearing, rather than the reception of sound itself.

05:39 That would be something called conductive deafness.

05:42 So that's where the conduction is impaired.

05:45 So that sound wave is not reaching the sensory neural apparatus.

05:51 And conductive deafness can be anywhere from the outer portion where the ear canal might be blocked by maybe very thick ear wax plugs, or maybe a perforation in the eardrum, or in otitis media which is an inflammation of the middle ear.

06:10 So it's a common area to be infected and in part, because we do have a connection to the pharynx through.

06:17 the Eustachian tube.

06:18 So there is always a pathway for organisms to get up there.

06:22 And if that creates inflammation via an infection, that can also create conductive deafness.