Internal Ear

00:01 Now we'll take a look at the internal ear.

00:04 The internal ear is divided into two major parts.

00:09 The first is a bony area that we see in through here, and then within the bony part, we have a membranous region, which is outlined in this lighter blue color.

00:25 More details, here we're looking at the bony part of the inner ear, and specifically this region here is referred to as the vestibule, and the vestibule contains the oval window and the stapes.

00:42 When the ears are oscillating due to sound waves, we'll be transmitting through the oval window.

00:54 Associated with the vestibule, our orifices, five of these orifices are from the semicircular canals, which are these structures in through here.

01:09 And the sixth one is from the scala vestibuli, which we'll take a look at later.

01:16 The scala vestibuli is associated with the cochlea.

01:20 The semicircular canals were mentioned a little bit earlier with regards to the orifices that communicate with the vestibule.

01:29 There are three semicircular canals in each ear.

01:34 One is the anterior semicircular canal based on its orientation.

01:39 Another is the posterior semicircular canal, and then this one that loops around here is going to be the lateral semicircular canal.

01:51 This portion of the lateral semicircular canal is referred to as its bony limb and then at the base of each of the semicircular canals, you have an area of dilatation and that area or dilatation is the ampulla, ampullae for plural.

02:13 And then the last bony part that's associated with the inner ear is the cochlea.

02:18 We see the cochlea and we do see that it has a snail-like appearance associated with it.

02:28 The round window which is shown here, or the cochlear window is an area of communication with the middle ear.

02:42 The membranous areas are found within the bony parts.

02:48 So we're seeing the semicircular ducts again, or actually the semicircular canal's the bony part, And in the shaded yellow to orange area, but within each of those semicircular canals you have ducts, and those ducts are the membranous portions of the semicircular canal.

03:08 This would be your superior semicircular duct.

03:13 This is the posterior semicircular duct, and then this is your horizontal semicircular duct.

03:21 And then within the vestibule you have two membranous areas, one of which is the utricule, and the other is the saccule.

03:31 Within the bony cochlea, you have a membranous cochlear duct, which we see shaded here in blue.

03:40 This is specifically looking at the cochlea.

03:42 You can see the spiraling nature of the cochlea and that is referred to as the osseous labyrinth.

03:53 Within the osseous labyrinth, you have a spiral canal, and this is the spiral canal of the cochlea.

04:02 Projecting into the spinal canal is the osseous spiral lamina.

04:13 And then at this particular region we have the modiolus.

04:18 This is a cone-shaped central axis of the cochlea.

04:23 It consists of spongy bone, and this is where the cochlea turns and spirals about 2.75 times around its central axis.

04:36 The cochlear nerve and the spiral ganglion are located inside of this, and then the cochlear nerve will then convey impulses from the sensory receptors for audition coming from the cochlea.

04:54 And this is the very large cochlear nerve that's receiving all these impulses that are being conveyed as the cochlea turns or spirals 2.75 times around its central axis.

05:11 Now, this single spiral canal is going to be divided into three partitions and this division will occur through the presence of two membranes.

05:26 The first membrane is shown in through here and this is the basilar membrane.

05:32 And then right above up we have the vestibular or Reissner's membrane.

05:37 And now we have three partitions within what was a single canal.

05:47 In addition, in this central area or partition, we have a structure known as the spiral ligament.

05:56 The middle region is referred to as the cochlear duct.

06:01 This is also referred to as a scala media and then the other two scala are shown here.

06:09 This is the scala vestibuli and then the scala tympani, or tympani and then resting on the basilar membrane gives a structure called the spiral organ of Corti.

06:31 Within these partitions, or scala, we have fluid.

06:36 The cochlear duct is filled with fluid called endolymph.

06:41 And then the scala vestibuli and the scala tympani are going to be filled with a type of lymph too but its composition is a little bit different than the endolymph and because the difference in composition, this is the perilymph.

06:58 And then here we're looking at, again, the inner ear, looking at the bony portions of the inner ear, and then the membranous portions here as well.

07:08 Here is the vestibular nerve coming from the vestibular apparatus of the inner ear.

07:14 So this would be conveying impulses related to maintenance of balance.

07:20 Here is the cochlear nerve coming from the cochlea conveying audition impulses centrally.

07:29 And then we have the facial nerve that travels with both of these divisions.

07:38 So facial nerve, cranial nerve VII, vestibulo and the cochlear nerves from the vestibulocochlear nerve, which is cranial nerve at number eight.