Anatomy of the Sensorineural Mechanism - PowerPoint Presentation

Slide1

Anatomy of the Sensorineural MechanismSlide2
Slide3

Three

subdivisions

of the

labyrinthcochleasemicircular canals (vestibular system)vestibule (vestibular system, mainly)

The Bony Labyrinth

(from Zemlin, 1998)Slide4

Bony labyrinth

: Hard, bony outer shell

.

Membranous labyrinth

: Fully contained inside the bony labyrinth; like a convoluted-shaped water balloon stuff inside the bony labyrinth. The membr labyrinth is all one system; i.e., it’s all one balloon.

(from Minifie, Hixon, & Williams, 1973)Slide5

Another view of the membranous labyrinth

(from Perkins & Kent, 1986)Slide6

https://www.dartmouth.edu/~humananatomy/figures/chapter_44/44-8_files/IMAGE001.jpg

One more: membranous

labyrinthSlide7

Again with the membranous labyrinth, this time all by itself; i.e., with the entire bony labyrinth stripped away

. Note once again: It’s

all one fluid system serving both hearing and balance.

(from Deutsch & Richards, 1979)Slide8

Schematic and partially unrolled view of the middle ear and labyrinth showing the

scala

vestibuli, the scala media (cochlear duct), and the scala tympani, along with the cochlear fluids (endolymph & perilymph).

(adapted from Zemlin, 1998)Slide9

Cuts through an unrolled and a rolled cochlea

(from Deutsch & Richards, 1979)Slide10

Cut through a rolled-up cochlea

(from Deutsch & Richards, 1979)

modiolus

(core of bone that cochlea is wrapped around)

spiral ganglion

(8N cell bodies)

Organ of Corti

basilar membrane

Reissner’s membrane

tectorial membraneSlide11

Detail of a single cut through the cochlea showing the

Organ of

Corti

, 8th N fibers entering through a tunnel in the spiral lamina (the habenula perforata), the spiral ligament, and the stria vascularis.

(from Deutsch & Richards, 1979)Slide12

(from

Zemlin

, Fig. 6-48)

Notice the

stria vascularis (also area vascularis) – the only good picture I have of this. The s.v. secretes endolymph.

Notice also the spiral ligament, which attaches the b.m. to the bony wall of the cochlea, and the limbus (or limbus spiralis), a fibrous covering of the spiral lamina.

modiolus

spiral ligamentSlide13

Detail of the Organ of Corti

(from Stevens,1951)

Any cut through the cochlea will show 1 inner hair cell (IHC) and 3 (sometimes 4) outer hair cells (OHCs). This unit –

1 IHC & 3-4 OHCs

–

is referred to as a hair cell channel. There are about 3,000 channels in the human cochlea. (That number will become important later when we discuss cochlear implants.)Slide14

Another view of the Organ of Corti

(Note: In this figure, and many others you will see, each HC has one nerve fiber. This is way wrong. More later.)Slide15

Quiz

: Which way to the modiolus, which way to spiral ligament?

Note: Innervation pattern shown here is accurate:

many-to-one for IHCs, one-to-many for OHCs. More later.Slide16

Note the different

shapes

of the two hair cell types:

IHC: flaskOHC: test tubeSlide17
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Electron micrograph of a hair bundle as seen from above. Note: (1) cilia are arranged according to height, (2) cilia are arranged in a very distinctive pattern, variously described as a ‘W’ or sometimes a ‘V’ shape.

modiolus

spiral ligamentSlide19

modiolus

spiral ligament

IHCs

OHCsSlide20

The cochlear and vestibular braches of the 8

th

cranial nerve

(from Deutsch & Richards, 1979)Slide21

The

cochlear

and

vestibular braches of the 8th cranial nerve