L19 & L20 - Ear IV/V (inner ear)

Question 1

Inner ear: what does it contain?

Answer 1

vestibulocochlear organ

Question 2

Vestibulocochlear organ: what does it do and where is it located?

Answer 2

Involved in the reception of sound and the maintenance of equilibrium (balance)

Vestibulocochlear organ is contained within the
otic cavity

Question 3

Otic cavity: what is it, where is it found, what is it inferior to, and what does it have?

Answer 3

The otic cavity is in a region of dense bone located in the petrous part of the temporal bone

Inferior to the middle cranial fossa

The otic cavity contains ‘tunnels’ – the bony labyrinth

Question 4

Complete anatomy

Answer 4

Look at inner ear

Question 5

Bony labyrinth: what is it, what does it have, what is it suspended with, what parts of it are there, and what are the differences in the fluids of the different parts?

Answer 5

‘Tunnels’ within the otic cavity

Fluid-filled space (perilymph)

Filaments on some parts

• Cochlea
• Vestibule
• Semicircular canals
• The membranous labyrinth (series of ducts and sacs) is suspended inside the bony labyrinth

Membraneous labyrinth - endolymph
Bony labyrinth - perilymph

Question 6

Labyrinth: what are the branches?

Answer 6

Branches of bony labyrinth are canals
Branches of the membranous labyrinth are ducts

Question 7

Bony labyrinth: its orientation anteriorly to posteriorly

Answer 7

Most anteriorly is the cochlea, there is a landmark which articulates with the stapes, then the vestibule is in the ‘middle’, with the three semicircular canals extending from it all at right angles with each other

Question 8

Membraneous labyrinth: what are its components

Answer 8

• Scala media
• Saccule
• Ultricle
• Semicircular ducts

Utricle and sacculeSemicircular ductsScala media

Spiral ligament secures scala media within the
cochlear canal
Otherwise secured by filaments through the perilymph

rewatch leccy

Question 9

Cochlea: what is it, how many turns does it have, what does the basal turn do, what is the basal turn punctured by, what is the round window covered by, and what are the chambers in the cochlea?

Answer 9

Shell-shaped part of the ear

Two and a half turns (basal turn, second turn, apex/modiolus) starting at vestibule

First (basal) turn produces the medial (labyrinthine) wall of the tympanic cavity

First turn is punctured by the round window

Round window is covered by the secondary tympanic membrane

• Scala vestibule (forms roof of scala media)
• Scala media
• Scala tympani (forms floor of scala media)

Question 10

Scala media: what is it, what is it also called, how is it in its cross-section, how does it interact with the cochlear canal, and what is it supported by?

Answer 10

Spiral tube, blind at one end - concerned with hearing

Cochlear duct

Triangular in cross-section (rewatch leccy)

Follows cochlear canal all the way around, reaches apex but doesn’t pass it

Supported by the spiral ligament superficially and spiral lamina deeply

Question 11

Sound wave transmission of unheard sounds

Answer 11

Stapes transmits sound vibrations to oval window

Sound travels through scala vestibuli, ending at the apex of the cochlea where it becomes continuous with the scala tympani

Sound then passes towards the round window

Extra energy gets dissipated there (must be fluid, not solid because of compression??)

Question 12

Sound wave transmission of heard sounds

Answer 12

Sounds that we can hear take a ‘short cut’ from the vestibuli to the media

They move the vestibular membrane

Then the endolymph

Then the basilar membrane

Question 13

What type of fluid is within each chamber of the cochlea?

Answer 13

Scala vestibuli - perilymph
Scala media - endolymph
Scala tympani - perilymph

Question 14

Organ of Corti

Answer 14

Rewatch leccy

Spiral?

Situated on basilar membrane

Lies under gelatinous tectorial membrane

Sound waves move basilar membrane

This in turn bends the hair (receptor) cells in relation to the tectorial membrane where their ends are embedded

Hairs move up and down, opening/closing mechanically gated ion channels

Therefore movement of hairs converted into a receptor potential - travels to spiral ganglion, cochlear division of CN VIII (vestibulocochlear) transmits info to brain

Question 15

Determining frequencies

Answer 15

Volume
determined
from
amplitude
of basilar
membrane
oscillation
Low frequency
(pitch) sounds
travel further
than those
of higher
frequencies
<50 Hz cause movements
of entire basilar membrane
Excites hair cells near apex

Basilar membrane varies in thickness
and width along its length
It is thick and narrow at the base
This is where high
frequency (20000 Hz)
sounds are detected
It is thin and wide at the apex
This is where low frequency
(200 Hz) sounds are detected
Loudness:
greater amplitude of basilar membrane
Two ears – stereoscopic sound

Apex - low frequency
Base - high frequency

rewatch leccy (attention snapped)

Question 16

Internal acoustic meatus

Answer 16

The internal acoustic meatus transmits the vestibulocochlear nerve (CN VIII) from the cranial cavity to the middle ear
It also transmits blood vessels and the facial nerve (CN VII)

Question 17

Neural pathways
of hearing

Answer 17

Fibres of cochlear division of CN VIII
pass to cochlear nucleus of medulla
Synapse with neurons that pass to the
inferior colliculi of midbrain
These neurons project to the thalamus
This sends axons to auditory cortex of
temporal lobe: perceived as sound

Question 18

Hearing loss

Answer 18

Maybe either conductive or sensorineural
Conductive hearing loss results from problems in the
external and middle ears:
external auditory meatus (stenosis),
tympanic membrane (perforation)
tympanic cavity (fluid retention)
auditory ossicles (inflammation, scarring)
Sensorineural hearing loss results from problems with the
inner ear or neurological pathway:
cochlea (e.g. cochlear ossificans)
cochlear nerve
cortical connections
brain stem

Question 19

Semicircular canals

Answer 19

There are three semicircular canals: anterior, posterior & lateralActually describe 2
/3
of a circle
Cross sectional diameter about 1.5mm except at the
bony ampulla
Lie postero-superior and open in to the vestibule

At right angles to each other
Therefore one in each plane
Important for balance
Semicircular ducts inside each canal

Question 20

Semicircular ducts

Answer 20

Semicircular ducts communicate with the utricle
Each have an ampulla at one end

Ampullae contain a sensory area, the ampullary crest
Crests contain hair cells
Sense movement of endolymph caused by movements of the head in that plane

Question 21

Semicircular ducts: ampullae

Answer 21

Three ducts, one in each plane:
* Anterior detects rotational movement in the sagittal plane
* Posterior detects rotational movement in the coronal plane
* Lateral detects rotational movement in the transverse plane

Inertia of the endolymph causes hairs in cupula to bend

Question 22

Vestibule of the bony labyrinth

Answer 22

An oval chamber about 5mm long
Contains utricle and saccule of membranous labyrinth Lateral wall has an oval window
Baseplate of the stapes sits in the oval window

Communicates with:
The cochlear anteriorly
The semicircular canals posteriorly
Posterior cranial fossa via the aqueduct of the vestibule

Question 23

Vestibular labyrinth

Answer 23

Comprised of two sacs, the utricle and saccule
Joined by utriosaccular duct

Utricle is continuous with the semicircular ducts
Saccule is continuous with the cochlear duct via the ductus
reuniens
Both utricle and contain sensory epithelium - maculae

Question 24

Vestibular labyrinth: hair cells

Answer 24

Hair cells of maculae involved in equilibrium
Hair cells of maculae are innervated by vestibular division of the vestibulocochlear nerve (CN VIII)

Question 25

Vestibular labyrinth: maculae

Answer 25

Macula of the utricle is in its floor, parallel with the cranial baseMacula of the saccule is placed vertically against its medial
wall

SACCULE: detects vertical linear motion and tilting of the headout of the horizontal (transverse) plane
UTRICLE: detects horizontal linear motion (in the transverseplane) and tilting of the head out of the vertical plane

Question 26

Petrous part of temporal bone

Answer 26

This is talked about so motherfucking much pls look at it on complete anatomy