8.3 middle and inner ear

What part of the body does Lecture 8-3 focus on?

The ear specifically the middle and inner ear

What is sound in the context of hearing?

Vibrations of air molecules

Which part of the ear collects sound vibrations from the air?

The outer ear

What is the pinna?

The outer visible part of the ear that collects sound

What is the function of the pinna?

It acts as a sound concentrator

What does the outer ear do overall?

It collects sound vibrations from air molecules

What is the main function of the middle ear?

To amplify and transmit sound

What is the main function of the inner ear?

To collect and process sound

What does the outer ear do during sound transmission?

It concentrates and funnels sound

Where does the outer ear funnel sound?

Down the external auditory canal

What is the external auditory canal?

A passage that carries sound toward the eardrum

What is another name for the eardrum?

The tympanic membrane

What happens to the tympanic membrane when sound reaches it?

It vibrates

What causes the middle ear bones to vibrate?

Vibration of the tympanic membrane

Which structure sends vibrations into the inner ear?

The oval window

What are the three bones of the middle ear?

Malleus incus and stapes

What is the malleus also called?

The hammer

What is the incus also called?

The anvil

What is the stapes also called?

The stirrup

Which middle ear bone sits on the oval window?

The stapes

What connects the middle ear to the inner ear?

The oval window

What happens when the middle ear bones vibrate?

Sound is transmitted into the inner ear

What can damage to the middle ear bones cause?

Deafness

What are two causes of damage to middle ear bones?

Fracture and infection

What is the cochlear duct?

A duct in the inner ear involved in hearing

What is the tympanic duct?

A duct involved in sound transmission in the inner ear

What is the round window?

A membrane that moves in response to pressure changes in the cochlea

What nerve carries hearing signals to the brain?

The cochlear branch of the VIII nerve

What is the VIII nerve also known as?

The vestibulocochlear nerve

Where does the cochlear branch of the VIII nerve send signals?

To the brain

What medical devices are used for the ear?

Middle ear implants and cochlear implants

What must middle ear implants fit?

The middle ear

Why must middle ear implants be reasonably tough?

To withstand mechanical forces

Why must middle ear implants have high density?

To transmit sound effectively

What is the purpose of cochlear implants?

To restore hearing by converting sound to electrical signals

What must cochlear implants be able to do with sound?

Pick it up and convert it to an electrical signal

Why must cochlear implants know position along the inner ear?

To determine pitch

Where must the surface component of a cochlear implant attach?

To the skull

What is one treatment for middle ear deafness?

Reconnecting the tympanic membrane to the oval window or stapes

What material is typically used for middle ear prosthesis heads?

Hydroxyapatite

What materials are used for the shaft of middle ear prostheses?

Polymer or composite

Why is the shaft cut to fit?

To match the individual patient

What is HAPEX™

A composite material used in middle ear implants

Who developed HAPEX™?

Bonfield and colleagues at QMUL

When was HAPEX™ developed?

In the 1990s

What materials make up HAPEX™?

Hydroxyapatite and polyethylene

What is the volume percentage of hydroxyapatite in HAPEX™?

40 volume percent

What is the approximate weight percentage of hydroxyapatite in HAPEX™?

About 70 weight percent

Why is hydroxyapatite content optimized in HAPEX™?

To increase stiffness without brittleness

Why must the implant not be brittle?

To avoid fracture

Why is toughness important in middle ear implants?

So they can be carved to fit the patient

What design solution is used in improved implants?

A 100 percent hydroxyapatite head with a HAPEX shaft

What part contacts the tympanic membrane?

The hydroxyapatite head

What cells attach to hydroxyapatite particles?

Osteoblasts

What does osteoblast attachment lead to?

A mechanically strong interface

What scale is shown in the HAPEX images?

10 micrometres

What is shown in HAPEX in vitro studies?

Osteoblast attachment to HA particles

Who manufactured HAPEX™ middle ear implants?

Smith and Nephew ENT then Gyrus ENT

How many HAPEX™ implants have been used worldwide?

Over one million

What is known about long term effects of HAPEX™?

Only a few studies exist

What did Meijer et al 2003 show?

Good acceptance with no inflammatory response

What did SEM images show?

Retrieved implant after recurring infection

What happens when the oval window moves?

It compresses and extends fluid in the cochlear ducts

What do pressure changes in the cochlea cause?

Movement of the round window

What determines how far waves travel down the cochlear duct?

Wavelength which is the inverse of frequency

What auditory property does this enable?

Pitch detection

Which nerve detects signals from the cochlea?

The cochlear branch of the VIII nerve

What is the goal of treating inner ear deafness?

To transform sound waves into electrical signals

Which nerve is connected during treatment?

The cochlear branch of the VIII cranial nerve

How many auditory nerve fibres are typically present?

About 30000

How many nerve fibres do cochlear implants currently use?

Between 20 and 80

What is the trend in cochlear implant nerve usage?

The number is gradually increasing

What component picks up sound in cochlear implant systems?

An external microphone

What does the cochlear implant do with the sound?

Transduces it into the inner ear

What components are part of the signal chain?

External processor internal processor controlled current sources

What separates internal and external components?

The skin

What are the three main components of cochlear implants?

External receiver internal processor and electrode array

Where does the electrode array sit?

In the scala tympani of the cochlea

How are signals transmitted to electrodes?

Via a multiconductor cable

Which nerve ultimately receives the signal?

The VIII cranial nerve

What type of signal is applied in cochlear implants?

An electrical signal

Why must the signal be kept low?

To prevent nerve damage

What is the maximum safe charge density?

Less than 1.50 coulombs per square metre

Why must the detector be anchored?

To keep it stable on the skull

What is the success rate of cochlear implants?

Between 40 and 90 percent

What materials are used for cochlear implant electrodes?

Platinum or platinum 10 percent iridium

Why is platinum used?

For electrical conductivity

Why is platinum biocompatible?

It is the most noble and least reactive metal

Why is iridium added to platinum?

To increase strength

What material is used for bone bioactive components?

Commercially pure titanium

What is an example of a titanium implant?

The Brånemark prosthesis

What happens to titanium implants in bone?

They become ingrown into the skull bone

What is a concern regarding cochlear implant electrodes?

Lack of biocompatibility

What is a power related concern?

Heating of the inner ear

What mechanical concern exists?

External receiver becoming loose

What biological risk is present?

Risk of infection

What year did Zhang et al publish the composites reference?

2020

What section is referenced from Zhang et al?

Section 1.3.7

Who authored the cochlear prostheses reference?

F A Spelman

What year was the cochlear prostheses reference published?

2013