Today's Plan

• Questions about the Reading?

• 'Transduction'

• Overview of the Structures of the Ear

• The Pinna

• The Ear Canal

• The Tympanic Membrane

Any questions?

'Transduction'

We're going to talk a lot about 'transduction'

• Transduction is a process by which one kind of signal, energy, or stimulus is converted into another form

We are surrounded by transducers

• Microphones

• Speakers

• Seismographs

• Thermometers

• What else?

The auditory system is all about transduction!

• Transducing air pressure to mechanical pressure

• Transducing mechanical movements to neural signals

• Transducing neural signals into a model of the world

• Thinking about transduction will help you all quarter!

No transduction is perfect!

• Energy is often lost

• The signal is often distorted subtly

• Sometimes parts of the signal are discarded entirely

• "What is being lost?" is another valuable question to ask!

The Structures of the Ear

Three 'Zones' that most folks discuss

• The 'Outer Ear'

• The 'Middle Ear'

• The 'Inner Ear'

The Outer Ear

• The Pinna, Ear Canal, and Typmpanic Membrane

• Offers protection of the sensitive bits

• Provides Amplification

• Helps with localization

The Middle Ear

• The Ossicular Chain, the Eustachian tube, and the surrounding space

• Provides transduction from air to mechanical movement

• Provides pressure regulation

• Provides limited protection via the Acoustic Reflexes

  • ... and dislocateable bones

Functions of the Inner Ear

• The Semicircular Canals, Cochlea, and Auditory Nerve

• Provides perception of orientation and motion

  • Via the Vestibular System

• Provides transduction from physical vibration to neural signals

  • Via the Cochlea and auditory nerve

We're going to go through the system in that order

• Outer, middle, inner

• ... and today, we're starting with the outer ear!

The Outer Ear

The Pinna

The Pinna

• Also called the Auricle

• The external apparatus of the ear

• Serves to protect the ear canal

• Helps with localization of sound

• Helps amplify sounds

What does the Pinna protect against?

Ear canal protection

• Against pressure seals

• Against rain and water

• Against wind

How does the Pinna direct hearing?

Localization of Sound

The human pinna is fixed

Not all animals have a fixed pinna

Not all animals have a fixed pinna

The Pinna still provides some location cues

• Front vs. Back

• Up vs down

Pinna Amplification

The Pinna Amplifies sounds!

• Amplification is strongest around 3000Hz

  • Where lots of speech is!

• This is our first distortion step in hearing

Some people pour rum and pineapple juice into the outer ear

• ... to make a pinna colada

• 😂😂😂😂😂

Once sound leaves the pinna, it goes into...

The Ear Canal

The Ear Canal

• A long tube for air to travel into the skull

• Contains hairs, cerumen glands

• Around 1" long, 0.25" in diameter in adults

Ear Canal Subareas

• Cartilaginous portion contains hairs and cerumen glands

• Bony portion has none

Ear Canal (with surrounding anatomy)

The Ear Canal is mostly protective

Cerumen (Earwax)

• Cerumen lubricates, cleans, and protects the ear canal

  • Also helps prevent some infections and fungal growth

• Naturally 'pumped' out of the ear with chewing and jaw movement

  • Let's check that!

• Should exit the ear naturally at the pinna

Cerumen types

• People produce two different types of cerumen!

• The ABCC11 gene controls your earwax type

• Wet wax (AA Genotype) is common in European and African folks

  • Apparently also linked to body odor issues...

• Dry-Flaky wax (GA/GG) is common in East Asian and Indigenous American folks

  • Comes out more readily

Cerumen Impaction

Cerumen impaction is a common cause of hearing loss

• ... and it's really easy to treat!

• There are even at-home kits

• Do not stick things into your ears to 'dig it out'

Ear Candling is... not supported by science

• Not enough suction

• Nothing is removed

• There are no proven health benefits

• At best, you're getting ripped off

Cerumen ≠ Saruman

(Although, actually, both can be removed by flushing the area with water...)

The Tympanic Membrane ('eardrum')

The Tympanic Membrane

• Blocks water and debris from entering the middle ear

• Partially transparent, made up of layers

• Captures sound vibrations, transmitting them into the ossicular chain

From here out, 'TM' unmarked means 'Tympanic Membrane'

• ... so don't (tym)panic

The Tympanic Membrane forms a seal!

Why is this seal a Good Idea?

• Stops things from going into the middle ear

• Allows water to fill the outer ear without filling the middle ear

• Drums with holes have problems...

• One other issue we'll discuss later!

The seal is not required for hearing

• People can still hear with holes or perforations

• Causes some troubles, but can be done therapeutically

• It can be rebuilt!

• ... but generally, you want that seal!

The TM captures sound!

• It moves with air pressure variations

• ... and transduces them into bone movement

• More on those bones next time!

So that's the Outer Ear

Wrapping Up

• The Auditory system is all about transduction

• The Ear is divided into Outer, Middle, and Inner areas

  • Eareas?

• The Outer Ear has the Pinna, Ear Canal, and TM

• ... and combined, they protect, amplify and transmit!

Next time, we'll journey beyond the Tympanic Membrane

• ... and into...

The Middle Ear!

Thank you!