LIGN 113 - Outer Ear Anatomy

# The Anatomy of the Outer Ear

Will Styler - LIGN 113

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### Today's Plan

- Questions about the Reading?

- 'Transduction'

- Overview of the Structures of the Ear

- The Pinna

- The Ear Canal

- The Tympanic Membrane

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## Any questions?

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## 'Transduction'

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### 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*

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### We are surrounded by transducers

- Microphones

- Speakers

- Seismographs

- Thermometers

- What else?

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### 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!**

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### 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!

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## The Structures of the Ear

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### Three 'Zones' that most folks discuss

- The 'Outer Ear'

- The 'Middle Ear'

- The 'Inner Ear'

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### The Outer Ear

- The Pinna, Ear Canal, and Typmpanic Membrane

- Offers protection of the sensitive bits

- Provides Amplification

- Helps with localization

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### 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

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### 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

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

- Outer, middle, inner

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

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# The Outer Ear

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## The Pinna

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### 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

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### What does the Pinna protect against?

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### Ear canal protection

- Against pressure seals

- Against rain and water

- Against wind

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### How does the Pinna direct hearing?

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### Localization of Sound

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### The human pinna is fixed

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### Not all animals have a fixed pinna

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### Not all animals have a fixed pinna

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### The Pinna still provides some location cues

- Front vs. Back

- Up vs down

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### Pinna Amplification

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### The Pinna Amplifies sounds!

- Amplification is strongest around 3000Hz

- Where lots of speech is!

- This is our first *distortion* step in hearing

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### Some people pour rum and pineapple juice into the outer ear

- ... to make a pinna colada

- 😂😂😂😂😂

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

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## The Ear Canal

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### 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

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### Ear Canal Subareas

- Cartilaginous portion contains hairs and cerumen glands

- Bony portion has none

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### Ear Canal (with surrounding anatomy)

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### The Ear Canal is mostly protective

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### 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

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### 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

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### Cerumen Impaction

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### 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'**

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### 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

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### Cerumen ≠ Saruman

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

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### The Tympanic Membrane ('eardrum')

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### 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*

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

- ... so don't (tym)panic

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### The Tympanic Membrane forms a seal!

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### 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!

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### 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!

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### The TM captures sound!

- It moves with air pressure variations

- ... and transduces them into bone movement

- More on those bones next time!

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### So that's the Outer Ear

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### 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!

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### Next time, we'll journey beyond the Tympanic Membrane

- ... and into...

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## The Middle Ear!

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<huge>Thank you!</huge>