SHS 221 Module 5: Inner Ear

Transduction

Converting mechanical vibrations into neural impulses

Vestibule, semicircular canals, and cochlea

What are the three main structures of the inner ear?

A fluid-filled, coiled structure involved in hearing

What is the cochlea?

2.5 turns

How many turns does the cochlea have?

Approximately 3.5 cm

How long is the cochlea?

Modiolus

The porous, perforated bony core of the cochlea

Blood vessels and nerve fibers leading from the hair cells

What does the modiolus contain?

Scala vestibuli, scala media, and scala tympani

What are the three cochlear compartments?

Perilymph

What fluid is found in the scala vestibuli?

Perilymph

What fluid is found in the scala tympani?

Endolymph

What fluid is found in the scala media?

High potassium and low sodium and calcium

What is the ionic composition of endolymph?

Ressiner’s membrane

What separates the scala media and scala vestibuli?

The basilar membrane

What separates the scala media and scala tympani?

Function of the stria vascularis

Produces and maintains the potassium ion balance in the endolymph

Stria vascularis

A highly vascularized layer along the lateral wall of the scala media

Helicotrema

The opening at the cochlear apex connecting the scala vestibuli and scala tympani

Function of cochlear fluids

Transmit sound vibrations and help create the electrical energy needed for hearing

Function of the basilar membrane

Separates the scala media and scala tympani and responds to sound vibrations

The Organ of Corti

What structure sits above the basilar membrane?

Function of the Organ of Corti

Converts mechanical energy from the middle ear into electrochemical neural information

Inner hair cells, outer hair cells, and supporting cells

What type of cells are found in the Organ of Corti?

The wide, less stiff apical region

Which part of the basilar membrane responds best to low-frequency sounds?

The narrow, stiffer basal region

Which part of the basilar membrane responds best to high-frequency sounds?

Three rows

How many rows of outer hair cells are there?

12,000

Approximately how many outer hair cells are in each ear?

Yes, they show motility

Do outer hair cells change shape when stimulated?

Prestin

What protein allows outer hair cells to move?

Cochlear amplifier

The outer hair cell system that boosts quiet sounds and sharpens frequency tuning

Otoacoustic emissions (OAEs)

Low-intensity sounds produced as a byproduct of outer hair cell activity

With a microphone placed in the ear canal

How are OAEs measured?

They are present when outer hair cells are healthy

What do OAEs indicate?

Ototoxic drugs

What can damage outer hair cells?

Efferent nerve fibers

Which nerve fibers innervate outer hair cells?

One row

How many rows of inner hair cells are there?

3,500

Approximately how many inner hair cells are in each ear?

No, they do not change shape upon stimulation

Are inner hair cells motile?

Approximately 10-30

How many afferent auditory nerve fibers innervate each inner hair cell?

Main function of inner hair cells

Convert basilar membrane movement into neural activity

Inner hair cells

Which hair cells primarily detect sound and send information to the auditory nerve

Inner hair cells signal the auditory nerve; outer hair cells amplify vibrations and sharpen frequency tuning

What is the main difference between inner and outer hair cells?

Inner hair cells

Which hair cells receive many afferent nerve fibers?

Efferent nerve fibers

Which nerve fibers innervate outer hair cells?

Outer hair cells amplify the vibration, and inner hair cells detect it and signal the nerve

How does the cochlea process soft sounds?

Sound moves the basilar membrane enough for inner hair cells to detect it with little help from outer hair cells

How does the cochlea process loud sounds?

Carries impulses from the inner ear to the brain

What does the auditory nerve do?

Auditory processing can be negatively affected

What happens if the auditory nerve is damaged or does not function properly?

Auditory nerve synchrony

Auditory nerve fibers working together in a coordinated way

It is essential for accurately encoding auditory information

Why is auditory nerve synchrony important?

Nerve fibers working together

What is normal neural synchrony?

Nerve fibers are not working together properly

What is severe neural dyssynchrony?

A strong neural pathway

What type of pathway is emphasized in the neural central auditory pathway slides?