Auditory System 1: Structure & Function of the Middle & Inner Ear

Question 1

The auditory system is designed to transform _________ into ________ activity and ultimately to ______________ that are transmitted to the ______ to provide us with what we call hearing

Answer 1

• acoustic information
• mechanical
• electrochemical signals
• brain

Question 2

The auditory system is divided into sections:

Answer 2

1. outer ear
2. middle ear
3. inner ear
4. auditory nerve
5. central auditory pathways

Question 3

Outer Ear Structures:

Answer 3

• pinna
• external auditory meatus (canal)

Question 4

Middle Ear Structures:

Answer 4

• tympanic membrane
• tympanic cavity
• ossicular chain
  
  • with all associated muscles, ligaments, and tendons
• Eustacian tube

Question 5

Inner Ear Structures:

Answer 5

• oval window
• cochlea
• vestibular structures

Question 6

Describe the Pinna:

Answer 6

• Skin-covered cartilaginous structure
• Channels sound waves into ear canal
• Pits, tags, or other malformations of the pinna indicate issues with ear development that may affect hearing

Question 7

Describe the Ear Canal (External Auditory Meatus):

Answer 7

• From concha to eardrum
• Outer third is cartilaginous
• Inner two-thirds is bony
• The skin of the cartilaginous portion is thick and contains wax and oil glands:
  
  • lubricate the canal
  • protect the ear from foreign objects and debris
• Deep ear canal stimulation can cause referred sensation to vagus nerve making people cough

Question 8

What function do the pinna and ear canal both share?

Answer 8

provide a boost in high frequency sound intensity

Question 9

The handle of the malleus is directly attached to the _____________, which vibrates in response to ________________ funneled in by the external ear

Answer 9

• tympanic membrane
• sound pressure waves

Question 10

• The malleus is attached to the ______, which is attached to the ______.
• The footplate of the stapes directly contacts the ________ on the inner ear.

Answer 10

• incus; stapes
• oval window

Question 11

How do ossicles of the middle ear amplify sound vibration?

Answer 11

1. lever mechanism
2. area difference between the tympanic membrane & the footplate of the stapes

• This increases the force per unit area of the vibrations of the footplate of the stapes on the oval window of the inner ear

Question 12

Describe the protective feedback mechanism for loud sounds:

Answer 12

• dampens the vibration of the ossicles
• activation of two muscles:
  
  1. tensor tympani
     
     • attached to the handle of the malleus
  2. stapedius muscle
     
     • attached to the neck of the stapes
• When these muscles contract, vibration of these ossicles are reduced
• tensor typani = trigeminal nerve
• stapedius muscle = facial nerve

Question 13

What are the functions of the inner ear?

Answer 13

1. hearing
2. balance

Question 14

The inner ear is contained in the __________ of the temporal bone, and is encased in a bony structure called the ____________.

Answer 14

• petrous apex
• osseous or bony labyrinth

Question 15

Labyrinth:

3 Sections

Answer 15

• vestibule
• cochlea
• semicircular canals

Question 16

Desrcibe communication in the inner ear:

Answer 16

• initial point of communication:
  
  • at the oval window of the vestibule where the stapes footplate abuts the oval window membrane.
• Basal end of the cochlea:
  
  • round window membrane
  • which communicates with the middle ear space

Question 17

What is the modiolus?

Answer 17

• core of the cochlea
• highly porous bone
• allows passage of auditory nerve fibers as they travel from the internal auditory meatus to the hair cell synapse

Question 18

What is the osseous spiral lamina?

Answer 18

• extends from the modiolus
• coils around the center of the cochlea
• provides partial division of the upper and lower cochlear chambers:
  
  • scala vestibuli
  • scala tympani
• point of attachment for the basilar membrane
  
  • which encases the scala media

Question 19

The scala media bordered superiorly by ____________ and inferiorly by the ____________.

Answer 19

• Reissner’s membrane
• basilar membrane

Question 20

What can be found within the membranous labyrinth?

Answer 20

• sensory organ of hearing: organ of Corti
• lateral wall: stria vascularis

Question 21

Stria vascularis:

Answer 21

highly vascular tissue that is responsible for the metabolic environment of the scala media

Question 22

What does the organ of Corti consist of?

Answer 22

• 1 row of inner hair cells
• 3 rows of outer hair cells
• Cell bodies are surrounded by supporting cells

Question 23

Two Fluid Systems:

Answer 23

1. Perilymph
2. Endolymph

Question 24

Where is the perilymph found?

Answer 24

In the scala vestibuli and scala tympani:

• High [Na⁺]
• Low [K⁺]

Question 25

Where is the endolymph found?

Answer 25

Within the **scala media:** * Low [Na⁺] * High [K⁺]

Question 26

What does the **stria vascularis** do?

Answer 26

**Maintains** the ionic concentrations of the **endolymph**

Question 27

**Hair cells are contacted** by dendrites from **what type of neurons**?

Answer 27

**afferent bipolar neurons**

Question 28

**Many afferent fibers** synapse on the same \_\_\_\_\_\_\_\_\_\_, while **single afferent fibers branch** to synapse with several \_\_\_\_\_\_\_\_

Answer 28

* inner hair cell * outer hair cells

Question 29

**Efferent fibers** have cell bodies in the ________________ of the brainstem and synapse directly on __________ and on the afferent fibers of \_\_\_\_\_\_\_\_\_\_\_

Answer 29

* superior olivary complex * outer hair cells * inner hair cells

Question 30

Inner and outer hair cells transduce \_\_\_\_\_\_\_\_\_\_movement into an _________ signal to stimulate the \_\_\_\_\_\_\_\_\_\_.

Answer 30

* mechanical * electrochemical * auditory nerve

Question 31

What do the **motile properties** of the outer hair cells result in?

Answer 31

* increased basilar membrane motion * responsible for the **cochlear amplifier**

Question 32

**Stereocilia:**

Answer 32

* project through the reticular lamina * stiff hair-like structures that **deflect with mechanical disturbances** * connected to each other by filamentous **cross-links and tip-links** * move as a unit to ensure connection

Question 33

How is the **base of the cochlea** different compared to the **base of the apex**?

Answer 33

* start of **_tonotopic organization_** **At the base:** 1. the basilar membrane is **narrow and stiff** 2. where **high frequencies** are detected **At the apex:** 1. basilar membrane is **wide and floppy** 2. where **low frequencies** are detected

Question 34

Describe the **"traveling wave":**

Answer 34

1. **pressure waves:** * transmitted from **middle ear ⇒ cochlea ** 2. **cochlear fluid is displaced:** * causes **wave-like motion** along the **length of the basilar membrane**

Question 35

Hair cell function and synaptic stimulation:

Answer 35

1. Movement of the endolymph produces **deflection of the stereocilia** 2. Deflection of the stereocilia (in one direction) **opens ion channels** of stereocilia 3. **Positive ions flow inward**, through open channels, **depolarizing** the hair cell 4. Depolarization causes **neurotransmitter release,** stimulating the auditory nerve fibers.

Question 36

What are the 2 types of hearing loss? How are they diagnosed?

Answer 36

1. Conductive Hearing Loss * Occlusion or dysfunction of the **external and/or middle ear** 2. Sensorineural Hearing Loss: * Dysfunction of the **cochlea and/or auditory nerve** * By **comparing the threshold for detection** of an **airborne stimulus compared to a matched stimulus to the temporal bone**, the audiologist can distinguish hearing defects that originate in different parts of the ear