Nsp Week 3: Auditory System (Blair)

Front 1

What determines the pitch and loudness of the sound you hear?

Back 1

Frequency of sound waves --> pitch
Amplitude of sound waves --> loudness

Front 2

Our ears are most sensitive to what range of frequencies?

Back 2

1 - 5 kHz
(frequencies used in speech)

Front 3

Which ear structure converts sound waves to mechanical dispacements?

Back 3

Tympanic membrane (eardrum)

Front 4

List the components of the outer ear

Back 4

1. Pinna (auricle)
2. External auditory canal
3. Tympanic membrane

Front 5

The middle ear consists of which 3 small bones?

Back 5

1. Malleus (hammer)
2. Incus (anvil)
3. Stapes (stirrup)

Front 6

What is the malleus and stapes attached to?

Back 6

Malleus is attached to the tympanic membrane
Stapes is attached to the oval window

Front 7

How much does the middle ear amplify the sound signal?
How does this amplification occur?

Back 7

By about 20 times

*Sound force that is displaced over a larger surface area (tympanic membrane) is concentrated on a smaller surface area (oval window)

Front 8

Which tube connects the middle ear to the pharyx and maintains the middle ear at atmospheric temperature?

Back 8

Auditory (eustachian) tube

Front 9

What are the two muscles of the inner ear and which cranial nerves innervate them?

Back 9

1. Tensor tympani (CN V)
2. Stapedius (CN VII)

Front 10

Which muscles are reflexively contracted during loud sounds, and how do they confer protection?
What is the threshold for activating this reflex?

Back 10

1. Tensor tympani --> pulls on malleus to reduce movement of tympanic membrane
2. Stapedius --> pulls on stapes to reduce movement of oval window

*~85 dB

Front 11

What are the 2 functions of the tensor tympani and stapedius muscles?

Back 11

1. Protection against loud sounds
2. Attenuate sounds (filter out ambient low tones)

Front 12

What are the two compenents of the labyrinth and what are they filled with?

Back 12

Bony labyrinth --> perilymph (fluid)
Membranous labyrinth --> endolymph

Front 13

The cochlea forms a bony spiral around a central core of bone called the _______.

Back 13

Modiolus

Front 14

What are the 3 divisions of space in the cochlea?

Which structures separate these areas?

Back 14

1. Scala vestibuli
---Reissner's membrane---
2. Scala media
---Basilar membrane---
3. Scala tympani

Front 15

Which structure divides the perilymph-containing space into 2 components?

Back 15

Osseous spiral lamina

Front 16

What is the name of the small foramen at the apex of the cochlea?

Back 16

Helicotrema

Front 17

What structures sit on the basilar membrane?

Back 17

Organ of Corti
(neural components for hearing)

Front 18

Where are the stria vascularis located?

Back 18

On the outer wall of the scala media

Front 19

Which fluids are found in which compartments of the cochlea? Describe the ionic concentrations of these fluids.

Back 19

Scala vestibuli and tympani --> perilymph (high Na+, low K+)
Scala media --> endolymph (high K+, low Na+)

Front 20

Where is sound converted from mechanical displacement to hydraulic displacement?

Back 20

From the stapes/oval window --> movement of the perilymph

Front 21

How is sound wave converted from hydraulic displacement to neuronal action potentials?

Back 21

Movement of fluid displaces the basilar membrane, which contains the organ of Corti

Front 22

Describe the different frequencies of wave lengths that hit the base of the basilar membrane and the apex

Back 22

Base (stiff and narrow)--> high frequencies (shorter wavelengths)

Apex (floppy and wide)--> low frequencies (longer wavelengths)

Front 23

Which structure isolates the hair cells from the endolymph within the organ of Corti?

Back 23

Reticular lamina

Front 24

What structure is found at the end of hair cells, and which hair cells attach to the tectorial membrane?

Back 24

Stereocilia are at the ends of the hair cells, which project through the reticular membrane

Outer hair cells attach to tectorial membrane
Inner hair cells do NOT attach to the tectorial membrane

Front 25

The stereocilial project into the endolymph of which area?

Back 25

Scala media

Front 26

Describe the fluid movement is converted to neural action potentials in the inner ear.

Back 26

Perilymph moves--> movement of Reissner's membrane --> movement of endolymph --> movement of basilar membrane --> shear movement of stereocilia with respect to tectorial membrane

*Bending of the stereocilia in one direction causes depolarization, while bending in the opposite direction causes hyperpolarization

Front 27

Describe how K+ channels are opened and closed in stereocilia

Back 27

If the stereocilia move towards the tallest stereocilia, the tension on the tip lengths is enhanced, and more K+ open
If stereocilia move towards shortest sterocilia, there is less tension--> K+ channels close

*Mechanical mechanism

Front 28

What happens when the hair cells are depolarized by K+?

Back 28

Voltage-gated Ca2+ channesl open--> neurotransmitter (glutamate) is released onto sensory neurons

Front 29

Describe the unique mechanism in which hair cells repolarize?

Back 29

1. When K+ enters the cell from the endolymph, voltage-sensitive K+ channels at the base of the hair cell open
2. Ca2+-dependent K+ channels open when Ca2+ enters the cell

Front 30

Where are the cell bodies of the auditory sensory bipolar neurons located?

Back 30

Spiral ganglion

Front 31

How many rows do inner and outer hair cells form?

Back 31

Inner hair cells --> one row
Outer hair cells --> three rows

Front 32

Do the majority of sensory neurons innervate inner or outer hair cells?

Back 32

Inner (95%)

Front 33

Which hair cells do Type I and Type II axons innervate?

Back 33

Type I --> inner hair cells
Type II --> outer hair cells

Front 34

Which hair cells amplify sound, and how is this done?

Back 34

Outer hair cells = "cochlear amplifier"

*They enhance the movement of the basilar membrane by contracting/relaxing to change the sensitivity of the basilar membrane in response to sound.

Front 35

Do otoxic drugs damage/destroy outer or inner hair cells or both?

Give 5 examples of ototoxic drugs

Back 35

Outer hair cells

1. Aspirin
2. Aminoglycoside antibiotics
3. Quinine
4. Diuretics (some)

Front 36

Describe how frequency and loudness is coded through neurons

Back 36

Frequency --> encoded by which neurons are excited
Loudness --> encoded by the FREQUENCY of action potentials and the NUMBER of neurons activated by the sound.

Front 37

Describe the pathway that is important in horizontal sound localization

Back 37

Ventral cochlear nucleus --> Superior olivary nucleus --> inferior colliculus (via lateral meniscus) --> Medial geniculate nucleus --> Primary auditory cortex

Front 38

What is the primary nucleus where horizontal sound location occurs?

Back 38

Superior olivary nucleus

Front 39

What are the two coincidence detectors and what do they detect?

Back 39

"George" --> interprets sound as coming from the right or left, depending on the time delay of neuronal signals from each ear (>0.6 ms)

"Emily"--> Interprets sound coming from midline (<0.1ms signal delay between ears)

Front 40

Describe how the superior olivary nucleus interprets interaural intensity differences as sound coming from one side or the other?

Back 40

Each superior olivary nucleus receives excitatory input from the ipsilateral ear, and inhibitory input from the contralateral ear.

Front 41

Which structures are involved in vertical sound localization?

Back 41

1. Pinna
2. Concha

*Shape of the outer ear transmits higher frequencies in a sound if the sound is elevated above ear level

Front 42

Which structure is an integrative center that combines sound information from both ears, and creates an "auditory space map?"

Back 42

Inferior colliculus

Front 43

Where is the primary auditory cortex located, and how is it arranged?

Back 43

Superior portion of temporal lobe in the transverse temporal gyrus (Heschl's gyrus)

*Neurons have a tonotopic arrangement