Pt10 Audition

Question 1

Describe the auditory system.

Answer 1

-hearing = 1 ear
-localization = 2 ears
>auditory system detects difference in time arrival/intensity

Question 2

What are sounds?

Answer 2

-pressure waves in air with frequencies & amplitudes
-alternating changes in pressure make sound after they strike the tympanic membrane
-auditory system perceives:
>freq of sounds = pitch
>amplitude of sound = loudness

Question 3

Describe amplitude.

Answer 3

-intensity
-decibels (dB)
-logarithmic scale
-express energy of sound relative to energy of standard reference sound (0 dB) = threshold for human hearing
-tolerable sound for human = 120 dB
>dogs bark = 108 dB

Question 4

Describe frequency.

Answer 4

-# of pressure oscillation cycles per unit time
-hertz (Hz)
-1 Hz = # of cycles per sec
-dogs detect 30 Hz (dog whistle = 20 Hz)
>humans 1000-4000 Hz

Question 5

What is the sensory receptor located in the inner ear?

Answer 5

Organ of corti
-hearing involves external, middle, & inner ear

Question 6

Describe the external ear.

Answer 6

-direct sound waves into ear canal
-separated from middle ear by tympanic membrane or eardrum
-pinna & ear canal

Question 7

Describe the middle ear.

Answer 7

-air filled cavity in temporal bone
-connected to nasopharynx by auditory tube
>Eustachian tube
>drains middle ear cavity
-contain ossicles = 3 bones

Question 8

Describe the ossicles of the middle ear.

Answer 8

1. Malleus
   -connected to ear drums
2. Incus
   -between malleus & stapes
3. Stapes
   -connected to oval/round window
   -membrane separation between middle & inner ear

Question 9

What is the function of ossicles.

Answer 9

-transfer vibration of eardrum to oval window
-avoid loss of vibration as sound wave is transferred
>from air filled outer ear to fluid filled inner ear
>to where sensory receptor is located
-decrease amplitude of sound waves protecting sensory cells

Question 10

Describe the inner ear.

Answer 10

-labyrinth
-sensory organs for auditory & vestibular systems
>vestibular system = detects acceleration & static tilt of head
-auditory portion of inner ear = cochlea
>spiral shaped
>fluid (peri lymph)
>contains organ of corti & hair cell receptors

Question 11

Describe the organ of corti.

Answer 11

-sensory hair cell = mechanoreceptors
-stereocilia connected by tips
>tip links attached to K channels
>open channels when bending of stereocilia pulls tip links apart
-stereocilia dont regenerate = hearing loss
>loud sounds & moving excessively destroy them

Question 12

What are the two membranes of the organ of corti?

Answer 12

1. Tectorial membrane
   -overlies sensory cells
   -anchored gel-coated ridge
2. Basilar membrane
   -floor of organ of corti
   -elastic
   -imp for sound transmission

Question 13

Describe the transduction of sound waves to AP.

Answer 13

1. Sound waves transmitted to inner ear = vibration to organ of corti
2. Vibration = bends cilia of hair cells & push against tectorial membrane
3. Bending of cilia = change in K+ of hair cell membrane
   -depol
   -K+ influx
   -Ca channel opens & release neurotransmitter ‘Glutamate’ = excitatory
   -AP in afferent cochlear nerves

Question 14

Describe what would happen if the bending of cilia happens in the OTHER direction.

Answer 14

-hyperpolarization
-K+ efflux
-glutamate not released
-AP not formed
-oscillatory pattern = cochlear microphonic potential
>release of glutamate = afferent nerves
>mirrors waveform of acoustic stimulus

Question 15

KNOW THE STEPS INVOLVED IN HEARING!

Answer 15

Question 16

Describe the encoding of sound.

Answer 16

-diff auditory hair cells activated by diff freq
-hair cells at basilar membrane (inner cells) = high freq
-hair cells at apex (outer cells) = low freq
-basilar membrane = sound freq analyzer
-spatial mapping of freq = tonotopic map
>tells where sound of diff freq are processed in brain

Question 17

Describe the ascending pathways.

Answer 17

-info transmitted from hair cell to cochlear nerve
-relay auditory impulse to cochlear nuclei in medulla
-axons ascend brainstem go to thalamus
-info processed in auditory CC