Anatomy & Physiology of Hearing

Question 1

Parts of the outer ear

Answer 1

• auricle/ pinna

- external auditory canal

Question 2

auricle/pinna

Answer 2

• the outer most part of the ear made up of mostly cartilage
• funnels sound into ear to help localize sound

Question 3

External Auditory Canal

Answer 3

• aka external auditory meatus
• muscular tube made up of mostly cartilage
• resonates sounds that enter- frequency 2500 Hz
• contains the cells that produce cerumen that lubricates and cleans canal

Question 4

Parts of the middle ear

Answer 4

• TM- tympanic membrane
• Ossicular chain
• Eustachian tube

Question 5

Middle Ear

Answer 5

T-Air filled cavity separated from the outer ear by the TM

Question 6

Tympanic Membrane

Answer 6

• elastic, thin, cone shaped
• vibrates in response to sound pressure
• whole thing responds to low freqs but only a certain portion responds to high freq
• EASILY DAMAGED, may repair spontaneously but repeated damage will decrease mobility

Question 7

Ossicular Chain

Answer 7

• Suspended in the air by muscles
• smallest bones in the body
• malleus, incus, stapes
• transmits sound with no distortion
• amplifies sound by approx 30 dB before transmitting it into the inner ear fluid

Question 8

Malleus

Answer 8

• largest of 3 ear bones
• first in the chain
• attached to the TM and vibrations are transmitted to malleus from TM

Question 9

Incus

Answer 9

second bone in the ossicular chain

Question 10

Stapes

Answer 10

last bone if the ossicular chain that is attached to the oval window

Question 11

Muscles of the Acoustic Reflex

Answer 11

Tensor Tympani and Stapedius

Question 12

Tensor Tympani

Answer 12

• innervated by cranial nerve V (trigeminal)

- tenses the TM to reduce vibrations (sound intensity)

Question 13

Stapedius

Answer 13

• innervated by the cranial nerve VII (facial)
• smallest muscle in the body
• stiffens the ossicular chain to reduce vibrations (sound intensity)

Question 14

Eustachian Tube

Answer 14

• connect the middle ear with the nasopharynx. Goes from anterior middle ear to the posterior wall of the nasopharynx

Question 15

Function of Eustachian Tube

Answer 15

• helps to maintain equal air pressure within and outside the middle ear
• yawning or swallowing can open the nasopharyngeal side by letting in fresh air this ventilates the middle ear

Question 16

Eustachian tube opening

Answer 16

the tensor veli palatini and the levator veli palatini

Question 17

Eustachian tube and PEDS population

Answer 17

• eustachian tube is flatter in infants so ir allows fluid to spread into the middle ear from the nasoparynx
• infants with cleft palate frequesntly have eustachian tube dysfunction which makes them vulnerable to eharing loss

Question 18

Inner ear

Answer 18

• most complex part of the ear
• begins at the oval window (on the other side of the stapes footplate)
• The oval window is a small hole in the temporal bone- the stapes footplate moves in and out of the oval window to to send mechanical vibrations of sound

Question 19

Labyrinths

Answer 19

Interconnecting tunnels filled with perilymph

Question 20

Two major structures of the inner ear

Answer 20

• vestibular system with 3 semi-circular canals responsible for equilibrium
• cochlea the snail shaped coiled tunnel- filled with endolymph

Question 21

Basilar membrane

Answer 21

the floor of the cochlear duct which contains the organ or corti

Question 22

Organ of Corti

Answer 22

• bathed in endolymph snd contains many thousand (approx. 15,000 per ear) hair cells (cilia)
• hair cells on the OOC respond to the vibrations and cause a shearing action
• turns mechanical energy is changed to electrical energy which communicates with the nerve endings
• this is important because nerve endings will not understand mechanical vibrations

Question 23

Reissner’s membrane

Answer 23

transmits movements to the endolymph from the perilymph and the stapes footplate

Question 24

Basilar membrane

Answer 24

• movement transmitted here from the endolymph
  -organized by frequency:
  ~low frequency sounds stimulate the apex
  ~high frequency sounds stimulate the base
• that stimulation sets off waves in the fluid that moves the membrane

Question 25

Cranial Nerve VIII

Answer 25

Acoustic Nerve (aka vestibulocochlear nerve)- picks up the neural impulses created by the movement of the hair cells in the cochlea (cilia on the organ of Corti)
-bundle of neurons with two branches: vestibular and auditory/acoustic

Question 26

CN-VIII vestibular

Answer 26

concerned with body equilibrium and balance

Question 27

CN-VII auditory/acoustic

Answer 27

concerned supplies many hair cells of the cochlea & conducts electrical sound impulses from the cochlea to the brain

Question 28

Internal Auditory Meatus

Answer 28

-where the auditory nerve exits the inner ear

Question 29

Cerebellopontine Angle

Answer 29

• space filled with spinal fluid

- where the suditory nerve exits the temporal bone through the EAM

Question 30

Sound localization

Answer 30

• at the brainstem level most of the auditory nerve fibers from one ear decussate (cross over) the the other side (contralateral pathways)
• some continue of the same side forming ipsilateral pathways which helps with sound localization

Question 31

Parts of the brain

Answer 31

From the brainstem–> acoustic nerve fibers project sound to the temporal lobe–> temporal lobe contains the primary auditory area (responsible for receiving and interpreting sound stimuli)