Audition

Question 1

Describe the destruction of the ear

Answer 1

Outer - pinna 
(tympanic membrane)
Middle - ossicles, eustachian tube
(oval window)
Inner - cochlear, vestibular apparatus

Question 2

What are the first stages of the auditory pathway?

Answer 2

• tympanic membrane
• ossicles
• oval membrane
• fluid in the cochlea
• sensory neurones

Question 3

What are the 3 ossicles?

What is their function?

Answer 3

malleus, incus, stapes

amplify mechanical wave x20

Question 4

What is the function of the Eustachian tube?

Answer 4

• allows secretions of middle ear to empty

- allow equalisation of air pressure

Question 5

Which patients are more sucesptible to middle ear infections?

Answer 5

children - short eustachian tube –> reflux

patients with cleft palate

Question 6

What are the 3 functions if the attenuation reflex?

Answer 6

Functions:

• adaptation
• protection
• help discern high frequency sounds

Question 7

What is the attenuation reflex?

What muscles are involved?

Answer 7

Loud sound –> muscle contraction –> conduction in middle ear is reduced

• tensor tympani muscle = pulls handle of malleus medially, tensing the tympanic membrane
• stapedius muscle = pulls stapes posteriorly and tilts base in the oval window, tightening the annular ligament and reducing the oscillatory range, also can prevent movement of stapes

Question 8

What are the 3 functions of the attenuation reflex?

Answer 8

adaptation (to loud sounds)
protection (prevent tympanic rupture)
help discern high frequency sounds (minor)

Question 9

What are the 3 tubes of the inner ear?

Where is the organ of corti and the sensory cells?

Answer 9

• scala vestibuli
• scala media (organ of corti, sensory cells)
• scala tympani

Question 10

Describe how the inner ear carries out its function

Answer 10

• stapes pushes against oval window
• fluid moves in opposite directions in two tubes as vestibule and tympani communicate
• basilar membrane vibrates up and down
• this moves the organ of corti

Question 11

Describe the response of the basilar membrane to sound

Answer 11

High frequency sounds –> base is narrow and stiff
Low frequency sounds –> apex is wide and floppy
Different frequencies produce maximum amplitude at different places along length of basilar membrane

Question 12

Describe the structure and function of the organ of Corti

Answer 12

• moves when the basilar membrane moves as it is sitting on it
• tectorial membrane slides on stereocilia of the inner and outer hair cells to produce movements which are translated to action potentials

Question 13

How does the movement of hair cells produce action potentials?

Answer 13

• mechanically gated potassium channels linked the stereocilia together
• when the hairs move apart the channels open, when the hairs move together the channels close
• ## allowing/disallowing K+ to depolarise the hair cell

Question 14

What happens following entry of K+ into the hair cell?

Answer 14

• depolarisation of the cell
• opens voltage gated potassium cells
• Ca2+ entry
• vesicles containing excitatory GLUTAMATE fuse with membrane
• NT release onto spiral ganglion neurite

Question 15

What is the fluid in the organ of corti called?

Answer 15

endolymph

Question 16

What are the structural and functional differences between inner and outer hair cells?

Answer 16

Outer hair cells 
- modulatory signals in signal, integration 
- one neurone for several cells 
- convergent signals 
Inner hair cells 
- conscious sensory input 
- many neurones per cell 
- divergent signal

Question 17

What is meant by amplification by outer hair cells?

Answer 17

• motor proteins expand/contract in outer hair cells
• contraction –> steriocilia tug tectorial membrane –> moves inner hair cilia
  This acts of amplify low level sound

Question 18

What is the hair cell receptor potential a reflection of?

Answer 18

sound pressure waves

- graphs look identical

Question 19

What does sound intensity change?

Answer 19

• number of cells firing

- firing rate of these cells

Question 20

What is tonotopy?

Answer 20

• the organisation of sound frequencies
• different frequencies preserves throughout tracts, from basilar membrane, to auditory nerve, to cochlear nucleus
• high freqeuncies detected at the base of the basilar membrane
• low frequencies detected at the apex of the basilar membrane

Question 21

What phase locking?

Answer 21

• allows frequency discrimination
• neurones fire in synchrony with phase of a stimulus
• doesn’t work at high frequencies as AP is a single length

Question 22

Is phase locking, tonotopy or both, involved in the identification of the following:

• very low frequency sounds
• intermediate frequency sounds
• high frequency sounds

Answer 22

• very low frequency sounds –> phase locking
• intermediate frequency sounds –> both
• high frequency sounds –> tonotopy

Question 23

How is sounds localisation achieved?

Answer 23

• interaural delay allows us to identify where the sound comes from
• the same sound hits the ipsilateral cortex earlier than the other ear
• inner ear bisons go on ipsi and contralateral auditory nerve
• contralateral is longer - delay
• presence of sound shadows produces this difference

Question 24

Describe the cochlear nerve and auditory pathway

Answer 24

cochlea –> spiral ganglion –> ventral/dorsal cochlear nucleus –> inferior colliculus –> medial genticulate nucleus –> auditory cortex
- some cross and synapse in the superior olive

Question 25

Where is the auditory cortex located?

Answer 25

- lateral temporal lobe - tonotopic organisation - 500Hz --> 16,000Hz

Question 26

What are the other projection of the auditory pathway?

Answer 26

- inferior colliculus = MGN and superior colliculus: integration of auditory and visual signals - brainstem neurones = innervates outer hair cells, regulates sound amplification - auditory cortex = MGN and inferior colliculus

Question 27

What are the cortical connections with the auditory cortex? What are they responsible for?

Answer 27

- interconnections between regions - Broca's area, Wernicke's area, primary motor area, angular gyrus, visual areas - learn to speak and interpret written language

Question 28

Give examples of conductive deafness

Answer 28

- obstruction of the auditory canal - otosclerosis (sclerotic degeneration between 3x bones) - ruptured eardrum - middle ear infection - head trauma

Question 29

What are the genetic causes of nerve deafness?

Answer 29

- >40 greens, 300 syndromes with related hearing loss - recessive, dominant or X linked --> structure or metabolism of the inner ear - some genetic causes give rise to a late onset hearing loss

Question 30

What are the acquired causes of nerve deafness associated with noise?

Answer 30

- cochlear damage - permanent or temporary - environmental or occupational noise - acoustic trauma

Question 31

What are the disease that cause acquired nerve deafness?

Answer 31

- inflammation - DMII - iodine deficiency, hypothyroidism - tumours - meningitis viruses e.g. AIDS, mumps, measles, herpes zoster oticus - trauma - stroke (transient/permanent)

Question 32

What are the some of the iatrogenic causes of acquired nerve deafness?

Answer 32

Ototoxic and neurotoxic drugs - aminoglycosides (partial recovery) - antibiotic, mitochondrial mutation makes you more susceptible - methotrexate (not recovered) - various other medication - reversible hearing loss

Question 33

What perinatal conditions can cause acquired nerve deafness?

Answer 33

- premature birth - foetal alcohol syndrome - syphilis

Question 34

What is the clinical application of amplification by outer hair cells?>

Answer 34

Tinnitus - dysfunction of outer hair cell s - motor neurones contract unnecessarily - tugs on tectorial membrane - inner hair cells detect movement