18, 19, 20 HEARING

Question 1

Give essential reasons for hearing

Answer 1

Education, learning, social engagement, mobility, health/ well being

Question 2

What percentage of people have hearing loss in NZ

Answer 2

13-18%

Question 3

Describe some etiological factors in hearing loss

Answer 3

Age
Noise exposure
Genetic
Trauma
Tumours
Anti cancer drugs, amino glycoside antibiotics

Question 4

Describe a common tumour that effects hearing

Answer 4

acoustic neuroma/ vestibular schwannoma
Non malignant.
Grows in vestibular cochlear nerve schwann cells

Question 5

Impact of hearing and hearing impairment

Answer 5

Poor speech
Language and cognitive impairment
Literacy, learning and employment impairment
Social isolation
Depression
Tinnitus

Question 6

Describe frequency

Answer 6

Number of sound waves per second.

Question 7

Describe amplitude

Answer 7

magnitude of the vibration considered as pressure or intensity

Question 8

How is amplitude measure

Answer 8

In decibels (sound pressure level) using logarithmic scale

Question 9

Describe features of the outer ear

Answer 9

Pinna are cartilaginous folds which amplifies and direct sound.
External auditory meatus is cartilage tubing whereby cerumen gland within it secrete earwax which is cleaning and antibacterial and reeks water/ traps debris.

Question 10

Describe the anatomy of middle ear

Answer 10

Air filled cavity.
Starts at tympanic membrane-
Contains three auditory ossicles; malleus, incus, stapes joined by synovial joints and ligaments.
Has eustachian tube for pressure equalisation and aeration.
Oval window at base of stapes.
Round window (pressure release) inferior to oval

Question 11

What are the two small inner ear muscle called, what nerve innervate them and what are their functions

Answer 11

The stapedius and the tensor tympani. Attached to the stapes and malleus and innervated by the facial and trigeminal nerves respectively. Muscle contractions initiated by loud noises stiffen the ossicular chain and protect the inner ear from loud noises. called middle ear reflex.

Question 12

What nerve sits between the malleus and the incus

Answer 12

The chords tympani, a branch of the facial nerve that senses taste

Question 13

Why do we need a middle ear?

Answer 13

The middle ear acts as a transformer to match the low impedance of air to high impedance of inner ear fluid. The large surface eardrum and shape of the ossicles means that movements in the larger bones (malleus) are transmitted to more forceful movements in the stapes (snow boot/ high heel) to do with distribution of energy.

Question 14

Where is the inner ear situated in the skull

Answer 14

In the petrous part of the temporal bone

Question 15

Describe the anatomy of the cochlea

Answer 15

Connected at its basal end to the middle ear via the oval window. Coiled bony structure with three inner tubes; scala vestibuli, scala media, scala tympani. Bisected by the cochlear partition from basal to almost apical end, just before the apical end is the helicotrema a gap where the scala vestibular scala tympani mis their perilymph. The scala media sits within the cochlear partition. The cochlear partition supports the basilar and tectorial membranes.
The organ of corti sits on the basilar membrane. The organ of corti is made up of sensory hair cells

Question 16

Describe the anatomy of the organ of corti

Answer 16

Sits on the basilar membrane which is wider and more flexible at the apical end.

Question 17

How does the travelling wave transmit sound signals

Answer 17

The travelling wave results in the stereocillia of inner hair cells being bent against the tectorial membrane. Tip links join adjacent stereocillia. Stretching of the tip links (that occurs in the wave) opens mechanically gated ion channels depolarising the hair cells which in turn leads to an action potential on CVIII.

Question 18

Describe how the cochlear determines different frequencies of sound

Answer 18

The difference in width and flexibility of the basilar membrane means that it vibrates maximally at different positions. This is what results in the tonotopical distinction of frequencies. With high frequencies best detected at the stiffer narrow basal end and low frequencies at the apical end. The travelling wave reaches a point of maximum displacement (in relation to the width/ flexibility of the basilar membrane) at this point the energy is transmitted into the sensory cells the hair cells.

Question 19

What is the function of outer hair cells

Answer 19

Connected with efferent fibres from the superior olivary complex. Thought to have an important role in modulating basilar membrane motions and as a cochlear amplifier.

Question 20

Describe the composition of perilymph and endolymph and the function of this

Answer 20

Perilymph is similar to normal extracellular fluid with high Na+ and low K+. Endolymph as high K+. Assists in creating electrochemical gradient conducive with fast ion transduction and minimal energy consumption by hair cells. Also voltage differences acts as sound amplifier

Question 21

What produces the endolymph

Answer 21

The stria vascularis

Question 22

What is Meniere’s disease

Answer 22

An fluid imbalance with excess fluid in the labyrinth of the inner ear. Causes hearing loss, tinnitus and balance disorders.

Question 23

What is a major cause of congenital deafness

Answer 23

A genetic abnormality in the production of Cx26, a protein that forms gap junctions imprtotant in the recycling of K+ to the stria vascularis.

Question 24

Define a conductive hearing loss

Answer 24

Hearing loss as a result of conduction of sound waves along the outer, middle ear, and tympanic membrane.

Question 25

Define sensorineural hearing loss

Answer 25

Hearing loss due to inner ear, vestibularcochlear nerve, or neural processing pathology

Question 26

Describe the two principles of detecting frequencies

Answer 26

The place principle- tonotopic organisation of detection mirrored from cochlear to auditory processing areas in cortex.
Volley principle- whereby auditory nerve is stimulated in time to the frequency of the stimulus.

Question 27

What are the components of the auditory pathway

Answer 27

Cochlea
Cochlear nucleus (medulla)
Superior olivary complex (pons)
Inferior colliculus (midbrain)
Medial geniculate body (thalamus)
Primary auditory cortex (cerebrum)

Question 28

What occurs in the cochlear nucleus

Answer 28

End point of auditory fibres, takes away extraneous information, somatosensory to remove biological input.

Question 29

What occurs in the superior olivary complex

Answer 29

Binaural hearing centre, involved in localisation of sound and detecting speech in noise.

Question 30

What occurs in the inferior colliculus

Answer 30

Integrative centre, interacts somatosensory and visual systems. Enhance sound localisation.

Question 31

Medial geniculate body of thalamus

Answer 31

Radiates signals to auditory cortex

Question 32

Primary auditory cortex

Answer 32

Spatial localisation, speech recognition, integrates with language centre brokers and wernikes.