Bb1 Auditory System

Front 1

What are the components of the external ear?

Back 1

Auricle/pinna
External auditory meatus
Tympanic membrane

Front 2

What are the 3 ossicles of the middle ear? How are they attached?

Back 2

Malleus
Incus
Stapes

Malleus is attached to the TM, the stapes is bound to the oval window

Front 3

What is the middle ear continuous with and why?

Back 3

Nasopharynx via the eustachian tube, allowing for pressure regulation of and fluid drainage from the middle ear

Front 4

What is the function of the middle ear?

Back 4

Conduct sound waves that vibrate the tympanic membrane to the oval window, which induces waves in the fluid-filled compartment of the inner ear.

Front 5

What muscles are in the middle ear and what is their function?

Back 5

Tensor tympani and stapedius

Protect the auditory system from high intensity sounds by dampening vibrations of the ossicles and reducing the amplitude of the waves in the fluid-filled inner ear

Front 6

Tensor tympanic: innervation? connection?

Back 6

CN V
Malleus

Front 7

Stapedius muscle: innervation? connection?

Back 7

CN VII
Stapes

Front 8

What fills the membranous labyrinth?

Back 8

A potassium rich fluid called endolymph

Front 9

What 2 cavities of the cochlea are formed by the cochlear duct? Are they continuous?

Back 9

Scala vestibuli
Scala tympani

Continuous at the apex of the cochlea, the helicotrema

Front 10

How are the scala vestibuli and tympani related to the middle ear cavity?

Back 10

Scala vestibuli is a direct extension of the vestibule and is separated from the middle ear cavity by the oval window.

The scala tympani is separated from the middle ear cavity by the round window.

Front 11

How is the cochlear duct separated from the scala vestibuli and tympani?

Back 11

2 membranes: vestibular membrane (from the scala vestibuli) and the basillar membrane (from the scala tympani)

Front 12

What produces the potassium rich endolymph?

Back 12

Striae vascularis in the lateral wall of the scala media (cochlear duct)

Front 13

What is the central core of the cochlea called and what does it contain?

Back 13

Modiolus

Spiral ganglia and peripheral segments of the cochlear nerve

Front 14

Organ of Corti: location?

Back 14

Lies on the basilar membrane of the cochlea

Front 15

What are the 2 types of hair cells?

Back 15

Single row of inner hair cells
Several rows of outer hair cells

Front 16

What extends from hair cells?

Back 16

About 100 stereocilia of varying height (arranged in ascending height) and a single kinocilium longer than the stereocilia.
Tips of the cilia are embedded in the overlying tectorial membrane.

Front 17

What are the functions of the inner and outer hair cells?

Back 17

Inner - relay much of everyday sounds
Outer - modulate the sensitivity and frequency specificity of inner hair cells

Front 18

Give the 'pathway' from hair cells.

Back 18

The base of each hair cell forms synaptic connections with the peripheral processes of bipolar cochlear neurons. The central processes of these neurons form the cochlear division of the vestibulocochlear nerve.

Front 19

What movements cause hair cells to depolarize and hyperpolarize?

Back 19

Depolarize - deflection of stereocilia towards kinocilium
Hyperpolarize - deflection of stereocilia away from the kinocilium

Front 20

What is the MOA of depolarization and hyperpolarization of the hair cells?

Back 20

Intracellular hair cell K concentrations are high. Apex of hair cells is bathed in endolymph, separated from interstitial fluid bathing the bodies of hair cells, that has a low K concentration. Endolymph has a high concentration of K and a net + charge. Deflection of stereocilia toward the kinocilium causes K channels to be pulled open by tip links and there is an influx of K from endolymph into the hair cell due to electrical gradient. Results in depolarization of the hair cell membrane and influx of Ca into the hair cell. This facilitates fusion of synaptic vesicles within the basement membrane of the hair cell and increase in the release of glutamate, which binds receptors on the post-synaptic cochlear nerve, resulting in an increase in the firing rate of the afferent cochlear nerve fibers.

Front 21

What determines sound intensity/loudness?

Back 21

Amplitude of the resonating basillar membrane. The higher the amplitude, the greater the displacement of the basilar membrane and hair cells.

Front 22

What determines the tonotopic organization of the auditory system?

Back 22

Properties of the basilar membrane - narrow at the base but becomes wide as it extends towards the apex. Thickness and stiffness of the fibers decreases from base to the apex. Narrower, stiffer fibers near the base resonate selectively to high frequency sounds, while the wider, more pliable fibers near the apex resonate selectively to low frequency sounds.

Front 23

Describe the underlying structure of the basilar membrane.

Back 23

Elastic reed-like fibers extend from the bony shelf into the lumen. These are fixed at the modiolus and relatively mobile at their distal ends and vibrate in response to pressure waves induced by sound transmission.

Front 24

Cochlear nerve: type of neurons? location of cell bodies?

Back 24

Bipolar neuron axons

Spiral ganglion in the modiolus of the inner ear

Front 25

Cochlear nerve: pathway?

Back 25

Central processes enter the skull via the internal auditory meatus and the brainstem at the pontomedullary junction, then synapse in the ipsilateral dorsal and ventral cochlear nuclei. These nuclei lie respectively over the inferior cerebellar peduncle.
Neurons project into ipsilateral and contralateral lateral lemniscus. This ascends to the tectum of the midbrain, where fibers synapse in the inferior colliculus. Axons then project to the medial geniculate body of the thalamus, which then projects to the primary auditory cortex via the sublenticular limb of the internal capsule.

Front 26

Superior olivary complex: function? general pathway?

Back 26

Localizing sound

Axon collaterals from the ventral cochlear nuclei synapse bilaterally in nuclei of the superior olivary complex, which then projects axons bilaterally into the lateral lemniscus.

Front 27

What are the 2 types of hearing loss?

Back 27

Conductive hearing loss
Sensorineural hearing loss

Front 28

Causes of conductive hearing loss?

Back 28

Lesions or anomaly peripheral to the oval window, such as buildup of cerumen in external auditory canal

Front 29

Cause of sensorineural hearing loss?

Back 29

Lesion or anomaly involving the cochlea, cochlear nerve, of cochlear nuclei

Front 30

Describe lesions of the auditory pathways central to the cochlear nuclei.

Back 30

Subtle hearing deficits, more contralateral than ipsilateral, due to extensive bilateral distribution of the ascending auditory nerve fibers.

Front 31

Describe the results of a Weber test in the 2 types of hearing loss.

Back 31

Sensorineural - hear better on normal side
Conductive - hear better on abnormal side

Front 32

Describe the results of a Rinne test in the 2 types of hearing loss.

Back 32

Sensorineural - will hear better with air conduction
Conductive - will hear better with bone conduction

Front 33

CPA: what is it? what are the contents and what does this result in?

Back 33

Cerebellopontine angle - anatomic space between the pons and cerebellar hemisphere

CN VII and VIII traverse the CPA and are vulnerable to lesions that develop here.