L08: Hearing Flashcards
What structures does the outer ear contain
Pinna
Auditory canal
Tympanic membrane
What structures does the middle ear contain
Ossicles (3 small. Bones)
A connection to the Eustachian tube
What structures does the inner ear contain
Cochlear
Semilunar canals
What are the 3 small bones that form the ossicles
Malleus
Incus
Stapes
What is the 2 roles of the 3 small bones in the middle ear
- Transmit sound wave form the tympanic membrane to the oval window of the inner ear
- amplify the sound they transmit the sound
What is the oval window
The window that allows connection of the stapes bone to the inner ear
How is the mechanism to reduce amplification of loud sound achieved
By 2 muscles of middle ear
What are the 2 muscles of the middle ear
Strapedious muscle
Tensor tympani muscle
What happens to these 2 muscles where there is loud sound
Contract
What does the contraction of the 2 muscles allow
Stop amplification of sound via 3 bones- attenuation reflex
What are the 3 tubes in the cochlear known as
Scala vestibuli
Scala media
Scala tympani
What does the scala media contain
Organ of corti
What lining separtes the scala media and scala tympani
Basilar membrane
Where does the scala tympani and scala vestibuli connect to
Helicotrema (a hole at apex of ear)
What liquid found inside the scala media
Endolymph
What happens to the endolymph when the stapes pushes the oval window membrane in the cochlear
The endolymph moves back and forth
As the endolymph moves what structure does it also move
The basilar membrane
How does the rigidity of the basilar membrane change along its length
From narrow and stiff (at base) to wider and floppy (at apex)
Which type of sound influences the apex
Low frequency sound
What type of sound influences the base
High frequency sound
Where is the organ of orti located
In the scala media on the basilar membrane
Therefore when the basilar membrane moves what happens to the organ of corti
Organ of corti moves as the basilar membrane moves
What type of cells are found at the organ of corti
Hair cells
What membrane does the hair cells touch
Tectorial membrane
What structure does the tectorial membrane also sit on top of
Sterocilia
What is the sterocilia
A structure that sits on the hair cells
As the organ of corti moves what happens to the tectorial membrane
It moves
As the tectorial membrane moves what happens to the sterocilia
Moves
What happens when sterocilia bend in and out
Open different ion channels
If ion channels open on the hair called as a result of sterocilia bending what happens to the hair cells
Depolarisation
On the outer/inner hair cell which specific channel opens to cause depolarisation as the stereocilia moves
Mechanically gates pottasium channels
What happens to potassium when the mechanically gated potassium channels open
Potassium influx into the outer hair cell
When there is a depolarisation in the outer/inner hair cell what channel opens
Voltage gated calcium channels
What does calcium influx as a result of voltage gated calcium channels cause
Exocytosis of neurotransmitters (glutamate) in the pre-synaptic vesicles to the spiral ganglion neurite
What does glumate get released to
Spiral ganglion neuritis
What do many spiral ganglion cells form
The auditory nerve
How many spiral ganglion cells transmit a signal from inner hair cell
Many (divergent)
How many spiral ganglion cells connect to outer hair cells
Small number (convergent)
What is the main role of outer hair cells of the organ corti
Amplify sound for inner hair cells
How does outer hair cells amplify sound
1) Outer hair cells have motor proteins that contract and relax
2) when the motor protein contracts it pulls the stereocilia into one direction
3) pulling the stereocilia pulls the tectorial membrane with it
4) this amplify the sound by the inner hair cells
What is tonotopy
Because the basilar membrane has different rigidity along its length from base to apex, every part of the membrane is responsive to a characteristic frequency that the hair cells are sensitive to
What does the tonotopy organisation allow us to do
Distinguish sound at different frequency
What is a characteristic frequency
Highest spikes the hair cell can produce in repsonse to its frequency that it is specific to
Which ascending pathway takes the info from the ear to the brain
Auditory pathway
Which side of the brain does info from the left ear go to
Both sides of the brain i.e left and right
What side of the brain does info form the right ear go to
Both sides of the brain i.e left and right
Where does info form the auditory pathway go to
Auditory cortex
How is the auditory cortex organised
Tonotopy
What does tonotopy of the auditory cortex mean
Specific frequency terminate at specific regions of the auditory cortex that correlates to that frequency
What is the primary auditory cortex surrounded by
Secondary auditory cortex
What is phase locking
Firing an action potential with every cycle of frequency sound
When does phase locking occur
In low frequency sound
Why is phase locking not possible in high frequency
The sensory neurones cannot be continuously stimulates to produce rapid cycles of action potential
What limits the phase locking in high frequency sound
Refractory period of the nerve cells
What do we rely on for high frequency sounds if phase locking doesn’t occur
Tonotopy (organisation of the auditory system)
In loud sound what is the firing of spikes like
High
In soft sound what is the firing of spike like
Low firing
How can we localise sound
Message from the ipsilateral ear goes to the superior Olive quickly than the message from the other ear which reaches the superior olive slower due to it needing to pass to the other side = interaural delay
What is another way of localising sound
When sound waves hit your head it creates a sound shadow, so the contralateral ear has a lower intensity than the ipsilateral ear,
What is nerve deafness
Damage to the inner ear or auditory pathway
What are the 3 main causes of nerve deafness
Genetic disorder: affected hair cell structures
Congenital: congenital rubella syndrome, toxoplasmosis- lead to hypoplastic auditory nerves
Presbycusis: normal age related loss (not reversible)
What is acquired nerve deafness
Cochlear damage due to noise from environment or occupation
Which drugs can damage the ear
Aminoglycosides (anitbiotics)
Methotrexate (immunosuppressant drugs)
If the motor proteins in the outer hair cell contracts when there is no sound what can this cause
Tinnitus i,e noisy ear
