Neuro 12 - Sound Conduction and Transuduction Flashcards
What scale is used to measure how loud a sound is?
Decibels
What is the audible range for humans in terms of frequency?
20 -20,000
What is the name given to the wing shaped flap skin and cartilage that makes up the outer ear?
Pinna
Describe the shape of the outer ear and its importance?
Conical
this focuses the noise and increases the pressure on the tympanic membrane
Is the tympanic cavity air or fluid filled?
Air filled
State two ways in which the ossicles increase the pressure of the vibration of the tympanic membrane.
- Focussing vibrations from the large surface area of the tympanic membrane to the small surface area of the oval window
- incus has a flexible joint with the stapes so uses leverage to increase the force on the oval window
increases by 30dB
What is the point of the middle ear?
Cochlear is fluid
if tympanic membrane was continuous with cochlea, you would go straight from air to fluid so 99% of energy would be lost because of impedance
What 2 muscles are involved in making sure that the ossicles aren’t damaged by excessive vibration due to loud noise?
Tensor Tympani
Stapedius
- muscles contract and reduce the vibration
What is the name given to the reflex where the tensor tympani and stapedius contract?
auditory reflex
50-100ms
What is hyperacusis?
Painful sensitivity to low intensity sounds
can be caused by flaccid paralysis of auditory reflex muscles e.g. Bells palsy
Which test is used to determine the site of damage to the auditory system that is causing hearing loss?
Weber test
What are the 2 specialised membranes of the cochlea?
Oval window
Round window
What are the three components of the inner ear?
Scala Vestibuli
Scala media
Scala tympani
Which types of fluid do each compartment contain?
Scala vestibuli + tympani = perilymph
Scala media = endolymph
What structure connects the two perilymph compartments?
Helicotrema
Describe how the cochlear functions.
The vibration of the tympanic membrane is conducted and amplified to a vibration of the oval window by the footplate of the stapes.
This vibration induces a pressure wave in the perilymph in the scala vestibuli.
This vibrates the scala media leading to vibration of the basilar membrane.
The round window vibrates as well to equalise the pressure in the cochlea.
Describe the difference in sensitivity of different parts of the basilar membrane?
Higher frequency = base
Lower frequency = apex
What is the organ of Corti?
sense organ of the cochlea, which converts sound signals into nerve impulse
transmitted to the brain via the cochlea nerve
Where is the organ of corti found?
inner and outer hair cells
Describe the features and function of inner hair cells?
Found on their own
Not in contact with the tectorial membrane
Send impulses to the brain
They have stereocilia that move in response to the movement of
endolymph in the scala media
Roughly 3500 in the body
Describe the features and function of the outer hair cells.
Found in groups of three
They are in contact with the tectorial membrane
They receive input from the brain
Electromotile so can expand and contract to amplify the amount of vibration (this is the basis of the cochlear amplifier)
Damage can result in sensorineural hearing loss
Roughly 20,000 in the body
Which compartment of the cochlea does the stereocilia of the hair cells project into?
endolymph
What internally generated sounds are the outer hair cells responsible for?
Otoacoustic emissions
What are stereocilia connected by?
Tip links
What bony conical structure is found at the middle of the cochlea?
Modiolus
Describe what happens when the basilar membrane is displace upwards?
Depolarisation
stereocilia move away from the modiolus
K+ channels open
K+ enters from the endolymph
Describe what happens when the basilar membrane is displaced downwards.
Hyperpolarisation
Stereocilia move towards the modiolus
K+ channels open
Describe the difference in K+ and Na+ concentration in the different compartments of the cochlea.
Scala Media = High K+ and Low Na+
Scala Tympani = High Na+ and Low K+
Describe the auditory pathway from the cochlea to the primary auditory cortex.
Spiral ganglion — cochlea nuclei — superior olive — inferior colliculus — medial geniculate nucleus — primary auditory cortex
Up to what point is the auditory pathway from one ear ipsilateral?
Cochlear nuclei
The inferior colliculus receives input from both cochlea. What is the inferior colliculus responsible for?
reflex associations - turning your head towards loud sound
Describe a phenomenon that is involved in sharpening the signal coming from the cochlea.
Lateral inhibition
To which parts of the CNS do collaterals from the auditory pathway go?
Reticular formation
Cerebellum
In which lobe is the primary auditory cortex?
Temporal
What is the secondary auditory cortex responsible for?
responding to sounds coming off/on
responding to the duration of the sound
What i sthe name given to the axons that project from the medial geniculate nucleus to the primary auditory cortex?
Acoustic radiations
How do you localise short sound burst?
Interaural time delay
How do you localise continuous sound?
interaural intensity difference
What is conductive hearing loss?
Diseases of middle ear damage the ossicles or stiffen their joints so amplification system is eliminated
What is sensorineural hearing loss and what can it be caused by?
when the cochlea or nerve gets damages, the signal transmitted to the primary auditory cortex is reduced or lost
can be caused by acoustic schwannoma (tumour of cochlea) or cerebellar tumours and putting pressure on cochlear nerve
What is the term used to describe loss of hearing due to death of hair cells in normal ageing?
presbyacusis
