2. Special senses: hearing Flashcards
What is sound
Areas of compression and refraction in the air, pressure change movement not change the air molecules.
Longer the wavelength means….
Deeper the pitch of the sound
Amplitude of sound waves relates to…
Volume.
High amplitude = High volume
Infra and ultra sound?
Frequencies above (ultra) and below (infra) the normal range of frequencies in speech.
Where is the physical discomfort level?
100 dB of sound pressure
Where is the pain threshold level?
140 dB of sound pressure
General anatomy of ear
Outer ear: Pinna
Tympanic membrane: Made of connective tissue, attached to malleus, cone shaped
Middle ear:
- Air filled
- Ossicle bones: Malleus, incus, stapes.
- Small muscles
- Auditory/eustrachian/ pharyngotympanic tube (all the same)
Inner ear:
- Coclea
- Semicircular canals
- Vestibulocochlear nerve
- Vestibule (fluid filled)
- Round window for pressure equalisation
- Fluid. Endolymph and perilymph
Why is there amplification between the tympanic membrane and ossicles
Allows amplification with tympanic membrane due to transmission from air medium to fluid medium in cochlea
Muscles of middle eat
Tensor tympani= Can turn down sound sensitivity when you don’t want to be listening e.g. eating
Stapedius
Role of round window
For pressure equalisation as oval window is sealing by stapes
What are the 2 types of fluid found in the inner ear?
- Endolymph
- In scala media; semicircular canals; vestibule
- Produced by Stria vascularis - Perilymph
- In scala vestibuli and Scala tympani)
What connects the basilar and tectorial membrane in vestibule?
Outer hair cells, so any movement/vibration of cells stimulates the membranes
Conversion of sound wave into neural correlate via force transduction
FIRST TRANSDUCTION Sound waves strike the tympanic membrane and become vibrations
The sound wave energy is transferred to the three bones of the middle ear which vibrate
SECOND TRANSDUCTION
The stapes is attached ot the membrane of the oval window. Vibrations of the oval window create fluid waves within the cochlea
THIRD TRANSDUCTION
The fluid waves push the flexible membranes of the cochlear duct. Hair cells bend and release neurotransmitter
FIFTH TRANSDUCTION
Neurotransmitter release onto sensory neurones created action potentials that travel through the cochlear nerve to the brain.
How do we detect the sound as pitch?
Hint: Role/change of basilar fibres
Basilar fibres structure changes from short and stiff, to long and floppy along the length of the cochlea.
Role? This means they have resonant frequencies that are graded along the cochlea with high frequency at the base and low at the apex.
When the resonant frequency is activated, it absorbs all the kinetic energy of the wave and effectively stops it at that point.
Other frequencies carry on however
Signal detection at the organ of Corti:
______ deflection of the basilar membrane moves the inner and ____ hairs laterally with respect to the tectorial membrane
95% of the cochlea nerve ending terminate on the ____ hair cells even though there are many less of them.
Mechanical activation + neuronal signals from the brainstem to the outer hair cells are thought to ____ and ____ them.
Signal detection at the organ of Corti:
Upward deflection of the basilar membrane moves the inner and outer hairs laterally with respect to the tectorial membrane
95% of the cochlea nerve ending terminate on the inner hair cells even though there are many less of them.
Mechanical activation as well as neuronal signals from the brainstem to the outer hair cells are thought to shorten and stiffen them.
What is the purpose of the shortening/stifferening the other hair cells at Organ of Corti (via mechanical activation + neuronal signal from brains stem)
This can tune the cochlea by amplifying select frequencies
Proportion of innervation to inner and outer hair cells>
95% of cochlea nerve –> Inner hair cells
5% –> outer
What is the process of cochlea tuning?
Purpose?
- Sound waves displace the basilar membrane
- Inner hair cells become depolarised and send signals to the cochlea nerve then to the CNS
- Out hair cells are stimulated by basilar membrane to depolarise, and the cells contract
Purpose: Enhance the auditory signal at the centre of the standing wave and inhibit on either wide