21: Hearing Flashcards
What are zones of high pressure in the air
Zones of compression
What are zones of low pressure in the air
Zones of refraction
What are the two forms of sound that we are able to detect?
The amplitude and the pitch
Describe to impact of the threshold of hearing
- Our receptors for sound are more responsive when we are young
- We are most sensitive to sounds about 500-3000hertz
- Hearing is optimised in the range of the sound of human speech
(Brief) discription of the movement of soundwaves to ear
External auditory canal (outer ear/pinna) –> tympanic membrane (eardrum) –> middle ear cavity –>inner ear (cochlea)
What is the role of the outer ear (pinna) and the external auditory canal?
Can help to amplify and direct the soud
What is the role of the tympanic membrane? (eardrum)
- Vibrates at the same frequency as the sound wave
- It separates the external auditory canal from the middle ear
What is the inner ear/cochlea?
-Fluid-filled, spiral-shaped passage in the temporal lobe
What are the two main roles of the cochlea?
- Hearing
- Vestibular (balance)
What is the role of the three small bones: the malleus, incus and stapes (in the inner ear)
Since the inner ear is filled with fluid, and liquid is more difficult to move compared to air, the sound pressure transmitted to the inner ear must be amplified.
These bones act as a piston and couple the vibrations of the tympanic membrane to the oval window
What are the three chambers of the cochlea?
- Upper chamber: Scala Vesticuli
- Middle chamber: Scala Media
- Lower chamber: Scala Tempani
What fluid is the scala vesticuli filled with?
Perilymph, which has a composition similar to ECF
What fluid is the scala media filled with?
Endolymph, which has a composition similar to ICF
What chamber of the cochlea does signal transduction occur in?
Scala Media
Where is chamber of the cochlea is the organ of corti present in?
Scala Media
Describe the receptor cells of the organ of corti
They are hair cells. They are mechanoreceptors that have hairlike stereocilia protruding from one end
The hair cells transform the pressure waves in the cochlea into receptors for potential
Where are the hair cells of the organ of corti attached to?
They are attached to the basilar membrane which stimulate the hair cells
Where is the stereocilia of the hair cells of the organ of corti in contact with>
Tectorial membrane, which overlies the organ of corti
What fluid is the scala tempani filled with?
It is filled with the fluid perilymph which has a composition similar to ECF
Describe the movements transmitting sound vibrations through the middle and inner air (air to fluid)
- Tympanic membrane deflects
- Middle ear bones move
- Membrane in oval window moves
- Basilar membrane moves
Describe the tuning of the basilar membrane
- Low frequency when it is far from the basilar membrane
- High frequency when it is close to the basilar membrane
Describe signal transduction in hair cells
The longest specialised stereostilia is the kinocilum.
Fibrous connections called tip links pull open mechanically gated ion channels
Mechanical deformation toward the kinocilium opens K+ channels in the stereocilia.
Mechanical deformation away form the kinocilium causes the K+ channels to close
The resulting depolarisation caused by opening these mechanically gated ion channels goes on to open voltage gated Ca2+ channels and permits Ca2+ influx and neurotransmitter release.
Mechanically gated ion channels are a fast form of opening channels (compared to signal transduction in the vision etc.
Where is pitch (frequency) determined?
Discrimination is determined by activity in hair cells at specific points on the basilar membrane
Where is the intenisty (loudness) encoded?
Encoded in the number of impulses per second in auditory nerve fibres
Where is duration of sound signalled?
Duration of the sound is signalled by duration of afferent discharge caused by the stimulus
How is the direction of the sound source detected?
Direction of the sound source is indicated by time difference in activation or receptors in each ear,, and by intensity differences in each ear.
Where are the central pathways of hearing?
- Auditory receptors in cochlear
- Brain stem neurons
- Medial Geniculate Nucleus
- Auditory cortex (each side receives info from both ears)
What is deafness?
Raised threshold to sound stimuli
What are two causes of deafness
Impaired sound transmission through outer or middle ear (conduction deafness). Can be due to blockage or infection
Damage to receptors or neural pathways (sensorineural deafness). Can be due to exposure to loud noises, some antibiotics, menigitis etc
What can be a result of prolonged exposure to loudnesss?
Hair cells of the organ of corti can get damaged. Once they are damaged, they are damaged forever and cannot be healed
