Hearing Flashcards
What is sound?
pressure waves in the atmosphere
zones of rarefaction and zones of compression create sound waves
Frequency/pitch
number of waves per second measured in Hertz
Loudness/volume/intensity
amplitude of the waves
Frequency range we can hear
20Hz to 20,000Hz
Optimal range of hearing/volume of speech
500Hz to 5000Hz
Speech dB
60dB
Air filled cavities of ear (2)
Outer and middle air
- external auditory canal
- middle air cavity from auditory (eustachian) tube from the pharynx
Fluid filled cavities of ear (1 region, 3 cavities and type of fluid)
Inner ear Scala vestibuli (perilymph) Scala tympani (perilymph) Cochlear duct (endolymph)
Name of ear drum
Tympanic membrane
Ossicles
what, function and names
3 small bones in middle air cavity ear, vibrations are transmitted through these from ear drum to cochlea
- malleus, incus and stapes
What is the Origin of Corti
Neural apparatus responsible for sound transduction
Origin of Corti membranes (2)
tectorial membrane and basilar membrane
Stereocilia - where and function
Project from hair cells in the origin of corti responsible for beginning sound transduction pathways
What do sheer forces do?
perpendicular to a surface, deflect the stereocilia and cause a mechanical shift
Sound waves reaching cochlea
Sound vibrations cause a pressure change in the fluid in the scala vestibuli, causing a bowing displacement into the cochlea duct, displacement of the basilar membrane (part of origin of corti) bending the stereocilia
Deflection of stereocilia to neural output
Bending of the hair cells cause the opening of mechanically gates K+ channels causing influx of potassium. This depolarises the cell and causes voltage gated Ca+ channels to open, and the Ca+ triggers release of vesicles containing the neurotransmitter glutamate which is released onto afferent neuron fibres (cochlear nerve)
Endolymph (in cochlea duct)
very similar to ICF fluid so has a high K+ concentration and low Ca+ concentration
Perilymph
very similar to ECF fluid so has high conc of Ca+ and low K+
Central pathway
Depolarisation of hair cells release glutamate onto afferent nerve fibres on cochlear nerve, synapses onto auditory receptors on the cochlea nucleus located in the brain stem. These axons project to the lateral meniscus to the medial genicular body, then project to the primary auditory cortex.
Start of the basilar membrane detects high or low frequency?
Start of basilar membrane is stiff and tight and narrow and good at detecting high frequencies
End of the basilar membrane detects high or low frequency?
End of the basilar membrane becomes wider and more floppy/loose and can detect low frequencies
Discrimination of pitch (frequency) is determined by?
The activity in hair cells at specific points on basilar membrane
Direction of sound
the sound source is indicated by time difference in activation of receptors in each ear and by intensity differences
Deafness definition
Raised threshold to sound stimuli
Deafness may be due to: (2)
- Blockage or infection
- Impaired sound transmission through outer or middle air (conduction deafness)
Sensorineural deafness
Damage to receptors or neural pathways - due to meningitis, tumors, or exposure to loud noises
Acoustic neuroma aka vestibular schwannoma
benign brain tumor on vestibulocochlear nerve
- tinnitus
- hearing loss in one ear
Glomus Tympanicum
Growth behind the tympanic membrane
Ear Canal Cancer
Need to remove auditory canal, ear drum and ossicles resulting in permanent hearing loss
- very rare with 5 year survival rate at 35%
Eustachian Tube
maintains air pressure between middle air and outside air (from pharynx)
What does the amount of displacement of the basilar membrane depend on?
Amplitude of the sound
