Auditory system Flashcards
how is sound conducted from the outer ear to the inner ear?
- sound waves cause the tympanic membrane to vibrate
- the tympanic membrane vibrates malleus which vibrates incus and then stapes
- stapes’ foot process then vibrates the membrane of the oval window.
what are the types of hearing loss? and what are they?
Conductive
-reduction in the mechanical conduction of sound waves to the oval window
sensorineural
-damage to some part of the inner ear e.g. organ or corti or a nerve lesion
what are the 2 muscles in the middle ear? what are their function? what innervates them?
tensor tympani - innervated by the mandibular branch of the trigeminal
stapedius - innervated by the facial nerve
their function is to regulate the stiffness of the ossicle chain regulating the amplitude of sound conductance (basically dampens sound wave to inner ear)
how are sound waves transduced once in the inner ear?
- vibrations in the perilymph of the scala vestibuli pass through the vestibular membrane
- they then vibrate the basilar membrane
- stereocillia are displaced by the vibrations causing tip linkages to open
- K+ from the endolymph enters the sterocillia and causes the rapid depolarisation
- depolarisation travels down the cell and causes Ca2+ channels to open
- Ca2+ causes glutamate to be exocytosed
- causing action potentials on the afferent neurone
describe the arrangement of hair cells.
1 row of inner hair cells
3 rows of outer hair cells
how are the features of sound transduced?
amplitude - frequency of action potentials by number of nerves firing
frequency - individual hair cells detect a specific frequency
high - closer to the oval window
low closer to the helicotrema
what is the difference between inner and outer hair cells?
inner hair cells - stereocilla are in the endolymph and transduce pressure waves in the fluid
outer hair cells - stereocilla are embedded in the tectorial membrane and alter tectorial membrane movement to sharpen and fine tune frequencies
where is the basilar membrane at it’s widest?
widest and least stiff at it’s apex
narrowest and stiffest at it’s base
what is the auditory pathway?
fibres from the cochlea nerve go to the Inferior colliculus which then go to the medial genticulate body via the inferior brachium
what makes up the vestibular apparatus?
3 semi circular canals - superior, lateral and posterior
2 sac like swellings - utricle and saccule
what is the function of the semi circular canals?
detects rotation
what is the function of the saccule and utricle?
detects acceleration of the head when at rest
saccule - verticle acceleration (s = stairs = up and down)
utricle - horizontal acceleration
where are the stereocilla located in the semi circular canals?
in the ampulla contained within a cupula (gelatenous mass that contains sterocilla)
