Hearing and Vestibular System Flashcards
What consists of the Outer ear and what is it’s function
1- Pinna ( auricle )
2- ear canal
3- Tympanic membrane ( ear drum )
Function : direct sounds to the eardrum
What does the Middle ear consist of , and what is it’s function
Ossicular lever system ( 3 bones ) 1- Malleus ( hammer ) 2- Incus ( anvils ) 3- Stapes ( stirrup ) Function : transmit vibration from the tympanic membrane to the inner ear
What does the inner ear consist of and what is it’s function
1- cochlea : hearing
2- vestibule & semicircular canals: balance
Function: conversion of mechanical vibrations to electrical signals
What are the smallest muscles int he body and which cranial nerve controls them
The tensor timpani and strapedius muscles controlled by cranial nerve 7
Explain in detail the process of critical damping in the middle ear ( of the bones + muscles )
1- Critical damping :
Ear drum resonates to a variety of frequencies , but also must stop resonating when frequency ends. The ear drum is connected to the Malleus, stapes and incus to stop vibrating as soon as sound stops. Allows ear drum to be critically damped.
2- Protective Reflex :
Tensor timpani and stapedius muscles contract reflexly before a sound occurs. Tighten up to prevent vibrations from being too loud and damaging hair cells of cochlea.
What is a situation in which the Reflex of the Tensor timpani and stapedius muscle might not work ?
Reflex takes longer than 150 milliseconds, therefore loud sounds with rapid onset can cause damage to cochlea since reflex wouldn’t have had time to tighten muscles ( ex: gun shot sound )
Why is the ear affected in Bell’s palsy
Cranial Nerve 7 is affected which controls the muscles in the ear. One of the clinical signs of Bells palsy is that you can hear sounds more loudly in the affected ear, long term might cause hearing damage
What are the 3 jobs of the middle ear
1- Critical Damping
2- Amplification
3- Impedance Matching
Explain the process of amplification of the middle ear
Lever action gives 130% of force at the oval window at the stapes of the force at the tympanic membrane.
The tympanic membrane is a large area vibrating the oval window, a small area. = greater pressure = amplification
Explain the process of Impedance Matching of the middle ear
Because more force is generated at the oval window , over a smaller area , there is greater pressure. This means humans can vibrate same magnitude in liquid as air. Amplification is necessary in order to vibrate at same frequency in liquid cochlea.
= Air impedance matches liquid impedance
What does the cochlea consist of ?
1- 3 chambers : Scala vestibuli , scala media , scala tympani 2- Vestibular membrane 3- Organ of Corti 4- Basilar membrane 5- Spiral ligament 6- Cochlear nerve + spiral ganglion 7- stria vascularis ( blood supply )
Which chambers are linked at the end of the cochlea (Helicotrema )
Scala tympani and vestibuli
What is the purpose of the round window
Allows free vibration of the Scala vestibuli and tympani
Vibration in the stapes results in what ?
Vibration in the basilar membrane of the cochlea
What is the cation in Scala tympani and vestibuli
Sodium
What is the cation in the Scala media
Potassium
Where is the basilar membrane
Membrane between organ of cortisones and the Scala tympani
Explain what happens to movement of the oval window from the Stapes bone
1- Transmitted to scala vestibuli and scala media
2- Vibrate the basilar membrane
3- Rod of corti attached to the basilar membrane will vibrate = inner/outer sensory hair cells attached will move vertically and basilar fibre attached will move laterally
4- Hair cells will induce an AP in cranial nerve 8
What does the organ of cortisones consist of and what is it’s purpose e
1- basilar membrane 2- 1 row of inner hair cells 3- 3-4 rows of outer hair cells 4- tectorial membrane 5- reticular lamina 6- rods of corti Function : convert mechanical signals to nerve signals
What is the purpose of the inner and outer hair cells
Inner : Transducers
Outer: modulators ( of frequency ,moderate sound we are hearing )
What are the hair cells in the cochlea made of
Rows of stereocilia , with filaments linking one hair cell to another
What is the purpose of the filaments in the hair cells of the cochlea
Filaments opens ion channels allowing potassium into the hair cell = depolarizes it.
Neurotransmitter is released which creates an AP in the 8th cranial nerve
How do we detect low and high notes ?
The basilar membrane end closest to oval window is stiff and narrow , and on the opposite end ( helicotrema ) it is wide and floppy. This means that each part of the membrane vibrates maximally for different frequencies.
High frequency: displace hair cells near oval window
Low frequency: displace hair at helicotrema
Depending on which hair cells displace , the Brian is sent signals
Where do High frequency sounds resonate
Near oval window
