Normal hearing Flashcards
How do sound waves travel through the ear?
- Sound waves travel through the ear canal, are conducted through the middle ear and are converted to an electrical signal in the inner ear
- There are three bones in the middle ear to conduct sound waves as vibrations: malleus, incus and stapes
Structures found in the middle ear
Tympanic membrane, oval and round windows, the facial, chorda and tympani nerves, the stapedius and tensor tympani muscles, the Eustachian tube and air
What is found in the inner ear?
The inner ear is full of fluid spaces, membrane structures and hair structures to convert mechanical vibrations into electrical energy
3 fluid spaces in the inner ear
Scala vestibuli/tympani/media
What are the Scala vestibuli and tympani made of?
Perilymph
What is the Scala media formed from?
Endolymph - lots of potassium
What are the tips of hair cells bathed in in Scala media?
Endolymph
Three important structures in the inner ear
Basilar membrane, tectorial membrane and organ of Corti
How do inner hair cells help us to hear?
Transduce mechanical energy of sound into electrical activity for brain
Where are stereo cilia found?
On top of hair cells
How are stereo cilia joined?
Tip links
How do waves of vibration cause an AP?
Make hair cells bend
What is the pitch of a noise?
Frequency of signal
How does pitch determine where a noise is detected?
Higher frequencies are detected closer to base of basilar membrane, lower frequencies are detected closet to apex
Normal hearing range
20 to 20000 Hz
What is loudness?
Amplitude of deflection at given part of cochlea
Depends on amount of pressure exerted by sound waves on tympanic membrane
What is a decibel?
Logarithmic ratio between two sounds
How to calculate decibel difference?
10 x log10 (sound 1/sound 2)
What does the acoustic reflex do?
Dampens down loud noises
What does the stampedes do?
Contracts in response to loud noise
Pulls footplate away from oval window
Reduces intensity of sound reaching cochlea
Muscle fatigues very quickly and doesn’t protect against loud noise
What is bone conduction?
Vibration of sound waves go through bones of skull, very slow
How to tell if someone has hearing loss
- Bone conduction: vibrations of sound waves go through bones of skull, very slow
- Louder in front of ear is normal (bone conduction) - conductive change, air is not able to get into inner ear
- When centre of forehead and the volume is the same in both ears, this is normal and means normal hearing whereas unequal volume means sensory neural deficit
What is conductive hearing loss?
Outer/middle ear affected - e.g. infection/wax/fluid
What is sensorineural hearing loss?
Damage to inner ear/brain
e.g. damage to hair cells, nerves
What are the types of results from Rinne’s test?
- Normal result: air conduction > bone conduction (Rinne’s positive)
- Sensorineural deafness: air conduction > bone conduction (Rine’s positive) but both air and bone conduction reduced equally
- Conductive deafness: bone conduction > air conduction (Rinne’s negative)
What are the different results from Weber’s test?
- Normal: sound is heard equally in both ears
- Sensorineural deafness: sound is heard louder on side of intact ear
- Conductive deafness: sound is heard louder on side of affected ear
Middle of forehead
Characteristics fo audiogram
- Closer to 0 line indicates better hearing
- Triangles represent bone conduction, circles represent air conduction
- Normal audiogram - line is below 20 decibels
What does the ampulla do?
Contains crista amputaras - senses balance
What do the utricle and saccule contain?
Endolymph and perilymph
How is an AP conducted in crista ampularis?
1) Head moves
2) Movement of semicircular canal with body movement
3) Endolymph causes movement of cupula
4) Stereocilia bent by endolymph
5) Tiplinks stretch
6) Ion channels open causes depolarization
7) A.P. in vestibular nerve
What do the otolith organs do?
Acceleration/gravity causes otoliths to move, creating a shearing effect in the gel matrix that activates the hair cells
