Hearing Flashcards
What functional nerve component is the hearing system?
Special Somatic Afferent
What is meant by the pitch of a sound?
Its frequency
What frequencies can the human ear hear?
20 - 20k
At what frequencies is the ear most sensitive to?
2k - 4k
What is the frequency of a normal human voice?
500 - 2k
What frequencies are vowels and bass sounds?
Low
What frequencies are consonants and treble sounds?
High
What is loudness of sound a function of?
Amplitude (db)
What decibels can humans hear?
1 - 120 db
Above what db is sound damaging to the human ear?
100 db
Above what db can sound not be heard?
120 db
What are the 2 portions of the external ear?
- Pinna (auricula) that acts as a funnel, channeling airborne sound into ear
- Auditory canal
How large is the opening of the auditory canal?
2.5 cm
What is the function of the middle ear?
Converts air sound waves into fluid waves
What are the 5 components of the anatomy of the inner ear?
- Tympanic membrane
- Ossicles
- Malleus
- Incus
- Stapes (stirrup)
How is the tympanic membrane shaped?
- Conical with the pointed end projecting into the cavity
What is the function of the ossicles?
Sound amplification
What is the function of the malleus?
Hammer (connects rigid to incus)
What is the function of the incus?
Anvil (connects flexible with stapes)
What is the function of the stapes?
- Stirrup (Flat bottom/ footplate) that moves in and out like a piston
How does the middle change with altitude?
- Expands at high altitudes
- Condenses at low altitudes
How can the auditory tubes be used when adjusting to altitudes?
- Connect middle ear to oropharynx
- Can move air in at lower altitudes
- Can move air out at high altitudes
Why do children have more ear infections than adults?
They do not clear the middle ear as well
What are the 2 ways that bone amplifies air waves?
- Force
- Surface area (tympanic membrane is larger than membrane of oval window; lever system of ossicles increases mechanical advantage)
What are the 2 muscles associated with the inner ear?
- Tensor tympani
- Stapedius
What structure does the tensor tympani insert into?
The malleus
What is the function of the tensor tympani?
Decrease amount of movement of the ear drum
What nerve innervates the tensor tympani?
CN V
What is the function of the stapedius?
Restricts movement of the footplate of the stapes against the oval window
What nerve innervates the stapedius?
CN VII
How do the muscles protect the ears?
Prevent the bone and membranes from moving as much
How fast the attenuation reflex produced by the stapedius and tensor tympani?
50 - 100 ms
What is the shape of the canal of the cochlea?
- Spiral
How many turns does the cochlea make? How long is it? What is its diameter?
2.5 turns
32mm long
2 mm diameter
What divides the bony labyrinth into 2 portions? What are the 2 portions?
Cochlear partition divides:
- Scala vestibuli
- Scala tympani
What is contained within the cochlear partition?
Cochlear duct
What are the 2 membranes of the cochlear partition?
- Vestibular membrane/ Reissner’s membrane
- Basilar membrane
What do the 2 membranes of the cochlear partition separate?
- Endolymph filled cochlear duct from perilymph filled with scala vestibuli and scala tympani
What is the name of the apex of the duct?
Helicotrema
Where is the basilar membrane wider?
At apex (5X greater than base)
Where is the basilar membrane tension greater?
100x stiffer at base than apex
What occurs in the basilar membrane with a high frequency sound?
Base will vibrate dissipating most of the nergy and the wave will not propogate
What occurs in the basilar membrane with a low frequency sound?
Waves travel to apex before energy dissipates
What is stimulated by movement of the basilar membrane?
Hair cells of organ of corti
Is the oval window an entrance or exit?
Entrance
Is the round window an entrance or exit?
Exit
What is the order of canals through which a propogated sound travels through?
Scala vestibuli
Helicotrema
Scala tympani
What window creates the fluid waves that bend the basilar membrane?
Oval window
Where is the organ of corti found?
Longitudinally along the length of the basilar membrane
What is the organ of corti?
A transducer
Where are the hair cells of the organ of corti located?
Sandwiched between basilar membrane and reticular lamina
What membrane do the hair cells extend into?
The tectoral membrane
How do fluid waves cause depolarization of hair cells?
- Waves move basilar membrane, moving entire unit, bending hair cells as the unit moves up towards the tectoral membrane
- Bending of hair cells causes depolarization
What are the 2 types of hair cells?
Inner and outer
How many outer hair cells are there to one inner?
3
What type of cells communicate with outer hair cells?
Spiral ganglion
What is the roll of the spiral ganglion of the auditory nerve in the organ of corti?
Selection of attention
What type of neuron cell types are found in the auditory nerve spiral ganglion?
Bipolar
Toward what structure is the basilar membrane stiffer?
Basilar window
Toward what structure is the basilar membrane less stiff/ wider?
Toward helicotrema
How can inner hair cells help dampen sound?
- 95 % go out sensory nerve, but 5 % go to outer hair cells to stiffen the comlex
Are higher frequency sounds processed in the anterior or posterior cochlear nucleus? Low frequency sounds?
High frequency: Posterior
Low frequency: Anterior
What fibers ascend to higher centers?
Auditory fibers to perceive sound
Describe the pathway of cochlear nerve fibers from the spiral ganglion to higher centers.
- Enter through cochlear nerve, and synapse on dorsal cochlear nucleus
- Ascend and some fibers cross at trapezoid body onto superior olive
- Fibers ascend as LATERAL LEMNISCUS
- Synapse on nucleus of lateral lemniscus
- Some fibers cross over
- Synapse on inferior colliculus
- Some fibers cross over
- Fibers synapse on medial geniculate body
- Synapse on sublenticular fasciculus and auditory thalamocortical radiation
How is low frequency sound localized on the horizontal plane?
Interaural time delay
- Difference in sound between 2 ears
- High frequency sound doesn’t work because 1 cycle of sound is smaller than the distance between the ears
How is high frequency sound localized in the horizontal plane?
Interaural intensity differences
- Head casts a sound shadow that dampens the sound on the side blocked by the head
- Low frequency diffracts around head, eliminating this effect
How are sounds localized in the vertical plane?
- Bumps and ridges of pinna produce reflections of entering sounds
- The delay between direct and indirect paths cause sound delays
What is the function of olivocochlear efferent reflexes?
- Selective tuning
- Focusing
- Possibly protection
What is the function of somatic motor auditory reflexes?
- Contracts ear muscle during loud sounds
- Start responses
What tract processes startle responses?
Tectospinal tracts
What is conduction deafness?
- Interference with passage of sound waves through external or middle ears
What is nerve deafness?
- Damage to receptor cells of spiral organ or the cochlear nerve
- Damage to organ of cordi/ afferent fibers
- Can occur in both directions
Which type of hearing loss is NEVER complete or total?
Conduction deafness
What determines the amount of deafness due to nerve deafness?
Amount of damage
When are high frequencies typically lost?
In older populations
What sounds are most damaging when individuals are young?
Low bass
What is Weber’s test?
- 256 Hz tuning fork placed on themidline of the head
- If the patient hears it normally in both ears, then this is normal
Conduction deafness: Sound localized in decreased hearing ear
Nerve deafness: Sound localized in unaffected ear
What is Rinne’s test?
- 512 Hz tuning fork placed on mastoid process
- Place it nera ear and hold until it can’t be heard
Normal: Air conduction is louder than vibration
