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Hearing

Terms in this set (30)

What makes up the external ear?
auricle/pinna
external auditory canal
tragus
tympanic membrane/ear drum
ceruminous glands
What makes up the middle ear?
3 bones (auditory ossicles); malleus, incus, stapes
2 skeletal muscles (stapedius, tensor tympani)
auditory tube/eustachian tube
What makes up the inner ear?
bony labyrinth
membranous labyrinth
What is the ear drum made up of?
epidermis, collagen and elastic fibers
Where is the middle ear located?
air filled cavity in the temporal bone
What is the purpose of tensor tympani? what innervates it?
limits movement, increases tension on eardrum to prevent damage to inner ear by loud noises
innervated by trigeminal nn (mandibular branch)
What does the stapedius do? What innervates it?
dampens large vibrations of the stapes due to loud noises to protect the oval window
innervated by facial nn
What does the eustachian tube do?
connects to nasopharynx, opens at medial end during swallowing and yawning to equalize with atmospheric pressure
What is another name for the inner ear?
labyrinth
Where is the bony labyrinth located?
inner ear, in the temporal bone
what makes up the bony labyrinth? What is the purpose of these divisions?
semicircular canals (equilibrium)
vestibules (equilibrium)
cochlea (hearing)
What is the fluid that lines the bony labyrinth?
perilymph (chemically similar to cerebrospinal fluid)
Where is the membranous labyrinth found?
series of tubes and sacs, found inside the bony labyrinth
What makes up the membranous labyrinth?
utricle, saccule, ampulla, 3 semicircular ducts, cochlea
What is the fluid found in the membranous labyrinth?
endolymph (similar to interstitial fluid)
What nerves innervate the inner ear?
vestibulocochlear nerve
Describe the events involved in hearing?
- auricle directs sound waves into external auditory canal
- sound waves strikes eardrum, alternating high and low pressue of air causes ear drum to vibrate back and forth
- central area of eardrum connects to malleus, which starts to vibrate, transmitted to incus then stapes
- vibration of stapes causes oval window membrane to move in and out (more vigorous vibration then ear drum)
- mvmt of oval window causes fluid pressure waves in perilymph of cochlea (as oval window bulges in, pushes perilymph in scala vestibuli)
- pressure waves go from scala vestibuli to scala tympani, also push vestibular membrane back and forth, causing waves in endolymph of cochlear duct
- waves in endolymph causes basilar membrane to vibrate, moving hairs of the spiral organ against the tectorial membrane- producing receptor potentials ans ultimately generate nn impulses
What do inner hair cells do? Outer hair cells?
inner- transform sound wave vibrations into action potentials that travel along cochlear nn
outer- enhances sensitivity of inner
How do hair cells cause a generator potential?
movement causes opening and closing of K+ channels
- opening of K+ channels leads to depilarization of hair cell, influx of Ca2+ and release of glutamate
- closing of K+ channels does the opposite
What causes sound waves?
alternating compression and decompression of air
What measures the frequency of a sound wave?
What measures the amplitude of a sound wave
hertz
decible
What frequency of sound waves can the human ear detect?
20-20,000 Hz, but hears best between 1000-4000 Hz
speech is 300-3000 Hz
How many decibles is speech? When does damage occur?
speech is 60 dB
damage at >85 dB
pain at 120-140 dB
What causes differences in pitch?
differences in width and stiffness of basilar membrane
high pitch=high frequency- vibration of basilar membrane near base of cochlea
low pitch=low frequnecy- basilar membrane vibrates near apex of cochlea (wide and flexible)
How does pitch relate to volume?
loud sounds cause greater vibration amplitude, vibrating multiple areas of basilar membrane, increasing amount of electrical signals sent which translates to "loud"
Describe the auditory pathway
- bending of hair cells causes release of glutamate, generates nn impulse in cells bodies of spiral ganglia
- axons of spiral ganglia form cochlear branch of vestibulocochlear nn (CN VIII)
- cochlear branch sends signal to cochlear (ipsilateral) and superior olivary nucleaus (bilateral) within medulla oblongata and pons (respectively)
-fibers then ascend to midbrain (inferior colliculi)
- thalamus (medial geniculate nucleus)
- primary auditory area of temporal lpbe (areas 41 and 42)

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Where does the R primary auditory area recieve nerve impulses from?
both ears- many axons decussate in the medulla, but not all of them
What is nerve deafness?
usually due to damage of hair cells, but sometimes due to nn damage
person usually doesnt notice until they realize they have difficulty with frequncies of speech
What is conduction deafness?
perforated eardrum, osteosclerosis, vibrations not conducted to hair cells
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