The auditory system Flashcards
what is sound
are audible variations in air pressure
what do we perceive high frequency waves as
a high pitch
what do we perceive high intensity waves as
louder
what is the range the human auditory system can respond to pressure waves
20Hz-20 000Hz
for a sound to be perceived as having a pitch (low and high) its determined by what
frequency
what does sound intensity determine
the loudness we perceive
the outer ear extends from where to where
pinna to the tympanic membrane
what makes sound waves stronger / amplifies sound in the outer ear
pinna
what is the design of the human pinna like
has a poor design ( when you cup your ears the sound quality improves)
what is the tympanic membrane
its a thin semi transparent partition between the outer ear and middle ear
what covers and lines the tympanic membrane
its covered by the epidermis and lined by simple cuboidal epithelium
how long do tears on the tympanic membrane take to heal
a month
what lines the eternal acoustic meatus
hair cells and specialized sweat glands called ceruminous glands
what do ceruminous glands do
secrete cerumen/ earwax
what are the functions of ear wax
-keeps skin in ear canal soft
-keeps bugs out
what happen to sound waves in the middle ear
they change to mechanical energy
what separates the middle ear from the inner ear
the round and oval window
what parts make up the middle ear
-the back of the tympanic membrane
-3 auditory ossicles (malleus, incus, stapes)
-eustachian tube
what do the ossicles do
they transmit vibrations from the tympanic to the oval window
what is the handle of the malleus attached to
the inner wall of the tympanic membrane
what is the head of the malleus attached to
its attached by a tiny synovial joint to the incus
which part of the stapes is in contact with the oval window
the foot plate
what keeps the foot plate of the stapes held in place in the oval window
a flexible annular ligament
why cant sound waves simply directly move the membrane at the oval window
-because the cochlea is filled with fluid not air
-because the fluid in the inner ear resists being moved much more than air does, so more pressure is needed to vibrate the fluid than the air can provide
-because ossicles provide the necessary amplification in pressure
when will the pressure at the oval window become greater than the pressure at the tympanic membrane
- when the force on the oval window membrane is greater than that on the tympanic membrane
-when the surface area of the oval window is smaller than the area of the tympanic membrane
how does the middle ear increase pressure at the oval window
by altering both the force and surface area
what innervates the tensor tympani muscle
the trigeminal nerve
what is the tensor tympani attached and anchored to
its attached to the malleus and anchored to bone in the middle ear cavity
what innervates the stapedius muscle
the facial nerve
where is the stapedius muscle anchored and attached to
its anchored to a bone in the middle ear cavity and attaches to the stapes
what happens when the stapedius and tensor tympani muscle contract
the chain of ossicles become much more rigid and sound conduction to the inner ear is greatly diminished
what does an onset of a loud sound trigger
a neural response i.e. the attenuation/ acoustic reflex that causes the muscles to contract
when is sound attenuation much greater
at low frequencies that at high frequecies
why does the attenuation reflex not offer much protection
this is because it has a 50-100msec delay from the time that sound reaches the ear, hence why it doesnt offer much protection from very sudden loud sounds, so damage might already be done by the time the muscles contract
when is the attenuated reflex thought to be activated since the reflex suppresses low frequencies more than high
when we speak, so we don’t hear our own voices as loudly as we otherwise would
what does the eustachian tube do
-drains cells/tissues
-it equalizes air pressure between the outside air and middle ear cavity
how is the eustachian tube normally closed or open
yawning, chewing and swallowing opens the tube by contracting the tensor palatini muscles
how does the eustachian tube play a role on otitis media
pathogens travel from the throat and nose via the eustachian tube
why are children more susceptible to ear infections (otitis media)
because their auditory tubes are shorter, narrow, and almost horizontal which decreases drainage efficiency
the first 1/3 of the tube is surrounded by what
bone
the remainder 2/3 of the eustachian tube is surrounded by what
an incomplete ring of elastic cartilage
what is the meeting point of the bony and cartilaginous portions of the eustachian tube
isthmus
why is constant supply from the eustachian tube necessary
because cells lining the middle ear absorb air
what happens when the eustachian tube is blocked
the eardrum is sucked into the middle ear and this causes pai, pressure and hearing loss
how can fullness in ears be alleviated
by popping the ears (when eustachian tube opens)
what normally keeps the eustachian tube in the closed state
the hook shaped arrangement of the eustachian tube cartilage
what does the inner ear consist of
the cochlea and labyrinth
the cochlea is part of what system
auditory system
the labyrinth is a part of what system
the vestibular system
what is the cochlea
its a snail shaped, pea sized and filled with fluid
what are the 3 tubes of the cochlea
- scala vestibuli
- scala media
- scala tympani
what does the scala vestibuli contain
perilymph which is similar to CSF and has low K+ and high Na+
what does the scala media contain
endolymph which has ionic concs similar to intracellular fluid i.e. high K+ and low Na+
what does the scala tympani contain
perilymph, which is similar to CSF and has low K+ and high Na+
what does the scala vestibuli meet
oval window
what does the scala tympani meet
the round window
what does inward motion at the oval window do
pushes perilymph into the scala vestibuli, and because the fluid pressure has no where to escape the membrane at the round window then bulges out in response to the inward movement of the membrane at the oval window
what is the cochlear duct
its a small canal in the bony labyrinth that contains the perilymphatic which drains perilymph into the CSF of the subarachnoid space
where does the lateral end of the cochlear duct arise from
the scala tympani
where is the endolymphatic sac and duct
the membranous labyrinth
what does the endolymphatic duct do
drain endolymph from the auditory and vestibular apparatus
what does the endolymphatic sac do
it acts as both a reservoir for endolymph and the site for reabsorption into the epidural space
on the surface of the basilar membrane of the cochlea lies what
the organ of corti
what does the organ of corti contain
hair cells
where are the hair cells in the cochlea
they are sandwiched between the basilar membrane and the reticular lamina
what do the rods of corti (pillar cells) do
they span the basilar membrane and tectorial membrane and provide structural support
in the organ of corti hair cells between the modiolus and the rods of corti are called what
inner hair cells (arranged in a single row)
in the organ of corti cells farther out than the rods of corti are called what
outer hair cells (arranged in 3 rows)
each hair cell in the organ of corti has what
about 100 stereocilia on its apical border
the hair cells in the organ of corti extend how
they extend above the reticular lamina into the endolymph
where do the tips of the hair cells in the organ of corti end
in the gelatinous substance of the tectorial membrane (outer hair cells) or below the tectorial membrane (inner hair cells)
what do the hair cells in the organ of corti do
generate impulses in response to sound vibrations
where do stereocilia become progressively longer
on the side of the hair cell away from the modiolus
what are the tops of the shorter stereocilia are attached to what
to the back sides of the longer adjacent longer stereocilia by thin filaments
what happens when the cilia are bent in the direction of the longer stereocilia (auditory signal transduction)
-the tips of the smaller stereocilia are tugged outward from the surface of the hair cells
-this causes a mechanical transduction, where cation conducting channels open and there is a K+ influx from the surrounding scala media fluid into the stereocilia and the hair cell membrane gets depolarized
-this then opens voltage gated calcium channels
-Ca2+ influx then triggers the release of the neurotransmitter glutamate which activates the spiral ganglion fibres lying postsynaptic to the hair cell
what are the central pathways for the auditory system
-afferents from the spiral ganglion enter the brain stem in the auditory vestibular nerve
-at the level of the medulla the axons innervate the dorsal cochlear nucleus and the ventral cochlear nucleus ipsilateral to the cochlea where the axons originated
-from the cochlear nucleus auditory info is transmitted to:
1. superior olivary nucleus (pons, decussation)
2. lateral lemniscus (midbrain)
3. inferior colliculus (midbrain)
4. medial geniculate nuclei (thalamus)
all levels of the central auditory system receive and process info from where
both the ipsilateral and contralateral sides
what is otitis externa
inflammation of the outer ear
what is otitis media
inflammation of the middle ear
what is cholesteatoma
its a skin lined cyst that begins at the margin of the eardrum and invades the middle ear and mastoid (benign tumor)
what is conductive hearing loss
its damage to or obstruction of the outer or middle ear
what is sensorineural hearing loss
its gradual loss of hearing resulting from an abnormality in either the inner ear, auditory nerve or both
what is tinnitus
ringing in the ear
what causes tinnitus
-exposure to loud noises
-aging
-infections
what things can block the auditory tube
-inflammation of the nasal lining, which narrows the opening
- nasal allergy
-obesity (excess fat deposits along passageway)
What other things can block the eustachian tube
-inflammation of the nasal lining
-nasal allergy
-obesity
