equilibrium and hearing (theory) Flashcards
what are the two functions of the structures of the ear?
- hearing
- balance
what are the 3 subdivisions of the ear?
- external ear
- middle ear
- inner ear
components of the external ear
- auricle
- external acoustic meatus
- elastic cartilage
components of the middle ear
- tympanic membrane
- auditory ossicles (MIS)
- tympanic cavity
- stapedius
- tensor tympani
components of the inner ear
- cochlea
- round window
- oval window
- vestibule
- semicircular canals (vestibular region)
- cochlea branch (CN VIII)
- vestibular branch (CN VIII)
- facial nerve (CN VII)
- auditory tube (eustachian)
- bony labyrinth
- utricle
- saccule
external acoustic meatus function
- air conduction of the sound waves
- cone shape lends itself to sound wave collection
tympanic membrane function
AKA the ear drum
to vibrate when struck by incoming sound waves
this moves the malleus ossicle which moves the stapes
malleus function
the malleus facilitates air to bone conduction
this is the transition of sound waves of the air to bone movement which can be transferred into an impulse by hair receptors
stapes function
the foot of the stapes is imprinted onto the oval window which transfers the bone vibrations to the cochlea
cochlea function
to receive transmitted sound waves
the smaller diameter receives low pitch sound
the larger diameter receives high pitch sound
auditory tube function
AKA eustachian tubes
these minimize the air pressure of the middle ear
you can open your auditory tubes by swallowing
stapedius function
it is attached to the round window and contracts with high sound intensity protect the cochlea
which is better air or bone conduction of sound?
air
ceruminous gland function
a modified apocrine gland
this secretes earwax which moistens the external ear canal
if there was no moisture, the canal would crack which would be VERY painful
3 auditory ossicles (MIS)
- malleus
- incus
- stapes
tensor tympani function
protects the tympanic membrane from high intensity sound
it contracts and stops the tympanic membrane from moving
it is attached to the malleus bone
semicircular canal function
to establish orientation and provide balance, it is part of the vestibular complex
what does the vestibular complex detect?
- rotation
- gravity
- acceleration and deceleration
what does the vestibular complex consist of?
- semicircular canals
- utricle
- saccule
semicircular canal duct contents
contains…
- endolympth (fluid)
- cupula (gel)
- ampulla
- crista (within the ampulla)
- kinocilium
- stereocilia
head movement and endolympth
due to physics the endolymph fluid inside the ducts of the semicircular canals, the fluid moves with the rotation of the head (opposite) and bends the stereocilia and kinocilium which fires an AP
endolymph and dizziness
moving ones head in a circle and stopping abruptly results in dizziness because the hair cells bend back and forth causing confused signaling
utricle and saccule
they are connected to each other and to the ampulla
macullae
clustered hair cells of the utricle and saccule
cupula
a gel like material that encases the hair cells and has a crystal layer of calcium carbonate on top of it (statoconia)
the capula moves according to gravity
otolith
the cupula and the statoconia
anterior semicircular duct
for forward head movement (nodding yes)
lateral semicircular duct
for lateral head movement (shaking no)
posterior semicircular duct
for tilting the head up
vestibular branch sensory relay
the vestibular branch of the vestibulocochlear nerve synapses onto the vestibular nuclei between the pons and the medulla
where does the vestibular nuclei signal to?
- to the cerebellum
- to the accessory nerve
- to the abducens nerve
- to the trochlear nerve
- to the oculomotor nerve
- to the red nucleus
- to the superior colliculus
- vestibulospinal tract
- cerebral cortex
why does the vestibular nuclei signal to nerves of eye?
because the eye is also involved in orientation of balance and position
what is the main structure involved in hearing
the cochlea
the center of the cochlea
called the modiolus which contains sensory neurons
what cranial nerve innervates the cochlea?
the cochlear branch of the vestibulocochlear nerve (CN VIII)
spiral organ of the cochlea
organ of corti
3 layers of the cochlear spiral
- scala vestibuli
- scala tympani
- scala media
scala vestibuli
the vestibular duct
it contains perilymph and the vestibular membrane
scala tympani
the tympanic duct
contains perilymph also
scala media
the cochlear duct
contains endolymph, this layer is between the vestibuli and the tympani
basilar membrane of the cochlea
there is a basilar membrane between each of the 3 layers
the scala vestibuli and tympani are attached apically to the cochlea
sense organs rest on the basilar membrane in the scala media
the organ of corti function
AKA the spiral organ
this rests on the basilar membrane between the scala media and tympani
it contains hair cells which are contact with tectorial membrane of the scala media
tectorial membrane movement and hair cell firing
sound waves cause the tectorial membrane to move which causes hair cells to bend and fire APs down the cochlear branch of CN VIII
hair cell damage (hearing)
- loud work environments
- loud music
this is not felt immediately but later in life
perilymph function
it is present in the scala tympani and vestibuli
as the stapes pushes against the oval window causing the scal tympani to move, so does the perilymph which causes the scala media to move
where does auditory info end up?
in the inferior colliculus of the midbrain (corpus quadrigemina)
if sound is loud enough
if sound is loud enough to reach the inferior colliculi, it will rotate the head in the direction of the sound
what is the nucleus that auditory info goes to? (MGN)
medial geniculate nucleus
where does the auditory info ultimately end up?
in the auditory cortex of the temporal lobe
auditory pathway
- specific section of the cochlea is stimulated
- fire AP down cochlea branch
- reach the cochlear nucleus
- reach the inferior colliculus of the midbrain
- send to the medial geniculate nucleus
- send to the auditory cortex of the temporal lobe
distribution of high, middle and low frequency sounds in the auditory cortex
- high –> innermost
- middle –> middle of the cortex
- low –> periphery of the cortex
inferior colliculi signalling to the ipsilateral side
normally, most auditory information crosses over at the cochlear nucleus onto the contralateral side
but the inferior colliculi does receive some auditory information and sends it to the auditory cortex on the same side of the body
