middle ear Flashcards
tympanic cavity
overview or the middle ear
-contains 3 ossicles
-bones and air
function of the middle ear
turns acoustic sound waves into mechanical vibrations
epitympanum
upper portion
-attic
-from top of TM and up
mesotympanum
middle part that contains the height of the TM
hypotympanum
lower part
-basement
-goes to eustachian tube
tympanic membrane
starting point of middle ear and the ending point of the outer ear
-walls off from ear canal air
mastoid antrum
the air space in petrous portion of temporal bone that communicates with mastoid cells
aditus ad antrum (inlet)
the opening into the mastoid antrum
-part of the epitympanum portion
mastoid air cells
a protective mechanisms appearing like bubbles within the mastoid bone
-pockets of air within the bone
mastoiditis
infection of the mastoid process
-middle ear infections that leads through the aditus ad antrum
roof of middle ear
“attic” made of temporal bone
floor of middle ear
bottom of the tympanic cavity
lateral wall of middle ear
membranous wall in the tympanic membrane
medial wall of the middle ear
labyrinthine wall, separates the cavity from the inner ear
-oval and round window
anterior wall of the middle ear
carotid wall
-separates cavity from carotid canal
posterior wall of the middle ear
mastoid wall
-connecting the cavity to the mastoid cells
tympanic membrane landmarks
pars flaccida, manubrium of malleus, umbo, cone of light, pars tensa, and tympanic annulus (ring around the membrane)
left vs. right ear with view of tympanic membrane
left : cone of light on left side, manubrium facing left
right : cone of light on right side, manubrium facing right
normal tympanic membrane view
membrane appears translucent, cone of light, no bulging or indent
abnormal tympanic membrane view
can include a bulge, may not be translucent, could have holes or tears, could appear red
eustachain tube
directed downwards, forward, and medially from middle ear and into the pharynx
lateral third of the eustachian tube
bony portion arising from the anterior wall of the cavity
-widest at the tympanic end
medial two thirds of the eustachian tube
fibrocartilaginous portion entering the nasopharynx
-consists of a plate of cartilage
direction of the eustachian tube
comes off of middle ear and comes into behind the turbinates of the nose
-cartilaginous eustachian tube is attached to the skull base in a groove between the petrous part of the temporal bone and the greater wing of sphenoid
functions of the eustachian tube
ventilation of middle ear, drainage of middle ear secretions, protection from excessive nasopharyngeal sounds and secretions
patulous eustachain tube
a disorder when the valve of the tube remains open
-can cause you to hear your own voice or own breathing too loudly
effect of eustachain tube dysfunction
can cause unequal pressure
how does the orientation differ between a child and adult’s eustachian tube
a child’s lies lower and the tube is generally more horizontal
-less angulated to those in adults
issues of a eustachian tube in a child vs. adult
in a child, ventilatory functions is less effective, there are repeated incidences of middle ear disorders, and functions can be impaired by presence of cleft palate
4 muscles related to the ET
tensor veli palatini, levator veli palatini, salpingopharyngeus, and tensor tympani
valsalva
how to correct the negative middle ear pressure lock
-a maneuver to force expiration against a closed glottis
3 ossicles
malleus, incus, and stapes
malleus
head, anterior process, manubrium, neck, articulatory facet for incus, and lateral process
-1st bone in the sequence
incus
facet for malleus, body, short and long process, lenticular process
-2nd bone in the sequence
stapes
head, neck, anterior crus, posterior crus, and stapes footplate
-3rd bone in the sequence
functions of the ossicles
transports the mechanical vibration
-supports from ligaments and support from muscles
-bones works as a lever
function of the ossicles and the TM
increased force is picked up by the TM and by the time it pushed on the footplate, there is enough force to push the fluids within the cochlea
-remember oval window is pushed on and round window is the fluid escape
tendons of the ossicles
tensor tympani : on manubrium of malleus
stapedial muscle : comes off stapes
ligaments of the ossicles
anterior mallear, lateral mallear, superior mallear, superior incudal, posterior incudal, and stapedial annular
middle ear impedance matching function
trying to match the amount of resistance in outer vs. inner ear
3 contributions of impedance matching
lever action, area difference of the TM compared to stapes footplate and the buckling of the tympanic membrane
what bones are involved in the lever action
malleus and incus
if we did not have the impedance matching, what would occur
would lose around 99% of energy because it would bounce off the eardrum
how much gain occurs with impedance matching
33-34 dB
-size difference contributes the most
middle ear muscle reflex
contraction of the stapedius muscle occurs as a response to loud sounds
-protects our ear from our own voice
-stapedius muscle contracts 50 msec prior to vocalization
what is required for a MEMR to occur
normal ME mechanics and normal TM movement, a loud sound, and neural synchrony
ipsilateral reflex arc
3 arch : CN 8 to antero-ventral cochlear nuclei to facial motor nucleus to stapedial muscle
4 arch : nerve fibers to antero-ventral cochlear nucleis to medial superior olive to facial motor nuclei to stapedial muscle
contralateral reflex arc
1st route : CN 8 to antero-central cochlear nuclei to medial supeior olive crossover to facial motor nucleus to stapedial muscle
2nd route : CN 8 to antero-central cochlear nucleus crossover to medial superior olive to facial motor nucleus to stapedial muscle
how we measure middle ear muscle reflex
measure with immittance testing
-tympanograms, reflex, and reflex decay
what would cause the middle ear muscle reflex to be absent
any blockage along any point within the arc that would allow the signal to no longer pass through
for contralateral pathways, how would a deaf ear impact the transmittance
if the deaf ear was on the opposite side of the sound, there will still be a reflex as no “lines” were impacted HOWEVER if the deaf ear was on the side of the sound, there would be no signal detected therefore no reflex
which auditory brainstem structure is the first to receive binaural input and therefore serve to analyze interaural differences for the purpose of spatial localization
the superior olivary complex
what brainstem nuclei are the first stopping point for incoming auditory projections from the cochlea being carried on cranial nerve 8
cochlear nuclei
when an auditory stimulus reaches the cochlea what occurs to excite inner hair cells
potassium flows through the open ion channels to depolarize the cell, causing a receptor potential
why do we have two ears with 2 auditory and vestibular systems
2 ears for auditory and vestibular because the brainstem takes both sides information and processes and compares it
