UNIT 7: External Ear and Middle Ear Flashcards
3 transduction/transmission parts of hearing
transduction of sound from acoustical energy to mechanical energy
transduction of mechanical energy into electrochemical energy
transmission and interpretation of electrochemically produced siganl
the ear is a structure that houses the….
vestibulocochlear organs for senses of equilibrium and hearing
3 divisions of ear
external ear
middle ear
inner ear
main function of the external/outer ear
gathering and conducting sound to tympanic membrane
external outer ear includes
auricle and concha
external auditory meatus
lower animals have an advantage w their external ear
can control position of auricles to capture sound using auricular muscles (innervated by CN VII)
Most visible part of hearing apparatus
auricle/pinna
auricle/pinna are made of…. and attached to the ….
flexible, thin elastic cartilage core = auricular cartilage
attached to skull around opening of external auditory meatus by muscles and ligaments
cartilaginous core of pinna is continuous w ______
cartilaginous portion of EA
structures of auricle/pinna are constant despite…
genetic variation in shape and size
auricle/pinna reaches adult size by
9-12 years
external auditory meatus is ____ in length, from ____ to _____, roughly ____ shaped in path
2.5 cm
concha to tympanic membrane
S shaped
external auditory meatus’s lateral 1/3 is _____ and medial 2/3 is ____
cartilaginous
bony
bony portion of EAM diameter is slightly ____ then cartilaginous portion, _____ end is sloped, EAM has its own _____ characteristics
less then cartilaginous portion
medial
resonant
EAM’s bony portion has a narrow concentric groove called
tympanic sulcus
tympanic membrane is a ____ and ____ membrane, ___mm in diameter - separates the ___ from _____
thin and oval
10 mm
external ear from tympanic cavity
differences in lengths of roof and floor of EAM put the TM in an _______
oblique position
angle formed bw TM and floor of the EAM is about 55’
under the light the tympanic membrane has a
glistening pearly grey appearance
bc of the TM’s concavity and oblique orientation the anterior/inferior quadrant…
glows brightly and is called the cone of light
TM is _____, w its center point called the ____
concave
umbo
TM is semitransparent - the outline of the _____
handle of malleus (attached to medial surface) can be seen extending upwards and forwards
two regions of the TM are
pars flaccida and pars tensa
malleolar fold in the TM is
created by ligament attaching lateral process of malleus to TM
the TM is attached to the tympanic sulcus of the EAM by
a fibrous ring = annular ligament - aka a circular ring of CT …. annular meaning it runs all the way around
annular ligament has ____ CT in the region of the pars flaccida and ____ CT in region of the pars tensa
sparse CT
fibrous CT
TM is a trilaminar membrane, its 3 layers are
lateral surface = continuous w skin of EAM
middle layer = core of fibrous CT
inner (medial) layer = continuous w mucosa of TM
the skin covering the auricle and lining the ear canal and lateral surface of the TM is …. what is found in this skin?
closely attaches to underlying cartilage and bone
hair follicles, sebaceous and ceruminous glands - cerumen (ear wax) formed from glandular secretions entraps foreign particles, protecting the hearing apparatus
concha and pinna are innervated by
facial nerve VII
Auricular branch of vagus X
glossopharyngeal IX
EAM and external TM innervated by
facial nerve VII
auricular branch of vagus X
auriculotemporal branch of mandibular nerve (V3)
why is the ear innervated by so many CNs?
its important
rly wanna be able to feel foreign particles
otitis externa is …. caused by …
inflammation of the skin of the external ear
swelling is v painful - inc tension on the epithelium that is tightly bound to underlying cartilage or bone
bacterial infection following trauma or abrasion
viral infection, including herpes zoster
trauma - destruction cartilaginous infrastructure
tympanic cavity is
the space w/i the petrous portion of the temporal bone
the tympanic cavity contains the ossicles which
transmit sound vibrations from TM to the inner ear mechanism
Tympanic cavity is lined w … communicates with ….
mucous membrane
communicates w nasopharynx by eustachian tube
communicates w mastoid air cells by mastoid antrum
tympanic cavity can be divided into 2 parts
tympanic cavity proper - lies opposite the tympanic membrane
epitympanic recess (attic) - part of the tympanic cavity above the limits of the TM - head of malleus and most of the incus are w/i the epitympanic recess
size of the tympanic cavity - which dimension is smallest?
very small cavity approx 2 cm cubed
vertical 15mm
ant/post 15mm
transverse (lat/med) = 6mm superiorly, 2mm opposite umbo of TM
tympanic cavity can be thought as a ___ sided ___
6 sided box
floor, roof, anterior wall, posterior wall, medial wall, lateral wall
what are the walls of the tympanic cavity made of
all walls are bony except the lateral wall, which is the tympanic membrane
floor of the tympanic cavity is the … and contains the …
jugular wall
thin plate of bone overlying the jugular fossa
contains the tympanic canaliculus - near the medial wall
roof of the tympanic cavity is the …. also called the…. directly above the roof is the
tegmental wall
thin plate of bone called tegmen tympani
middle cranial fossa
the anterior wall is relatively small because
the roof and floor slope toward each toher
the upper most structure of the anterior wall is the
canal of the tensor tympani muscle
tensor tympani m is enclosed in
a bony canal above the eustachian tube - separated by a thin shelf of bone called processes cochleariformis
opening of the eustachian tube into the tympanic cavity is located
just below the tensor tympani m on anterior wall
on the anterior wall is the _____ fissure, where ______ of CN VII exits the tympanic cavity
petrotympanic fissure
chorda tympani
Tubes placed in ear if there is a faulty eustachian tube …. where is it placed and why?
middle ear is filled with air because of the eustachian tube, so if this tube is not functioning the air cannot be maintained, mucous may build up …. need another tube to equivalize pressure, so they put a tube through the pars tensa so that they can equalize this pressure and maintain air in the middle ear
skin of TM will grow around it and eventually tube will need to be replaced
the posterior wall is _____ and its lower portion is made of _____
incomplete
bone
upper portion of the posterior wall consists of
an opening called the aditus through which the tympanic cavity is in communication w the mastoid antrum and mastoid air cells
mastoid air cells
series of communicating mucosa-lined air filled spaces located w/i the mastoid part of the temporal bone
assist in pressure equalization w/i the TC
pyramidal eminence is ….and is located on ….
a conical projection of bone near the junction w the medial wall - on posterior wall tho
close to oval window
stapedius m is enclosed in….
the pyramidal eminence - tendon passes from the pyramid to the neck of the stapes
posterior canaliculus is on the …. what enters through it?
posterior wall - near supero-posterior edge of TM
chorda tympani of CN VII enters TC thru it
what is the lateral wall
TM w attached handle of malleus
chorda tympani crosses the upper part of the TM along its course from the posterior wall to its exit on the anterior wall
median wall is also called the _____ wall and forms the ____ surface of the inner ear
labyrinthine wall
lateral surface
surface of the median wall is
furrowed and lodges the nerves of the tympanic plexus (CN IX fibres that provide sensory inn of middle ear)
the promontory is … and is located on…
prominent buldge that is formed by the basal turn of the cochlea of the inner ear
on median wall
fenestra vestibuli aka oval window is located ….. and leads to/is closed by
on median wall
above and behind promontory
leads to scala vestibuli of the inner ear
closed/covered by the base or footplate of the stapes
fenestra cochleae aka the round window is located … and is closed by…
median wall
located below and posterior to promontory
end of scala tympani of inner ear
closed by the secondary tympanic membrane
processes cochleariformis is located on … it is a … what tendon is involved
the median wall
thin curled ledge of bone that separates the canal for the tensor tympani muscle from the bony part of the eustachian tube
tendon of the tensor tympani m lies on this bony shelf prior to turning and inserting on the handle of the malleus
how are the ossicles held in the TC?
suspended via 8 ligaments - the joints are synovial
the ossicles are … and transmit…
3 bones that form a chain across the TC
malleus, incus, stapes
transmit sound vibrations
malleus attaches to ____, incus articulates with ___ and _____, stapes attaches to _______
TM
Incus w/ malleus and stapes
stapes attaches to fenestra vestibuli
since the malleus, incus, stapes are connected via synovial joints that means
they are subject to all probs associated w synovial joints like arthritis
describe dev of ossicles
reach final size and are completely ossified at birth
tensor tympani: O, I, A, Inn
O = cartilage of eustachian tube and adjoining greater wing of sphenoid
I = tendon inserts onto upper end of manubrium of the malleus
A = tenses the tympanic membrane by drawing the malleus medially
Inn = CN V
stapedius: O, I, A, Inn
O = internal walls of pyramidal eminence on posterior wall of tympanic cavity
I = neck of stapes, via stapedius tendon
A = rotates stapes posteriorly (prevents excessive oscillations)
Inn = CN VII (stapedial branch)
describe the acoustic reflex
stapedius muscle applies a force to footplate of stapes, reducing amplitude of footplate’s movement, reducing sound pressure level reaching cochlea
stimulation of either ear results in response in both ears
the acoustic reflex is a basic protective mechanism for the cochlea as it
is triggered by loud sounds (>85 dB SPL)
attenuates intensity of own speech
most effective for low frequencies
the eustachian tube provides…
communication bw TC and nasopharynx
the eustachian tube is about ___ cm long, has a ____ and ____ part
3.5 cm
bony and cartilaginous
the eustachian tube allows for…. describe opening/closing
allows for aeration of the middle ear sys and clears mucous from the ME into the nasopharynx
opening = equalizes pressure in the ME w atmospheric pressure, thereby permitting free movement of the TM
closing = protects ME from pressure fluctuations and loud sounds
whats the bad part of having a eustachian tube…. how is this avoided?
inadvertently forms passageway for infections to travel from nasopharynx to middle ear
mucocilliary action drains mucous away from ME into NP, in attempts to prevent infection from travelling up into ME
in infants the ET is ____ long, and is more _____
18 mm
more horizontal, less angulated
in adults the ET is ____ long, direct ____ and _____ from ME
36 mm
directed downward and forward, medially
as orientation of the ET changes during dev, it….
dec the likelihood for bacteria to pass from NP to ME
lateral 1/3 of ET is ____ and medial 2/3 of ET is ____
bony
cartilaginous
describe the bony part of the ET
arises from anterior wall of the TC
passes thru petrous portion of temporal bone
opens on the base of the skull bw the petrous bone and sphenoid bone
describe the cartilaginous part of the ET
lateral end joins bony portion at petrous bone
lumen is roughly triangular in shape
wider medial end opens into the mucosa of the NP; end of cartilaginous tube raises the mucosa to form the tubal elevation aka torus tubaris
lined w resp epi (columnar ciliated cells, mucous glands)
4 muscles originate from the ET
tensor veli palatinin
levator veli palatini
tensor tympani
salpinogopharyngeus m
which muscles open the cartilaginous part of the ET
tensor veli palatini (does most of the work)
levator veli palatini
tensor tympani
which muscle helps to close the ET
salpingopharyngeus m
otitis media is….
any condition in which fluid accumulates in the middle ear
ET does not allow equalization of pressure bw ME and enviro
relative neg pressure can dev in ME
serous fluid is drawn into the ME from the blood of the ME tissues, and mucous secretion can also be stimulated from ME tissues
may need tube in TM
