Anatomy of the External and Middle Ear Flashcards
Temporal bone is comprised of _______ separate bones and the _____________ portion develops known as the ____________
3; 4th; mastoid
What are the bones present at birth
a) squamous
b) petrous
c) tympanic portions
d) none of the above
e) all of the above
All of the above
flat sheet like bone on the outer superior surface of the temporal bone that forms part of the external auditory canal
squamous portion
the _______ process extends forward from the anterior edge of the squamous temporal bone
zygomatic
horse-shoe shaped structure that forms the floor and part of the anterior and posterior walls of the external auditory canal
tympanic portion
bulk portion with a large prominence that can be felt behind the ear
mastoid portion
what portion houses the middle and inner ear structures as a pyramid-shaped bone attached to the inside surface of other temporal bone
petrous portion
an opening on the posterior surface of the petrous temporal bone, ____________________, allows passage of the auditory vestibular and facial nerves and blood vessels
what are the small muscles that attach the auricle to the temporal (that are pointless in humans)
ant, sup, post auricularis muscles
shape determined by a cartilaginous fame, that exists everywhere but the ear lobe
pinna/auricle
the ________ plays an important role in faciliating speech percepth
concha (described as the funnel shaped portion of the external ear)
external auditory meatus is approx. ______ cm long and _____ cm in diameter
2.5cm ; 0.7 cm
the outer ______ is framed by a flexible cartilaginous frame
one third
the inner ______ is attached to the temporal bone of the skull
two thirds
WHAT IS THE PRIMARY FUNCTION OF THE OUTER (EXTERNAL) EAR
resonance !!!
state of a system where a lot of vibration is produced in response to external stimulus
(freq of stimulus is the same as the natural vibration freq of the system)
define resonance
external ear resonates with sound wave stimulation, ________. the sound pressure at the tympanic membrane
increasing (particulary in the 2k-7khZ range)
the ear canal and TM resonate to enhance pressure gain around ______
2-3kHz
concha resonates to enhance gain around _______
5-6kHz
Name all the functions of the outer (external ear)
- acoustic gain (resonance)
- aid localization of sound of space
- protection via:
- narrow channel, twisted route, hairs in outer third, wax, epithelia migration
- auriculotemporal branch of CN V
- greater auricular nerve of the cervical plexus (C2, C3)
- auricular branch of CN X
The three sources providing sensory innervation to the external ear
malleus, incus, stapes
ossicles
handle/manubrium embedded in the TM, head tightly joined by the body of the incus
malleus
lies between malleus and stapes with 2 processes (short and long)
incus
footplate attached to flexible oval window by an annular ligament
stapes
oval window
inlet for sound pressure to cochlea
tensor tympani
attaches to manubrium of the malleus
tensor tympani innervation
CN V (trigeminal nerve)
stapedius
attached to the head of the stapes
stapedius innervation
CN VII (facial nerve)
2 purpose of the middle ear muscles
(tensor tympani & stapedius)
- contraction stiffens ossicular chain (prevent noise damage)
- stiffening ossicular chain reduces transmission of low freq sounds and enhances perception of higher freq that can be masked by low frequencies
WHAT IS THE PRIMARY FUNCTION OF THE MIDDLE EAR
IMPEDANCE MISMATCH
obstruction or hindrance to movement or progress
impedance mismatch
how does middle ear accomplish impedance mismatch
1) area of TM larger than OW (most important - increases force of OW)
2) lever action of coupled malleus and incus (increases forced applied to stapes)
3) conical shape and flexibility of TM allows it to buckle as it moves (increases force slightly)
what are all the functions of the middle ear
1) impedance mismatching
2) sound transmission
3) selective application of sound energy
4) protection/damping via acoustic reflex (increase speech perception)
contraction of stapedius muscle induced by noise
acoustic reflex
what is the threshold of the acoustic reflex for individuals with normal hearing
85 dB
T/F The contraction of the stapedius muscles does NOT decrease sound transmission to the cochlea, more so for low frequencies than high frequencies
False; The contraction of the stapedius muscles DOES decrease sound transmission to the cochlea, more so for low frequencies than high frequencies
T/F The acoustic reflex is bilateral, but stronger in the ear that receives the signal
True
Functional significance of acoustic reflexes
1) amplitude compression
2) protection from loud noises
3) aids in speech discrimination at sound levels above about 90 dB
4) elevated middle ear reflex thresholds and poor growth of reflex with increasing amplitude of the sound stimulus are indicators of auditory nerve damage
functional significance for acoustic reflexes: ____________ allows changes in sound level to be still be perceived, but keeps sound levels at a more constant level
amplitude compression
functional significance for acoustic reflexes: ____________ temporary threshold shifts are much greater in persons with paralyzed stapedius muscle (i.e facial nerve damage)
protection from loud noises
T/F It is the middle and inner ear together which “model” the curve of the sensory auditory threshold, according to the quantity of acoustic energy transmitted at each frequency
False; It is the EXTERNAL EAR AND MIDDLE EAR
T/F The inner ear is a detector whose threshold for each frequency is constant across almost the whole of the audible range
True
