Middle Ear

Question 1

Posterior View

Answer 1

Fossa of incus, stapedius tendon

Question 2

Fossa of incus

Answer 2

short process of incus attachs

Question 3

stapedius tendon

Answer 3

emerges from pyramidal eminence and attaches to stapedius muscle

Question 4

ossicular chain

Answer 4

bones are small because doesn’t impact transmission of sound through middle ear

malleus, incus, stapes

Question 5

malleus

Answer 5

• head: large structure at top, forms saddle shaped joint with incus (incudo-mallear articulation)
• neck: attachment of tensor tympani, lateral process of malleus, anterior process of malleus (along axis of rotation)
• handle/manubrium: where eardrum attaches –> umbo=connection to TM

Question 6

incus

Answer 6

-body: incudomallear articulation (stiff joint)

-crura (legs):
short process –> goes posterior and is attached to posterior incustapedial articulation incuodal ligament, lies along axis of rotation (delicate joint)
long process –> incudo-

Question 7

stapes

Answer 7

thin sheet of bone with outer rim

• head: stapedius tendon inserts
• crura
• footplate: held into oval window by annular ligament

Question 8

Eustachian Tube

Answer 8

runs from anterior wall of middle ear cavity to nasopharynx

lateral 1/3 is in musculotubal canal
medial 2/3 is cartilaginous

Question 9

resting position of eustachian tube

Answer 9

naturally shut so stuff can’t go up into it, mucosal lining is sticking when open and close eustachian tube

Question 10

salpingopharyneus muscle & tensor & levator palatini muscles

Answer 10

helps to contract eustachian tube

Question 11

ME Muscles

Answer 11

When ME muscles contract, stapedius pulls on tensor tympani on the stapes footplate and stiffens ossicular chain

transmission drops

primary for low frequencies

ME muscles move slowly and smoothly because otherwise creates more internal noise –> work obliquely and are pennate-striated muscles

Question 12

Tensor Tympani

Answer 12

Motor Innervation: V
Motor unit size ~7 (# muscle fibers controlled by 1 neuron, smaller means more richness of innovation)

Activation: acoustic and non acoustic (startle reflex)

Question 13

Stapedius

Answer 13

Motor innervation–> VII

Activation: acoustic–>acoustic reflex (sounds above 80dB produce activation) motor unit size 1.16:1

Automatic gain control for ME, turn down volume more and more at low frequencies