ossicles, muscles of middle ear, 3 mechanisms associated with middle ear's impedance matching function

ossicles

the three smallest bones in the human body, forming a chain that transmits sound vibrations from the tympanic membrane to the inner ear

hammer

malleus nickname

anvil

incus nickname

stirrup

stapes nickname

malleus

attached to the tympanic membrane (eardrum)

incus

bridge between the malleus and stapes

stapes

smallest bone in the body, footplate rests in the oval window of the cochlea, transmitting mechanical energy to the inner ear fluids

oval window of the cochlea

where does the footplate of the stapes rest?

tensor tympani

Origin: Auditory tube and surrounding bone.

Insertion: Malleus (manubrium).

Function: Tenses the tympanic membrane to reduce vibration — protects against loud sounds (especially self-generated ones like chewing).

Innervation: Mandibular nerve (V3) of the trigeminal nerve

stapedius

Origin: Posterior wall of the tympanic cavity.

Insertion: Neck of stapes.

Function: Pulls stapes away from the oval window to reduce transmission of strong vibrations (acoustic reflex).

Innervation: Facial nerve (CN VII)

area ratio effect

• most effective mechanism of the middle ear

• the tympanic membrane is 17x larger than the stapes footplate / the oval window

• the size difference concentrates force, increasing pressure at the oval window

• amplifies 20/25 dB

ossicular lever

• mechanical lever system formed by the malleus and incus

• The manubrium of the malleus is longer than the long process of the incus, creating a lever with mechanical advantage

catenary lever (bucking effect)

• The pressure at the umbo is about 2 times (6 dB) greater than the pressure across the entire membrane.

• A "catenary" is a curve formed by a hanging flexible structure. The tympanic membrane behaves like a catenary due to its conical shape.

• This curvature focuses energy toward the central attachment point (manubrium), increasing force applied to the malleus.

• Acts like a lever, enhancing transmission efficiency beyond what a flat membrane could achieve

32 dB

40 times increased sound pressure at the stapes footplate, which
results in roughly what?