Hearing Anatomy: Inner Ear Part 1

Cochlea

o Oval Window

o Round Window

o 3 Chambers

Vestibular System

o Semi circular canals

• Housed in petrous portion of

temporal bone

o Cavity in bone

Labyrinth

intricate maze of

connecting pathways

o Osseous labyrinth

o Membranous Labyrinth

Bony Labyrinth

– complex cave in solid bone (hardest bone in body)

Three Primary Parts of Bony Labyrinth

 Vestibule

 Semicircular Canals

 Cochlea or cochlear canal

Membranous Labyrinth

delicate membranes lining the bony labyrinth

Neuropethelium

– stem cells of the central nervous system

Vestibule

• Separates cochlea and semicircular canals

• Large, central room/compartment to which other components open

• Has the oval and round window

The Oval Window

Opening of labyrinthine wall of the ME space, leading to the scala vestibuli of the cochlea

The Round Window

• Membrane covered opening in the labyrinthine wall of ME space leading into the scala tympani of the cochlea

• Pressure release valve

• Inferior

Cochlea

• Auditory portion of the inner ear

• Contains sensory organ of hearing

• Function: Hearing

• Greek: land snail

• 30-35 mm in length; 1 cm wide

• Snail shaped structure approximately 2 ½ turns

• Coils around modiolus

Modiolus

• Central spongy bone core of the cochlea

o Modiolus is the middle

• Conical shaped central axis

Chambers of the Cochlea

3 fluid filled chamber called "scalae"

o Aka ducts or sacs

Chambers of the Cochlea: Scala Vestibuli (top)

o Perilymph filled

 Neutral charge

Chambers of the Cochlea: Scala Tympani (bottom)

o Perilymph filled

 Neutral charge

Chambers of the Cochlea: Scala Media (Middle)

o Endolymph filled

 Ionic charge

Helicotrema

• Cochlear chambers are not completely isolated

• Small passage at the apical end of the cochlea

• Connects the scala vestibuli and scala tympani

Cochlear Fluids

Perilymph and Endolymph

Cochlea Fluids: Perilymph

High in sodium

Cochlea Fluids: Endolymph

high in potassium

Fluid Movement

Stapes footplate movement in oval window causes waves in fluid of cochlea

• Fluid displacement occurs

Scala Media: Reissner's Membrane

ceiling

Scala Media: BM and osseus spiral lamina shelf

– floor

Scala Media: Spiral Ligament & Stria Vasularis

wall

Membranes of the Cochlea - dividing membranes

– divide scalae from each other

Reissner's Membrane

• Separates scala vestibuli from scala media

• Permeable so chemicals and nutrients can pass through, but not the fluid itself

• Thin so can tear with significant head/ear trauma

• Functions as a division

Basilar Membrane

• Base FLOOR of the scala media

• Divides scala media from scala tympani

More sturdy than Reissner’s membrane

Tonotopic Organization

• Basilar membrane is tonotopically organize

Tonotopic Organization: • Base is narrow and stiffer -

o High Frequency Dominant

Tonotopic Organization: • Apex is wider, more massive, and more flaccid

o Low Frequency Dominant