The Cochlea

Question 1

Cochlea as unrolled long test-tube shape

Answer 1

Heliocotema - rounded tip
Perilymph - fluid that fills the tube
Membraneous tube - in the bony tube
Endolymph - fluid that fills membraneous tube (fluids don’t mix)
Spiral ligament - attaches membraneous tube to bony tube
-Cochlea looks like spiral starcase

Question 2

Cochlea continued

Answer 2

Spiral lamina - bony shelf in bony tube half way into it, attaches to the membranous tube

• Scala vestibull - space above lamina
• Scala tympani - space below lamina
• Scala dedia - space, cochlear duct, triangular wedge shape

Question 3

Basiliar membrane

Answer 3

Basiliar membrane - base of scala media
-Spiral lamina - right hand wall of scala media
-Reissner’s membrane - left hand wall of scala media
You see this wherever you slice cochlea, except helicotrema

Question 4

Scala media

Answer 4

Organ of Corti - on top of the basilia membrane, foundation on which rests series of cells (hair cells)
Inner hair cells - most medial most row of hair cells, leans laterally and meets with 4 other rows of hair cells - outer hair cells
Tunnel of Corti - area between inner and outer hair cells
Tectorial membrane - gelatinous structure hanging over hair cells

Question 5

Movement of hair cells

Answer 5

1. Sound moves stapes, sets perilymph of scala vestibuli in motion
2. Waves travel down scala vestibuli, around helicotrema, down scala tympani, ending at round window
3. Wave hits round window and starts to go back
4. As perilymph moves, vibrations move the endolymph - sets basiliar membrane and hair cells into motion

Question 6

Movement of hair cells

Answer 6

1. When hair cells move, brush up against Tectorial membrane
   - when there is enough movement, sweeping action of air cells in membrane creates a spark (mechanical energy)
2. This movement is transformed to electrical energy and flows through neurons. Neurons are all over hair cells.
   - Cochlea is designed to change the mechanical to electrical energy