Lecture on the Cochlea and Inner Ear

Overview of the Cochlea

• Cochlea Structure: Snail-like structure, can be unrolled and laid flat.
• Key Components:
  • Stapes: Bone that moves back and forth with the eardrum's frequency.
  • Elliptical Window: Membrane connected to the stapes, moves in and out.
  • Fluid: Inside the cochlea, moves in a specific direction due to the organ of Corti.
  • Circular Window: Membrane that gets pushed out as fluid compresses it.
  • Organ of Corti: Splits the cochlea into two parts, directs fluid flow.

Cross-Section of the Organ of Corti

• Structure:
  • Upper Membrane
  • Lower Membrane
  • Hair Cells: Have hair bundles on top.
• Fluid Flow: Moves membranes up and down, causing hair cells to vibrate.

Hair Cells and Hair Bundles

• Hair Bundle: Composed of many filaments called kinocilium.
• Kinocilium: Attached to one another via tip links (spring-like structures).

Mechanism of Sound Transduction

• Tip Links: Attached to the gate of potassium channels.
• Movement of Hair Cells: Causes tip links to stretch and open potassium channels.
• Potassium and Calcium Influx:
  • Potassium flows into the cell first.
  • Calcium channels activate, allowing calcium to flow into the cell.
• Action Potential:
  • Caused by the influx of potassium and calcium.
  • Stimulates the spiral ganglion cell.
  • Signal is transmitted to the auditory nerve and then to the brain.

Summary

• Sound waves move the eardrum and stapes.
• Movement is transferred to the elliptical window and into the cochlea's fluid.
• Fluid motion affects the organ of Corti, activating hair cells.
• Hair cells transform fluid motion into neural impulses that travel to the brain.