Overview
This lecture explains how the cochlea in the inner ear converts sound waves into signals that the brain can interpret as sound.
Sound Transmission in the Ear
- Sound waves enter the ear canal and strike the tympanic membrane (eardrum), causing it to vibrate.
- Vibrations are transmitted through the ossicles, three tiny ear bones, to the oval window of the cochlea.
Structure of the Cochlea
- The cochlea is a coiled, snail-shaped structure located in the inner ear.
- Inside, it contains three parallel fluid-filled canals: scala vestibuli, scala media, and scala tympani.
- The scala vestibuli and scala tympani contain perilymph fluid; the scala media contains endolymph fluid.
Basilar Membrane and Sound Frequency Processing
- Movement of the oval window creates waves in the cochlear fluid, moving the basilar membrane.
- Different parts of the basilar membrane respond to different sound frequencies.
- Each sound frequency peaks at a specific place along the basilar membrane, enabling frequency discrimination.
Role of the Organ of Corti and Hair Cells
- The organ of Corti, located on the basilar membrane, is the ear’s main receptor organ.
- Hair cells within the organ of Corti have stereocilia (small hair-like projections) that respond to basilar membrane vibrations.
- Movement of stereocilia opens ion channels, leading to neurotransmitter release.
Neural Signal Transmission
- Neurotransmitter release from hair cells generates electrical impulses.
- These impulses travel via the vestibulocochlear nerve to the brain for auditory processing.
Key Terms & Definitions
- Tympanic membrane (eardrum) — vibrates in response to sound waves.
- Ossicles — three small ear bones transmitting vibrations to the cochlea.
- Cochlea — spiral-shaped, fluid-filled inner ear structure for hearing.
- Basilar membrane — membrane that moves in response to sound and spatially separates different frequencies.
- Organ of Corti — structure atop the basilar membrane containing hair cells.
- Hair cells — sensory cells with stereocilia that detect vibrations.
- Stereocilia — hair-like projections on hair cells that trigger ion channels.
- Vestibulocochlear nerve — nerve carrying auditory information to the brain.
Action Items / Next Steps
- Review diagrams of cochlear anatomy and the auditory pathway.
- Practice labeling cochlear structures and explaining their roles in hearing.