Main Function:
- Transmit sound waves from the air-filled external ear to the fluid-filled inner ear with minimal intensity loss.
- Protect the inner ear from loud sounds.
Parts:
- Ossicles: Three tiny bones (malleus, incus, stapes) that vibrate in response to sound waves hitting the eardrum.
- Tensor tympani muscle: Tightens the eardrum, increasing sensitivity to higher frequencies. This reflex is activated during chewing to distinguish chewing sounds from external sounds.
- Stapedius muscle: Contracts in response to loud noises, reducing the intensity of vibrations transmitted to the inner ear. This reflex protects the inner ear from damage.
How it Works:
- The eardrum vibrates due to sound waves.
- The ossicles transfer these vibrations to the oval window of the cochlea in the inner ear.
- The small size of the ossicles and the area difference between the eardrum and the oval window help minimize intensity loss during transmission.
- The tensor tympani muscle adjusts the tension of the eardrum to improve hearing of speech frequencies during chewing.
- The stapedius muscle dampens loud sounds to protect the inner ear.
Additional Points:
- The middle ear muscles are involuntary muscles.
- Hyperacusis, a condition where sounds are perceived as too loud, can occur if the stapedius reflex fails.