Middle Ear

Middle ear

• oval shaped air-filled space

• roof is a think layer of bone separating it from the brain

• connected to the back of the throat by the eustachian tube

• lined with mucous membrane

Ossicles

• must carry sound waves from the air-filled EAC to the fluid filled inner ear

• sound waves cause the tympanic membrane to vibrate

• bones are malleus, incus, and stapes

Eustachian Tube

• A tube that connects the middle ear to the nasopharynx

• The tube is typically closed, but opens (about 1 X per minute) when

you yawn, sneeze, swallow or blow air through it. It opens once every 5 min while sleeping.

• Valsalva Manuever- Autoinflate ME Close nose, force air up ET

• Toynbee Manuever- close jaw, hold nose swallow

Mastoid Process

• Honeycombed with air cells

• Aditus ad antrum (Thin bony plate)

windows of the middle ear

• Oval window

• Round window

Stapedius muscle

responds to sound..bilaterally

Tensor tympani

responds to jet of air in the earcanal or eye or change in temperature or touch in the earcanal

Impedance matching

• Vibrations in air must be transmitted efficiently into the fluid of the cochlea.

• If there were no middle ear most of the sound would just bounce off the cochlea.

• The middle ear helps transfer a large amplitude vibration in air into a small amplitude vibration (of the same energy) in fluid.

• The large area of the ear-drum compared with the small area of the oval window helps to achieve this, together with the lever action of the three ossicles.