• a transducer
• converts energy from one from to another
• detects changes in frequency and intensity over time

• The pinna- esternal portion on the side of the head made of flexible cartilage
• channels sound waves into ear and assists w/sound localization

External auditory meatus (canal)

What does it look like, how long, and function?

• s-shaped tube that leads to eardrum
• 2.5cm long in adults
• has layers of epithelium and cilia to filter
• cerumen produced in meatus

Function

• protection
• quarter wave resonator
  • tube closed at one end
  • amplifies high freq. sounds
• ends at eardrum, and always stays closed

Tympanic Membrane aka eardrum

What does it look like, function etc

• semi-transparent, oval-shaped
• boundary btwn. outer and middle ear
• the Malleus is embedded in the TM

Function

• TM vibrates when sound waves impact it
• vibration of TM transmitted to malleus
• sensitive to small variations in pressure across wide range of freq.
• transduces pressure waves to mechanical energy

THE MIDDLE EAR!

where, function,other stuff

• directly behind the TM
• small space (0,6 cm wide and 0.4 cm deep)
• air filled with 3, conncected bones or ossicles

1. Malleus (hammer)- on TM
2. Incus (anvil)- connected to malleus
3. Stapes (stirrup)- conncected to anvil and oval window

1. Stapedius- protects the ear from loud sounds by contracting, which pulls the stapes to one side, limiting the amt. of mech. energy applie to oval window, reduces intensity by 10 dB
2. Tensor Tympani- opens the Eustacian tube

Eustachian Tube

length, info, function

• about 3.5 cm in length
• runs from middle ear to nasopharynx
• typically closed at middle ear and open in nasopharynx
• opening occurs b/c of tensor palatini

Functions

• clears mucus from middle ear via draining to pharynx
• equalizes air pressures in middle ear

• increases the amt. of acoustic energy transmitted to the inner ear
• overcomes the impedance mismatch btwn. the middle and inner ears
  • impedance= the ease with which signals are transmitted

• sound wave encountering a medium with higher impedance is reflected rather than transmitted
  • middle ear= air and inner ear= fluid
• pressure amplitude at oval window must increase to overcome impedance
  • ossicles= +2 dB
  • size difference btwn. TM and oval window = +25dB

• located deep w/in the temporal bone
• contains:
  • cochlea- organ of hearing
  • semicircular canals
  • connecting vestibule
• Cochlea involved in hearing
• semicircular canals and vestibule are part of vestibular sys. 

small, bony, spiral, snail-shped canal

spiral has 2.75 turns

• Cochlea duct= middle canal
• seperated from scala vestibuli by bestibular membrane
• bsilar membrane separates cochlear duct from scala tympani
• filled w/endolymph

Three Canals of the Inner Ear

1. Scala Vestibuli= top canal, filled w/perilymph fluid, located at the oval window (where stapes contacts inner ear structure)
2. Scala Tympani- bottom canal, also filled w/perilymph fluid, round windo connects scala tympani to middle ear, but no ossicle connection
3. Scala Media- middle canal

Organ of Corti (Inner Ear)

• w/in cochlear duct
• contains thousands of hair cells or cilia
• top of cilia make contact w/tectorial membrane
• bottom attached to auditory nerve

When basilar membrane vibrates, cilia are bent, which stimulates auditory nerve to 'fire'

Transduces mechanical energy in the fluid to electrical that can travel along a nerve

• TM set into motion by increases and decreases in air pressure
• vibration transferred to ossicles
• malleus sets other ossicles into motion, ending with the stapes, which is inbedded in oval window