FINALS - UNIT 3 Flashcards
Outer Ear
Collects sound and funnels it to the tympanic membrane
Changes frequency of sound to aid localization
Middle Ear
Sound wave cause eardrum to vibrate
setting bones to in the to motion
Inner (Cochlea)
Mechanical vibrations into neural signals
Temporal Bone
Components?
- Squamous
- Petrous
- Mastoid
- Tympanic
Squamous
thin, fan like
Mastoid
contains air cells
Styloid Process
No auditory contribution
Tympanic Membrane
Pars tensa & Pars Flaccida
Connected to middle ear by Manubrium Malleus
Middle Ear components
- Tympanic Cavity or Tympanum
- Epitympanic Recess or Attic
- Mastoid Antrum
Tympanic Cavity
Also known as Tympanum
space in the temporal bone behind the TM
Epytympanic Recess or Attic
Superior to the level of the TM
Contains portions of the incus and malleus
Mastoid Antrum
Enlarged Space in the mastoid part of the temporal lobe
Posterior to epitympanic recess
Ossicular Chain is made of
- Malleus
- Incus
- Stapes
Three smallest bones in the body
Malleus
Attaches to TM along the manubrium
Head extends into the epitympanic recess
connects to the incus
Incus
Transmits vibrations from the malleus to the stapes
Stapes
Head attaches to the incus
Anterior crus, posterior crus, and footplate form a stirrup
Footplate attaches to the oval window
Sound Transmission through the Middle Ear System
TM → Malleus → Incus → Stapes → Inner Ear
Muscles of Middle Ear
Stapedius Muscle
- Smallest in body
- Innervated by 7th Cranial
- Contraction pull stapes posteriorly, stiffening ossicular chain
Tensor Tympani
Innervated by the 5th cranial (trigeminal)
Contraction pulls malleus in the anterior direction and stiffens ossicular chain
Acoustic Reflex
Reflexive contraction of stapedius muscles in both ears
stiffens ossicular chain and reduces the transmission of low frequency sounds
Acoustic Reflex Functional Importance
- Acts as an automatic volume control
- Protect against long term noise damage
- may improve signal to noise ratios for speech
Eustachian Tube
Connects middle ear to pharynx
tilt at 45°
opened by tensor palatini muscle during swallowing and yawning
Azmuith
Location of sound source in horizontal plane
Elevation
location of sound in the vertical plane
Head Shadow Effect
- Head impedes the transmission of high freqs to the far ear
- Because high freq sounds have wavelengths that are smaller, cannot bend around head
Pinna Effect
- Affects sounds with Freq > 4000 Hz
- How sound is changed depends on the location of sound source
- Sound Localization
Resonant Frequency of Ear Canal
Increases sound levels for frequencies between 2000-5000 with peak gain of 15 dB at 3000-4000 Hz
Head Related Transfer Function
Shows changes in sound level due to presence of the head, pinna, and ear canal as a function of frequency
>1500 Hz
Binaural Cues
Used for sound localization when two ears present
Impendance Matching Mechanisms
- Area ratio
- Ossicular Lever
- Curved membrane
Gain created by these middle ear mechs compensate for 30 dB loss of energy
Total gain of the middle ear transformer
Area Ratio 25 dB
Curved Membrane Buckling 6 dB
Ossicular Lever Action 2 dB
total gain 33 dB
