1. CHAPTER 6
Outer and Middle Ears

2. Which Way? Anterior/Ventral = toward the front
Posterior/Dorsal = toward the back
Lateral = toward the side
Medial = toward midline
Superior = toward upper surface (rostral)
Inferior = toward lower surface (caudal)

3. Gotta Catch a Plane Sagittal- dividing right from left
Coronal (Frontal) -dividing front from back
Horizontal -dividing up from down

4. The Temporal Bone - Part of the Skull

5. Temporal Bone:Lateral/Medial Views

6. The Temporal Bone houses the “Ear”

8. The Outer Ear Consists of:
The Pinna - cartilaginous, highly variable in appearance, some landmarks.
External Auditory Canal (or external auditory meatus) cm tube.

9. Pinna Landmarks Helix Antihelix Concha Tragus Intertragal Notch
Antitragus

10. External Auditory Canal
lateral portion-cartilage
medial portion-osseous
lined with epidermal (skin) tissue
hairs in lateral part
cerumen (ear wax) secreted in lateral part.

11. Outer Ear Functions 1 Amplification / Filtering
-- increases sounds between 1500 and 7000 Hz by 10 to 15 dB
-- because of the resonance of
Concha Hz
E.A.Canal Hz

12. Outer Ear Functions 2 Protection -- medial displacement of ear drum
-- curvature of canal
-- hairs
-- cerumen
-- skin migration

13. Outer Ear Functions 3 Localization
-- The ability to identify the location of a sound source
-- (Will be covered more later)

14. The Middle Ear: A cleft within the temporal bone
Lining is mucous membrane
Tympanic Membrane separates it from EAC
Eustachian tube connects it to nasopharynx
Also Connected to Mastoid Air Cells

15. Middle Ear Structures 1- Malleus 2- Incus --Ossicles 3- Stapes
4- Tympanic Membrane (Eardrum)
5- Round Window
6- Eustachian Tube

16. Middle Ear Muscles 1. The Stapedius
Attaches to Stapes
Contracts in Response to Loud sounds, chewing, speaking
Innervated by the Facial (VIIth cranial) nerve

17. M.E. Muscles 2. The Tensor Tympani
Attaches to Malleus manubrium, E-tube cartilage
Contraction draws TM medially

18. Middle Ear Functions
Impedance Matching -- amplification of sounds to overcome difference in impedance between the air of EAC and the fluid of the inner ear.
Filtering -- resonant frequency is approximately 1000 Hz, functions as bandpass filter.
Acoustic Reflex -- Contraction of Stapedius muscle in response to loud sounds

19. Middle Ear Function
Impedance Matching is accomplished through pressure increase produced by the middle ear.
From 2 main effects:
Reduction in AREA
Increase in FORCE

20. Reduction in AREA
sound striking the (relatively large) tympanic membrane
is delivered to the (much smaller) stapes footplate
Areal Ratio = 18.6 to 1

21. Increase in FORCE The malleus and incus act like a lever
Whenever there is a pivot:
Force x Length in = Force x Length out
Force is greater on short side (Think of wheeled luggage)
Malleus manubrium = 1.3 times as long as Incus long process

22. Leverage Small force (baby’s weight) supports man
because of the difference in length on either side of the pivot point

23. Increase in Pressure Remember that Press. = Force/Area
force is increased 1.3 times
area is decreased 18.6 times
Pressure is increased 24.2 times (27.7 dB)

24. Other Key Middle Ear Function
Oval Window Isolation-- Sound striking the tympanic membrane is delivered through the ossicular chain to the oval window
Without the middle ear, both the oval and round windows would receive sound energy and energy would cancel out.

25. Middle Ear Filtering: Band Pass filter Resonant Frequency near 1kHz
Effect can be seen in Minimum Audibility Curves (MAP/MAF) (Figure 10.2)

26. Tympanometry Acoustic measures of middle ear health
Made using an immittance (or impedance) bridge:
PRESSURE PUMP/MANOMETER
MINIATURE SPEAKER
MICROPHONE
ALL CONNECTED THROUGH A SMALL PROBE INSERTED IN EAR CANAL

27. Compliance: opposite of stiffness.
middle ear system is not massive, largely a stiffness-controlled system.
Changes in stiffness/compliance have large effects on functioning of system.
at point where air pressure in canal and middle ear are equal the most sound will be conducted through.

28. Tympanogram:
A plot of middle ear compliance as a function of ear canal pressure
Pressure is swept from +200 to -200 or -400 dPa
Should see peak at point where pressures are equal

29. Tympanogram types: A: peak between +100 and -200 dPa: normal
C: peak beyond -200 dPa: neg pressure
B: no peak flat tymp: effusion
As: peak but shallow: stiff: otosclerosis
Ad: peak off scale: floppy: dysarticulation

30. Tympanogram Types

31. The Acoustic Reflex
Stapedius contraction measured as change in compliance
Reflex arc:
peripheral ear,
VIIIth n.
Cochlear nucleus
Superior olivary complexes
VIIth n. to the middle ear
Reflex is bilateral.

32. Clinical Tests using Acoustic Reflexes:
A.R. Threshold: how intense sound must be to elicit the reflex?
A.R. Decay: Is the degree of a contraction maintained throughout a 10 second stimulus?