1. 1 Review of Physical Terms Sound –By definition, all sounds require three components Source - must vibrate with sufficient force to affect the surrounding environment Medium - required to propagate energy from one location to another Receiver - a perceiver or device that can have its physical state altered by the energy produced by a vibrating source

2. 2 Review of Physical Terms Source - Requirements –Must vibrate –To vibrate, it must have mass and stiffness Vibration is the interplay between inertial force, associated with mass, and restoring force, which is associated with the stiffness of the source The rate of vibration is the FREQUENCY The amount of time for one cycle to be completed is the PERIOD The size (power) of the vibration is its AMPLITUDE The amount of time vibration lasts is its DURATION

3. 3 Review of Physical Terms Medium - Requirements –Mass and stiffness –May be comprised of air, fluid, solid The type of medium dictates the speed of sound More rarefied the medium, the slower the propagation –Inverse square law – mathematical representation of the loss of acoustic energy as sound travels

5. 5 Review of Physical Terms Receiver - Requirements –Must have its physical state changed by the presence of the sound –Change in physical state excites neural mechanism – for us, it’s a sensory cell and, ultimately, a series of neurons –Auditory mechanism, therefore, features structures that vibrate in synchrony with the source and medium, and transduce the vibration into another form of energy (bioelectric)

6. 6 Review of Physical Terms Vibration - moment by moment account –Initial force creates displacement –Interplay between inertia and stiffness keep object in motion The restoring force (proportional to stiffness) contributes to the damping the object will experience and applies force in the direction of the resting position The inertia contributes to the continuation of the vibration, driving the object in whatever direction it happens to be moving at that moment High damping, short duration Low damping, long duration –PHASE is the term for the object’s location at any moment (out of 360 degrees)

7. 7 Review of Physical Terms

8. 8 Filtering - types of filters and their depiction on an amplitude spectrum –low pass – passes energy below a certain frequency –high pass – passes energy above a certain frequency –band pass – passes a range of frequencies –band reject – eliminates a range of frequencies

10. 10 Review of Physical Terms Filtering – analogy to your stereo –The bass control shifts the pass band of the filter to progressively lower frequencies –The treble control shifts the pass band upward in frequency –The selectivity, or tuning of the filter indicates how wide the pass band is For example, a radio or TV is tuned to a very narrow bandwidth at any given moment In this way, only one station at a time is “passed”

11. 11 Review of Physical Terms Basic Associations between physical components of sound waves –F=1/T –F=1/λ –Displacement  1/F –Duration  1/Damping –Damping is proportional to stiffness, inversely proportional to mass (Tacoma Narrows Bridge) –Fres  stiffness/mass Therefore, the greater the stiffness, the higher the resonance frequency; in general, the higher the mass, the lower the Fres

12. 12 RESONANCE Resonance - occurs when a force is applied to a body at the frequency at which the body would vibrate if set in motion, and then left to itself (Stevens and Davis, 1938) –Equation: F(res)  s/m –Consider effect of increasing stiffness – will raise the resonance frequency –Consider effect of increasing mass – will lower the resonance frequency –Recognize the effect of damping is minimal at the resonance frequency –Therefore, the object will vibrate at the greatest duration and amplitude at its resonance frequency

13. 13 RESONANCE Resonance – May also occur when an object is driven at a rate equal to the rate at which it would vibrate if left alone: in this way, the energy of the vibration is reinforced –Tuning forks of different frequencies versus forks ‘tuned’ to the same frequency –Child on a swing –Pushing a car out of ditch –The Tacoma Narrows Bridge (1940)

14. 14 RESONANCE

15. 15 RESONANCE http://www.youtube.com/watch?v=3mclp9QmCGs http://www.youtube.com/watch?v=17tqXgvCN0E&feature=r elated

16. Audition: Anatomy Outer ear Middle ear Inner ear Peripheral Nerves Central Pathway Primary Auditory Cortex

17. Outer ear: Primary function is to focus acoustic energy onto the eardrum and increase high-frequency components.

18. Middle ear: Primary function is to amplify mechanical vibration produced by the soundwave’s pressure.

19. Inner ear: Primary function is to convert mechanical vibration into electrical impulses. Also houses balance organ.

20. Divisions of the Auditory System: “Outside” “Inside” Conductive Sensorineural

21. Sensori-neural system

22. A & P of the Auditory System Two pathways that sound can take but both must route sound through the cochlea –Air conduction pathway includes the outer and middle ear, as well as the cochlea and neural structures (conductive and sensorineural systems) –Bone conduction pathway includes the cochlea and neural structures (sensorineural system) The cochlea is where vibratory energy is transformed into neural energy Sound is filtered/processed throughout the auditory system at all stages

23. A & P of the Auditory System The Outer ear - the visible portion of the ear, consists of: –Pinna –External auditory meatus –Lateral surface of the TM –Comprised of cartilage (lateral 1/3) and bone (medial 2/3)

24. Helix: the prominent ridge which begins superior to the opening of the EAM Antihelix: a ridge which runs parallel to the helix The lobule (ear lobe): bottom of the pinna (no cartilage) Concha: a deep depression which forms the mouth of the EAM Tragus: a backward folding ridge located on the anterior wall of the ear canal

25. External Auditory Canal Architecture: An average horizontal diameter of 6 mm An average vertical diameter of 9 mm Approximately 23-25 mm in length The skin of the cartilaginous portion contains glands that produce cerumen (earwax) Earwax keeps the epithelium in the meatus moist (prevents chapping) Shape of the canal, the hairs at the entrance, the secretion of cerumen helps keep foreign objects out of the canal and aids in self-cleansing it The ossification is typically completed by the end of the third year Bony portion fixed in diameter Cartilaginous changes with jaw movement (note that HA fittings occupy cartilaginous portion)

26. A & P of the Auditory System

27. Congenital microtia (small, malformed auricle / pinna) and external canal atresia

28. Congenital microtia without canal atresia.

29. Preauricular appendage (supernumerary auricle)

30. Bifid earlobe

31. TYMPANIC MEMBRANE Doorway between outer ear and middle ear Takes up the vibration of air particles in the EAC and passes it to the middle ear system Primary function is to overcome the loss of energy as vibration moves from the air to the fluid of the inner ear

32. TYMPANIC MEMBRANE

34. Tympanic membrane (eardrum) The medial limit of the EAM is formed by the TM TM sits at an angle of about 55  to the ear canal

35. Tympanic membrane (eardrum) The TM is thin (0.1 mm), very compliant but resistant to breaking Cone-shaped (like a miniature loudspeaker), the TM is displaced inward near its center by about 2 mm; the peak of this broad cone is called umbo Very small mass (  15 mg), compliance and cone shape make the TM suitable for sound absorption The pars tensa formed of several layers of tissue The pars flacccida contains very few fibers

36. Tympanic membrane (eardrum) Umbo coincides with the tip of the manubrium of the malleus Malleus extends upward, appearing at “1 o’clock” in a right ear, “11 o’ clock” in a left ear Healthy TM is translucent

37. Development of the Outer Ear At birth the floor of the external auditory canal has no bony portion External Auditory Canal (EAC) is cartilaginous at birth, ossifies through the first seven years In the infant the EAC is short and straight, whereas in the adult the canal is longer and curves TM is present at a nearly horizontal angle at birth

38. Development of the Outer Ear Conductive system maturation The pinna Continues growing until the child is 5-9 yrs External Auditory Meatus Ossification continues for the first few years Changes primarily the flexibility of the canal, as newborn canals are very flexible

39. Maturation of the Peripheral Auditory System The TM Angled obliquely at birth Because the superior side is shorter, pulling upward on the pinna lengthens the canal, and straightens the TM so that it may be viewed As canal ossifies, TM straightens Along with changes to the ossicles (specifically the stapes) conductive system transmission changes

40. Anatomy An adult middle ear cavity is an almost oval, air-filled space of roughly 2 cm 3 and is enclosed within the temporal bone. –Lined with mucous membrane with cilia (small hair-like projections) that periodically moves in a wiping action to cleanse the middle ear via the eustachian tube It contains a chain of movable bones (ie., ossicles), which connects the lateral wall to its medial wall.

41. MIDDLE EAR STRUCTURES

44. Walls of the Middle ear

45. –Note - Lateral wall (the tympanic membrane) has been removed to see the interior of the middle ear. RED: Internal carotid BLUE: Internal jugular vein PURPLE: Tensor tympani YELLOW: Facial nerve (VII) with nerve to stapedius & chorda tympani DARK GREEN: Eustachian tube, oval and round windows LIGHT GREEN: Cochlea Black : Mastoid air cells

46. Walls of the Middle ear The Labyrinthic or Medial Wall is vertical in direction, and constitutes the oval window and round window, the promontory, and the prominence of the facial canal.

47. Walls of the Middle ear The promontory is a rounded hollow prominence, formed by the projection outward of the first turn of the cochlea; it is placed between the round and oval windows. The prominence of the facial canal indicates the position of the bony canal in which the facial nerve (CN VII) is contained.

49. The Middle Ear Ossicles The tympanic cavity contains a chain of three movable ossicles (2 - 6mm in length), the malleus, incus, and stapes (latin for mallet, anvil, and stirrup). The malleus is attached to the tympanic membrane, The stapes - to the circumference of the oval window The incus being placed between and connected to both by delicate ligaments.

51. The Malleus The Malleus consists of a head, neck, and three processes, viz., the manubrium, the anterior and lateral processes. 3D ossicles

52. The Middle Ear Ossicles The Head has a cavity or facet for the incus to articulate. The manubrium is connected by its lateral margin with the tympanic membrane. Near the upper end of the manubrium is a slight projection into which the tendon of the Tensor tympani muscle is inserted.

53. The Incus The Incus consists of a body and two crura

54. The Middle Ear Ossicles The body of the Incus articulates with the Malleus. The long crus ends in a rounded projection, the lenticular process, which is tipped with cartilage, and articulates with the head of the stapes.

55. The Stapes The Stapes consists of a head, neck, two crura, and a base.

56. Stapes The stapes is the smallest bone in the human body being roughly the size of a grain of rice.

57. The Middle Ear Ossicles The head presents a depression, which is covered by cartilage, and articulates with the lenticular process of the incus. the base is fixed to the margin of the oval window by a ring of ligamentous fibers. Animation

58. Muscles of the Tympanic Cavity Two muscles - Tensor Tympani & Stapedius The Tensor tympani is the larger muscle (about 25 mm in length). It originates from the anterior wall near the cartilaginous part of the eustachian tube. Inserts into the manubrium of the malleus.

59. Muscles of the Tympanic Cavity Tensor Tympani Innervated by the Trigeminal (CN V) nerve. Action - The Tensor tympani draws the tympanic membrane medial-ward, and thus increases its tension Non-auditory stimulation

60. Muscles of the Tympanic Cavity The stapedius is the smallest muscle in the human body (length - 7mm). It originates from the mastoid or posterior wall. It inserts into the neck of the stapes. Innervated by the facial (CN VII) nerve.

61. Muscles of the Tympanic Cavity Stapedius Muscle Action - pushes the stapes into the oval window and thereby tenses the oval window and tympanic membrane Modifies the mode of stapedial vibration, greatly reducing energy delivered

62. Muscles of the Tympanic Cavity Serve a protective function for the inner ear by increasing middle ear impedance –Elicited by acoustic stimuli of 70-90 dB above threshold –Reflex contraction stiffens the ossicular chain, reducing sound transmission by 5-10 dB, primarily at frequencies below 1.2 kHz. The acoustic stapedial reflex is an important clinical tool and serves as a reliable objective test.

63. Ligaments of the Ossicles The ossicles are connected with the walls of the tympanic cavity by 5 ligaments: three for the malleus, and one each for the incus and stapes Connective tissue that stiffens with age

64. Middle Ear - Muscles & ligaments

65. Middle Ear Muscles Tensor Tympani muscle Stapedius muscle

66. Parts of the Middle Ear

67. Eustachian Tube The Eustachian or auditory tube is the channel through which the tympanic cavity communicates with the nasal part of the pharynx (nasopharynx). Its length is about 36 mm, and it is oriented downward, forward, and medial-ward, forming an angle of about 45 degrees with the sagittal plane and from 30 to 40 degrees with the horizontal plane.

68. Eustachian Tube It is formed partly of bone(1/3rd), partly of cartilage and fibrous tissue (2/3rd). The osseous portion is about 12 mm. in length. It begins in the carotid or anterior wall of the tympanic cavity. The cartilaginous portion about 24 mm. in length, is formed of a triangular plate of elastic fibrocartilage.

71. Tensor Veli Palatini Levator Palatini

72. Eustachian Tube The diameter of the tube is not uniform throughout, being greatest at the pharyngeal or oral orifice (opening), least at the junction of the bony and cartilaginous portions, and again increased toward the tympanic cavity. The narrowest part of the tube is termed the isthmus.

73. Eustachian Tube In adults, the tube is normally kept closed by the spring mechanism of cartilage. It is opened by the action of three sets of muscles at the nasopharynx orifice. –One of which is the tensor veli palatini muscle. –Contracts and opens the Eustachian tube during yawning, sneezing, or swallowing, or when excessive pressure is applied from the nose.

74. MIDDLE EAR STRUCTURES

75. A & P of the Conductive System The Outer ear - function –Not a mere passive conduit of sound –Along with the EAC, it high-pass filters sound - acts like a HF amplifier (10-15 dB of gain at frequencies above 1500 Hz) Helps with the localization of sound Helps with speech perception –Cerumen is produced by sebaceous glands in the cartilaginous portion - protective

76. OUTER EAR TRANSFER (Filter) FUNCTION At the opening to the ear At the eardrum

77. MIDDLE EAR FUNCTION Eustachian Tube - responsible for aerating the middle ear space –The only pathway for air to enter the middle ear –Middle ear must remain aerated so that the TM can vibrate most efficiently –The most common precursor to middle ear infection is E. Tube dysfuction or obstruction More common in pedes than adults

78. Middle Ear Impedance Mismatch When sound waves travel from gaseous to a liquid medium, energy is lost (99.9% would be reflected back). –auditory meatus air  cochlear fluids –(low impedance)(high impedance) This lost of energy equates to an intensity loss of about 30 dB. The middle ear serves to overcome this loss

79. Middle Ear Transformer Function Area ratio –The tympanic membrane’s area (~50 mm 2 ) is larger than the oval window’s area (~3.5mm 2 ). –This results in a 14-fold (or about 25 dB) increase in acoustical pressure at the footplate relative to the pressure at the eardrum.

80. Middle Ear Transformer Function Lever action- –The manubrium of the malleus is about 1.3 times as long as the long process of the incus. –This yields a lever advantage of about 2 dB increase in acoustical pressure at the oval window

81. Middle Ear Transformer Function Thus it can be seen that the middle compensates for ~27 dB of the 30 dB energy loss due to the impedence mismatch. Recent data indicate that the pressure gain contributed by the middle ear is greatest at the lower frequencies. –The middle ear pressure gain is relatively flat at frequencies below 1 kHz, averaging 23 dB and peaking at 26-27 dB at 0.9 kHz. –At frequencies higher than 1 kHz, the gain decreases by 8-9 dB per octave, contributing little amplification above 7 kHz.

82. MIDDLE EAR FUNCTION Passage of acoustic energy through the middle ear –The TM vibration is taken up by the ossicular chain Malleus, Incus, and Stapes pivot against each other Their movement is facilitated by the coupling of ligaments to the walls of the middle ear space, as opposed to the articulation of bone into bone The ossicular chain selectively stimulates the oval window They transform airborne energy into mechanical energy

83. MIDDLE EAR FREQUENCY RESPONSE Input to the middle ear Resonance Peaks

84. MIDDLE EAR FUNCTION The Acoustic Reflex –Changes the stiffness of the middle ear system, thereby reducing the efficiency of sound transmission –Protects the cochlea from intense sound by reducing the amount of stapes footplate vibration –Carried out by the stapes muscle (primarily) and also by the tensor tympani Stapes is considered the primary effector of the reflex because the TT can by stimulated by non-acoustic stimuli Tightens the stapes footplate in the oval window

85. MIDDLE EAR FUNCTION Eustachian Tube Dysfunction –The E. Tube normally opens passively during swallowing, yawning, chewing –If occluded or not functioning properly, it doesn’t open often enough to keep the tympanum’s air pressure equal to that of the atmosphere At any other pressure, sound may be blocked from passing through the conductive system –More importantly, fluid may build up in the space and result in a middle ear infection

86. MIDDLE EAR FUNCTION Summary of Middle Ear Function: –Mechanical amplifier that helps overcome loss of energy to the cochlea Surface area advantage, lever action, buckling action, and selective oval window stimulation –Protects the cochlea from intense sounds through the contraction of the Acoustic Reflex –Must remain aerated to facilitate TM vibration and health of the ME tissues

87. Eustachian Tube In infants the Eustachian tube is shorter and wider, and in a more horizontal plane. The nasopharyngeal orifice remains open to till approximately 6 months of age. This has clinical implications and, eventually, educational.