2.  Wide range of sound pressure  20-20,000 Hz  Differentiating small increments in frequency and intensity  Listening to a signal embedded in background noise  Extremely rapid sequences of sounds

3.  Outer ear collects sound and “shapes” its frequency components  Middle ear matches the airborne acoustic signal with the fluid medium of the cochlea  Inner ear performs temporal and spectral analyses on the ongoing acoustical signal  Auditory pathway conveys and further processes the signal  Cerebral cortex interprets the signal

4.  Collector of sound- localizes sound in space  Pinna has ridges, grooves, and dished-out regions  Excellent funnel for sound directed toward the head from the front or side  Less effective for sound arising from behind the head  No active/moveable elements- has a passive effect on the input stimulus.  Pinna focuses the acoustic energy into the EAM  EAM funnels sound to the TM  The shape of the pinna and EAM boost the relative strength of the signal (approximately 20 Hz)  The wax, oils and shape prevent foreign bodies

5.  Transmits acoustic vibrations from the tympanic membrane to the inner ear.  Designed to increase the pressure approaching the cochlea  Overcomes the (resistance to flow of energy=impedance)  Uses the strategy of decreasing the area over which the force is being exerted  Primary function is to match the impedance of two conductive systems- increasing the pressure of a signal as it travels from the outer ear to the cochlea

6.  Muscle contraction increases the stiffness of the ossicular chain.  Tensor Tympani  Innervated by a branch of the mandibular nerve of the trigeminal nerve  Attaches to the manubrium of the malleus  Stapedius Muscle  Inserts on the posterior surface of the neck of the stapes  Innervated by the stapedial branch of the facial nerve

7.  1 st Mechanicsm of Impedance matching  17 times larger than the Oval window  Sound energy reaching the TM is “funneled” to the much smaller oval window which translates to an overall increase of 25 dB  Pressure exerted by a lightweight individual with a spike heel vs. a piano mover in sneakers

8.  2 nd Impedance matching function  Lever difference  Length of the manubrium is 9 mm  Long process of the stapes is about 7mm  Overall gain of approximately 2 dB

9.  3 rd Mechanism of Impedance matching  As the TM moves in response to sound, it buckles  Arm of the malleus moves a shorter distance than the surface of the TM  Reduction of displacement of the malleus  Average increase of 4-6 dB increase in the signal

10.  All 3 mechanisms result in a signal gain of about 31 dB  If the middle ear were removed, a signal entering the EAM would have to be 31 dB more intense to be heard.  Any process that reduces the effectiveness of this function (otitis media) can have a serious impact on the conduction of sound to the inner ear.

11.  Extends downward, forward, and medially from tympanic cavity to the nasopharynx  Lateral portion is osseous, medial portion is cartilage and other connective tissue  Normally closed by elastic recoil forces to protect the middle ear from pathogens  Equalizes pressure between the middle ear and external atmospheric pressure  Allows tympanic membrane to operate efficiently  Drains the middle ear cavity and aerates tissues.

12.  Semicircular canals respond to rotatory movements of the body  All movements of the head can be mapped by combinations of outputs of the sensory components, cristae ampulares  Activation of the sensory element arises from inertia  As your head rotates, the fluid in the semicircular canals tends to lag behind  The cilia are stimulated by relative movement of the fluid during rotation.  The utricle and saccule sense acceleration of the head rather than rotation  Major input serving the sense of one’s body in space

13.  Cochlea- structure would fit on the eraser of a pencil, fluid within it would be a drop on the table  Extracts or defines the various frequency components of a given signal=Spectral analyses  Sort out the frequency components  Determine the amplitude  Identify basic temporal aspects of the signal

14.  Sound is a disturbance in air  The disturbance causes the TM to move  TM moves in- stapes footplate in the oval window moves in; TM moves out- foot plate moves out  Stapes compresses the perilymph of the scala vestibuli via the oval window  Reissner’s membrane is pushed down toward the scala media

15.  Basilar membrane is pushed down toward the scala tympani  Frequency of a sound is determined by the number of oscillations or vibrations per second- i.e. a 100Hz signal results in the footplate moving in and out 100 times per second  Vibration is translated to the basilar membrane where it initiates a wave action=traveling wave

16.  BASILAR MEMBRANE  Designed to support wave action that directly corresponds to the frequency of vibration  High frequency sounds cause vibration of the basilar membrane closer to the vestibule  Low frequency sounds result in a longer traveling wave that reaches the apex  Basal end near the vestibule is “stiffer” than the apical end  Becomes increasingly massive, from base to apex  Becomes progressively wider from base to apex  The 3 components- graded stiffness, mass and width combine to make the basilar membrane an excellent frequency analyzer.

17.  WAVE ACTION  Wave roll in from the ocean- swell to a large amplitude as they break on the beach  Point of maximum amplitude of the traveling wave on the basilar membrane is the primary point of neural excitation of the hair cells within the organ of Corti  Only one true strong point of disturbance from the traveling wave  Low frequency sounds cause the traveling wave to “break” closer to the apex  Traveling wave can be stimulated in the absence of the middle ear mechanism (bone conduction testing)  Always travels from base to apex

18.  Cilia of the outer hair cells are embedded within the tectorial membrane  As the traveling wave moves along the basilar membrane, the hair cells are displaced relative to the tectorial membrane  Produces a shearing action  Inner hair cells are not embedded in the tectorial membrane  Not subjected to the same forces as the outer hair cells

19.  Inner hair cells depend on fluid movement of the endolymph to excite them  Traveling wave moves along the basilar membrane, fluid moves relative to the hair cell.  Cilia are displaced by the fluid movement  Outer hair cells are important for coding intensity  Inner hair cells are essential for frequency coding

20.  Stimulation of hair cells permits the mechanical energy arriving at the cochlea in the form of movement of the stapes footplate to be converted into electrochemical energy  Basilar membrane displaces towards the scala vestibuli, the hair cells are activated  Basilar membrane is displaced towards the scala tympani, electrical activity of the hair cell is inhibited