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

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

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

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

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

1st 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

2nd 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

3rd 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

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.

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.

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

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

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

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

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.

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

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

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

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