• a vibration
• a medium must be capable of being set into vibration
• must have mass & elasticity to do so

• amount of matter present
• applies to gases, liquids, & solids
• related to density
• has inertia - opposes change in motion
• scalar

• = ma
• measured in N or dynes
• push or pull on an object
• applied to overcome inertia (mass)
• a vector

• mass per unit volume
• effects how sound is transmitted
• ↑ ρ = ↑ speed of sound

• deform in shape, size, or length
• enables recovery from distortion
• measured in stiffness or its reciprocal, compliance
• seen when a force is applied to an object

• movement from an original position
• force > friction
• vector
• length & direction

• no displacement
• no movement
• net force
• zero

• always opposes motion
• occurs when surfaces are in contact with one another
• = resistance
• < force = displacement

• form of motion used in acoustics
• AKA oscillation
• back-and-forth type of movement through equilibrium
• Simple Harmonic Motion (SHM) is the simplest type

1. force is applied to an object
2. displacement occurs
3. amount of displacement is a result of a combination of force applied, mass, elasticity of medium, friction, etc.
4. results in oscillation (vibratory motion)

• represented mathematically by SINE
• AKA sinusoidal motion or sine wave

• one type of oscillating movement
• direction of vibration is perpendicular to the direction of the force that propagated the vibration
• e.g. guitar strings, pebble dropped in water, moving a rope up & down causes a wave to go outward

• a type of oscillating wave
• oscillation is parallel to the force 
• e.g. a spring, sound waves
• forms compressions & rarefactions

• are longitudinal waves
• particles oscillate about their equilibrium & cause a force on neighboring particles which puts them in motion

1. Frequency
1. Period
2. Wavelength
2. Phase
3. Amplitude

• are all independent of each other

• how fast the oscillation is
• cycles per second
• Hertz (Hz)
• reciprocal of period
• = 1/p
• the eardrum vibrates at the same frequency of sound

• time required to complete one cycle
• seconds
• reciprocal of frequency
• = 1/freq.

p = 1 / f

(s)

f = 1 / p

(Hz or cps)

• the distance between successive points on a sine wave
• inversely related to frequency
• ↑ freq. = ↓ λ

• is affected by humidity, elasticity, density, temperature
• 340 m/s (through air; 0 degrees C; at sea level)
• = √(E/ρ)
• proportional to elasticity
• inversely proportional to density
• not affected by frequency

s = √E/ρ

(m/s)

λ = s / f

(mm)

s = speed of sound (340 m/s)

• AKA resonant frequency
• the frequency with which a system oscillates freely
• dependent on a system's mass & elasticity (stiffness)

f_nat = √ (s / m)

s = stiffness (elasticity)

m = mass

• quantify a point on the graph
• 0°, 90°, 180°, 270°, 360°
• what direction
• one cycle = 360°

• 90° & 270° = x_MAX
• 0°, 180°, & 360° = equilibrium
• 360° = one cycle

• the ear is the most sensitive to
• the angle the moment rotation begins[image]

• = displacement
• AKA intensity; pressure
• y-axis

• one particular part on the graph

• only one side of graph (either positive or negative)
• (P-P)/2

[image] 

• displacement from one side to the other
• = 2(A)

[image]

• best measurement for complex sounds
• an average of amplitude
• = .707 amplitude peak
• = .3535 peak to peak amplitude
• = standard deviation

• limits particle displacement
• causes amplitude of vibration to dampen over time
• A - loss-less system
• B - low-dampened system
• C - high-dampened system

 [image]

• Metric: MKS & cgs
• US: fps

[image]

• = F/m
• change in velocity
• positive or negative (deceleration)
• e.g. a car going 65 mph (velocity) speeds up to 75 mph = 10 mph (acceleration)

• vector (m/s; mph)
• your speed
• a change = acceleration/deceleration

• 1 N = 100,000 dynes

• force applied to a surface area
• measured in dynes/cm² or Pa (N/m²)
• = √(intensity)
• vector

inversely proportional

Density ↑

Speed of Sound ↓

directly proportional

Speed of Sound ↑

Elasticity ↑

directly proportional

m ↑ = ρ ↑

inversely proportional

P ↑ = f ↓

inversely proportional

λ ↑ = f ↓

a = F / m

F = force

m = mass

F = ma

 (dynes or N)

inversely proportional

m ↑ = a ↓

directly proportional

F ↑ = a ↑

• the range between the least amount of pressure detected & the pain threshold of the ear

• .0002 dynes/cm² — 200,000,000 dynes/cm²

• is the capacity to exert energy or force
• is measured in horsepower or watts

• same relationship with intensity that force has with pressure

• power distributed over a surface area
• measured in watts/cm²
• = pressure²

• the range that the human ear can detect

• 1 x 10^-16 watts/cm² — 1 x 10^-2 watts/cm²

• simply exponents
• exponent = log
• log 10⁶ = 6

• (power/intensity)

• need calculator or log table
• e.g. log 4 = .6

• (force & pressure)

• ADD

• log (A x B) = log A + log B

• SUBTRACT

• log (A / B) = log A - log B

• MULTIPLY

• log A^B = B log A

• = a ratio scale
• one unit on a scale is so many times greater or less than another

     (/10)   (/10)    (/10)     (/10)    (x10)    (x10)    (x10)   (x10)

<------l-------l-------l-------l-------l-------l-------l------->

        -1000  -100    -10       0       10      100     1000

• artificial
• ratio between whatever sound is being measured & the softest sound a human ear can detect
• log I_x / I_r
• use log to reduce the amount of 0s

• a decibel is 1/10 of a bel
• dB / 10 = 1 bel
• 1 bel = 10 decibels

• 10 log 2 / 1
• = 10 (log 2 - log 1)
• = 10 (.3 - 0)
• = 3 dB IL

• 20 log (2/1)
• 20 (log 2 - log 1)
• 20 (.3 - 0)
• = 6 dB spl

20 = 10 log (I_x / 10^-16 watts/cm²)

20/10 = log I_x - log 10^-16

2 = log I_x + 16

-14 = log I_x

antilog = 10^-14 watts/cm²

• Intensity (dB IL)
• Pressure (dB spl)

20 log (p_x / p_r)

p_r = .0002 dynes/cm²

• the smallest variation detected by a young, normal-hearing individual
• .0002 dynes/cm² and 10^-16 watts/cm²

• the signal is identical in every aspect (frequency, amplitude, phase) from each sound source
• unrealistic

• the signal is not identical
• frequency, amplitude, phase are independent
• real world

dB_i + 10 log N = total dB (IL or spl)

dB_i = dB of source

N = number of sources

1. Convert dBs (IL or spl) to watts/cm²
• A dB = 10 log x / 10^-16 watts/cm²
• B dB = 10 log x / 10^-16 watts/cm²
2. Add watts/cm²
• must have equal exponents
3. Convert back to dBs
• dB = 10 log _____ / 10^-16 watts/cm²

.0002 dynes/cm²

or

.00002 dynes/m²

1 x 10^-16 watts/cm²

or

1 x 10^-12 watts/m²

• any sound that is NOT sinusoidal
• composed of 2 or more sine waves that can differ in amplitude, frequency, & phase
• graphed on a spectrum
• line graph
• x-axis is frequency
• y-axis is usually amplitude

• make a complex wave
• add instantaneous amplitudes together

 [image]

• a complex wave that consists of a series of simple sinusoids that can differ in amplitude, frequency, & phase
• can be derived from Fourier analysis

• Fourier's Theorem

• a process of decomposing or analyzing a complex waveform to determine its individual sinusoidal components
• this is what the cochlea does

• Fourier's Theorem

• a wave that repeats itself over time
• AKA periodic time function
• can be either sinusoidal or complex

[image]

• must satisfy a harmonic relation
• sinusoidal components cannot be selected at random

• the lowest common denominator
• f₀= 1/t
• represented by the first harmonic on a spectrum

• the frequencies of all of the sinusoids must be integer (whole number) multiples of the lowest frequency component (f₀)
• 1/t, 2/t, 3/t, 4/t, etc.
• added together you get a complex sound
• e.g. if f₀=100 Hz, then...
• f₁= 100 Hz, f₂=200 Hz, f₃=300 Hz, f₄=400 Hz

• a doubling or halving of frequency
• a frequency ratio of 2:1 or 1:2 (not a frequency difference)
• 3000 Hz is 2 octaves above 1000 Hz

• combination of sounds not harmonically related
• continuous (can be sustained)
• noise (unwanted sounds)

• instantaneous amplitude varies over time
• 3 types:
1. Gaussian noise
2. Sawtooth noise
3. Pink noise

• a type of white noise (static) with random amplitudes
• amplitudes vary according to a normal curve
• contains all frequencies and random phases

• high frequencies emphasis
• random amplitude & phases

• low frequencies emphasis
• random amplitude & phase

• way of describing the level of noise in relation to the level of signal
• signal : noise
• e.g. 60 dB/ 50 dB = +10 dB (signal is 10 dB more intense than the noise)
• e.g. 50 dB/ 70 dB = -20 dB

• brief acoustic events
• short durations (e.g. clicks)
• the shorter, the broader the frequency spectrum
• e.g. t = 1 ms -> 1/t = 1000Hz ->1000 different frequencies

• periodic force is applied to an elastic system
• system is forced to vibrate at frequency of applied force (not at f_nat)
• the closer the frequency of the applied force to the    f_nat of the system, the greater the amplitude of vibration

• a filter
• an object vibrates the greatest at its natural frequency and lessen in magnitude as it moves away

• a type of resonator
• is a frequency-specific elastic system
• allows the frequency of the vibrating object to be modified

1. Center Frequency
2. Upper Cut-off
3. Lower Cut-off
4. Bandwidth
5. Rejection Rate/Attenuation Rate/Roll-Off/Slope

• f_c
• AKA natural frequency 

• parameter of a filter

• f_u 
• frequency above f_c at which the power is 3-dB-down

[image]

• parameter of a filter

• f_l 
• frequency below f_c at which the power is 3-dB-down

 [image]

• Δf or BW
• = f_u - f_l
• defines the bandpass of the system
• the range of frequencies passed by the filter
• quantifies how narrowly or broadly tuned the filter is

• parameter of a filter

• the rate at which energy for frequencies is rejected
• the slope of the filter curve
• dB/octave
• AKA rejection rate, roll-off, slope

• parameter of a filter

1. Low-Pass
2. High-Pass
3. Band-Pass
4. Band-Reject

• attenuates energy above f_u
• passes energy below some f_u
• 2 parameters:
1. f_u
2. attenuation rate
• Δf = f_u [image] 

• a type of filter

• attenuates energy below fL
• passes energy above some fL
• [image]
• type of filter

• is a combination of a low-pass & high-pass filter connected in series
• signal → LP → HP  (or vice versa)

[image] 

• type of filter

• rejects energy between some f_L & f_U
• is a combination of a low- & high-pass filter connected in parallel
• signal → LP & HP

[image] 

• type of filter

• frequencies or amplitudes are in the output that were not there in the input
• all electrical systems produce it
• different types:
• frequency
• amplitude

 [image]

• when filtering has occurred
• related to harmonics
• summation tones (e.g. f1+f2, 2f1+f2, f1+2f2)
• difference tones (e.g. f1-f2, f1-2f2, f1-3f2)
• magnitude
• expressed in a percentage
• proportion of total energy that is undesired energy x 100%

• medium needs elasticity & mass to conduct sound
• sound must be propogated or have a source
• sound source transfers energy to the air, allowing for the energy to actually move through the air

• air molecules pass energy from one molecule to the next
• each molecule only moves an infinitesimal amount from its equilibrium
• creates a force on the molecule next to it
• sound waves constantly encounter barriers in their travels

• is the opposition that energy encounters when it is transferred from its source to a system (load)
• e.g. larynx (source) → air (medium) → wall (barrier)
• a vector
• reactance—mass & elasticity
• resistance—friction

• 1 or a combination of 4 things happen...

1. transmission
2. reflection
3. absorption
4. diffraction

• energy is not lost or created; only changes form

• can happen when impedance occurs (1 of 4)
• amount of energy that successfully travels from the source to the load
• the impedance of the source must be similar to the impedance of the load
• opposite of reflection

H = 4 Z_a Z_b / (Z_b + Z_a)²

H = proportion of energy transmitted

Z_a = impedance of medium (source)

Z_b = impedance of medium (load)

• can happen when impedance occurs (1 of 4)
• the amount of energy that is not transferred from the source to the load
• opposite of transmission
• 2 waves:
• incident
• reflective

H = 4 Z_a Z_b / (Z_b - Z_a)²

H = proportion of energy transmitted

Z_a = impedance of medium (source)

Z_b = impedance of medium (load)

• the original wave
• a wave of reflection (1 of 2)

• the energy that bounces back
• is always at the same angle as the incident wave
• perpendicular
• travel at the same speed as the incident wave
• can interact with the incident wave in a medium
1. standing waves
2. destructive interference
3. constructive interference

• time it takes, in seconds, for a sound to decrease 60 dB
• .001 of its original amplitude
• (damping)
• longer time—highly reflective surfaces; larger rooms
• shorter time—absorptive surfaces
• none—anechoic chambers

• 0.8 - 1.1 seconds
• ↑ reverberation time = ↓ speech intelligibility

• the 2 waves are identical except they are out-of-phase
• the waves cancel creating a dead spot in the environment
• created by complete destructive interfence
• appears as if the vibrations are standing still
• an interaction between the reflected wave and the original wave (1 of 3)

• the amplitude of the interacting wave is less than the original
• complete interference creates standing waves
• an interaction between the reflected wave and the original wave (1 of 3)

• the amplitude of the interaction is increased
• an interaction between the reflected wave and the original wave (1 of 3)

• can happen when impedance occurs (1 of 4)
• minimizes transmission & reduces reflections
• energy is absorbed & dissipated in the form of heat
• inversely proportional to the amount of reflection

• can happen when impedance occurs (1 of 4)
• sound goes around an object
• dependent of the wavelength and the size of the object
• object < λ → sound passes
• object > λ → sound stops
• object = λ → sound shadow
• can either be wanted or unwanted
• does not bend like during refraction

• a special type of reflected wave
• encountering something in its path causes it to bend
• travels at a slower speed than the incident wave
• e.g. traveling through an open door

• occurs during diffraction when the size of an object equals the wavelength
• equals the size of the wavelength
• AKA dead spot

• perceptual change in the pitch of a sound caused by the movement of a sound source
• source moving towards listener
• waves are compressed - ↓ λ
• raises the pitch & the frequency 
• source moves away from listener
• waves are stretched - ↑ λ
• pitch is perceived as lower because the frequency decreases
• e.g. train passing by a stationary listener

• away from listener:
• f' = f [s / (s + s_s)]
• towards listener:
• f' = f [s / (s - s_s)]

f' = altered frequency

f = frequency

s = speed of sound (340 m/s)

s_s = speed of moving sound source

• when sound is propagated in a free, unbounded medium (no obstacles), intensity decreases in a lawful way
• energy twice as far from the source is spread over four times the area, hence one-fourth the intensity

1 / (d_i / d_r)² = -20 log (d_i / d_r)

• intensity is inversely proportional to the square of the distance from the source
• intensity decreases by 6 dB everytime the distance from the sound source is doubled (-20 log 2/1)

1. environment in which sound exists
2. soundproof or anechoic
3. free field
4. near field
5. far field

• within 1 meter of source
• no inverse square law
• no decrease in amplitude
• acts as a free field
• no standing waves

• further than 1 meter from source
• diffraction, absorption, & reflection possible
• inverse square law applies

• the complex periodic waves can be represented by a set of lines
• energy is present only at frequencies represented by the vertical lines

[image]

• representation of an aperiodic waveform of noise
• energy is present at all frequencies between certain lower and upper frequency limits
• graph is a straight horizontal line

• outer ear
• middle ear
• inner ear
• VIII nerve

• brain stem
• cerebrum
• corpus callosum

• contains the organs of hearing and balance
• 4 parts:
1. squamous portion
2. mastoid process
3. tympanic portion
4. petrous portion

• lies in front & above the ear canal
• fan-like portion
• 1 of 4 parts of temporal bone

• behind ear
• very thick
• filled with holes & air
• 1 of 4 parts of temporal bone

• forms bottom & sides of ear canal
• 1 of 4 parts of temporal bone

• medial portion projecting inward
• contains organs of hearing & balance
• 1 of 4 parts of temporal bone

A. temporal bone                

B. malleus                          

C. incus                              

D. stapes                            

E. semi-circular canals        

F. vestibular nerve             

G. facial nerve                    

H. internal auditory meatus

I. cochlear nerve

J. cochlea

K. eustachian tube

L. tympanic cavity

M. tympanic portion

N. tympanic membrane

O. internal auditory meatus

P. pinna

A. squamous portion

B. zygomatic arch

C. mastoid portion

D. external auditory meatus

E. tympanic portion

F. ramus of the mandible

• most lateral & inferior portion of auditory pathway
• part of the peripheral auditory system
• includes the pinna & the external auditory canal

• AKA auricle
• made of cartilage
• functions:
• a resonator for frequencies around 5 kHz
• small muscles attach to cartilage (vestigial)
• several small muscles within (vestigial)

A. helix                        

B. scaphoid fossa          

C. anti-helix                 

D. cymba concha          

E. cavum concha          

F. helix                         

G. anti-tragus

H. ear lobe

I. triangular fossa

J. crus of helix

K. tragus

L. intertragal incisure

• opening into external auditory canal

• extends medially & posterior for about 2.5 cm in adults
• begins & ends with a slope downward allowing for drainage
• fungus may form at far end
• s-shaped
• lined with skin

• cartilage continuous from pinna
• ceruminous glands (sweat) & sebacious glands (sebum)
• together form cerumen
• slight antibacterial & antifungal characteristics
• contains cilia that push out debris & cerumen

• passes through tympanic portion
• no glands or hair
• begins at osseocartilaginous junction
• ends at tympanic membrane

• point where the outer 1/3 & inner 2/3 of EAC meet
• lies directly above the temporomandibular joint
• site of secondary pain for TMJ syndrome
• can get otalgia (pain) & edema (swelling)

• cosmetic nature
• protects TM
• cerumen helps collect foreign objects
• cerumen moves itself out of EAC
• amplification
• localization

• acts as a resonator
• pinna: increase of 3-4 dB at 3-4 kHz
• concha: increase of 10-15 dB at 1.5-7 kHz
• EAC: increase of 10-15 dB at 2.5 kHz

• filtering properties cause a boost in high frequencies which help
• locate sounds, particularly from above & below
• speech perception of consonants, particularly in background noise
• color the spectrum of sounds
• an individual gets use to the sound of his own pinna & EAC

• boundary of outer & middle ear
• concave structure
• made of 3 membranes (outer, middle, inner)
• consistes of 2 areas (pars flaccida & pars tensa)

• same skin as in the canal

• elastic conductive layer; fibrous
• 2 sets of fibers:
• radial
• linear

• same mucous cells that line the middle ear cavity

• AKA Shrapnell's membrane
• most superior 1/4 of TM
• does not contain the fibers that make the TM tight

• inferior 3/4 of TM
• very tight or tense due to fibers

A. pars flaccida

B. long process of incus

C. manubrium of malleus

D. umbo

E. pars tensa

F. tympanic annulus

G. light reflex (cone of light)

• 85 mm² of area
• only 2/3 (55 mm²) vibrates at any given time

• holds the TM in place at the edges

• energy transducer
• changes acoustic vibrations to mechanical vibrations

• air-filled cavity
• 1/2" high by 1/2" wide by 1/4" deep
• surrounded by bone
• inferior: jugular bulb
• anterior: eustachian tube & carotid artery
• medial: oval window, promontory, & round window

• AKA auditory tube
• equalizes pressure between ME & environment
• opens to nasopharynx
• lined with cilia
• normally closed (attenuates voice)
• opened by tensor veli palatini & levator veli palatini muscles

• superior: epitympanic recess or attic
• posterior: parts of chorda tympani & stapedius muscle
• anterior: eustachian tube
• medial: oval window, round window, promontory
• ossicular chain
• very rigid (vibrate, but doesn't move around)
• 5 ligaments, , 2 tendons, 2 muscles

A. tympanic membrane

B. tympanic annulus

C. malleus

D. epitympanic recess

E. incus

F. stapes

G. oval window

H. eustachian tube

A. malleus

B. head

C. articular facet

D. neck

E. anterior process

F. lateral process

G. manubrium

A. incus

B. short process

C. anterior facet

D. articular facet

E. long process

F. lenticular process

A. stapes

B. head

C. neck

D. anterior crus

E. obturator foramen

F. posterior crus

G. footplate

1. lateral ligament
2. superior ligament
3. anterior ligament
4. posterior ligament
5. annular ligament

• manubrium of malleus to temporal bone in inferior part of attic

• malleus head to temporal bone

• malleus manubrium to anterior portion of temporal bone

• incus to temporal bone

• stapes to temporal bone in medial wall
• holds footplate in OW

1. tendon of the stapedius muscle
2. tensor tympani

• stapes to stapedius muscle
• able to measure contraction (stapedius reflex)
• tendon in middle ear

• tensor tympanic muscle to malleus
• tendon in middle ear

1. stapedius muscle
2. tensor tympani

• reduces vibration by twisting
• innervated by facial nerve (VII)
• helps protect the cochlea
• muscle of the middle ear

• impedes the vibration of the malleus & TM
• innervated by trigeminal nerve (V)
• helps protect the cochlea
• muscle of the middle ear

• branch of the facial nerve
• taste info
• runs from posterior of IE and below the incus

• transducer (TM changes acoustic energy to mechanical)
• conducts mechanical energy to the IE
• an impedance matcher (tensor tympani muscle)
• otherwise 99% of energy would be reflected back
• would lose 30 dB if energy went from air to fluid
• makes up for this by area difference, lever action & buckling of eardrum

• 1 of the 3 ways the ME makes up for the loss of energy
• 55 mm² : 3.2 mm² (area of TM : area of footplate)
• 24.7 dB increase
  
• number changes depending on how much the TM is vibrating
• takes the energy and concentrates it to a small area
• e.g. thumbtack

• 1 of the 3 ways the ME makes up for the loss of energy
• the fulcrum of the ossicular chain is closer to the stapes & not in the middle
• allows for a 1.3 : 1 increase of pressure at the oval window
• about 2-3 dB increase

• 1 of the 3 ways the ME makes up for the loss of energy
• TM doesn't vibrate uniformly across surface
• more at the curved areas
• less at the umbo
• which creates an increase in force at umbo
• 3-4 dB increase

• a maze of connected tunnels in the IE
• Osseous Labyrinth:
• bony section
• carve bone around organs of hearing & balance
• contains perilymph
• Membranous Labyrinth
• inside bony portion
• contains endolymph
• 3 divisions (cochlea, semi-circular canals, vestibule)

A. endolymphatic sac

B. vestibular aqueduct

C. endolymphatic duct

D. saccule

E. utricle

F. semi-circular canals

G. ductus reuniens

H. cochlear aqueduct

I. round window

J. oval window

K. scala vestibuli

L. scala media

M. scala tympani

• organ of balance
• epsilateral
• 3 canals at right angles to each other
• superior (anterior), posterior, lateral (horizontal)
• contain endolymph
• are sensitive to rotations that lie in the plane of the canal
• one side is excitatory & the other side is inhibitory
• superior is paired with posterior
• lateral is paired with lateral

• organ of balance
• encodes angular acceleration or rotation
• bulges found where the canals attach to vestibule
• contain crista ampullaris & cupula

• organ for balance
• in the ampulla (semi-circular canals)
• contains ciliated sensory cells embedded in cupula
• release NT during angular acceleration

• in the semi-circular canals
• a gelatinous mass where the cilia from the crista ampullaris is embedded
• composed of a crystalized lime
• may harden with age & break off, causing dizziness
• encodes angular acceleration

A. ampulla

B. cupula

C. crista ampullaris

D. cilia

E. semi-circular canal

• located in vestibule
• 2 parts:
1. utricle
2. saccule
• contains endolymph, maculae, & otoliths
• encodes linear acceleration
  

• organ for balance
• in the utriculosaccular portion
• contains ciliated sensory cells 
• covered by otolith
• release NT during linear acceleration

• in the utriculosaccular portion
• a gelatinous mass covering the maculae
• made of calcium carbonate crystals
• movement causes cilia to pull on the maculae, which causes a chemical reaction (graded potential)
• encodes linear acceleration

• stereocilia on top of the cells move as the fluid moves
• hair cell changes the mechanical energy to electrochemical energy of a graded potential
• carried by the vestibular portion of the VIII CN

• go to vestibular nuclei in medulla
• major connections to the cerebellum
• feedback from cerebellum back to the brain stem
• major projections:
• vestibulocular projections (visual)
• vestibulospinal projections (motor)

• output to the medial longitudinal fasiculus
• then projections are sent to the ipsilateral...
• oculomotor
• trochlear
• abducens
• spinal accessory
• allows for the coordination of eye movement & head/neck movement
• innervated by the CN VIII

• III
• innervates 4 of 6 eye muscles
• receives projections from superior vestibular nuclei through the MLF

• IV
• innervates 1 of 6 eye muscles
• receives projections from superior vestibular nuclei through the MLF

• VI
• innervates 1 of 6 eye muscles
• receives projections from superior vestibular nuclei through the MLF

• XI
• head & neck movement
• function in speech & swallowing
• receives projections from superior vestibular nuclei through the MLF

• receives info from the superior vestibular nucleus
• a fiber tract that connects motor nuclei III, IV, VI, & XI
• runs midline through the medulla, pons, and midbrain

A. cerebellum

B. VIII (balance portion)

C. superior

D. oculomotor

E. trochlear

F. abducens

G. medial

H. inferior

I. lateral

J. medial longitudinal fasciculus

K. spinal accessory

• output to the cerebellum
• innervated by the CN VIII

• output to the cerebellum
• innervated by the CN VIII

A. annular

B. lateral

C. posterior

D. anterior

E. superior

F. stapedius muscle

• organized horizontally
• from spinal cord, pons, & vestibular system
• how many muscles to be stimulated & timing

• organized vertically (right & left):

 [image]

• input from spinal cord
• horizontal division of cerebral cortex

• input from pons
• horizontal division of cerebral cortex

• input from vestibular
• input from lateral, medial, & inferior nuclei
• horizontal division of the cerebral cortex

• input from spinal cord, pons, & vestibular
• output through the fastigial nuclei to the 
• lateral vestibular nuclei (primarily)
• reticular formation (some)
• to spinal cord
• lies directly on the seam
• "worm"
• vertical division of the cerebral cortex

• input from the vermis
• output to
• lateral vestibular nuclei &
• reticular formation
• to spinal cord

• input from spinal cord, pons, & vestibular
• output through interposed nuclei to the
• red nuclei (primarily)
• ventrolateral nucleus (some)
• to spinal cord
• middle area of cerebellum
• vertical division of cerebral cortex

• gray matter (lack myelin sheath)
• outer portion of cerebellum
• input (horizontally) from spinal cord, pons & vestibular
• output (vertically) from vermis, paravermis & lateral hemisphere
• functions:
• fine movement coordination
• balance & equillibrium
• muscle tone

• in the 4th ventricle (floor of medulla)
• superior, lateral, medial, & inferior
• innervated by the balance portion of the VIII CN
• sends info to cerebellum, MLF, & vestibulospinal tract

• concerning proprioception
• constantly updated, which allows equilibrium maintenance

• input from the vermis through the fastigial nuclei
• output to spinal cord  & cerebellum 
• innervated by the CN VIII

• input from the vermis through the fastigial nuclei 
• output spinal cord

• input from the paravermis
• output to red nuclei (primarily)
• ventrolateral nucleus (some)

• primary input from the paravermis through the interposed nuclei (motor-efferent)
• output to the spinal cord

• input from the lateral hemisphere through the dentate nuclei 
• output to the motor cortex
• to the spinal cord

• input from the paravermis through the interposed nuclei (sensory - afferent)
• output to the spinal cord

• primary input from the lateral hemisphere through the dentate nuclei
• output to the motor cortex
• to spinal cord
• of the thalamus (sensory relay station)

• input from spinal cord, pons, & vestibular
• output through the dentate nuclei to
• ventrolateral nuclei (primarily)
• red nucleus (some)
• to the motor cortex (#4)
• to spinal cord via corticospinal tract
• the largest part of the cerebellar cortex
• vertical division

• input from the lateral hemisphere
• output to the
• ventrolateral nuclei (primarily)
• red nucleus (some)
• to the motor cortex (#4)
• to the spinal cord
• largest of the nuclei

• input from the lateral hemisphere via the ventrolateral nuclei & the red nucleus
• output to the spinal cord via the corticospinal tract
• Brodmann's area #4

• movement of the eye in the opposite direction of the movement of the head
• the eye's attempt to stabilize an image and make sense of what you're seeing so that it isn't just a blur
• can be measured by an ENG or in a rotary chair
• what cops test drunk drivers for

• electronystagmography
• a test to measure nystagmus

• 3.5 cm long - 1 cm wide
• part membrane & part bone
• 2 ³/₄ turns
• base to apex (large to small)
• similar to a snail & spiral stair case

• central core of cochlea made of bone
• osseous spiral lamina extends outward

[image]

• bony shelf that extends outward from the modiolus
• BM is connected
• wider at base & narrower at apex (opposite of BM)

• separates scala vestibuli from the scala media

• top section
• oval window & stapes footplate at base
• contains perilymph
• high in Na⁺
• separated at bottom from scala media by the Reissner's membrane

• middle section of cochlea
• aka cochlear duct
• contains endolymph
• high in K⁺
• shared with saccule of vestibule
• contains electro-mechanical transducing structures
• hair cells
• membranes
• support cells

• bottom section of cochlea
• contains perilymph
• high in Na⁺
• round window at base
• separated at the top from scala media by basilar membrane

• separates scala media from scala tympani
• provides a stiffness gradient
• narrow near base (.04 mm)
• stiffer
• higher resonant frequency
• wider at apex (.5 mm)
• looser
• lower resonant frequency
• logarithmic (nonlinear)
• the base is tuned to more frequencies than the apex

• lateral wall of cochlea (opposite modiolus)
• no direct blood supply (despite the name)
• possibly a generator of endolymph

• lateral wall of cochlea (opposite modiolus)
• support ligament for the stria vascularis

• in scala media
• made of sensory cells & support cells
• sits on BM
• covered by the TM

• Deiter's cells
• Hensen's cells
• Claudius' cells
• Pillar cells
• inner supporting cells

1. IHC
2. OHC
3. tunnel of Corti
4. BM
5. reticular lamina
6. TM
7. Deiter's cells
8. space of Nuel
9. Hensen's cells
10. inner spiral sulcus

• two types:
• IHC & OHC
• aka mechanoreceptors
• sense mechanical stimulation
• changes it to electrical/graded potential

• rudimentary stereocilia
• thicker than regular stereocilia

• cilia at base of cochlea
• top row is IHC
• bottom 3 rows are OHC

• one type of sensory cell in the Organ of Corti
• single row (3500)
• flask shaped - linear
• closest to modiolus
• not embedded in tectorial membrane
• shorter stereocilia
• senses movement of the endolymph
• high metabolic activity
• contain many Golgi & mitochondria
• supported by inner sulcus
• divergent neural pathway
• separated from OHC by pillars of Corti

1. nucleus
2. stereocilia
3. cuticular plate
4. radial afferent ending (dendrite)
5. lateral efferent ending

IHC

• the holes in the tectorial membrane for the stereocilia to fit

1. nucleus
2. stereocilia
3. cuticular plate
4. radial afferent ending (dendrite)
5. lateral efferent ending
6. medial efferent ending
7. spiral afferent ending (dendrite)

OHC

• many cells connect to one neuron
• OHC

• one cell connects to many neurons
• IHC

• separate OHC from IHC

• input from VIIIth nerve
• acoustic branch
• vestibular branch
• dendrites attach to the hair cells
• cell bodies are located outside of the cochlea in the spiral ganglion

• holes in the osseous spiral lamina
• where dendrites from the VIIIth nerve leave the cochlea

• small bundles that innervate the OHC
• not much known except they get some kind of feedback

• detects sounds
• encodes information
• performs Fourier Analysis
• receives energy from stimulus
• uses energy to make some change in the sensory cell
• initiates some electrical activity in the nerve leading to the CNS

• vibratory
• passes through the middle ear
• stapes footplate vibrates in OW
• displaced fluid is released at the oval window

http://www.iurc.montp.inserm.fr/cric/audition/english/ear/fear.htm    

• pressure in the scala vestibuli
• creates pressure on scala media
• moves the BM (stiffness gradient)

• travels from base to apex
• tonotopic organization
• maximum displacement at the point the BM is tuned to input frequency
• different frequencies are encoded at different places
• high frequences at base (20k Hz)
• low frequencies at apex (20 Hz)
• quickly dies off

• sits on top of hair cells
• thickened plate
• with the phalange, they form the reticular lamina

• a support cell for the OHC
• cup-like
• each one has a phalange

• a plate formed by the phalange plus the cuticular plate
• lies at the top of the hair cell, only the stereocilia stick above it

• supports the inner hair cells

• as BM moves up
• TM moves upward & away from modiolus
• as BM moves down
• TM moves downward & towards the modiolus

• sits on top of sensory cells in the Organ of Corti
• attached to the BM at the spiral limbus
• movement of the 2 membranes will be relative to each other
• connective tissue made of collagen
• jello-like mass
• has Hensen Stripes

• are embedded in the TM

• are affected by the movement of fluid under the TM

• attaches the stereocilia to one another
• found in muscle tissue & suggests movement

• a contractile protein
• found in stereocilia & walls of OHC
• moves into OHC during depolarization & back into the walls during hyperpolarization

• sit on top of IHC & OHC
• attached to one another via actin fibers
• move with fluid/membrane
• contains prestin
• are very rigid & the entire piece moves

• sensory cell in the Organ of Corti
• three rows (12-16000) that are tube-shaped
• gradually gets larger from base to apex
• convergent neural pathway
• walls contain prestin
• contract when depolarizing & rotate at their base in the cups of the Dieter's cells
• elongate when hyperpolarize

• contractile protein that is very stiff
• stereocilia is made from

• shearing of the OHC stereocilia
• the stereocilia move towards the kinocilium
• causes channels to open in the stereocilia
• K⁺ flows into cell from the endolymph
• causes the release of Ca⁺⁺ within the stereocilia
• results in the release of myosin (contractile protein)
• contraction of stereocilia help them move back upright
• a chemical change (graded potential) occurs within the hair cell when K⁺ flows in

• glutamate is released at the base of the hair cell
• it is absorbed by the neuron which is attached to the hair cell
• when enough is absorbed, depolarization occurs
• this causes a graded potential

• an electrical change (less negative)
• electro-mechanical transduction
• occurs when enough glutamate is absorbed by the neuron
• causes a graded potential

• excitation of the neuron
• caused by depolarization

• bottom of hair cell
• Glutamate
• efferent synapse
• Acetylcholin
• GABA
• Dopamine
• Enkephalins
• Dynorphins
• CGRP

• TM moves back towards the modiolus
• stereocilia move away from kinocilium
• aided by myosin
• causes the hair cell channels to close
• release of neurotransmitter is stopped
• hyperpolarization of the neuron which is inhibitory

• contractile protein that causes cilia to contract & close channels
• results from the release of Ca⁺⁺ when OHC channels open 

• contraction during depolarization
• elongation during hyperpolarization
• due to prestin movement

• voltage change indicating activity
• resting potentials:
• endolymphatic potential
• intracellular potential
• summating potentials
• cochlear microphonic

• no stimulus is needed
• 2 types:
1. endolymphatic potential
2. intracellular potential
• these two allow for a 150 mV difference across the top of the hair cell when channels open

• one type of resting potential
• source is the endolymph from the stria vascularis
• in the scala media
• +80 mV charge at rest

• one type of resting potential
• from inside the hair cell
• -70 mV charge at rest

• only seen when acoustic stimulation is present
• source is unknown
• direct current
• shape always looks the same, regardless of stimulus

 [image]

• only seen when acoustic stimulation is present
• source is the root of the cilia on the hair cells
• alternating current
• reflects intensity & frequency of the input

[image]

• sounds produced by cochlea & sent out through the oval window, middle ear, & TM
• like an echo
• about -20 dB SPL
• reflects the OHC movement
• some evoked by a stimulus & others are spontaneous without a stimulus
• can be picked up by microphone in the ear canal

• produced by a stimulus
• 2 types:
• Transient evoked OAE
• Distortion product OAE

• one type of evoked OAE
• produced by clicks
• response from cochlea 10-20 ms after stimulus
• only in healthy ears
• reflects hearing to about 30 dB
• not necessarily frequency specific
• won't be able to find hearing loss at specific frequencies
• used in newborn screenings

• one type of evoked otoacoustic emissions
• produced by tones
• relies on the nonlinearities of the ear
• put in 2 tones, get a combination tone back
• summation/difference tones
• reflects normal hearing at the frequency range of the combination tone
• tests specific frequencies
• used in hearing testing & newborn screenings

• near threshold
• only in healthy cochlea
• in 1/3 of the population

• aka primary fibers because of its AP response
• afferent pathway (PNS to CNS)
• 30,000 fibers

• when AP firing in the fibers of the auditory nerve takes place in synchrony

• continuous APs in each fiber of the auditory nerve
• no stimulus
• due to random release of neurotransmitters

• 30,000 fibers
• 24 mm long (about 1 in)
• each has a characteristic frequency
• APs coming from each
• together can form a compound potential
• have a spontaneous discharge rate
• starts at the dendrites at the base of the hair cells
• 90-95% from IHC
• 5-10% from OHC

• aka radial fibers
• from IHC 
• 90-95% of auditory fibers
• corresponds to more of a physiological load associated with the IHC
• 3 categories:
1. High Spontaneous Rate Fibers
2. Medium Spontaneous Rate Fibers
3. Low Spontaneous Rate Fibers

• aka outer spiral fibers
• from OHC
• 5-10% of auditory fibers

• one category of type I auditory nerve fibers
• >18 spikes/sec (no stimulus)
• large diameter
• synapse to lateral edge of IHC
• fires at low intensity sounds

• one category of type I auditory nerve fibers
• <.5 spikes/sec (no stimulus)
• small diameter
• synapse at medial edge of IHC
• fires at high intensity sounds

• one category of type I auditory nerve fibers
• .5-18 spikes/sec (no stimulus)
• medium diameter
• synapse at inferior of IHC
• fires at middle intensity levels
• gradual intensity function
• (speech)