Audiology Exam 1

Acoustics

the study of the physical properties of sounds in the environment, how they travel through air, and how they are affected by objects in their environment

Psychoacoustics

the study of how we perceive sound

Unit of measurement of acoustics

quantitative

unit of measurement of psychoacoustics

qualitative

3 characteristics of acoustics

intensity/pressure(dB) (amplitude)
Frequency (Hz)
Spectrum

3 characteristics of psychoacoustics

loudness
pitch
richness/timbre

how the characteristics of acoustics and psychoacoustics relate to each other

amplitude \= loudness
frequency \= pitch
spectrum \= richness

Sound

an object being set into vibration

For sound to occur you need

a medium that has the properties of mass and elasticity for sound to travel through

Sound waves travel/propagate in the direction

longitudinally

Condensation

compression of air molecules

Rarefaction

expansion of air molecules

Time Domain Waveform

common way in which pure and complex tones are visualized

Time Domain Waveform x and y axis \=

x-axis \= time
y-axis \= amplitude of vibration

Pure-tone equals

1 frequency

Complex tone equals

multiple frequencies

Characteristics of a frequency

time-domain waveform
one cycle
cycles/second - Hz
Human audible range

higher frequency

higher pitch, shorter wavelength

lower frequency

lower pitch, longer wavelength

A cycle of vibration is

full range of motion one time (one condensation and one rarefaction)

Frequency

number of vibration cycles (1 up 1 down) per second measured in Hz

Period (T)

amount of time it takes for one cycle to occur

Wavelength

length of one cycle

Phase

defined in angular degrees
one cycle of sinusoidal vibration rotates through 360°

Amplitude

Magnitude if a sound analogous to volume/loudness (how loud is the sound)

Intensity (I) \=

power/area

Pressure (P) \=

force/area

How do Intensity and Pressure relate

I \= p^2
p \= √I

Bels

Ratio Scale
range of intensity only 0-14 Bels

Decibels

range of intensities from 0-140 dB
useful for any ratio in audible range

Signal-to-Noise Ratio (SNR)

the level of a signal relative to a background of noise

Resonance

the frequencies at which objects vibrate most easily

sagittal plane

divides body into left and right (two faced)

Coronal plane

divides body into front and back

transverse plane

line that divides the body into upper and lower sections (top/bottom)

Superior

toward the head

Inferior

towards feet

Anterior

front of the body

posterior

back of body

medial

toward the midline

lateral

away from the midline

proximal

closest to the body

distal

furthest from the body

5 general divisions of the auditory system

Outer Ear
Middle Ear
Inner Ear
Cranial nerve
Central Nervous System

Parts of the outer ear

pinna
external auditory canal

Parts of the middle ear

tympanic membrane
ossicles (M.I.S)
eustachian tube
stapedius muscle

tensor tympani muscle
epitympanic recess
supporting ligament

(T.O.E.S T.E.S)

parts of the inner ear

cochlea ( w/ oval and round windows)
semicircular canals
saccule, utricle (within the vestibule)

Cranial nerves

Eighth CN : cochlear/vestibular/auditory
Seventh CN : facial nerve

parts of the CNS

Brainstem
Cortices

4 parts of temporal bone

Tympanic
Petrous
Mastoid
Squamous
(TPMS)

2 processes of temporal bone

zygomatic process
styloid process

petrous portion of temporal bone

deep in skull
hardest part of human body
protects inner ear structures

2 areas of the external auditory canal

cartilagenous part
bony part

stapedius muscle

medial wall of middle-ear
attaches to head of stapes
innervated by 7th CN
involved in acoustic reflex (reflex to loud sounds)

tensor tympani muscle

bony wall above eustachian tube
upper part of manubrium
involved in acoustic reflex (reflex to loud sounds)

Eustachian tube

connects middle-ear to nasopharynx
pops/equalizes ears
downward sloping 45 degrees in adults
flat angle for children

two portions of the inner ear

bony labyrinth
membranous labyrinth

cochlea

2.5 turns
35 mm long if uncoiled
beginning of coil \= base (high-freq)
narrow tip of coil \= apex (low-freq)
contains perilymph and endolymph

perilymph

liquid similar to cerebral spinal fluid
high sodium (Na+) and low potassium (K+)
found in bony labyrinth

endolymph

only found in membranous labyrinth of cochlea
high potassium (K+) and low sodium (Na+)

modiolus

central core of cochlea
forms inner wall of cochlea
area where sensory nerve cells travel to 8th CN

osseus spiral lamina

divides the bony labyrinth into different sections (scalae)

scala vestibuli

contains perilymph
upper part of cochlea
ends at oval window

scala tympani

contains perilymph
bottom part of cochlea
ends at round window

scala media

primarily contains endolymph
contains sensory hearing organ : organ of corti
superior division \= reissner's membrane
inferior division \= basilar membrane
lateral division \= stria vascularis

helicotrema

where the scala tympani and scala vestibuli meet at the apex of the cochlea

Reticular lamina (RL)

tight mosaic of cells atop organ of corti
forms boundary between endolymph and perilymph
endolymph is above RL bathing stereocillia tips
perilymph is below in spaces of organ of corti

Inner hair cells

single row of about 3500 in cochlea
flask shaped
have centralized nucleus and cytoplasmic organelles
primary receptor/auditory nerve impulse
afferent neurons (ear to brain)

Outer hair cells

3 rows of about 12000 OHCs
cylinder shaped
nucleus close to base of cell and organelles on outer walls
efferent neurons (brain to OHC)

3 semicircular canals

anterior, posterior, horizontal

8th cranial nerve (auditory nerve)

cochlear nerve and vestibular nerve fibers
-auditory portion exits cochlea via modiolus and exits temporal bone via internal auditory canal

7th cranial nerve (facial nerve)

enters cranial cavity via internal auditory canal
passes through middle-ear space

Afferent neurons

30,000
95% from IHCs
exit organ of corti through habenula perofratum

efferent neurons

1200
connected to IHCs and OHCs

auditory brainstem nuclei (ascending order)

cochlear nuclei
superior olivary complex
lateral lemniscus
inferior colliculus
medial geniculate body
auditory cortex
(C-S.L.I.M.A)

Purpose of the auditory system

receive sound vibrations from the environment and convert them into neural information

Transduction process

the change in sound energy as it passes through the auditory system

The type of energy within the outer ear

acoustic energy

The type of energy within the middle ear

mechanical energy

the type of energy within the inner ear

hydro-mechanical energy

the type of energy past the inner ear to the brain

electrical energy

Impedence

total opposition to the flow of energy
how efficient energy is transferred

Efficient energy flow

happens when the impedance is low or when 2 systems have equal impedances ex:air

impedance mismatch

When 2 systems have different impedances.

Impedance mismatch leads to \___ dB loss of sound energy

30 dB

Pinna function

increases localization

External auditory canal function

primary connection of sound environment to middle-ear
increases protection
has ear-wax which protects body
increases sound pressure by 15-20 dB (1500-7000 Hz)

frequency range for speech

1500-7000 Hz

Functions of Middle Ear

converts acoustic energy (waves hitting tympanic membrane) into mechanical energy (ossicular chain moving)
-corrects impedance mismatch
-mechanical amplifier
-negates the 30dB that was lost

3 ways the middle ear overcomes impedance mismatch

1. Area ratio advantage
2. Curved membrane advantage
3. Lever advantage

Stapedius and Tensor Tympani muscles function

both contract to loud input sounds, greater than 80 dB
-acoustic reflex
-helps make sure there are no middle ear problems

Eustachian tube function

opens/closes to equalize atmospheric pressure outside of tympanic membrane with pressure inside middle-ear

How is sound vibration begun (hydromechanical events)

begun in the inner ear by movement of stapes footplate into and out of oval window with coinciding movement of the membrane of round window
( energy enters at oval window and exits at round window)

traveling wave

movement of the basilar membrane
- narrower and stiffer at the base
- becomes wider and less stiff near apex

tonotopic arrangement

organized by frequency
highs at the base, lows at the apex

Because the Basilar membrane is sensitive to frequency, the organ of corti which is atop is also

sensitive to frequency

Inner Hair Cell transduction

deflected when basilar membrane moves up and down causing sterocillia to be pushed by tectorial membrane
- takes hydromechanical bending of sterocillia to open ion channels leading to transduction

Outer hair Cells are the only \___ within the inner ear

motile (cell that can move)
- can contract like a muscle

OHCs function

sharpens our hearing
adds more displacement to the basilar membrane in resonance
-causes IHC sterocillia to make contact with tectorial membrane
-healthy OHC \= better sensitivity and better resolution

place theory

tonotopic arrangement along basilar membrane
- maintained in the nuclei of brainstem and at the cortical level