Audiology Exam 2

Central Auditory System Vestibular System Acoustics What is Sound The Audiogram

How Sound Travels Through The Ear

Acoustic energy > Mechanical energy > Hydraulic energy > Chemical signal > Electrical signal

Acoustic energy

sound waves enter the ear from the pinna and the sound hits the TM causing it to vibrate (changing it into mechanical energy)

Mechanical energy

the malleus (attached to TM) moves the ossicular chain and the stapes pushes in and out of the oval window and sound travels to the round window (creating a fluid motion/hydralic energy)

Hydraulic energy

the fluid movement causes the hair cells to shear the tectorial membrane in the organ of Corti (creating a chemical signal)

Chemical signal

chemical signal in inner hair cells that has chemical energy traveling down the hair cell to the synaptic junction (creating electric signal)

Electrical signal

electrical signal is sent up the auditory nerve to the brain

Functions of Central Auditory System

• sound localization

• speech recognition

• take sounds from two different areas to make into one sound

Afferent Pathway

• auditory nerve

• brainstem pathway

  • cochlear nucleus (medulla oblongata)

  • superior olivary complex (pons)

  • lateral lemniscus (midbrain)

  • inferior colliculus (midbrain)

• thalamus

  • medial geniculate body

• auditory cortex (in cerebral cortex)

Efferent Pathway

• might send a signal to OHC to relax

Contralateral processing of sound

the information ascends through the contralateral side of the brainstem and brain to the cortex (sound crosses over pathways)

Cochlear nucleus

• in the auditory portion of medulla oblongata

• tonotopically organized

Decussations

• cross-over points

• helps up figure out which side sound comes from

• localization and lateralization

Superior Olivary Complex

• first place along hearing highway where neurons receive and input from both ears (from both sides of the body)

• key player in binaural integration (being able to focus on a target sound)

• located in pons

Lateral Lemniscus

• tract of nerve fibers

• connects superior olivary complex to inferior colliculus

• sensitive to timing/amplitude changes in sound

• located in midbrain (crossing to opposite side of brain)

Inferior Colliculus

• responsible for the startle reflex and vestibulo-ocular reflex

• sensitive to changes in intensity and frequency

• responsible for detection of pitch

• located in midbrain

Medial Geniculate Body

• all sounds must stop at the medial geniculate body

• helps us direct and focus attention on target sound (high order processing of bineural inagration)

• located in thalamus

Auditory Cortex

• assigns meaning and value to sounds

• has tonotopic organization

Sound must travel through each portion of the _________ for hearing to occur

ear and to the brain

Outer hair cells are the…

amplifier that refines sensitivty and frequency from the vibrations in the cochlea

Tonotopicity occurs from..

the cochlea to the cortex

Detection and localiztion occur at..

the level of lower order neurons

Sound may be detected, but it is still processed at…

the level of auditory cortex

One can have severe cortical damage (in auditory cortex) but…

can still have “normal” hearing

What happens in the temporal bone?

peripheral system

Where is the central system?

in the brainstem

Vestibular pathways lead to…

large muscles in head, neck, torso, arms, legs, and feet

Vestibular ocular reflex

keeps images on our retina stable with our head movement

Three semi-circular canals

• superior/anterior

• posterior

• lateral

The semi-circular canals share which fluid with the cochlea?

endolymph

The semi-circular canals contain hair cells with cilia that are sensitive to…

movement of fluid (gravity and acceleration)

Vestibular system (functions)

• monitors the position of the head in space

• controls balance

• provides sensation of movement/acceleration

• sends signals to eyes for visual stablilization

• sends signals to muscles to keep us upright

The 8th nerve innervates the…

cochlea and vestibular part of the ear

Saccule and Utricule

• two otolith organs of the membranous labyrinth located within the vestibule

• use small stones (otoconia) and viscous fluid to stimulate hair cells to detect motion in a straight line

Acoustic filters

• selective device that allows some sounds to pass through and obstructs others

  • gain - applying emphais to certain sounds (presented to listener)

  • attenuation - obstructing certain sounds (not presented to listener)

Low Pass Filter

below point is given gain, above point is attenuated

High Pass Filter

below point is attenuated, above point is given gain

Band Pass Filter

• two knee points

  Hz between band are given gain, outside of the band are attenuated

Acoustic filters are determined by…

frequencies

Amplitude can be measured as…

sound pressure or sound power

Amplitude is the…

intensity & height of a waveform; loudness; reflection of power/pressure acoustic waveform is generating

Logarithic

• all units of measurement are larger than the preceding

• compresses large range of sounds into a smaller scale

0 db is not the absence of sound, it is…

the starting point with reference to human hearing ability

10dB Rule

every 10 dB increase in intensity is a doubling in loudness

Equal Loudness Contour

• comparing to be equally as loud

• loudness curves for the human ear

Intensity is described in units called…

decibels (dB)

Loudness is described in units called…

phons

Pitch is decribed in units called…

mel

The human ear is most sensitive to…

mid-frequencies (2000-5000 Hz)

Minimum Audibility/Threshold

the smalled amount of sound pressure required to produce a sound that is audible to a listener

Reference

the threshold of audibility for a particular listener at a particular frequency

dB (A)

• this filter is widely used

• makes sound level meter less sensitive to very high and very low freq.

dB (B)

• rarely used

db (C)

• used for subjective measurements at high sound pressure levels

• almost linear at several octaves

Inverse Square Law

the intensity of sound decreases as sound waves travel further from the source of sound

What is sound?

a tool to assess hearing

Complex sounds

speech and noise sounds (energy at more than one frequency)

Pure tones

tones at specific frequenices (all of the energy at one frequency)

Physics

vibration of air particles produced by the vibration of an object

Psychological

the perception of those waves and the enterpretation of the waves by the brain

Psychoacoustics

our perception of the physical attributes of sound

Pitch

subjective perception of frequency

Loudness

subjective perception of intensity

Sound is a result of…

back and forth motion of air particles

Longitudinal wave or compression wave

air particles move parallel to the direction of the wave motion

Condensation and rarefaction

increase and decrease regions of air pressure in a repeating manner

Simple harmonic motion

constant back and forth motion of sound

Amplitude

displacement in a wave form

Peak

maximum postive or negative displacment from baseline

Peak to peak

difference in displacement from the positive to the negative peaks

Root-mean-square

square all instantaneous amplitudes, then averaged

Damping

decrease of vibration due to resistance (amplitude fades or decreases)

Wavelength

wavelength (length of the wave) = velocity(the speed of sound)/frequency

Speed of sound

distance a sound travels in a space of time (1100 ft/sec or 345 m/s)

Low frequency sounds have a…

longer wavelength

High frequency sounds have a…

shorter wavelength

Phase

where the wave begins

• waves starting at the same point are in phase

• waves starting at different points are out of phase

Opposite phase

waveforms that are 180 degrees out of phase

Cycle

air particle movement from rest to max. displacment one one direction, back to rest, and max. displacement in other direction (one condensation and rarefaction)

Period

amount of time it takes to complete one cycle

Frequency

the number of cycles completed in period of time

Resonant frequency

the frequency where an object naturally vibrates on its own

As the mass of the vibrating body increases…

the frequency decreases

As the mass of the vibrating body decreases…

the frequency increases

As stiffness decreases, resonant frequency…

decreases

Fundamental frequency

lowest rate of a complex sound’s vibration

Formants

frequencies in a complex periodic sound that occur over the fundamental frequency

Fourier analysis

breaks down a given speech sound into individual parts

Degrees of Hearing Loss (Adult)

Degrees of Hearing Loss (Child)

Threshold

lowest level at which a person can detect a sound 50% of the time at a given frequency

Types of hearing loss

• conductive

• sensorineural

• mixed

Conductive Hearing Loss

sound breaks down at the pinna and middle ear

• cerumen stopping sound

• fluid or infection

• hole in TM

• ossicular chain not connected

Sensorineural Hearing Loss

affecting inner ear or auditory nerve

• hair cells damaged

• auditory nerve cells damaged

Mixed Hearing Loss

affecting outer/middle/inner ear or auditory nerve

• combo of conductive and sensorineural

Unilateral Hearing Loss

present in only one ear, the other is normal

• can be any hearing loss

Air-Bone Gap

the difference in sound transmission between air and bone conduction

• air conduction should be equal bone conduction threshold in normal hearing