Sensation9

sound wave

objects vibrate

when there is a lot of room between molecules

air molecules are compacted together

lower sounds

• Number of pressure changes per cycle
• Measured in hertz (Hz)

one cycle per second

Our perception of frequency

• Amount of change in pressure
• Also called intensity
• Measured in decibels (dB)

Our perception of amplitude

• measures the physical intensity of sound
• Logarithmic scale

large physical changes

Doubles the amount of sound pressure

1-2 dB

• Number of different frequencies in a sound
• Physical

• lowest frequency
• Determines pitch

Higher pitched tones related to the fundamental (makes things sound good or bad)

Any complex tone can be represented as a series of simple tones (sine waves)

composite wave

Because the auditory system does a Fourier analysis on complex tones, we are aware of each of the simple tones

Our perception of complexity

overtones

many overtones or harmonics

few overtones

• The reletive position of two or more sine waves
• physical
• means where the wave is in compression - rare fraction cycle

Peaks occure at the same time (troughs)

occur at different time

• Destructive interference
• Sound waves can cancel each other out if they are 180 degrees out of phase
• Cars and cell phones are doing this

• The frequency with which an object vibrates when hit
• Knocking on the body of a cello (strings start to vibrate)

will begin to vibrate if a sound wave matching the object's resonant frequency travels close to the object = resonant

The outer funnel-like part of the ear

The canal that conducts sound vibrations from the pinnato the tympanic membrane and prevents damage to the tympanic membrane

• The eardrum
• A thin sheet of skin at the end of the outer ear canal.

in response to sound

the external sound gathering portion of the ear, consisting of the pinna and the ear canal

an air filled chamber containing the middle bones or ossicles

vibration from the tympanic membrane to the oval window

Three tiny bones of the middle ear; malleus, incus, and stapes

• one of the ossicles
• Receives vibration from the tympanic mem. and is attached to the incus

• The middle ossicle
• Connects the malleus and stapes

Connected to the incus on one end, the stapes presses against the oval window of the cochlea on the other end

The flexible opening to the cochlea through which the stapes transmits vibration to the fluid inside

A hollow cavity in the temporal bone of the skull and the structures within this cavity: the cochlea and vestibular canals

the muscle attached to the malleus

decreases vibration

• The muscle attached to the stapes
• tensing this muscle decreases vibration

A reflex that protects the ear fromintense sounds, via contrasction of the stapedeus and tensor tympani muscles

A spiral structure of the inner ear containing the oran of corti

• One of three fluid filled passages in the cochlea.
• It extends from the round window at the base o the cochlea to the helicotrema at the apex
• Also called scala tympani

• one of three fluid filled passages in the cochlea
• Extends from the oval window to the helicotrama at the apex
• Scala Vestibula

• One of three fluid filled passages in the cochlea
• Is sandwiched between the tympanic and vestibular canals and contains the cochlear partition
• Scala Media

The opening that connects the tympanic and vestibular canals at the apex of the cochlea

A thin sheat of tissue separating the vestibular and middle canals in the cochlea

A plate of fibers that forms the base of the cochlear partition and separates the middle and tympanic canals in the cochlea

the combines basilar membrane, tectorial membrane, and organ of corti, which are together responsible for the transduction of sound waves into neural signals

organ of corti

• Transduce mechanical movement in the cochlea in to neural activity
• 3500 inner cells and 10,500 outer hair cells

inner hair cells

Afferent (sending)

Efferent (receiving)

• Sharpen information sent by inner cells (receive info. about which frequencies need to be heightened or amplified)
• Amplifies sounds

• Sound produced just by your ear, nothing else.
• Can be used to test newborn's hearing

Tonotopically organized

• Hair cells are tonotopically organized on basilar membrane
• Low frequencies cause maximal displacement furthest from the oval window (apex)
• High frequencies cause max displacement closest to oval window (base)

he got cochlea from fresh cadavers and cut windows in it, played tones to see if basilar mem. moved - high frequencies

intensity

the less likely it will be to be a crisp sound

dont see nice neat traveling waves for low frequency sounds

Time

Frequency of sound is coded by how many times auditory neurons fire

Firing of a single neuron at one distinct point in the cycle of a sound wave

• There arent enough hair cells to be tuned for all frequencies
• Nerve cells can only fire up to 1000 times

• Cells work in groups to code frequency
• Look at total output of group of cells to determine frequency of sound

• Frequency coded by the sum of action potentials produced by a group of cells
• Amplitude coded by determining how many cells in that group are firing at the same time
• The more cells firing means the louder the sound

• High frequencies: place theory (above 3000Hz)
• Low frequencies: temp. theory (below 1000 Hz)
• Between 1000 and 3000 Hz: both theories work
• Both theories say the same thing about amplitude

A map plotting the thresholds of a neuron or fiber in response to sine waves with varying frequencies at the lowest intensity that will give rise to a response

An idea stating that multiple neurons can provide a temporal code for frequency if each neuron fires at a distinct point in the period of a sound wave but doesnt fire on every period

the first brain stem nucleus at which afferent auditory nerve fibers synapse

an early brain stem region in the auditory pathway where inputs from both ears converge

the part of the thalamus that relays auditory signals to the temporal cortex and receives input from the auditory cortex

an arrangement in which neurons that respond to different frequencies are organized anatomically in order of frequency

hearing loss caused by problems with the bones of the middle ear

inflammation of the middle ear, commonly in children as a result of infection

abnormal growth of the middle ear bones that causes hearing loss

producing adverse effects on organs or nerves ivolved in hearing or balance