Auditory System

Auditory System

Adequate Stimulus for theauditory system is sound

What is sound?

Two components of sound displacement component

movement of molecules pressure component

alternating compression and rarefaction

Human ears are sensitive only to thepressure component, and only between 20 Hz and 20 kHz

Sound

Animation courtesy of Dr. Dan Russell, Kettering University

Sound

Animation courtesy of Dr. Dan Russell, Kettering University

Outer earPinna or auricleAuditory canal or ear canalTympanic membrane or eardrum

Middle earOssicles

Malleus or hammerIncus or anvilStapes or stirrup

http://www.youtube.com/watch?v=dyenMluFaUw&feature=player_detailpage

Latex-filled cochlea. Scala tympani and scalavestibuli shown in red; scala media in dark blue.

Scala tympani and scala vestibuli are filled with perilymph; scala media is filled with endolymph.

Viewed in cross section, the cochlea contains three small Viewed in cross section, the cochlea contains three small parallel chambers. These chambers, the scalae, are parallel chambers. These chambers, the scalae, are separated by Reissner’s membrane and the basilar separated by Reissner’s membrane and the basilar membrane. The organ of Corti contains the auditory membrane. The organ of Corti contains the auditory receptors; it sits upon the basilar membrane and is receptors; it sits upon the basilar membrane and is covered by the tectorial membrane.covered by the tectorial membrane.

The spiral ganglion so named because the cell bodies follow the spiral path of the bony cochlea around the modiolus.

It is also known as the cochlear ganglion.

a.k.a. cochlear ganglion

a.k.a. cochlear ganglion

http://www.youtube.com/watch?v=1VmwHiRTdVc&feature=player_detailpage

Na+ K+Na+ Na+

http://www.youtube.com/watch?http://www.youtube.com/watch?v=1JE8WduJKV4&feature=playv=1JE8WduJKV4&feature=player_detailpageer_detailpage

Place theory: Pitch perception based on PLACE of greatest displacement of basilar membrane and thus, WHICH spiral ganglion cells are most active.

Rate theory: Pitch perception based on theRATE of action potentials in spiral ganglion cells.

http://www.youtube.com/watch?v=bB3x7kp9El8&feature=related

Speed of sound ~ 335 m/sec, Interaural distance (I.D) ~ .2 mTherefore, maximum difference in time of arrival at the two ears is .2 m/335 m/sec, or about 6 msec.

Because shadows are cast only when wavelength is less than the size of the objectcasting the shadow, intensity differences areuseful when wavelengths are less thanthe I.D. (~.2 m; frequency greater than~ 1,700 Hz).

Differences in time of arrival at the two earsIs unambiguous only when wavelengths aregreater than 1/2 the I.D. (~.1 m; frequency lessthan about 3,400 Hz).

http://www.youtube.com/watch?v=dyenMluFaUw&feature=player_detailpage

Vertical sound localization based on reflectionsfrom the pinna.

Summary ofSound Localization

Three mechanisms:

1. Intensity differences: high frequencies

2. Interaural delay: sudden onsetand low frequencies

3. Spectral cues: effect of reflection by pinnaon sound spectrum

Because sounds are complex, consisting ofmany frequencies, all three mechanisms aretypically used simultaneously.

shepard illusion

Estimating Distanceto a Sound Source

1. Sound intensity Spherical spreading of sound energy

2. Spectral properties Atmospheric attenuation of high frequencies

3. Echoes Greater number of echoes with distance

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Audiogram Configurations:Audiogram Configurations: Progressive noise-induced hearing loss

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Speech SoundsSpeech Sounds

VestibularSystem

http://www.sumanasinc.com/webcontent/animations/content/vestibular.html

Vestibular Nystagmus

The macula of the utricle is oriented horizontally.

The macula of the saccule is oriented vertically.

Vestibular Pathways and their Functions

•vestibular nuclei to cerebellumposture, equilibrium

•vestibular nuclei to nuclei of CN III, IV & VI(short, fast disynaptic pathway)

vestibular nystagmuscapable of adaptation (plasticity)

•vestibulospinal tractresting postural muscle tonepostural reflexes

•vestibular nuclei to nucleus of CN XIrighting reflex, tonic neck reflexes