Auditory System
Auditory System
Adequate Stimulus for the
auditory 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 the
pressure 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 ear
Pinna or auricle
Auditory canal or ear canal
Tympanic membrane or eardrum
Middle ear
Ossicles
Malleus or hammer
Incus or anvil
Stapes or stirrup
http://www.youtube.com/watch?v=
dyenMluFaUw&feature=player_de
tailpage
Latex-filled cochlea. Scala tympani and scala
vestibuli 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
parallel chambers. These chambers, the scalae, are
separated by Reissner’s membrane and the basilar
membrane. The organ of Corti contains the auditory
receptors; it sits upon the basilar membrane and is
covered by the tectorial membrane.
a.k.a. cochlear ganglion
a.k.a. cochlear ganglion
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.
http://www.youtube.com/watch?v=1
VmwHiRTdVc&feature=player_deta
ilpage
Na+
Na+
K+
Na+
http://www.youtube.com/watch?
v=1JE8WduJKV4&feature=play
er_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 the
RATE 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 m
Therefore, 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 object
casting the shadow, intensity differences are
useful when wavelengths are less than
the I.D. (~.2 m; frequency greater than
~ 1,700 Hz).
Differences in time of arrival at the two ears
Is unambiguous only when wavelengths are
greater than 1/2 the I.D. (~.1 m; frequency less
than about 3,400 Hz).
http://www.youtube.com/watch?v=
dyenMluFaUw&feature=player_de
tailpage
Vertical sound localization based on reflections
from the pinna.
Summary of
Sound Localization
Three mechanisms:
1. Intensity differences: high frequencies
2. Interaural delay: sudden onset
and low frequencies
3. Spectral cues: effect of reflection by pinna
on sound spectrum
Because sounds are complex, consisting of
many frequencies, all three mechanisms are
typically used simultaneously.
shepard illusion
Estimating Distance
to 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
Audiogram Configurations:
Progressive noise-induced hearing loss
Frequency (Hz)
500
1000
2000
3000
4000
6000
0
10
20
dB HL
30
40
50
60
70
80
90
100
Mild Loss
Moderate Loss
Severe loss
40
41
Speech Sounds
Hz
Normal
0
250 500
1000
2000
3000 4000 6000
8000
10
20
f
30
40
p h
k
s
th
ch
50
dB
60
sh
70
80
90
100
42
Vestibular
System
http://www.sumanasinc.com/webconte
nt/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 cerebellum
posture, equilibrium
• vestibular nuclei to nuclei of CN III, IV & VI
(short, fast disynaptic pathway)
vestibular nystagmus
capable of adaptation (plasticity)
• vestibulospinal tract
resting postural muscle tone
postural reflexes
• vestibular nuclei to nucleus of CN XI
righting reflex, tonic neck reflexes