Physiology of Hearing: Departemen Fisiologi FK Usu

Physiology of Hearing
Departemen Fisiologi
FK USU
The Ear: Hearing and Balance
• The three parts of the ear are the inner, outer,
and middle ear
• The outer and middle ear are involved with
hearing
• The inner ear functions in both hearing and
equilibrium
• Receptors for hearing and balance:
– Respond to separate stimuli
– Are activated independently
The Ear: Hearing and Balance
Figure 15.25a
Properties of Sound
• Sound is:
– A pressure disturbance (alternating areas of high
and low pressure) originating from a vibrating object
– Composed of areas of rarefaction and compression
– Represented by a sine wave in wavelength,
frequency, and amplitude
Properties of Sound
• Frequency – the number of waves that pass a

given point in a given time
• Pitch – perception of different frequencies (we
hear from 20–20,000 Hz)
Properties of Sound
• Amplitude – intensity of a sound measured in
decibels (dB)
• Loudness – subjective interpretation of sound
intensity
Figure 15.29
Properties of sound waves
Mechanisms of Hearing
• Sound vibrations beat against the eardrum
• The eardrum pushes against the ossicles, which
presses fluid in the inner ear against the oval
and round windows
– This movement sets up shearing forces that pull on
hair cells
– Moving hair cells stimulates the cochlear nerve that
sends impulses to the brain
Transmission of Sound to the Inner Ear
• The route of sound to the inner ear follows

this pathway:
– Outer ear – pinna, auditory canal, eardrum
– Middle ear – malleus, incus, and stapes to the oval
window
– Inner ear – scalas vestibuli and tympani to the
cochlear duct
• Stimulation of the organ of Corti
• Generation of impulses in the cochlear nerve
Transmission of Sound to the Inner Ear
Figure 15.31
Resonance of the Basilar Membrane
• Sound waves of low frequency (inaudible):

– Travel around the helicotrema
– Do not excite hair cells
• Audible sound waves:
– Penetrate through the cochlear duct
– Vibrate the basilar membrane
– Excite specific hair cells according to frequency of
the sound
Keterangan gambar
• 1. Sound waves vibrate the tympanic membrane.
• 2. Auditory ossicles vibrate. Pressure is amplied.
• 3. Pressure waves created by the stapes pushing on the
oval window move through fluid in the scala vestibuli.
• 4a. Sounds with frequencies below hearing travel
through the helicotrema and do not excite hair cells.
• 4b. Sounds in the hearing range go through the
cochlear duct, vibrating the basilar membrane and
deflecting hairs on inner hair cells.
Excitation of Hair Cells in the Organ of Corti
• Bending cilia:
– Opens mechanically gated ion channels
– Causes a graded potential and the release of a
neurotransmitter (probably glutamate)
• The neurotransmitter causes cochlear fibers to
transmit impulses to the brain, where sound is
perceived
Auditory Pathway to the Brain
• Impulses from the cochlea pass via the spiral
ganglion to the cochlear nuclei
• From there, impulses are sent to the:
– Superior olivary nucleus
– Inferior colliculus (auditory reflex center)
• From there, impulses pass to the auditory cortex
• Auditory pathways decussate so that both
cortices receive input from both ears
Simplified Auditory Pathways
Figure 15.34
Auditory Processing
• The analytic powers of the auditory cortex are so great
that we are able to pick single instruments out of a
whole orchestra.
• Cortical processing of sound stimuli is complex.
• For example, certain cortical cells depolarize at the
beginning of a particular tone, and others depolarize
when the tone ends.
• Some cortical cells depolarize continuously, and others
appear to have high thresholds (low sensitivity), and
so on.
• Perception of Pitch : When a sound is composed of
tones of many frequencies, it activates several
populations of cochlear hair cells and cortical cells
simultaneously, and we perceive multiple tones.
• Detection of Loudness : Louder sounds→ larger
graded potentials in the hair cells → generate
more frequent action potentials. The brain
interprets more frequent action potentials as
greater loudness
• Localization of Sound :
• Several brain stem nuclei (most importantly the superior
olivary nuclei) help us localize a sound’s source in space by
means of two cues: the relative intensity and the relative
timing of sound waves reaching the two ears.
• If the sound source is directly in front, in back, or overhead,
the intensity and timing cues are the same for both ears.
• However, when sound comes from one side, it activates the
receptors of the nearer ear slightly earlier and also more
vigorously (because of the greater intensity of the sound
waves entering that ear).
Gangguan Pendengaran
• With conductive loss, sounds coming from within,
such as one’s own voice, are perceived as louder
because of reduced competing ambient noise.
• Plug your right ear with your finger, creating a
conductive loss, and note how your own voice
sounds louder on this side. This phenomenon is
known as autophony.
• A patient with a conductive loss often feels like he
or she is talking “in a barrel,” or “under water.”
• The audiometer distinguishes between conductive and
sensorineural hearing loss in the following way: When
earphones are placed on the ears for testing, air
conduction is measured. This is the way we normally
hear; sound waves go from outer through middle to inner
ear.
• The audiometer can also measure bone conduction. Here,
a bone-conducting transducer is placed on the subject’s
skull behind the ear and sound is transmitted by vibration
directly into the inner ear, bypassing the outer and middle
ear.
• Bone conduction measures how well the inner ear
(cochlea and auditory nerve) is working, regardless of
what troubles may impair the outer or middle ear.

Physiology of Hearing: Departemen Fisiologi FK Usu

Uploaded by

Copyright:

Available Formats

Physiology of Hearing: Departemen Fisiologi FK Usu

Uploaded by

Document Information

Original Description:

Original Title

Copyright

Available Formats

Share this document

Share or Embed Document

Sharing Options

Did you find this document useful?

Is this content inappropriate?

Copyright:

Available Formats

Physiology of Hearing: Departemen Fisiologi FK Usu

Uploaded by

Copyright:

Available Formats

Physiology of Hearing

• Frequency – the number of waves that pass a

• The route of sound to the inner ear follows

• Sound waves of low frequency (inaudible):

You might also like