PSYC314 Chapter Notes - Chapter 7: Inner Ear, Outer Ear, Sound
27 Apr 2018
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Chapter 7: Audition, the body senses and the chemical senses
Congenital insensitivity to pain – due to a gene mutation, the nervous system
develops without functional nociceptors, which are, specialized neurons activated
by painful stimuli
Audition:
• Hearing has 3 primary functions
1. To detect sounds
2. To determine the location of their sources
3. To recognize the identity of these sources
• The auditory system analyzes the vibrations that reach out ear
o Example – we can understand speech, recognize a persons emotion
from his or her voice, appreciate music, detect the approach of a
vehicle or another person, recognize an animals call
o We can recognize not only what the source of a sound is but also
where its located
The stimulus:
• We hear sounds that are produced by objects that vibrate and set molecules
of air into motion
• When an object vibrates, its movements cause molecules of air surrounding
it to alternate between compressing and expanding producing waves that
travel away from the object at about 1,200 kilometers per hour
• If the vibration ranges between 30-20,000 times per second- these waves
will stimulate receptor cells in human ears and will be perceived as sounds
• Sounds vary in their pitch, loudness and timbre
o The perceived pitch of an auditory stimulus is determined by the
frequency of vibration, which is measured in Hertz (Hz) or cycles per
second
o Loudness – is a function of intensity – the degree to which the
compressions and expansions of air differ from each other
➢ More vigorous vibrations of an object produce more intense
sound waves and hence louder ones
o Timbre- provides information about the nature of the particular
sound
➢ Example- the sound of a train whistle – most natural acoustic
stimuli are complex, consisting of several different frequencies
of vibration
➢ The particular mixture determines the sounds timber
Anatomy of inner ear:
• The anatomy of the ear helps to direct sound waves to the auditory receptors
• Structures of the ear can be organized by their location in the outer, middle,
and inner ear
find more resources at oneclass.com
find more resources at oneclass.com
Outer ear:
• Sound is funneled through the pinna (external ear) through the ear canal to
the tympanic membrane (eardrum) which vibrates with sound
➢ When the tympanic membrane is damaged by trauma, infection, or
autoimmune attack, hearing is impaired particularly for sounds with
low frequencies
• Demonstrating the role of the pinna in sound localization – researchers
created inserts that altered the shape of the pinna and asked volunteers to
wear the inserts in one ear for up to 6 weeks
➢ The volunteers ability to localize the source of various sounds was
significantly disrupted at first
➢ After several days auditory adaptation occurred and the volunteers
were able to accurately determine the location of sounds
Middle ear:
• The middle ear consists of a small hollow region behind the tympanic
membrane
• It contains the bones of the middle ear called the ossicles which are set into
vibration by the tympanic membrane
• The malleus (hammer) connects with the tympanic membrane and
transmits vibrations through the incus (anvil) and stapes (stirrup) to the
cochlea the structure that contains the receptors
• The bottom of the stapes presses against the membrane behind the oval
window – the opening in the bone surrounding the cochlea
Inner ear:
• The cochlea is part of the inner ear
➢ It is filled with fluid and sounds transmitted through the air must be
transferred into its liquid medium
➢ This process is normally is very inefficient – 99.9% of the energy of
airborne sound would be reflected away if the air impinged directly
against the oval window of the cochlea
• the chain of ossicles serves as an efficient means of energy transmission – the
bones provide a mechanical advantage with the baseplate of the stapes
making smaller but more forceful excursions against the oval window than
the tympanic membrane makes against the malleus
• the name cochlea comes from the Greek word meaning land snail
➢ it is snail shaped consisting of 2 and 3- quarters turns of gradually
tapering cylinder, 35mm long
➢ the cochlea is divided longitudinally into 3 sections
1. the scala vestibule – entrance stairway
2. the scala media – middle stairway
3. the scala tympani – tympanic stairway
• the receptive organ known as the organ of corti – consists of the basilar
membrane, the hair cells and the tectorial membrane
find more resources at oneclass.com
find more resources at oneclass.com
• the auditory receptor cells are called hair cells – they are anchored by rod
like deiter’s cells to the basilar membrane
➢ the cilia of the hair cells pass through the reticular membrane and the
ends of some of them attach to the fairly rigid tectorial membrane –
which hangs over head like a shelf
➢ sound waves cause the basilar membrane to move relative to the
tectorial membrane which bends the cilia of the hair cells
➢ this bending produces receptor potentials
• the vibrating energy exerted on the oval window causes the basilar
membrane to bend
➢ this portion of the basilar membrane that bends the most is
determined by the frequency of the sound
➢ high frequency sounds cause the base of the membrane – the end
nearest to the oval window- to bend
➢ a flexible membrane covered opening – the round window – allows
the fluid inside the cochlea to move back and forth
➢ the base of the stapes vibrates against the membrane behind the oval
window and introduces sound waves of high or low frequency into the
cochlea
➢ the vibrations cause part of the basilar membrane to flex back and
forth
➢ pressure changes in the fluid underneath the basilar membrane are
transmitted to the membrane of the round window
➢ when the base of the stapes pushes in – the membrane behind the
round window bulges out
➢ different frequencies of sound vibrations cause different portions of
the basilar membrane to flex
auditory hair cells and the transduction of auditory information:
• 2 types of auditory receptors – inner and outer auditory hair cells are
located on the basilar membrane
• hair cells contain cilia – fine hair like projections arranged in rows according
to height
• the human cochlea contains about 3500 inner hair cells and 12000 outer hair
cells
• the hair cells form synapses with dendrites of bipolar neurons whose axons
bring auditory information to the brain
• the inner hair cells are necessary for normal hearing
o mutant mice whose cochleas contain only outer hair cells apparently
cannot hear at all
o research indicates that the outer hair cells are effector cells –
involved in altering the mechanical characteristics of the basilar
membrane and influencing the effects of sound vibrations on the inner
hair cells
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Chapter 7: audition, the body senses and the chemical senses. Congenital insensitivity to pain due to a gene mutation, the nervous system develops without functional nociceptors, which are, specialized neurons activated by painful stimuli. Example- the sound of a train whistle most natural acoustic stimuli are complex, consisting of several different frequencies of vibration: timbre- provides information about the nature of the particular sound. The particular mixture determines the sounds timber. Anatomy of inner ear: the anatomy of the ear helps to direct sound waves to the auditory receptors, structures of the ear can be organized by their location in the outer, middle, and inner ear. Outer ear: sound is funneled through the pinna (external ear) through the ear canal to the tympanic membrane (eardrum) which vibrates with sound. The volunteers ability to localize the source of various sounds was significantly disrupted at first.
