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Thinking About Sound Waves
Waves vary in how many molecules are moved
(amplitude) and how many waves per second (frequency)
Book Fig. 7.3
Characteristics of Sound Waves
Book Fig. 7.5
The Outer, Middle & Inner Ear
Fluid Motion in Cochlea
• https://www.youtube.com/watch?v=flIAxGsV1q0 A diagrammatic
tour through the ear
• http://www.youtube.com/watch?v=U_HUgzhmq4U Real life views of
the auditory structures
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Book Fig. 7.2
Organ of Corti
Book Fig. 7.5
http://www.youtube.com/watch?v=8wgfowbbTz0
Cross section of Cochlea
Tectorial Membrane
Auditory Nerve fibers
Basilar Membrane
Basilar Membrane
http://www.youtube.com/watch?v=8wgfowbbTz0
Fluid Waves Traveling Thru Cochlea Cause
Basilar Membrane Movement
• Where wave
peaks varies
with pitch &
determines
which hair cells
will be most
stimulated.
“Tonotopic” Relationship Between Place
in Cochlea and Pitch
If our inner ear is working
perfectly we can hear sound
frequencies between
20-20,000 cps
Georg von Bekesy – 1961 Nobel Prize for his research on the traveling
waves in the cochlea.
http://www.youtube.com/watch?v=dyenMluFaUw&feature=related
http://www.youtube.com/watch?v=WO84KJyH5k8&feature=related
Friction on tips of hair cells opens
mechanically-gated K+ ion channels
Near middle ear
Normal & “Trampled” Hair Cells
Exposed to Loud Sounds
• http://www.youtube.com/watch?v=Xo9bwQuYrRo (dancing hair cell)
K+ enters hair cells causing depolarization & transmitter release!
(fluid in cochlea has a different ion balance – disruption of that
balance can lead to hearing abnormal sounds (tinnitus))
• http://www.youtube.com/watch?v=ulAISCEQzRo
• (stereocilia)
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Sound Localization
• Brain processes time of
arrival & intensity
differences in what the
right & left ears hear.
• Sound from right
arrives sooner and
louder in the right ear.
VIII
Book Fig. 7.6
“Tonotopic” Map
in cortex &
cochlea
VIII
Note: Input from each ear goes
to both sides of brain but more
strongly to contralateral side.
Brainstem areas involved in
quick unconscious sound
localization and auditory
reflexes. Input passed on to
cortex for our conscious
awareness of sound.
Notice that like the visual
pathway the auditory pathway
makes a processing stop in
thalamus before going to
cortex.
Types of Deafness
• ~250 million with hearing impairments; only a fraction are
completely deaf
• Conductive or Middle Ear Deafness – auditory stimulus does not
pass normally through middle ear to cochlea
• Nerve/Neural or Inner Ear Deafness – due to damage to inner ear
hair cells or auditory nerve due to:
• Genetics
• Perinatal problems (illness during pregnancy, hypoxia during birth, Fetal
Alcohol Syndrome)
• Illness (meningitis, MS, Meniere’s)
• Ototoxic drugs (quinine, some antibiotics, high doses of NSAIDS, nicotine),
• Loud sounds
• Test your hearing – have you lost your upper range already?
• http://www.youtube.com/watch?v=9g0yThhJcxY
• Mosquito tones
Primary auditory cortex surrounded by higher level processing areas, analyzing more
complex sequences or combinations of sounds. Seems to be separate regions devoted
to what the stimulus (frontal cortex) is & where the stimulus came from (parietal
cortex).
Cochlear Implant can take the place of missing or
damaged hair cells as long as auditory nerve fibers still
run from cochlea to brain.
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The Somatosensory System
Spinal Roots and Nerve
Book Fig. 7.14
(area of body surface providing sensory input to a particular pair of spinal nerves)
2 pathways carry sensations to brain
Discriminative touch & Proprioception
Pain & Temperature
Somatosensory Cortex
x
x
Cortical map
can change if
you lose body
part
Pain also activates
cingulate cortex to
trigger emotional
response
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The Experience of Pain
Somatosensory Agnosias
• Astereognosia – can’t recognize objects by touch
• Asomatognosia – failure to recognize body parts as yours
Cell Injury Causes Release of Compounds That
Irritate Pain Recpetor
• Tissue injury leads to release of irritating chemicals
(histamine, prostaglandins & others) which activate
pain receptors & make receptors more sensitive
• http://www.nlm.nih.gov/medlineplus/ency/anatomyv
ideos/000054.htm
• Receptors release glutamate (when pain is mild) &
also Substance P (when pain is more intense)
Pain pathway to
somatosensory cortex
locates & registers
pain, but another path
thru RF to limbic
system causes the
emotional distress
Over the counter
pain relievers work
mostly by
decreasing these
irritating chemicals
The pain you experience does not just depend on
the activation of pain receptors. It also depends on
whether the pain “gate” is open or closed.
The band of “old cortex”
just above the corpus
callosum (the “cingulate
cortex”) plays a key role in
the aversive, suffering
aspects of pain.
Interestingly, the cingulate
cortex is also activated by
emotional pain (hurt
feelings).
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• Several pain
treatments
probably
activate sensory
receptors which
can close the
gate:
• Acupuncture
• Linaments
• TENS
• Massage
• And even
placebos
• Gate can also be closed by
descending pain control
system.
Book Fig. 7.18
Taste
 these don’t have taste buds so
center of your tongue can’t taste
Fungiform Papillae
on the front of tongue)
Tastes Buds on Sides of Papillae
We only have taste receptors for these qualities: sweet, sour,
salty, bitter, and “umami” (meaty flavor). Most of what we call
“flavors” (orange, grape, bubble gum, etc) depend on smell
more than taste.
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10/16/2015
Taste Bud
Book Fig. 7-21
With cilia
• Many receptors in a bud
• Specialized skin cells replaced
every 10-14 days
• But have excitable membranes
and release transmitter like
neurons
• Receptors sensitive to salty, sour,
sweet, bitter & “umami”
• Salty opens Na+ channels,
• Sour receptors also seem to be
ionotropic.
• The others activate G proteins
(like metabotropic receptors).
Book Fig. 7-19
Olfactory Receptors
G-protein type
receptors on cilia.
In contrast to taste,
100’s of different
types of olfactory
receptors. In the rat
1% of its genome is
devoted to making
these receptors. In
humans at least 350
such genes.
Cilia are dendrites
dangling down from
your nasal membranes
Olfactory Nerves
Olfactory Nerves in a precarious
position in head injuries
Head injuries can cause “anosmia” by shearing off these connections.
People can also be born with specific anosmias (due to genetics)
Olfactory Bulbs connect to limbic system.
Cells in olfactory
bulb and olfactory
cortex organized
by type of odor
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