10/16/2015Somatosensory Agnosias •Astereognosia –can’t recognize objects by touch...
Transcript of 10/16/2015Somatosensory Agnosias •Astereognosia –can’t recognize objects by touch...
10/16/2015
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Thinking About Sound Waves Waves vary in how many molecules are moved
(amplitude) and how many waves per second (frequency)
Characteristics of Sound WavesBook Fig. 7.3
The Outer, Middle & Inner EarBook Fig. 7.5
• 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
Fluid Motion in Cochlea
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Cross section of Cochlea
Basilar MembraneAuditory Nerve fibers
Book Fig. 7.2
http://www.youtube.com/watch?v=8wgfowbbTz0
Organ of Cortihttp://www.youtube.com/watch?v=8wgfowbbTz0
Basilar Membrane
Tectorial Membrane
Book Fig. 7.5
Fluid Waves Traveling Thru Cochlea Cause Basilar Membrane Movement
• Where wave peaks varies with pitch & determines which hair cells will be most stimulated.
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
“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
Near middle ear
Friction on tips of hair cells opens mechanically-gated K+ ion channels
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))
Normal & “Trampled” Hair CellsExposed to Loud Sounds
• http://www.youtube.com/watch?v=Xo9bwQuYrRo (dancing hair cell)
• 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.
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.VIIIVIII
“Tonotopic” Map
in cortex &
cochlea
Book Fig. 7.6
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).
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 earhair 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
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
(area of body surface providing sensory input to a particular pair of spinal nerves)
Book Fig. 7.14
2 pathways carry sensations to brain
Discriminative touch & Proprioception Pain & Temperature
x
Somatosensory Cortex
x
Pain also activates
cingulate cortex to
trigger emotional
response
Cortical map
can change if
you lose body
part
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Somatosensory Agnosias
• Astereognosia – can’t recognize objects by touch
• Asomatognosia – failure to recognize body parts as yours
The Experience of Pain
• 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/anatomyvideos/000054.htm
• Receptors release glutamate (when pain is mild) & also Substance P (when pain is more intense)
Cell Injury Causes Release of Compounds That Irritate Pain Recpetor
Over the counter
pain relievers work
mostly by
decreasing these
irritating chemicals
Pain pathway to
somatosensory cortex
locates & registers
pain, but another path
thru RF to limbic
system causes the
emotional distress
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).
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.
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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.
Taste
these don’t have taste buds so
center of your tongue can’t taste
Book Fig. 7.18
Fungiform Papillaeon 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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Taste Bud• 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).
With cilia
Olfactory NervesBook Fig. 7-21
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
Book Fig. 7-19
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