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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