Download Think About the Dendrites We`ve Been Talking About

10/13/2016
Think About the Dendrites We’ve
Been Talking About
• The “typical” neuron is designed to receive
neurotransmitter messages from other neurons. Messages
activate ionotropic and/or metabotropic receptors on the
dendrites.
• Sensory receptors, on the other hand, are specialized to
receive sensory input from the outside world rather than
messages from other neurons.
Example 1: Light Sensitive Visual Receptors
• Specialized to respond to light waves, a form of electromagnetic
energy
(Book Fig. 6.7)
(Billionths of a meter)
Light travels
in straight
lines
Light waves are a small range of wavelengths
(~350-750 nanometers) of electromagnetic energy.
Of Macula
Lens becomes less
flexible later in life –
need reading glasses
Book Fig. 6.5 & 6.8
Rods
• ~120 million/eye
• more in periphery
• very sensitive (low threshold)
• ~100 rods share same optic
nerve fiber to brain
• night vision (scotopic vision)
vs Cones
• ~6 million/eye
• most in center, especially in the
fovea
• Need bright light to reach
threshold (photopic vision)
• have 1-to-1 lines to brain- good
for detail vision or “acuity”
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Looking Into Eye: Optic Disk or “Blind Spot”- axons
exit eye to form optic nerve
You can
locate your
own blind
spot with
the demo
on p. 156.
Center (Macula) of Retina Needed for Detail Vision
(Fovea especially)
Turning Light Waves Into Electrical
Messages (Transduction)
 Rods & cones have molecules of light sensitive
photopigments (11-cis-retinal+an opsin) embedded in cell
membrane.
Rods – rhodopsin
Cones – 1 of 3 iodopsins
 Like metabotropic receptors, except they receive light!
Absorption of light triggers change in protein releasing
second messenger inside the cell.
Thinking About Sound Waves
Waves vary in how many molecules are moved
(amplitude) and how many waves per second (frequency)
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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
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
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Fluid Waves Traveling Thru Cochlea Cause
Basilar Membrane Movement
Friction on tips of hair cells opens
mechanically-gated K+ ion channels
• 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
Scientific Theories Influenced by the Available Research
Tools
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))
“Tonotopic” Relationship Between Place
in Cochlea and Pitch
• Frequency theory of pitch perception
• Pitch directly represented by freq of impulses
If our inner ear is working
perfectly we can hear sound
frequencies between
20-20,000 cps
• Volley theory of pitch perception
• Pitch represented by the sequenced “volley” of firing by a set
of neurons
• Place theory of pitch perception
• Pitch perception for all but the deeper pitches depends on the
place in the cochlea maximally activated by the traveling
wave.
Near middle ear
2 Theories of Color Vision Proposed in 1800’s
Trichromatic Theory – 3 different types of color
receptors work together to represent all colors of
the spectrum.
 Opponent Process Theory – cells in the visual
pathway receive input about pairs of colors (R-G or
B-Y). One color makes them fire faster, the other
makes them fire slower.
Color “Opposites” on
the Color Wheel
“Afterimages” of strong
visual stimuli appear in
opposite colors
Cones
 3 different
types,
absorbing
different
ranges of
wavelengths
 Supports the
Trichromatic
theory
Short wavelengths  long wavelengths
Book Fig 6.8
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What Do You See?
Input from each ear goes to
both sides of brain but more
strongly to contralateral side.
Brainstem areas are involved in
quick unconscious sound
localization and auditory
reflexes.
Input is then passed on to
cortex for our conscious
awareness of sound.
~ 8% of men and <1% of women suffer R/G color deficiency
VIII
VIII
Primary Visual Pathway
Book Fig. 7.6
“Tonotopic” Map
in cortex &
cochlea
Primary auditory cortex surrounded by higher level processing areas (including
Wernicke’s area), analyzing more complex sequences or combinations of sounds.
Visual Fields
• Each half of your brain sees
the opposite half of your
visual world
Many Regions of Cortex Involved in Visual
Processing
 Primary visual cortex is just the first level of cortical
processing
 Damage here”cortical blindness”
 Secondary “visual cortex” has parallel pathways to
separate regions devoted to shape, color, location,
& movement that extend beyond occipital lobe.
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“Dorsal stream - where
is it, what are its
dimensions & how do I
get to it pathway
Ventral stream – what or who is it, what color is it pathway
Damage to either of these “streams” can
impair these visual abilities
Visual Agnosia (not recognizing)
 Damage to different parts of this system lead to different kinds of
visual agnosia (object agnosia, color agnosia, movement agnosia)
 Prosopagnosia- can’t recognize individual faces (or similar members
of other complex classes of visual stimuli) – most often seen after
damage to the inferior temporal lobe’s fusiform gyrus (in pink)
Visual Processing Cases






Object Agnosia
http://www.youtube.com/watch?v=rwQpaHQ0hYw
Object agnosia & trouble locating visual stimulus
http://www.youtube.com/watch?v=dG8JGg-d2Pk&feature=related
Prosopoagnosia (“face blindness”)
http://www.youtube.com/watch?v=vwCrxomPbtY&list=UU943Unaj
Vxe9SpFJpwxpLsQ&index=8
 Blindsight
 http://www.youtube.com/watch?v=RuNDkcbq8PY&feature=related
 Motion blindness
 http://www.youtube.com/watch?v=B47Js1MtT4w&list=PL22D01B36165478AD
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