Transcript Document

Sensory Transduction
Chemoreceptors
Photoreceptors
Mechanoreceptors
Olfactory
bulb
Audition
Olfaction
Vision
Anatomy of the Retina
Direction of light
Pigment layer
Choroid layer
Direction of retinal visual processing
Sclera
Front
of
retina
Back
of
retina
Fibers of
the optic
nerve
Ganglion
cell
Amacrine
cell
Bipolar Horizontal
cell
cell
Cone
Rod
Photoreceptor
cells
Back of retina
Cells of
pigment layer
Cone
Outer
segment
Inner
segment
Phototransduction
Rod
Discs
Mitochondria
Outer
segment
Nuclei
Inner
segment
Disc
Light
absorption
Retinene
Synaptic
terminal
Dendrites
of bipolar
cells
Front
of retina
Direction
of
light
Opsin
Synaptic
terminal
Rhodopsin in the dark:
retinene in 11-cis form
(inactive)
11-cis form
of retinene
Enzymes
Rhodopsin in the light:
retinene changes shape
to all-trans form
(active)
all-trans form
of retinene
LIGHT
(Absorption)
DARK
Activation of photopigment
High concentration
of cyclic GMP
Na+
channels open
in outer segment
Takes
place
in
outer
segment
Activation of transducin (G protein)
Activates PDE
Cells of
pigment layer
Cone
Rod
Discs
Membrane
depolarization
Takes
place
in
outer
segment
Opens Ca2+ channels
in synaptic terminal
Release of inhibitory
transmitter
Takes
place
in
synaptic
terminal
Outer
segment
Membrane hyperpolarization
(the receptor potential)
Nuclei
(inhibition)
Bipolar cells inhibited
Decrease in cyclic GMP
Closure of Na+ channels
in outer segment
(Spreads to synaptic terminal)
Takes
place
in
retina
(Reaction cascade)
Bipolar
dendrites
Inner
segment
Synaptic
terminal
(Spreads to synaptic terminal)
Takes
place
in
synaptic
terminal
Closure of Ca2+ channels
in synaptic terminal
Release of inhibitory transmitter
(Removal of inhibition)
Bipolar cells disinhibited
(or, in effect, excited)
Front of retina
No action potential
in cell ganglion cell
No action potential
propagation to
visual cortex
Graded potential change
in bipolar cell
(If of sufficient magnitude to
bring ganglion cell to threshold)
Action potential in
ganglion cell
Propagation of AP to visual cortex (occipital lobe)
visual perception
Takes
place
in
retina
Rods versus Cones
Properties of Rod and Cone Vision
RODS
CONES
100 M per retina
3 M per retina
Vision in shades of gray
Color Vision
High Sensitivity
Low Sensitivity
Low Acuity
High Acuity
Night vision
Day vision
Much convergence in retina
Little convergence in retina
More numerous peripherally
Concentrated in fovea
What about adaptation?
Color Vision
Anatomy of the Auditory System
The Middle Ear
and
Cochlea
APEX:
Wider, more
flexible end of basilar
membrane (vibrates best
with low-freq)
BASE: Narrower, stiffer
end of BM near oval
window (vibrates best
with hi-freq)
The Traveling Wave
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The Organ of Corti
(Stereocilia)
Outer
hair cells
Tectorial membrane
Inner hair cells
Supporting cell
Nerve fibers
Basilar membrane
The Hair Cell Potential
SOUND WAVES
Tympanic Membrane Vibrates
Ossicles Vibrate
Oval Window Vibrates
Vibration of
round window
Fluid Movement within Cochlea
Energy dissipates
(no sound perception)
Basilar Membrane Vibrates
Closure of Ca2+ channels
in synaptic terminal
Hair cell stereocilia bend as the
movement of the basilar membrane
displaces them in relation to the
overlying tectorial membrane in which
they are embedded.
Graded potential change
in bipolar cell
Graded potential change
in hair cell
Action potentials generated in
auditory nerve
Propagation of AP to auditory cortex
(temporal lobe)
sound perception
Takes
place
in
ear
The Transduction Channel
What about Adaptation?
What about the Outer Hair Cells?
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What about the Outer Hair Cells?
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Cochlear Implants