PSY290H5 Lecture Notes - Lecture 6: Retina, Posterior Column, Green Leaves
PSY290: Physiological Psychology
Lecture 6: Sensory Systems, Perception, and Pathways
Broad overview of the brain system that integrates action potential and graded potential: How are they
used?
Sensation and Perception
Question: What are the common features that all sensory systems share
oHow the energy from the environment is changed to a neural signal: Transduction
oHow our system is able to process complexity of stimuli: Range
oHow different areas of the brain process different kinds of sensory information:
Organization
While the occipital cortex is devoted to vision, there are other areas in our brain too
oHow the sensory information built up: Hierarchy
All sensory systems reflect an adaptation towards something
Given the wide variety of systems, animals are taking advantage of particular aspects within their
environment that help them survive and thrive
oExample: Eye
oDifferent shapes, forms, and colors that reflect their needs
oSome animals can independently move their eyes and see different things in each eye
oOther animals have lots of receptors, move than us
Our visual system has evolved to suit our needs in our environment
oCapable of perceiving 3 million colours
oThe pattern of colors we see is limited in the broader context of things
oWe only sense 360-740 nm of color
oAlthough it’s great, that is a really tiny portion of the electromagnetic spectrum
oThere are trillion or so wavelengths in the spectrum that we have NO chance in perceiving
(gamma rays, x-rays, FM signals, ultraviolet... etc)
oOur own perceptual system misses many energy signals
oWhat is our there for us to perceive is actually very limited fraction of all the information
that is around us
Example: What limits what we see?
The yellow flower looks yellow to us but using an ultraviolet camera, we see
purple and white as well
Different animals (honeybee) sees the ultraviolet elements on the tips of the flower
The hummingbird sees a completely different color
If the color reflects the needs, then the visual system will develop an adaptation to
it
Ultravioletness reflects when a flower is ready to pollinate
If bee can detect pollinating flowers, they are much more likely to navigate
towards them
Song birds relay ultraviolet light to find mates: ultraviolet plumage is very active in
males during the mating season
Serves purposes for finding a mate
oOur eyes have different receptors called photoreceptors
Rods and cones
Honeybee
We have 3 different kinds of cones that help us perceive colors
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find more resources at oneclass.com
Honeybees also have 3 different types of cones but are sensitive to below
300 nm (ultraviolet) and no sensitive to more than 600 nm (can’t perceive
redness)
Pigeons
Have 4 combinations of cones so if we multiple 4 million colors by an
additional photoreceptor, they can see many other colors
Nocturnal animals: wake up at night
There is not enough light present to make use of colors
Rather than having 3 different types of photoreceptors, they have 2
(mammals) except humans and primates
Almost colorblind
Can’t distinguish orange and red
In their ecology, it’s not THAT important so they don’t need it
Cat, dogs, bulls almost colorblind
What do sensory receptors have in common?
Our body is equipped with all kinds of sensory mechanisms
Corpuscle found inside the skin
Taste bunds, olfactory bulb, photoreceptors, stereo cilia.. etc
All sensory mechanisms that exists and their entire function is to convert the energy in the
environment into signals that our brain can interpret Transduction
oTransduce: change one energy to start another
oAction potentials and excitatory potentials
Transduction of a Skin Receptor
All transduction occurs as a result of EPSP NOT action potentials
We have to create enough depolarization inside a neuron that can trigger an action potential
Pacinian corpuscles
Neurons need ion channels to work
oVoltage gated ion channels
oLigand gated ion channels
oWhat these channels do is they bind something to allow a channel to open up to allow
sodium
oA Pacinian corpuscle is a mechanically gated ion channel
Have stretch receptors that open and close based on physical deformation
***The more you press on an object, the more these channels stretch open, the
more sodium they allow
Advantage: allows for soft touch to produce a weak potential and a bigger touch to
produce a greater depolarization. The bigger the stimulation, the bigger the
response.
The bigger the touch, the more sodium ions permeate through
Blue line: magnitude of stimulus
In the first picture, the stimulus is NOT big enough to cross the threshold and
produce action potential
First kind of EPSP that a sensory system is developing: generator
potential (the first EPSP that a sensory system generates)
oAs we move to a great stimulus, the more sodium floods in, the
more likely we are to produce an action potential
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find more resources at oneclass.com
Exam question: an EPSP is the same as generator potential
(interchangeably)
Exam question: something about EPSP and its relation to a generator
potential
oGenerator potential is EPSP for sensory transduction
Advantage of this system: the bigger the stimulation, the bigger the response that
you can have. Sensory systems are endowed with the ability to be sensitive to the
magnitude of the stimulus
Transduction of vision (listen again)
Transduction is NOT the result of mechanical deformation but change in state of molecule
sensitive to light
Change in a state of a molecule that is sensitive to light called rodoxin
The signal that the light has hit the phtoreepyor, the retinal molecule changes its change from bent
to straight and that straightness that happens in less than fraction of a millisecond is ALL that it
needs to excite photoreceptors to say that light has hit the eye
The retinal molecule, for the briefest moment, changes shape from being bent to straight.
That straight, in less than a fraction of a millisecond, is all it needs to excite photoreceptors to say
that light has hit the eye
Transduction of Hearing System
Stereo cilia make use of mechanically gated receptors as well: they have doors that sit on the
side of each of sterocilia connected to string at the end of the adjacent sterocilia
When the hair cells are moved back and forth as a result of sound waves vibrations, that
movement pulls those trapped doors to open allowing sodium ions to go through
The more the sound wave, the bigger the response
The more the sound, the bigger movement in our ear, the more response
Energy from out is helping channels in our system to open leading to generator potential: form of
ALL transduction
Perception is relative
Although transduction can tell us something about the magnitude of a stimulus, our perception of
what we see and hear is a relative process and is NOT dependant just on how strongly sensory
receptors depolarize
We perceive in context
In the illusion, our visual system is trying to place everything in context
oThe context of B is in presence of a shadow
oOur visual system makes uses of the position of B to adjust how brightly we see B as
Same perception despite huge variation
We can never truly access someone’s perceptual experience
oWe can’t tell if my red is the same as your red
When we look at the anatomy, we see a lot of variation that doesn’t help us to understand the
constancy of perceptual experience
Images of retinal mosaic: taking the picture of someone retina to allow us to understand what
kind of photoreceptors is present in each person’s eye
oBy shining a beam of laser at someone’s eye
oIf you shine red and you have a red photoreceptor in your eye, it will absorb it
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
While the occipital cortex is devoted to vision, there are other areas in our brain too: how the sensory information built up: hierarchy. All sensory systems reflect an adaptation towards something. The yellow flower looks yellow to us but using an ultraviolet camera, we see purple and white as well. Different animals (honeybee) sees the ultraviolet elements on the tips of the flower. The hummingbird sees a completely different color. If the color reflects the needs, then the visual system will develop an adaptation to it. Ultravioletness reflects when a flower is ready to pollinate. If bee can detect pollinating flowers, they are much more likely to navigate towards them. Song birds relay ultraviolet light to find mates: ultraviolet plumage is very active in males during the mating season. Serves purposes for finding a mate: our eyes have different receptors called photoreceptors. We have 3 different kinds of cones that help us perceive colors.
