Sensory Receptors Organisms perceive information about their environment via sensory receptors which...
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E.2 Perception of Stimuli
Sensory Receptors Organisms perceive information about their environment via sensory receptors which can detect various stimuli Sensory organs are a window
Sensory Receptors Organisms perceive information about their
environment via sensory receptors which can detect various stimuli
Sensory organs are a window to the brain. When stimulated, the
sense organs send a message to the central nervous system. The
nerve impulses arriving at the brain result in sensation. We
actually see, smell taste and feel with our brains rather than our
sense organs.
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Sensory cells also send messages to certain parts of the brain
that control emotion and memory. This is why we link tastes,
sights, and sounds with emotions and memories.
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Sensory Receptors CHEMORECEPTORS Have proteins in their
membranes that can bind to a particular substance and initiate an
action potential Chemoreceptors in the nose sense smell
Chemoreceptors on our tongues (taste buds) detect taste
Chemoreceptors in our blood vessels detect blood pH Pain receptors
are a type of chemoreceptors that respond to chemicals released by
damaged tissues.
Thermoreceptors Detect changes in temperature Cold receptors
can be found just under the skin surface Warm receptors are located
deeper. The hypothalamus contains thermoreceptors to monitor blood
temperature
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Mechanoreceptors Detect movement Stimulated by mechanical force
or pressure. Pressure receptors in your skin detect touch. Pressure
rectors in your arteries detect changes in blood pressure There is
a system in our ears that involves fluid filled canals and hairs
that detect our body positions and movement.
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Photoreceptors Detect light Include the rods and cones in our
eyes.
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Human Eye
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CONJUCTIVA: Covers the sclera Keeps the eye moist CORNEA Made
of a strong, transparent layer of tissue Covers iris and pupil
Helps focus images, refracting light AQUEOUS HUMOUR: Clear fluid
that supports the eyeball and transmits light Parts of the Eye
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PUPIL: the dark circle of the eye Actually a hole that allows
light into the eye IRIS: the coloured part of the eye circular band
of muscle surrounding the pupil regulates the size of the pupil In
dim light, the iris opens pupil dilates (becomes wider) to allow
more light in In bright light, the iris closes pupil contracts
(becomes smaller) SCLERA: The white part of the eye The protective
outer layer of the eye
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LENS: convex lens that focuses light rays and directs it to a
point. Your lens can change focus so that you can see an object
clearly regardless of whether it is right in front of you, or far
away. This is possible because it is surrounded by a circle of
muscles: ciliary muscles CILIARY MUSCLE muscles that surround the
lens and control the shape and therefore the focus of lens
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VITREOUS HUMOUR: Clear fluid that supports the eyeball and
transmits light RETINA: inner lining at the back of the eye that
acts as a projection screen for light rays entering your eye Made
of photoreceptors (rods and cones) ROD CELLS: photoreceptor cells
of the retina that detect shapes and movement in low light and
shades of grey CONE CELLS: photoreceptor cells of the retina that
detect colour.
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FOVEA: Area of retina where cone cells are densely packed
(vision is most acute here) OPTIC NERVE: connects your eye to your
brain contains nerves that will send information collected by the
photoreceptors to the brain BLIND SPOT: the place where the optic
nerve attaches to the retina. Therefore there are no photoreceptors
here and light cannot be detected.
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CHOROID: Vascular layer of the eye Contains blood vessels that
will provide oxygen to eye cells SCLERA: The white part of the eye
Protective outer layer of the eyeball
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How does the eye work to focus light and detect images? 1.
Light enters the eye at the cornea 2. Light passes through the
aqueous humour to reach the pupil 3. Light is then focused by the
lens through the vitreous humour to the retina. 4. The retina is
composed of photoreceptors: cells that are sensitive to light.
There are 2 types: rods, and cones.
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5. The rods and cones transmit the information to nerve cells
in the retina. 6. The nerve cells transmit the information to the
optic nerve which takes the information to the brain to be
processed. (The image formed on your retina is actually inverted
but your brain will flip it and interpret it right side up!)
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The RETINA
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Processing Visual Stimuli When light hits the retina, it passes
in between various neurons (the ganglions (and their axons in the
optic fibre) and the sensory neurons) and then finally hits the
rods and cones. The rods and cones will receive the stimuli (the
light) and initiate and action potential in the sensory (bipolar)
neurons that will be sent to the brain via the ganglion cells of
the optic nerve.
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The axons of the ganglion cells travel to the visual area of
the cerebral cortex of the brain. The brain corrects the position
of the image so that is it rights side up and not reversed
Contra-lateral Processing This refers to the fact that some of
the nerve fibres in the optic nerve will cross before reaching the
brain (optic chiasma) Info from the left side of each visual field
converge at the optic chiasma and pass to the right side of the
brain. Info from the right side of each visual field converge at
the optic chiasma and pass to the left side of the brain.
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Herman Grid Illusion A B
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Why do you see grey blobs in the white area between the black
squares that vanish when you try to look at them directly? Theory:
the areas where you see grey are in your peripheral vision where
there are fewer light sensitive cells than at your fovea. When you
directly at the grey area, you are using the center of the retina,
your fovea, which has a high concentration of light-sensitive
cells.
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Edge Enhancement The Hermann grid fools your eye because of the
extreme contrast between black and white edges. You have a special
mechanism for seeing edges known as edge enhancement Theory: light
sensitive receptors in your eye switch off their neighbouring
receptors. This makes the edges look more distinct, because of the
extreme contrast between dark and light.
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When you look at and intersection in the grid (such as A) there
is a lot of white surrounding it compared to looking at an area
such as B which is surrounded by black. Your brains receives the
info that the contrast at A is less than that at B. So B is seen as
a white spot, and A is seen as a grey spot.
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Blind Spot is the one place on the retina of every healthy eye
in which there are no photoreceptors. Since there are no
photoreceptors light cannot be detected here. There are no
photoreceptors because this is where the optic nerve attaches to
the retina. You do not notice your blind spot because your brain
fills it in.
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Find your blind spot Draw a small plus sign and a small dot on
a piece of paper, at least 5 cm apart. Cover your LEFT eye, and
stare at the plus sign. Slowly move away (or forward). When the
black spot has disappeared, you have found your blind spot. +