Biology Journal 3/17/2014
Suppose that you are driving on the freeway and
notice that the car in front of you has stopped. You
react by slamming on the breaks. But, this “reaction
time” process has taken up a certain amount of time.
What nervous system processes needed to happen?
Describe it, including what your motor neurons,
sensory neurons, and relay neurons did during that
process.
Biology Journal 3/18/2014
The back of your eye is full of specialized neurons
called rods and cones. What kind of neuron do you
think these cells are? What do you think would be
different about their dendrites?
Biology Journal 3/19/2014
What is the most interesting thing you
observed from the eye dissection?
Dissecting a whale eye.
Biology Journal 3/20/2014
What is the name of
the nerve that sends
signals from the eyes
to the brain?
The optic nerve
What part of the brain
processes the signals
from the eyes?
The primary visual
cortex, which is in the
back of the brain
This is called contralateral
processing
What part separates
the visual signals into
the left and right
sides?
The optic chaism
E.2 Perception of Stimuli
E.2.1
Outline the diversity of stimuli that can be detected by human sensory receptors, including:

Mechanoreceptors, chemoreceptors, thermoreceptors, photoreceptors
Details of how each receptor functions are not required.
E.2.2
Label a diagram of the structure of the human eye. The diagram should include:

sclera, cornea, conjunctiva, eyelid, lens, choroid, aqueous humour, pupil,

iris, vitreous humour, retina, fovea, optic nerve, blind spot
E.2.3
Annotate a diagram of the retina to show the cell types and the direction in which light moves. Include names of rod
and cone cells, bipolar neurons and ganglion cells.
E.2.4
Compare rod and cone cells. Include:

use in dim light versus bright light

one type sensitive to all visible wavelengths versus three types sensitive to red, blue and green light

passage of impulses from a group of rod cells to a single nerve fibre in the optic nerve versus passage from a single
cone cell to a single nerve fibre
E.2.5
Explain the processing of visual stimuli, including edge enhancement and contralateral processing.

Edge enhancement occurs within the retina and can be demonstrated with the Hermann grid illusion.

Contralateral processing is due to the optic chiasma, where the right brain processes information from the left
visual field and vice versa. This can be illustrated by the abnormal perceptions of patients with brain lesions.
E.2.6
Label a diagram of the ear. Include:

Pinna, eardrum, bones of the middle ear

oval window, round window, semicircular canals

auditory nerve, cochlea
E.2.7
Explain how sound is perceived by the ear, including the roles of the eardrum, bones of the middle ear, oval and round
windows, and the hair cells of the cochlea.
Perception of Stimuli
Name of sensory
neuron
What it detects
Pressure, texture,
Mechanoreceptors
vibration
Examples
Pain sensors in skin,
balance
Name of sensory
neuron
What it detects
Pressure, texture,
Mechanoreceptors
vibration
Chemoreceptors
Chemicals
Examples
Pain sensors in skin,
balance
Taste buds, smell, CO2
concentration in blood
Name of sensory
neuron
What it detects
Pressure, texture,
Mechanoreceptors
vibration
Chemoreceptors
Chemicals
Photoreceptors
Electromagnetic
radiation
Examples
Pain sensors in skin,
balance
Taste buds, smell, CO2
concentration in blood
rods, cones
Name of sensory
neuron
What it detects
Pressure, texture,
Mechanoreceptors
vibration
Examples
Pain sensors in skin,
balance
Taste buds, smell, CO2
concentration in blood
Chemoreceptors
Chemicals
Photoreceptors
Electromagnetic
radiation
rods, cones
Temperature
Temperature sensors in
skin
Thermoreceptors
Conjunctiva
Sclera
protective outer
layer of pupil,
secretes mucus
protective
outer layer
Eyelid
Choroid
protection, cleaning
layer of lightabsorbing pigment
Retina
mostly rod cells
Fovea
Pupil
area of
concentrated
cone cells
opening that
lets light in
Blind Spot
Aqueous Humor
no receptor
cells
transparent jelly
Lens
adjusts to focus light
Iris
on retina
muscles that control size
of pupil; gives “eye color”
Vitreous humor
transparent liquid
Optic Nerve
carries nerve
impulses to brain
What do your pupils do in bright light?
What do your pupils do in darkness?
Dilated pupils: when they’re open wide
Constricted pupils: when they’re small
Ever have your eyes get
sore from staring at a
bright computer screen,
TV, or phone?
That’s because you’re iris
muscles are sore from
constricting for so long!
I’d better check her
facebook page again…
Many drugs dilate the pupils
because they relax the body’s
muscles. This contributes to why
vision seems more intense
The lens changes shape to focus
an image on the retina.
Nearsighted: The focus of the image falls
short of the retina, so its blurry.
Farsighted: The focus of the image is
beyond the retina, so its blurry.
Rods respond to light intensity. They work
well in low light.
Cones are receptors respond to colors (blue,
green, red). They do not work well in low
light.
Your peripheral vision has mostly
rods. The focus of your retina
(called the fovea) contains mostly
cones.
How you see:
1. Light stimulates the receptors of the rods and cones.
2. Bipolar cells send the action potential from the rod/cone to the ganglion
cells.
3. Ganglion cells collect the action potentials from many rods or cones
and send this signal down the retina, toward the optic nerve, where it is
sent to the brain.
Direction of light
Choroid
Action Potential
Cone cell
Rod cell
Bipolar cell
Ganglion cell
Direction of
nerve signal
Direction of light
contralateral processing
An image is flipped
twice in visual
processing:
1. The lens flips it to
opposite sides of
the retina.
2. The optic chaism
flips the image back,
where it is carried
primary visual
cortex (back of the
brain) to be
interpreted.
Do you See what I See?
Which box is darker, A or B?
Explanation
Edge enhancement: Our photoreceptors inhibit neighboring
photoreceptors that are the same color. Thus, when color
borders a different color (there is an “edge”), a
photoreceptor won’t be inhibited on the edge, making the
edge appear. This helps us to see shapes better.
How might edge enhancement help us survive?
Explanation
Retinal Fatigue: Our rods and cones get “fatigued” when
being stimulated by the same wavelength of light for a long
time, and begin to shut down.
After fatiguing your photoreceptors…
 Subtle changes in color get “washed out.”
 When you look at a “blank” screen, colors are inverted.
Explanation
Retinal Fatigue: Your brain is adapted to reading faces. It
does this so well that we often see faces in when there are
none.
However, his can lead to distressing images when the faces
don’t meet our brain’s expectations…
Our Devine Savior the Holy Jesus Cheese Sandwich
Auditory Senses
Pinna
collects
sound
waves
Eardrum
Middle Ear Bones
vibrated by air pressure Stimulated by ear drum,
changers due to sound knock against each other
waves
to magnify sound
Semicircular
Canals
balance (is not involved
in hearing)
Auditory
Nerve
transmits
nerve signals
to brain
Cochlea
Round Window
dissipates vibrations
(lessens and lessens
“old” sounds)
Oval Window
transmits vibrations
from middle ear bones
to inner ear
tiny hairs respond
to individual
wavelengths of
sound, generating
action potential
Eustachian Tube
transmits nerve signals
to brain
E.2.7
Explain how sound is perceived by the ear, including the roles of the eardrum, bones of
the middle ear, oval and round windows, and the hair cells of the cochlea.
Youtube videos
How Vision Works
A simple, short video showing how light enters the eye and how it stimulates signals
to go to the brain.
https://www.youtube.com/watch?v=gBdyU1b0ADQ
Auditory Transduction
Computer generated animation with excellent sounds and narration.
http://www.youtube.com/watch?v=PeTriGTENoc
Hearing Test
A 5:59 frequency test. Shows the wavelengths, which is nice.
https://www.youtube.com/watch?v=H-iCZElJ8m0
Earphone Test
A 1:40 frequency test. Shows the progress of wavelength on a graph, which is not as
easy to visualize.
https://www.youtube.com/watch?v=cvBtQmY2B5I
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How you Hear
Sound waves are collected by the pinna
Ear drum vibrates from air pressure changes (due to
sound waves)
Middle ear bones are stimulated by the ear drum,
enhancing the sound (it is increased by about 20
times)
Oval window transmits vibrations from middle ear
bones to cochlea
Tiny hairs in cochlea are mechanoreceptors for
individual wavelengths of sound, and send action
potentials
Auditory nerve sends signals to brain
Round windows dissipate “old” sounds