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Sensation; Module 5
EYE: VISION
• Structure and function
– eyes perform two separate
processes
1. first: gather and focus light into
precise area in the back of eye
2. second: area absorbs and
transforms light waves into electrical
impulses
– process called transduction
EYE: VISION
• Structure and function
– Vision: 7 Concepts To Know
• Cornea
• Iris/Pupil
• Lens
• Retina/Macula/Fovea
• Optic Nerve
• Function of Light Waves
• Image Reversed
EYE: VISION
Retina
• located at the very back of the
eyeball, is a thin film that contains
cells that are extremely sensitive
to light
• light sensitive cells, called
photoreceptors, begin the process
of transduction by absorbing light
waves
p96 RETINA
Color Vision
• There are three types of specialized cones in our
retinas that allow us to see light.
1. Red equals long light rays; 500-700nm
2. Green equals medium light rays; 450-630 nm
3. Blue equals short light rays; 400-500nm
Color Vision
• When a person is born without one of these cone
types they are then color-blind to those specific
colors.
1. Monochromat = Total color blindness
2. Dichromat = Missing one cone type. Usually
trouble telling reds from greens.
• Very common in men; very seldom seen in women
EYE: VISION
• Visual pathways: eye to brain
– Optic nerve
1. nerve impulses flow through the optic
nerve as it exits from the back of the
eye
• the exit point is the “blind spot”
2. the optic nerves partially cross and
pass through the thalamus
3. the thalamus relays impulses to the
back of the occipital lobe in the right
and left hemisphere
EYE: VISION
• Visual pathways: eye to brain
4. Primary visual cortex
• the backs of the occipitals lobes is
where primary visual cortex
transforms nerve impulses into
simple visual sensations
5. Visual association areas
• the primary visual cortex sends
simple visual sensations to
neighboring association areas
Structures of the ear are
categorized into (3) areas:
1.Outer Ear
2.Middle Ear
3. Inner Ear
EAR: AUDITION
• We Hear:
– Sound waves
• stimuli for hearing (audition)
• ripples of different sizes
• Sound waves travel through space with
varying heights and frequency.
– Height
• distance from the bottom to the top of a
sound wave
• called amplitude
Amplitude = How loud something is to us
Small amplitude= whisper
Large amplitude= yell
Frequency/How close
sound waves are to one
another
Wavelength/How
Big or Small
Speed/How fast
they travel
What Is Sound?
Any sound that you hear as a tone is made of regular,
evenly spaced waves of air molecules. The most
noticeable difference between various tonal sounds is
that some sound higher or lower than others. These
differences in the pitch of the sound are caused by
different spacing in the waves; the closer together the
waves are, the higher the tone sounds. The spacing of
the waves - the distance from the high point of one wave
to the next one - is the wavelength.
All sound waves are travelling at about the same speed the speed of sound. So waves with a longer wavelength
don't arrive (at your ear, for example) as often
(frequently) as the shorter waves. This aspect of a sound
- how often a wave peak goes by, is called frequency by
scientists and engineers. They measure it in hertz, which
is how many wave peaks go by in one second. People
can hear sounds that range from about 20 to about
17,000 hertz.
What Is Sound?
Wavelength, Frequency, and Pitch
Figure 1: Since the sounds are travelling at about the same speed, the one with the shorter
wavelength will go by more frequently; it has a higher frequency, or pitch. In other words,
it sounds higher.
EAR: AUDITION
• Measuring sound waves
–decibel: unit to measure loudness
–threshold for hearing:
• 0 decibels (no sound)
• 140 decibels (pain and
permanent hearing loss
p101 DECIBEL CHART
p102 EAR DIAGRAM
EAR: AUDITION
• Outer, middle, and inner ear
– Middle ear
• bony cavity sealed at each end by
membranes
-the membranes are connected by three
tiny bones called ossicles
1.)hammer 2.)anvil 3.)stirrup
–hammer is attached to the back of the
tympanic membrane
–anvil receives vibrations from the
hammer
–stirrup makes the connection to the
oval window (end membrane)
EAR: AUDITION
• Outer, middle, and inner ear
– Inner ear
contains two structures sealed by bone
– cochlea: involved in hearing
– vestibular system: involved in
balanceCochlea
– bony coiled exterior that resembles a snail’s
shell
– contains receptors for hearing
– function is transduction which (once again!) is the:
transformation of vibrations into nerve impulses
that are sent to the brain for processing into
auditory information
EAR: AUDITION
• Auditory brain areas:
– there is a two step process occurs after
the nerve impulses reach the brain
1. primary auditory cortex which is at top
edge of temporal lobe:
– transforms nerve impulses into basic
auditory sensations
2. auditory association area:
– combines meaningless auditory sensations
into perceptions, which are meaningful
melodies, songs, words, or sentences
VESTIBULAR SENSE: BALANCE
• Position and balance
– vestibular system is located above the
cochlea in the inner ear in which are the
semicircular canals
– each semicircular canal is filled with
fluid that moves in response to
movements of your head
– These (3) canals have hair cells that
respond to the fluid movement
– function of vestibular system include
sensing the position of the head,
keeping the head upright, and
maintaining balance
Smell
Taste
CHEMICAL SENSES
• Taste
– is a chemical sense because the stimuli
are various chemicals
• organ: tongue
– surface of the tongue contains:
• taste buds
CHEMICAL SENSES (CONT.)
• Tongue
– Six basic tastes
1. sweet
2. salty
3. sour
4. bitter
5. umami: meaty-cheesy taste
6. fat
________________________________
7. Menthol?
CHEMICAL SENSES (CONT.)
• Surface of the tongue
1. chemicals, which are the stimuli for
taste, break down into molecules
2. molecules mix with saliva an run into
narrow trenches on the surface of the
tongue
3. molecules then stimulate the taste buds
http://www.ajinomoto.com/features/aji-no-moto/en/umami/index.html
CHEMICAL SENSES (CONT.)
• Taste buds
shaped like miniature onions
are the receptors for taste
 here the chemicals dissolved in saliva
activate taste buds…..
… which then produces nerve impulses that
reach areas of the brain’s parietal lobe…
… then the brain transforms impulses into
sensations of taste
CHEMICAL SENSES (CONT.)
• Smell, or olfaction
– Olfaction
• called a chemical sense because its stimuli are
various chemicals that are carried by the air
• Our smelling function is carried out by two small
odor-detecting patches – made up of about five or
six million yellowish cells – high up in the nasal
passages.
•The human nose can detect (approx.) 10,000 smells.
•The human nose (not as sensitive as a hound dog) can detect a
smell that is 1 part chemical per billion parts of air molecules
CHEMICAL SENSES (CONT.)
• Smell / Olfaction
– Stimulus
• we smell volatile substances…
…these volatile substances are released
molecules in the the air at room
temperature
example:
– a skunk’s spray, warm brownies;
perfumes/colognes of lovers, gasoline,
dog poo, I think you get it!
CHEMICAL SENSES (FYI’s)
– Sensations and memories
• nerve impulses travel to the olfactory
bulb…
…where we can identify as many as
10,000 different odors
• Why do we stop smelling our own
deodorants or perfumes? Because of
decreased responding!
…It’s called Adaptation
CHEMICAL SENSES (CONT.)
• Functions of olfaction
1. one function: to intensify the taste of
food
2. second function: to warn of potentially
dangerous foods
3. third function: elicit strong memories;
emotional feelings
TOUCH
• Our sense of touch is controlled by a huge network of
nerve endings and touch receptors in the skin known
as the somatosensory system.
• This system is responsible for all the sensations we
feel - cold, hot, smooth, rough, pressure, tickle, itch,
pain, vibrations, and more. Within the somatosensory
system, there are four main types of receptors:
mechanoreceptors, thermoreceptors, pain receptors,
and proprioceptors.
TOUCH
•
Receptors in the skin
1. Mechanoreceptors
2. Thermoreceptors
3. Pain receptors
4. Proprioceptors
5. Hair follicles
TOUCH
• Skin
– the outermost layer…
…is a thin film of dead cells containing no
receptors
just below, are the first receptors which
look like groups of threadlike extensions
 next: the middle and fatty layer
…encompass a variety of receptors with
different shapes and functions
TOUCH
•
1. Mechanoreceptors: These receptors perceive sensations such as
pressure, vibrations, and texture. There are four known types of
mechanoreceptors whose only function is to perceive indentions and
vibrations of the skin: Merkel's disks, Meissner's corpuscles, Ruffini's
corpuscles, and Pacinian corpuscles.
 are in the fatty layer of skin
– are the largest touch sensor
 are also highly sensitive vibration
•
2. Thermoreceptors: As their name suggests, these receptors
perceive sensations related to the temperature of objects the skin feels.
They are found in the dermis layer of the skin. There are two basic
categories of thermoreceptors: hot and cold receptors.
– Hot receptors start to perceive hot sensations when the surface of the skin
rises above 86 º F and are most stimulated at 113 º F. But beyond 113 º F,
pain receptors take over to avoid damage being done to the skin and
underlying tissues.
– Cold receptors start to perceive cold sensations when the surface of the
skin drops below 95 º F. They are most stimulated when the surface of the
skin is at 77 º F and are no longer stimulated when the surface of the skin
drops below 41 º F. This is why your feet or hands start to go numb when
they are submerged in icy water for a long period of time.
TOUCH
• 3. Pain receptors: These receptors detect pain or stimuli that
can or does cause damage to the skin and other tissues of the
body. There are over three million pain receptors throughout the
body, found in skin, muscles, bones, blood vessels, and some
organs. They can detect pain that is caused by mechanical
stimuli (cut or scrape), thermal stimuli (burn), or chemical stimuli
(poison from an insect sting).
4. Proprioceptors: these receptors sense the position of the
different parts of the body in relation to each other and the
surrounding environment. Proprioceptors are found in tendons,
muscles, and joint capsules. This location in the body allows
these special cells to detect changes in muscle length and
muscle tension. Without proprioceptors, we would not be able to
do fundamental things such as feeding or clothing ourselves.
TOUCH
• 5. Hair receptors
• free nerve endings wrapped around the base of
each hair follicle
– these hair follicles fire with a burst of activity when
first bent and give a sense of light touch.
• If the hair remains bent for a period of time, the
receptors will cease firing.
….. Sensory adaptation. example: wearing a
watch, wearing a shirt with a collar etc.
TOUCH
• Brain areas (that translate nerve firings
into sensation)
somatosensory cortex located in the
parietal lobe: transforms nerve impulses
into sensations of touch temperature, and
pain
PAIN
What causes pain?
 pain is the complex mixture of
sensation and perception that is in
part mediated by emotion; it may
result from physical damage, one’s
thoughts, or environmental stressors
…therefore pain results from many different
stimuli, most of which are subjective in
nature
Gate-Control Theory
 When we are occupied with other
physical/mental activities we often feel less or
no pain at all.
-such as when you stub a toe, then you
rub it
or…….
-when you nearly sever a finger with a
power tool and pound your fist into a wall
only to sense that your finger doesn’t feel
so bad anymore
Gate-Control Theory
….On a serious note… nearly five years ago now….
• For example: A NYC cop was shot through the heart
he didn’t realize until the situation was over b/c he
was physically/mentally absorbed in something.
PAIN
• Perhaps your thinking: How does the
mind stop pain? (according to the Gate Theory)
well……
 non-painful nerve impulses compete with
pain impulses in trying to reach the brain
…they create a bottleneck or neutral gate
so…shifting attention or rubbing an injured
area decreases the passage of painful
impulses
result: Pain is dulled!
PAIN (Biologically)
• What does the body do to help us cope?
Endorphins
neurotransmitters secreted in response to
injury or severe physical or psychological
stress
the……
…pain reducing properties of endorphins are
similar to those of morphine so our…..
…brain produces endorphins in situations
that evoke great fear, anxiety, stress or
bodily injury as well as intense aerobic
activity.

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