Module 5
Sensation
THREE DEFINITONS
• Adaptation:
– the decreasing response of the sense organs, the
more they are exposed to a continuous level of
stimulation
• Sensation versus perception:
– relatively meaningless bits of information that result
when the brain processes electrical signals that come
from the sense organs
– perceptions:
– meaningful sensory experiences that result after the
brain combines hundreds of sensations
THREE DEFINITONS (CONT.)
• eyes, ears, nose, skin, and tongue are complex,
miniaturized, living sense organs that automatically
gather information about your environment
• Transduction:
– process in which a sense organ changes, or
transforms, physical energy into electrical signals that
become neural impulses, which may be sent to the
brain for processing
EYE: VISION
• Structure and function
– eyes perform two separate processes
– first: gather and focus light into precise area in the
back of eye
– second: area absorbs and transforms light waves into
electrical impulses
– process called transduction
EYE: VISION (CONT.)
• Stimulus: Light Waves
– Invisible—too short
• wave lengths too short
• gamma rays, x-rays, ultraviolet rays
– Visible—just right
• Visible spectrum
• Particular segment of electromagnetic energy that
we can see because these waves are the right
length to stimulate receptors in the eye
– Invisible—too long
• wave lengths longer
• Radar, FM, TV, shortwave, AM
EYE: VISION (CONT.)
EYE: VISION (CONT.)
• Structure and function
– Vision: 7 steps
• Image reversed
• Light waves
• Cornea
• Pupil
• Iris
• Lens
• Retina
EYE: VISION (CONT.)
• Structure and function
– Image reversed
• In the back of the eye, objects appear upside
down.
• somehow the brain turns the objects right side up
– Light waves
• light waves are changed from broad beams to
narrow, focused ones
EYE: VISION (CONT.)
• Structure and function
– Cornea
• rounded, transparent covering over the front of
your eye
– Pupil
• round opening at the front of the eye that allows
light waves to pass into the eye’s interior
EYE: VISION (CONT.)
• Structure and function
– Iris
• circular muscle that surrounds the pupil and
controls the amount of light entering the eye
– Lens
• transparent, oval structure whose curved surface
bends and focuses light waves into an even
narrower beam
EYE: VISION (CONT.)
• Structure and function
– 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
EYE: VISION (CONT.)
• Retina:
– three layers of cells
• back layer contains two kinds of photoreceptors
that begin the process of transduction
• change light waves into electrical signals
• rod located primarily in the periphery
• cone located primarily in the center of the retina
called the fovea
EYE: VISION (CONT.)
• rods:
– photoreceptor that contain a single chemical, called
rhodopsin
– activated by small amounts of light
– very light sensitive
– allow us to see in dim light
– see only black, white and shades of gray
EYE: VISION (CONT.)
• cones:
– photoreceptors that contain three chemicals called
opsins
– activated in bright light
– allow us to see color
– cones are wired individually to neighboring cells
– allows us to see fine detail
EYE: VISION (CONT.)
• Visual pathways: Eye to brain
– Optic nerve
– Primary visual cortex
– Visual association areas
EYE: VISION (CONT.)
EYE: VISION (CONT.)
• Visual pathways: eye to brain
– Optic nerve
• nerve impulses flow through the optic nerve as it
exits from the back of the eye
• the exit point is the “blind spot”
• the optic nerves partially cross and pass through
the thalamus
• the thalamus relays impulses to the back of the
occipital lobe in the right and left hemisphere
EYE: VISION (CONT.)
• Visual pathways: eye to brain
– Primary visual cortex
• the back of the occipital lobes is where primary
visual cortex transforms nerve impulses into simple
visual sensations
– Visual association areas
• the primary visual cortex sends simple visual
sensations to neighboring association areas
EYE: VISION (CONT.)
• Color Vision
– Trichromatic theory
• three different kinds of cones in the retina
• each cone contains one of the three different lightsensitive chemicals, called opsins
• each of the three opsins is most responsive to
wavelengths that correspond to each of the three
primary colors
• blue, green, red
• all colors can be mixed from these primary colors
EYE: VISION (CONT.)
• Opponent-Process Theory
– Afterimage
• visual sensation that continues after the original
stimulus is removed
• ganglion cells in retina and cells in thalamus
respond to two pairs of colors—red-green and
blue-yellow
• when excited, respond to one color of the pair
• when inhibited, respond to complementary pair
EYE: VISION (CONT.)
• Color Blindness
– inability to distinguished two or more shades in the
color spectrum
– Monochromatic:
• total color blindness
• black and white
• result of only rods and one kind of functioning cone
– Dichromatic:
• trouble distinguishing red from green
• two kinds of cones
• inherited genetic defect
• mostly in males
• See mostly shades of green
EAR: AUDITION
• Stimulus:
– Sound waves
• ________________________________________
• _______________________________________
• ________________________________________
________________________________________
– Height
• ________________________________________
________________________________________
• ________________________________________
– Frequency
• ________________________________________
________________________________________
EAR: AUDITION (CONT.)
• Loudness
– __________________________________________
– brain calculates loudness from specific physical
energy (amplitude of sound waves)
• Pitch
– __________________________________________
– __________________________________________
– __________________________________________
– __________________________________________
__________________________________________
__________________________________________
EAR: AUDITION (CONT.)
• Measuring sound waves
– decibel: ___________________________________
– threshold for hearing:
• _______________________________________
• ________________________________________
________________________________________
________________________________________
________________________________________
EAR: AUDITION (CONT.)
EAR: AUDITION (CONT.)
• Outer, middle, and inner ear
– Outer ear
• consists of three structures
– _____________________________________
– _____________________________________
– _____________________________________
_____________________________________
_____________________________________
EAR: AUDITION (CONT.)
• Outer, middle, and inner ear
– Outer ear
• external ear
– _____________________________________
_____________________________________
_____________________________________
____________________
• function
– _____________________________________
_____________________________________
_____________________________________
EAR: AUDITION (CONT.)
• Outer, middle, and inner ear
– Outer ear
• auditory canal
– _____________________________________
_____________________________________
_____________________________________
_____________________________________
_____________________________________
_____________________________________
EAR: AUDITION (CONT.)
• Outer, middle, and inner ear
– Outer ear
• tympanic membrane
– _____________________________________
_____________________________________
_____________________________________
_____________________________________
– _____________________________________
_____________________________________
_____________________________________
_____________________________________
________________________
EAR: AUDITION (CONT.)
EAR: AUDITION (CONT.)
• Outer, middle, and inner ear
– Middle ear
• bony cavity sealed at each end by membranes.
• the membranes are connected by three tiny bones
called ___________________________________
• hammer, anvil and stirrup
– _____________________________________
_____________________________________
– _____________________________________
_____________________________________
________________
– _____________________________________
____________________________________
EAR: AUDITION (CONT.)
• Outer, middle, and inner ear
– Inner ear
• contains two structures sealed by bone
– cochlea:
_____________________________________
________________
– vestibular system:
_____________________________________
_____________________________________
_
EAR: AUDITION (CONT.)
• Cochlea
– bony coiled exterior that resembles a snail’s shell
– contains receptors for hearing
– _________________________________________
– transforms vibrations into nerve impulses that are
sent to the brain for processing into auditory
information
EAR: AUDITION (CONT.)
EAR: AUDITION (CONT.)
• Auditory brain areas
– sensations and perceptions
– two step process occurs after the nerve impulses
reach the brain
• primary auditory cortex
– top edge of temporal lobe
– transforms nerve impulses into basic auditory
sensations
– auditory association area
• combines meaningless auditory sensations into
perceptions, which are meaningful melodies,
songs, words, or sentences
VESTIBULAR SYSTEM: BALANCE
• Position and balance
– vestibular system is located above the cochlea in the inner
ear
– includes semicircular canals
– bony arches set at different angles
– each semicircular canal is filled with fluid that moves in
response to movements of your head
– 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
CHEMICAL SENSES
• Taste
– chemical sense because the stimuli are various
chemicals
CHEMICAL SENSES (CONT.)
• Tongue
– Five basic tastes
• ___________________________________
• ____________________________________
• _____________________________________
• ________________________________________
___
• ________________________________________
_______________________________________
CHEMICAL SENSES (CONT.)
• Surface of the tongue
– ________________, which are the stimuli for taste,
break down into molecules
– molecules mix with ______________ and run into
narrow trenches on the surface of the tongue
– molecules then stimulate the
____________________
CHEMICAL SENSES (CONT.)
• Taste buds
– shaped like miniature onions
– _____________________________________
– chemicals dissolved in saliva activate taste buds
– __________________________________________
_________________________________________
– ___________ transforms impulses into sensations of
taste
• Flavor
– __________________________________________
CHEMICAL SENSES (CONT.)
CHEMICAL SENSES (CONT.)
• Smell, or olfaction
– Steps for olfaction
• ______________________________
• _____________________________
• ___________________________________
• ________________________________________
CHEMICAL SENSES (CONT.)
CHEMICAL SENSES (CONT.)
• Smell, or olfaction
– Stimulus
• ____________________________________
• volatile substances are released molecules in the
air at room temperature
• example:
– _____________________________________
_____________________________________
_____________________________________
_____________________________________
________________________
CHEMICAL SENSES (CONT.)
• Smell, or olfaction
– Olfactory cells
• receptors for smell are located in a I-inch-square
patch of tissue in the uppermost part of the nasal
passages.
• olfactory cells _____________________________
• which dissolve volatile molecules and stimulate the
cells
• the cells trigger ______________ that travel to the
____________________________
• which interprets the impulses as different smells
CHEMICAL SENSES (CONT.)
• Smell, or olfaction
– Sensations and memories
• nerve impulses travel to the olfactory bulb
• impulses are relayed to the primary olfactory
cortex
• cortex transforms nerve impulses into olfactory
sensations
• can identify as many as _________ different odors
• we stop smelling our deodorants or perfumes
because of decreased responding
• called ____________________________
CHEMICAL SENSES (CONT.)
• Smell, or olfaction
– Functions of olfaction
• one function: ____________________________
• second function:
________________________________________
________________________________________
___________________
• third function:
________________________________________
________________________________________
________________________________________
____________________________
TOUCH
• Touch
– includes pressure, temperature, and pain
TOUCH (CONT.)
• Receptors in the skin
– ___________________________________
– ____________________________________
– ______________________________________
– __________________________________________
__________________________________________
TOUCH (CONT.)
• Skin
– ________________________________
– thin film of dead cells containing _________________
– just below, are first receptors which look like groups of
threadlike extensions
– middle and fatty layer
– variety of receptors with different shapes and
functions
– some are ___________________________________
TOUCH (CONT.)
• Hair receptors
– ___________________ wrapped around the base of
each hair follicle
– hair follicles fire with a burst of activity when _______
– if hair remains bent for a period of time, the receptors
will cease firing
– sensory adaptation
– example: wearing a watch
TOUCH (CONT.)
• Free nerve endings
– __________________________________________
– __________________________________________
• Pacinian corpuscle
– _____________________________________
– _____________________________________
– ________________________________________
– __________________________________________
__________________________________________
__________________________________________
TOUCH (CONT.)
• Brain areas
– ____________________________________
– located in __________________________________
– transforms nerve impulses into
__________________________________________
__________________________________________
__________________________________________
__________________________________________
_
PAIN
• What causes pain?
– pain:
__________________________________________
__________________________________________
__________________________________________
__________________________________________
__________________________________________
__________________________________________
– __________________________________________
__________________________________________
__________________________________________
__________________________________________
PAIN (CONT.)
• How does the mind stop pain?
– __________________________________________
__________________________________________
__________________________________________
– Non-painful nerve impulses compete with pain
impulses in trying to reach the brain
– creates a bottleneck or neutral gate
– shifting attention or rubbing an injured area decreases
the passage of painful impulses
– result: pain is dulled
PAIN (CONT.)
• Endorphins
– chemicals produced by the brain and secreted in
response to injury or severe physical or psychological
stress
– pain reducing properties of endorphins are similar to
those of morphine
– brain produces endorphins in situations that evoke
great fear, anxiety, stress or bodily injury as well as
intense aerobic activity
PAIN (CONT.)
• Dread
– connected to pain centers in brain
– not the act itself that people fear
– time waiting before event causes dread
• Acupuncture
– trained practitioners insert thin needles into various
points on the body’s surface and then manually twirls
or electrically stimulates the needles
– after 10-20 minutes of stimulation, patients often
report a reduction in various kinds of pain