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 light-

sensitive 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