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The SensesThe Senses

Chapter 19Chapter 19

Section 3Section 3

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Key ConceptsKey Concepts

How do your eyes enable you to see?How do your eyes enable you to see? How do you hear and maintain your How do you hear and maintain your

sense of balance?sense of balance? How do your senses of smell and How do your senses of smell and

taste work together?taste work together? How is your skin related to your How is your skin related to your

sense of touch?sense of touch?

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Key TermsKey Terms

CorneaCornea Pupil Pupil

IrisIris LensLens

RetinaRetina Nearsightedness Nearsightedness

FarsightednessFarsightedness EardrumEardrum

CochleaCochlea Semicircular canalSemicircular canal

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PreviewPreview

You waited in line to get on the ride You waited in line to get on the ride and now its about time to begin. You and now its about time to begin. You grip the wheel as the bumper cars jerk grip the wheel as the bumper cars jerk into motion. The next thing you know, into motion. The next thing you know, you are zipping around crazily and you are zipping around crazily and bump into cars driven by your friends.bump into cars driven by your friends.

You can thrill to the motion of You can thrill to the motion of amusement park rides because of amusement park rides because of your senses.your senses.

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VisionVision

Your eyes respond to stimulus of Your eyes respond to stimulus of lightlight

They convert that stimulus into They convert that stimulus into impulses that your brain interprets, impulses that your brain interprets, enabling you to seeenabling you to see

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How light enters our eyeHow light enters our eye

Light strikes the cornea-clear tissue Light strikes the cornea-clear tissue that covers the front of the eyethat covers the front of the eye

Then light passes through a fluid Then light passes through a fluid filled chamber behind the cornea and filled chamber behind the cornea and reaches the pupilreaches the pupil

Pupil is the opening through which Pupil is the opening through which light enters the eyelight enters the eye

The pupil changes size according to The pupil changes size according to the light in the room/outsidethe light in the room/outside

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The pupil size is adjusted by muscles The pupil size is adjusted by muscles in the irisin the iris

The iris is a circular structure that The iris is a circular structure that surrounds the pupil and regulates the surrounds the pupil and regulates the amount of light entering the eyeamount of light entering the eye

Iris also gives the eye its colorIris also gives the eye its color

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How light is focusedHow light is focused

Light that passes through the pupil Light that passes through the pupil strikes the lensstrikes the lens

Lens is a flexible structure that Lens is a flexible structure that focuses lightfocuses light

The lens of the eye bends the light The lens of the eye bends the light rays, the image it produces is upside rays, the image it produces is upside down and reverseddown and reversed

Muscles that attach to the lens adjust Muscles that attach to the lens adjust its shape, producing an image that is its shape, producing an image that is in focusin focus

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How you see an imageHow you see an image

After passing through the lens the After passing through the lens the focused light rays pass through a focused light rays pass through a transparent jellylike fluidtransparent jellylike fluid

Light rays strike the retina, the layer Light rays strike the retina, the layer of receptor cells that lines the back of receptor cells that lines the back of the eyeof the eye

The retina contain about 130 million The retina contain about 130 million receptor cells that respond to lightreceptor cells that respond to light

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Two types of receptors:Two types of receptors: Rods and conesRods and cones• Rod cells work best in dim light and Rod cells work best in dim light and

enable your to see black, white, and enable your to see black, white, and shades of grayshades of gray

• Cone cells work best in bright light and Cone cells work best in bright light and enable you to see colorsenable you to see colors

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When light strikes the rods and cones, nerve When light strikes the rods and cones, nerve impulses travel to the cerebrum through the impulses travel to the cerebrum through the optic nervesoptic nerves

One optic nerve comes from the left eye One optic nerve comes from the left eye and the other one comes from the right eyeand the other one comes from the right eye

In the cerebrum two things happenIn the cerebrum two things happen The brain turns the reversed image right side upThe brain turns the reversed image right side up It also combines the images from each eye to It also combines the images from each eye to

produce a single imageproduce a single image

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Correcting nearsightedness and Correcting nearsightedness and farsightednessfarsightedness

People with nearsightedness can see People with nearsightedness can see nearby objects clearly, but have trouble nearby objects clearly, but have trouble seeing objects far away. seeing objects far away.

To correct nearsightedness eyeglasses To correct nearsightedness eyeglasses with concave lenses are wornwith concave lenses are worn

Concave lenses are thicker at the edges Concave lenses are thicker at the edges than it is in the centerthan it is in the center

When light rays pass through a concave When light rays pass through a concave lens they are bent away from the center of lens they are bent away from the center of the lensthe lens

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Concave lenses in glasses make light Concave lenses in glasses make light rays spread out before they reach rays spread out before they reach the lens of the eyethe lens of the eye

After the rays pass though the lens of After the rays pass though the lens of the eye they focus on the retina the eye they focus on the retina rather than in front of itrather than in front of it

People with farsightedness can see People with farsightedness can see distant objects clearlydistant objects clearly

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Nearby objects look blurryNearby objects look blurry Eyeballs of people with Eyeballs of people with

farsightedness are too shortfarsightedness are too short The lens of the eye bends light from The lens of the eye bends light from

nearby objects so that the image nearby objects so that the image does not focus properly on the retinadoes not focus properly on the retina

If light could pass through the retina If light could pass through the retina the image would come into sharp the image would come into sharp focus at a point behind the retinafocus at a point behind the retina

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Convex lenses are used to help correct Convex lenses are used to help correct farsightednessfarsightedness

A convex lens is thicker in the middle than at A convex lens is thicker in the middle than at the edgesthe edges

Convex lens makes the light rays bend Convex lens makes the light rays bend toward each other before they reach the eyetoward each other before they reach the eye

The lens of the eye bends the rays even moreThe lens of the eye bends the rays even more This bending makes the image focus exactly This bending makes the image focus exactly

on the retinaon the retina

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Hearing and balanceHearing and balance

Your ears re the sense organs that Your ears re the sense organs that respond to the stimulus of soundrespond to the stimulus of sound

The ears convert the sound to nerve The ears convert the sound to nerve impulses that your brain interpretsimpulses that your brain interprets

Sound is produced by vibrationsSound is produced by vibrations Vibrations move outward from the Vibrations move outward from the

source of the sound-ex. Water ripplessource of the sound-ex. Water ripples

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Outer earOuter ear

Outer ear receives sound vibrationsOuter ear receives sound vibrations Outer ear is shaped like a funnelOuter ear is shaped like a funnel This funnel shape enables the outer This funnel shape enables the outer

ear to gather sound wavesear to gather sound waves Sound vibrations then travel down Sound vibrations then travel down

the ear canalthe ear canal

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Middle ear Middle ear

At the end of the ear canal, sound At the end of the ear canal, sound vibrations reach the eardrumvibrations reach the eardrum

The eardrum separates the outer ear from The eardrum separates the outer ear from the middle earthe middle ear

Eardrum is a membrane that vibrates Eardrum is a membrane that vibrates when sound strikes itwhen sound strikes it

Vibrations from the eardrum pass to the Vibrations from the eardrum pass to the middle ear-which contains the three middle ear-which contains the three smallest bones in the body-hammer, anvil smallest bones in the body-hammer, anvil and stirrupand stirrup

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Inner earInner ear

Stirrup vibrates against a thin membrane Stirrup vibrates against a thin membrane that covers the opening of the inner earthat covers the opening of the inner ear

The membrane channels the vibrations The membrane channels the vibrations into fluid in the cochleainto fluid in the cochlea

Cochlea is a snail shaped tube that is Cochlea is a snail shaped tube that is lined with receptor cells that respond to lined with receptor cells that respond to soundsound

When the fluid in the cochlea vibrates it When the fluid in the cochlea vibrates it stimulates these receptorsstimulates these receptors

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Inner ear and balanceInner ear and balance

Structures in your inner ear control Structures in your inner ear control your sense of balanceyour sense of balance

Above the cochlea in your inner ear Above the cochlea in your inner ear are the semicircular canals which are are the semicircular canals which are responsible for your sense of balanceresponsible for your sense of balance

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Smell and TasteSmell and Taste

Senses smell and taste work closely Senses smell and taste work closely togethertogether

Both depend on chemicals in food or Both depend on chemicals in food or in the airin the air

The chemicals trigger responses in The chemicals trigger responses in receptors in the nose and mouthreceptors in the nose and mouth

Nerve impulses then travel to the Nerve impulses then travel to the brain where they are interpreted as brain where they are interpreted as smells or tastessmells or tastes

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TouchTouch

Unlike vision, hearing, balance, smell Unlike vision, hearing, balance, smell and taste the sense of touch is not and taste the sense of touch is not found in one specific placefound in one specific place

Sense of touch is found in all areas of Sense of touch is found in all areas of your skinyour skin

Skin contains different kinds of touch Skin contains different kinds of touch receptors that respond to a number receptors that respond to a number of stimuliof stimuli

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(2)(2) Receptors that respond to light touch are Receptors that respond to light touch are

in the upper part of the dermis-let you feel in the upper part of the dermis-let you feel textures of objects such as smooth glass textures of objects such as smooth glass and rough sandpaperand rough sandpaper

Receptors deeper in the dermis pick up Receptors deeper in the dermis pick up the feeling of pressurethe feeling of pressure

Dermis also contains receptors that Dermis also contains receptors that respond to temperature and painrespond to temperature and pain

Pain is unpleasant but can be one of the Pain is unpleasant but can be one of the body’s most important feelings because it body’s most important feelings because it alerts the body to possible danger alerts the body to possible danger