15-3 the senses web

8/9/2019 15-3 the Senses Web

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The Senses

Chapter 15 Section 3


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Senses

Vision, hearing, balance,smell, taste, and touch

Each of your major senses

picks up a specific type ofstimulus from yourenvironment

The sense organs changethose stimuli into nerveimpulses and send theimpulses to your brain


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How Light Enters the Eye

Eyes respond to the external stimulusof light

They convert that stimulus intoimpulses that your brain interprets,and enables you to see

Light 1st strikes the cornea- clear tissuethat covers the eye

Light then passes through a fluid filledchamber to the pupil

Pupil- the opening through which lightenters the eye

Iris- circular structure that surroundsthe pupil and regulates the amount

of light entering the eye (eye color)


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How Light is Focused

Light passes through the pupil and strikes thelens

Lens- flexible structure that focuses light

Images produced by the lens are upside downand reversed

Light then passes through a transparent, jellylikefluid and strikes the retina

Retina- layer of receptor cells that lines the back of the eye

Receptor cells are rods and cones

Rod cells work best in dim light Cone cells work well in bright light and see color

Impulses begin after light strikes the receptorcells and travel to the cerebrum through theoptic nerve

The brain turns the image right-side up andcombines the ima es from both e es in the


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Correcting Vision Problems

Nearsightedness

Nearsightedness- CANsee nearby objects

clearly, but havetrouble seeing objectsfar away

Caused by an eyeballthat is too long

Distant objects do not

focus sharply on theretina

Farsightedness

Farsightedness- CAN seedistant objects clearly

Nearby objects areblurry

The lens of the eyebends light from

nearby objects and donot focus

Corrected with convexlenses


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Hearing

Ears are the senseorgans thatrespond to the

external stimulusof sound

Ears convert sound

to nerve impulsesthat the braininterprets


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How Sound isProduced

Sound is produced byvibrations

Vibrations createwaves that moveoutward from thesource

Waves consist ofmoving particles,such as molecules

of air

Waves also travelthrough liquids andsolids

Sound Vibrations andEars

Structure of the earfunctions to receivesound vibrations


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Structure of the Ear

3 parts of the ear- outer ear, middle ear, and innerear

Outer ear shaped as a funnel that enables the outerear to gather sound waves

Eardrum- separates the outer ear from the middleear; membrane that vibrates when sound wavesstrike it

Middle ear- 3 smallest bones of the body- hammer,anvil, and stirrup

Eardrum makes the hammer vibrate, hammerpasses

vibrations to the anvil, anvil pass them to the stirrup


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How You Hear

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

Membrane channels the vibrations into the fluid inthe cochlea

Cochlea- snail-shaped tube that is lined withreceptors that respond to sound

Fluid in the cochlea vibrates and stimulates these receptors

Sensory neurons then send nerve impulses to the cerebrum through

the auditory nerve


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Internal Stimuli and Balance

Ear also controls sense of balance Semicircular canals- structures in the ear that are responsible

for your sense of balance above the cochlea

Canals are full of fluid and are lined with tiny cells that havehairlike extensions

Movement causes fluid to move and make hairlike extensionsbend

Bending creates stimulus that produces nerve impulses insensory neurons

Impulses travel to the cerebellum to determine which way your

head is moving


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Smell and Taste

Smell and tastedepend onchemical thattriggerresponses in

receptors in thenose and mouth

50 different odors

4 tastes- bitter,

sweet, salty, andbitter

Flavor isdetermined by

both smell andtaste


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Touch

Sense of touch is found all over the body

Skin is the largest sense

organ Receptors responding to light touch are in

the upper part of the dermis; also let youfeel textures

Receptors deeper in the dermis pick up thefeeling of pressure

Receptors responding to temperature and

pain are found in the dermis


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Review

What function do the senses perform in the body? Describe the process by which your eyes produce an

image of your surroundings. Begin at the point atwhich light is focused by the lens.

How do sound vibrations affect structures in the ear to

produce the sensation of hearing?

How are the senses of taste and smell similar? How are

they different?

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