2 Key Concepts How do your eyes enable you to see? How do you hear and maintain your sense of balance?How do your senses of smell and taste work together?How is your skin related to your sense of touch?
4 PreviewYou waited in line to get on the ride and now its about time to begin. You grip the wheel as the bumper cars jerk into motion. The next thing you know, you are zipping around crazily and bump into cars driven by your friends.You can thrill to the motion of amusement park rides because of your senses.
5 Vision Your eyes respond to stimulus of light They convert that stimulus into impulses that your brain interprets, enabling you to see
6 How light enters our eye Light strikes the cornea-clear tissue that covers the front of the eyeThen light passes through a fluid filled chamber behind the cornea and reaches the pupilPupil is the opening through which light enters the eyeThe pupil changes size according to the light in the room/outside
7 (2) The pupil size is adjusted by muscles in the iris The iris is a circular structure that surrounds the pupil and regulates the amount of light entering the eyeIris also gives the eye its color
8 How light is focusedLight that passes through the pupil strikes the lensLens is a flexible structure that focuses lightThe lens of the eye bends the light rays, the image it produces is upside down and reversedMuscles that attach to the lens adjust its shape, producing an image that is in focus
9 How you see an imageAfter passing through the lens the focused light rays pass through a transparent jellylike fluidLight rays strike the retina, the layer of receptor cells that lines the back of the eyeThe retina contain about 130 million receptor cells that respond to light
10 (2) Two types of receptors: Rods and cones Rod cells work best in dim light and enable your to see black, white, and shades of grayCone cells work best in bright light and enable you to see colors
11 (3)When light strikes the rods and cones, nerve impulses travel to the cerebrum through the optic nervesOne optic nerve comes from the left eye and the other one comes from the right eyeIn the cerebrum two things happenThe brain turns the reversed image right side upIt also combines the images from each eye to produce a single image
12 Correcting nearsightedness and farsightedness People with nearsightedness can see nearby objects clearly, but have trouble seeing objects far away.To correct nearsightedness eyeglasses with concave lenses are wornConcave lenses are thicker at the edges than it is in the centerWhen light rays pass through a concave lens they are bent away from the center of the lens
13 (2)Concave lenses in glasses make light rays spread out before they reach the lens of the eyeAfter the rays pass though the lens of the eye they focus on the retina rather than in front of itPeople with farsightedness can see distant objects clearly
14 (3) Nearby objects look blurry Eyeballs of people with farsightedness are too shortThe lens of the eye bends light from nearby objects so that the image does not focus properly on the retinaIf light could pass through the retina the image would come into sharp focus at a point behind the retina
15 Convex lenses are used to help correct farsightedness A convex lens is thicker in the middle than at the edgesConvex lens makes the light rays bend toward each other before they reach the eyeThe lens of the eye bends the rays even moreThis bending makes the image focus exactly on the retina
16 Hearing and balanceYour ears re the sense organs that respond to the stimulus of soundThe ears convert the sound to nerve impulses that your brain interpretsSound is produced by vibrationsVibrations move outward from the source of the sound-ex. Water ripples
17 Outer ear Outer ear receives sound vibrations Outer ear is shaped like a funnelThis funnel shape enables the outer ear to gather sound wavesSound vibrations then travel down the ear canal
18 Middle earAt the end of the ear canal, sound vibrations reach the eardrumThe eardrum separates the outer ear from the middle earEardrum is a membrane that vibrates when sound strikes itVibrations from the eardrum pass to the middle ear-which contains the three smallest bones in the body-hammer, anvil and stirrup
19 Inner earStirrup vibrates against a thin membrane that covers the opening of the inner earThe membrane channels the vibrations into fluid in the cochleaCochlea is a snail shaped tube that is lined with receptor cells that respond to soundWhen the fluid in the cochlea vibrates it stimulates these receptors
20 Inner ear and balanceStructures in your inner ear control your sense of balanceAbove the cochlea in your inner ear are the semicircular canals which are responsible for your sense of balance
21 Smell and Taste Senses smell and taste work closely together Both depend on chemicals in food or in the airThe chemicals trigger responses in receptors in the nose and mouthNerve impulses then travel to the brain where they are interpreted as smells or tastes
22 TouchUnlike vision, hearing, balance, smell and taste the sense of touch is not found in one specific placeSense of touch is found in all areas of your skinSkin contains different kinds of touch receptors that respond to a number of stimuli
23 (2)Receptors that respond to light touch are in the upper part of the dermis-let you feel textures of objects such as smooth glass and rough sandpaperReceptors deeper in the dermis pick up the feeling of pressureDermis also contains receptors that respond to temperature and painPain is unpleasant but can be one of the body’s most important feelings because it alerts the body to possible danger
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