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33-3 The Senses

Bio 30 - NWRC

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Taste

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Taste

Taste is one of the five senses throughwhich all animals interpret the worldaround them. Specifically, taste is thesense for determining the flavour of foodand other substances. It is one of the twochemical senses (the other being smell)

and it is stimulated when taste buds on thetongue come in

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Taste

Clusters of small organs called taste buds arelocated in the mouth, mainly on the surface of the tongue. Taste buds (named so because

under the microscope they look similar to plantbuds) lie in small projections called papillae andcontain taste receptors that bind to foodmolecules broken down by saliva. Thesereceptors send messages along nerves to thebrain, which interprets the flavor as sweet, sour,salty, or bitter.

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Smell

Smell depends onsensory receptors thatrespond to airbornechemicals. In humans,these chemoreceptors are located in theolfactory epithelium a patch of tissue about

the size of a postagestamp located high in thenasal cavity.

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Sight

Light enters the front of the eye through the pupiland is focused by the

lens onto the retina.Rods and cone cells onthe retina respond to thelight and send amessage through theoptic nerve fiber to thebrain.

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Sight

The rods are morenumerous, some 120 million,and are more light sensitive

than the cones. However,they are not sensitive tocolour. The 6 to 7 millioncones provide the eye'scolour sensitivity Conesfunction in light and are mostsensitive to colours

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Sight The retina is a multi-layered

sensory tissue that lines theback of the eye. It containsmillions of photoreceptors

(rods and cones)that capturelight rays and convert theminto electrical impulses.These impulses travel alongthe optic nerve to the brainwhere they are turned intoimages.

Watch Cow Eye Dissection

http://www.exploratorium.edu/learning_studio/cow_eye/step01.htmlhttp://www.exploratorium.edu/learning_studio/cow_eye/step01.html

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Hearing and Balance

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Hearing and Balance3 regions: outer ear or pinna (collects anddirects sound waves),middle ear (transfers

and amplifies the soundwaves), and the inner ear (sensespitch/frequency,intensity/loudness, andquality/timbre). A snail-like structure called thecochlea is the sensoryelement of the inner ear.

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Hearing and Balance

The cochlea isa fluid-filledchamber whosefluid is set intomotion bymovement of the oval windowbetween middleand inner ears.

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Hearing and BalanceThe cochlea contains the basilar membrane that varies instiffness along its length. Highfrequencies deflect the basilar membrane nearer to the ovalwindow and low frequencies

farther from the window. Thisdeflection activate receptors,called the hair cells whichtrigger nerve impulses. Thesensory input travels along thecranial nerve to the brain

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Hearing and Balance3 fluid-filled semicircular canals, arranged at rightangles to one another Fluid movement

occurring within thecanals due to headmovement causes nerveimpulses to be sent tothe brain regarding headposition and movement.These structures sensehead position andacceleration.

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Touch

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TouchThe sense of touch is thename given to a network of nerve endings that reach justabout every part of our body.These sensory nerve endingsare located just below theskin and register light andheavy pressure on the skin

and also differences intemperature. These nerveendings gather informationand send it to the brain

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Assessment 1. 1. Sound, which is transmitted as

sound waves (vibration of the air),enters the ear canal and reaches theeardrum.

2. The sound waves lead to thevibration of the eardrum, which also

vibrates the small bones behind theear drum. 3. The vibration motion of the bones

makes the fluid in the inner ear or cochlea to vibrate.

4. The vibration waves in the inner ear fluid causes the sensory (hair)

cells in the inner ear (cochlea) tobend. The hair cells change themovement into electrical signals.

5. These electrical signals aretransmitted through the hearing(auditory) nerve and up to the brain,where they are interpreted.

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Assessment

2. If the cornea wasdamaged light mightbe distorted as itentered the eyecausing the image inthe brain to bedistorted

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Assessment

3. The variety of receptors areimportant becausethe fingersencounter manydifferent types of stimuli (pressure,pain, etc.)

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Assessment

4. The sense of tastecomes from thereceptors in themouth and nasalcavity. If the nasalcavity is blocked thebrain does not get allnecessaryinformation toidentify a particular taste.