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1 Essentials of Human Anatomy & PhysiologySeventh EditionElaine N. MariebChapter 8 Special SensesCopyright 2003 Pearson Education, Inc. publishing as Benjamin CummingsSlides SensesLecture Slides in PowerPoint by Jerry L. CookThe SensesThe Senses General senses of touch Temperature Pressure Pain Special senses Special sensereceptors are eitherlarge, complexsensory organsSlide 2003 Pearson Education, Inc. publishing as Benjamin Cummings Special senses Smell Taste Sight Hearing Equilibriumsensory organs(eyes and ears) orlocalized clusters orreceptors (tastebuds and olfactoryepithelium)The Eye and VisionThe Eye and Vision 70 percent of all sensory receptors arein the eyes Each eye has over a million nerve fibersSlide 2003 Pearson Education, Inc. publishing as Benjamin Cummings Each eye has over a million nerve fibers Protection for the eye Most of the eye is enclosed in a bony orbit A cushion of fat surrounds most of the eyeAccessory Structures of the EyeAccessory Structures of the Eye Eyelids Eyelashes Meibomian glands modifiedsebaceousSlide 2003 Pearson Education, Inc.

2 Publishing as Benjamin Cummingssebaceousglandsproduce anoily secretionto lubricatethe eyeFigure Structures of the EyeAccessory Structures of the Eye Ciliary glands modified sweat glandsbetween the eyelashes Conjunctiva Membrane thatlines the eyelidsSlide 2003 Pearson Education, Inc. publishing as Benjamin Cummingslines the eyelids Connects to thesurface of the eye Secretes mucusto lubricate the eyeFigure Structures of the EyeAccessory Structures of the Eye Lacrimalapparatus Lacrimal gland produces lacrimalSlide 2003 Pearson Education, Inc. publishing as Benjamin Cummingsproduces lacrimalfluid Lacrimal canals drains lacrimalfluid from eyesFigure Structures of the EyeAccessory Structures of the Eye Lacrimal sac provides passageof lacrimal fluidtowards nasalcavitySlide 2003 Pearson Education, Inc. publishing as Benjamin Cummingscavity Nasolacrimal duct empties lacrimalfluid into the nasalcavityFigure of the Lacrimal ApparatusFunction of the Lacrimal Apparatus Properties of lacrimal fluid Dilute salt solution (tears) Contains antibodies and lysozymeSlide 2003 Pearson Education, Inc.

3 Publishing as Benjamin Cummings Contains antibodies and lysozyme Protects, moistens, and lubricates theeye Empties into the nasal cavityExtrinsic (External) Eye MusclesExtrinsic (External) Eye Muscles Muscles attach to the outer surface of theeye Produce gross eye movements and make itpossible to follow moving objectsSlide 2003 Pearson Education, Inc. publishing as Benjamin CummingsFigure of the EyeStructure of the Eye The wall is composed of three tunics coatswhile the interior is filled with fluids called humors Fibrous tunic (sclera) outside layer Choroid Slide 2003 Pearson Education, Inc. publishing as Benjamin Cummings Choroid middlelayer Sensorytunic insidelayerFigure Fibrous TunicThe Fibrous Tunic Sclera White connective tissue layer Seen anteriorly as the white of the eye CorneaSlide 2003 Pearson Education, Inc. publishing as Benjamin Cummings Cornea Transparent, central anterior portion Allows for light to pass through Repairs itself easily The only human tissue that can be transplantedwithout fear of rejection no blood vesselsChoroid LayerChoroid Layer Blood-rich nutritive tunic Dark pigment prevents light from scatteringinside the eye Modified interiorly into two structuresSlide 2003 Pearson Education, Inc.

4 Publishing as Benjamin Cummings Ciliary body smooth muscle to which the lendsis attached Iris Pigmented layer that gives eye color Pupil rounded opening in the iris for light toenterSensory Tunic (Retina)Sensory Tunic (Retina) Contains receptor cells (photoreceptors) Rods Cones Signals pass from photoreceptors via aSlide 2003 Pearson Education, Inc. publishing as Benjamin Cummings Signals pass from photoreceptors via atwo-neuron chain Bipolar neurons Ganglion cells Signals leave the retina toward the brainthrough the optic nerveNeurons of the RetinaNeurons of the RetinaSlide 2003 Pearson Education, Inc. publishing as Benjamin CummingsFigure of the Retina and VisionNeurons of the Retina and Vision Rods Most are found towards the edges of theretinaSlide 2003 Pearson Education, Inc. publishing as Benjamin Cummingsretina Allow dim light vision and peripheral vision Perception is all in gray tonesNeurons of the Retina and VisionNeurons of the Retina and Vision Cones Allow for detailed color vision in bright light Densest in the center of the retina Fovea centralis area of the retina withSlide 2003 Pearson Education, Inc.

5 Publishing as Benjamin Cummings Fovea centralis area of the retina withonly cones lateral to each blind spot No photoreceptor cells are at the opticdisk, or blind spot where the opticnerve leaves the eyeballCone SensitivityCone Sensitivity There are three types ofcones Different cones aresensitive to differentwavelengthsSlide 2003 Pearson Education, Inc. publishing as Benjamin Cummingswavelengths Color blindness is the resultof lack of one cone type Impulses received at thesame time are interpretedas intermediate colorsFigure Biconvex crystal-like structure Held in place by a suspensory ligamentattached to the ciliary bodySlide 2003 Pearson Education, Inc. publishing as Benjamin CummingsFigure Eye Chamber FluidsInternal Eye Chamber Fluids Aqueous humor Watery fluid found in chamber between thelens and cornea Similar to blood plasmaSlide 2003 Pearson Education, Inc.

6 Publishing as Benjamin Cummings Similar to blood plasma Helps maintain intraocular pressure Provides nutrients for the lens and cornea Reabsorbed into venous blood through thecanal of SchlemmInternal Eye Chamber FluidsInternal Eye Chamber Fluids Vitreous humor Gel-like substance behind the lensSlide 2003 Pearson Education, Inc. publishing as Benjamin Cummings Gel-like substance behind the lens Keeps the eye from collapsing inward byreinforcing it internally Lasts a lifetime and is not replacedInternal Eye Chamber FluidsInternal Eye Chamber Fluids Cataracts form when thelens becomes increasinglyhard and opaque over timerequiring a transplant orspecial glassesSlide 2003 Pearson Education, Inc. publishing as Benjamin Cummingsspecial glasses Glaucoma results when the drainage ofaqueous humor is blocked and pressurewithin the eye increases dramatically andcompresses the delicate retina and opticnerve causing pain and blindnessLens AccommodationLens Accommodation Light must be focusedto a point on the retinafor optimal vision done by the lens The resting eye is setfor distance visionSlide 2003 Pearson Education, Inc.

7 Publishing as Benjamin Cummingsfor distance vision(over 20 ft away) The lens must changeshape to focus forcloser objects accommodationFigure Formed on the RetinaImages Formed on the RetinaSlide 2003 Pearson Education, Inc. publishing as Benjamin CummingsFigure Real image (reversed left to right, andupside down) formed on the retinaVisual PathwayVisual Pathway Photoreceptors ofthe retina Optic nerve Optic nerve crossesSlide 2003 Pearson Education, Inc. publishing as Benjamin Cummings Optic nerve crossesat the optic chiasmato the opposite side Fiber tracts thatresult are the optictractsFigure PathwayVisual Pathway Optic tracts contains fibersfrom the lateral side of theeye on the same side andthe medial side of theopposite eyeSlide 2003 Pearson Education, Inc. publishing as Benjamin Cummings The optic tract fiberssynapse with neurons inthe thalamus, whose axonsform optic radiation Visual cortex of theoccipital lobeFigure ReflexesEye Reflexes Internal muscles are controlled by theautonomic nervous system Bright light causes pupils to constrict throughaction of radial and ciliary muscles photopupillary reflexSlide 2003 Pearson Education, Inc.

8 Publishing as Benjamin Cummings Viewing close objects causes accommodation accommodation pupillary reflex External muscles control eye movement tofollow objects Viewing close objects causes convergence(eyes moving medially (toward nose))The EarThe Ear Houses two senses Hearing Equilibrium (balance) Receptors are mechanoreceptors Slide 2003 Pearson Education, Inc. publishing as Benjamin Cummings Receptors are mechanoreceptors respond to physical forces Although these two sense organs arehoused together in the ear, their receptorsrespond to different stimuli and areactivated independentlyAnatomy of the EarAnatomy of the Ear The ear is divided intothree areas Outer (external)ear MiddleSlide 2003 Pearson Education, Inc. publishing as Benjamin Cummings Middleear Inner (internal)ear Outer and middle ear structures involved inhearing only while inner ear functions in bothequilibrium and hearingFigure External EarThe External Ear Structures ofthe external ear Pinna (auricle) the earSlide 2003 Pearson Education, Inc.

9 Publishing as Benjamin Cummings Externalauditory canalFigure External Auditory CanalThe External Auditory Canal Narrow chamber in the temporal bone Lined with skin Ceruminous (wax) glands are presentSlide 2003 Pearson Education, Inc. publishing as Benjamin Cummings Ceruminous (wax) glands are presentthat secrete earwax cerumen Ends at the tympanic membrane(eardrum) where sound waves hit andcause vibrationsThe Middle Ear or Tympanic CavityThe Middle Ear or Tympanic Cavity Air-filled cavity within the temporal bone Two tubes are associated with the inner ear the oval window and the inferior, membrane-covered round window The opening from the auditory canal isSlide 2003 Pearson Education, Inc. publishing as Benjamin Cummings The opening from the auditory canal iscovered by the tympanic membrane The auditory tube connecting the middle earwith the throat Allows for equalizing pressure during yawningor swallowing This tube is otherwisecollapsedBones of the Tympanic CavityBones of the Tympanic Cavity Three bones spanthe cavity theossicles Malleus (hammer)Slide 2003 Pearson Education, Inc.

10 Publishing as Benjamin Cummings Malleus (hammer) Incus (anvil) Stapes (stirrup)Figure of the Tympanic CavityBones of the Tympanic Cavity Vibrations fromeardrum movethe malleusSlide 2003 Pearson Education, Inc. publishing as Benjamin Cummingsthe malleus These bonestransfer soundto the inner earFigure Ear or Bony LabrynthInner Ear or Bony Labrynth A maze of bony chambers within the temporalbone called the osseous or bony labyrinth Cochlea VestibuleSlide 2003 Pearson Education, Inc. publishing as Benjamin Cummings Vestibule Semicircularcanals Filled with a plasma-like fluid called perilymph Inside is a membranous labyrinth that containsa thicker fluid called endolymphFigure of HearingOrgans of Hearing Organ of Corti Located within the cochlea Receptors = hair cells on the basilarmembrane hearing receptorsSlide 2003 Pearson Education, Inc. publishing as Benjamin Cummingsmembrane hearing receptors Gel-like tectorial membrane is capable ofbending hair cells Cochlear nerve attached to hair cellstransmits nerve impulses to auditory cortexon temporal lobeOrgans of HearingOrgans of HearingSlide 2003 Pearson Education, Inc.