Chapter 8 jk - jkaser.com

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.

2 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. 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.

3 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.

4 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.

5 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.

6 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.

7 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. 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.

8 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. 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.

9 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.

10 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.