Presentation on theme: "Special Senses Objective 2"— Presentation transcript:
1 Special SensesObjective 2Identify the structures of the eye, and describe their functions.
2 The Eye and Vision 70 percent of all sensory receptors are in the eyes Each eye has over a million nerve fibersProtection for the eyeMost of the eye is enclosed in a bony orbitA cushion of fat surrounds most of the eye
3 Protective Structures of the Eye EyelidsEyelashesFigure 8.1b
4 Accessory Structures of the Eye Ciliary glands – modified sweat glands between the eyelashesFigure 8.1b
5 Accessory Structures of the Eye ConjunctivaMembrane that lines the eyelidsConnects to the surface of the eyeSecretes mucus to lubricate the eye
6 Accessory Structures of the Eye Lacrimal apparatus – Secrete TearsLacrimal gland – produces lacrimal fluidLacrimal canals – drains lacrimal fluid from eyesFigure 8.1a
7 Function of the Lacrimal Apparatus Properties of lacrimal fluidDilute salt solution (tears)Contains antibodies and lysozymeProtects, moistens, and lubricates the eyeEmpties into the nasal cavity
8 Extrinsic Eye Muscles Muscles attach to the outer surface of the eye Produce eye movementsFigure 8.2
9 Structure of the Eye The wall is composed of three tunics Fibrous tunic – outside layerChoroid – middle layerSensory tunic – inside layerFigure 8.3a
10 The Fibrous Tunic Sclera White connective tissue layer Seen anteriorly as the “white of the eye”CorneaTransparent, central anterior portionAllows for light to pass throughRepairs itself easilyThe only human tissue that can be transplanted without fear of rejection
11 Choroid Layer Blood-rich nutritive tunic Pigment prevents light from scatteringModified interiorly into two structuresCilliary body – smooth muscle that changes the shape of the lensIris – contracts/expands to let light inPigmented layer that gives eye colorPupil – rounded opening in the iris
12 Sensory Tunic (Retina) Contains receptor cells (photoreceptors)RodsConesSignals leave the retina toward the brain through the optic nerve in the back of the eye
13 Compare and contrast the structure and functions of rods and cones. Special SensesObjective 3Compare and contrast the structure and functions of rods and cones.
14 Neurons of the Retina and Vision RodsMost are found towards the edges of the retinaAllow dim light vision and peripheral visionPerception is all in gray tones
15 Neurons of the Retina and Vision ConesAllow for detailed color visionDensest in the center of the retinaFovea centralis – area of the retina with only conesNo photoreceptor cells are at the optic disk, or blind spot
17 Cone Sensitivity There are three types of cones Different cones are sensitive to different wavelengthsColor blindness is the result of lack of one cone typeFigure 8.6
18 Trace the pathway of light through the retina. Special SensesObjective 4Trace the pathway of light through the retina.
19 Lens Biconvex crystal-like structure Held in place by a suspensory ligament attached to the ciliary bodyFigure 8.3a
20 Internal Eye Chamber Fluids Aqueous humorWatery fluid found in chamber between the lens and corneaSimilar to blood plasmaHelps maintain intraocular pressureProvides nutrients for the lens and corneaReabsorbed into venous blood through the canal of Schlemm
21 Internal Eye Chamber Fluids Vitreous humorGel-like substance behind the lensKeeps the eye from collapsingLasts a lifetime and is not replaced
22 Lens AccommodationLight must be focused to a point on the retina for optimal visionThe eye is set for distance vision (over 20 ft away)The lens must change shape to focus for closer objectsFigure 8.9
24 Visual Pathway Photoreceptors of the retina Optic nerve Optic nerve crosses at the optic chiasmaOptic tractsThalamus (axons form optic radiation)Visual cortex of the occipital lobeFigure 8.11
25 Eye ReflexesInternal muscles are controlled by the autonomic nervous systemBright light causes pupils to constrict through action of radial and ciliary musclesViewing close objects causes accommodationExternal muscles control eye movement to follow objectsViewing close objects causes convergence (eyes moving medially)