Sensory Organs The Eye Free Powerpoint Templates

Sensory relationships All of our senses respond to stimuli in the environment Each sense has its own specific organ In each sense organ there are specific sense receptors cells The role of sense receptors is to register stimuli in the environment and to provide the other parts of the body with information about these stimuli

Sense organs (Fill out the following table) Perception Taste Tongue Salty, sweet, spicy, bitter

Sense organs Sense Organ Perception Taste Tongue Salty, sweet, spicy, bitter Smell Nose Nice odours, foul odours Hearing Ear Quiet, loud (intensity), tone Feeling Skin Soft, rough, smooth (texture) Seeing Eye Light/dark Colours, movement

The Eye The eye is the organ of sight Our eyes enable us to appreciate: Lines colours light properties movements of the things around us The eye is made up of a system of 4 membranes and 3 transparent substances

Anatomy of the Eye Membranes: - 1 membrane covers the front part of the eye  the cornea - it is transparent - under the cornea are: 1) The iris : the coloured ring of the eye 2) The pupil: the central portion of this ring (black dot) The eye is the organ of sight, a nearly spherical hollow globe filled with fluids (humors). The outer layer or tunic (sclera, or white, and cornea) is fibrous and protective. The middle tunic layer (choroid, ciliary body and the iris) is vascular. The innermost layer (the retina) is nervous or sensory. The fluids in the eye are divided by the lens into the vitreous humor (behind the lens) and the aqueous humor (in front of the lens). The lens itself is flexible and suspended by ligaments which allow it to change shape to focus light on the retina, which is composed of sensory neurons.

Anatomy of the Eye - the other 3 membranes line the posterior (back) of the eye They are all different: The sclera (outermost membrane) - rigid, gives the eye its shape The choroid (middle membrane) - provides nourishment for the eye The retina (innermost membrane) - active nervous membrane = receiver of stimuli

Anatomy of the Eye Transparent Substances: Found inside the eye The lens Aqueous humour - located between the cornea and lens - a liquid made up of water and minerals Vitreous humour - located between the lens and the retina - jelly like substance The eye is the organ of sight, a nearly spherical hollow globe filled with fluids (humors). The outer layer or tunic (sclera, or white, and cornea) is fibrous and protective. The middle tunic layer (choroid, ciliary body and the iris) is vascular. The innermost layer (the retina) is nervous or sensory. The fluids in the eye are divided by the lens into the vitreous humor (behind the lens) and the aqueous humor (in front of the lens). The lens itself is flexible and suspended by ligaments which allow it to change shape to focus light on the retina, which is composed of sensory neurons.

What path does light take as it travels through the eye? 1) Light must pass through a number of transparent media before it reaches the nerve cells of the eye. Where are these located?  On the retina. 2) Label these different structures in the order that light passes through: vitreous humour, lens, retina, cornea, aqueous humour 1) cornea  2) aqueous humour  3) lens  4) vitreous humour  5) retina

The Path Light Takes in the Eye Light passes through and is bent by the cornea and then the lens Images appear inverted on the retina When looking at near-by objects = the lens curves and thickens When looking at far object = the lens flattens The reflex that causes the lens to change shape is called the accommodation reflex near-far sightedness

Flattened lens thickened lens

Light rays enter the eye and focus on the retinal nerve cells (neurons) These retinal nerve cells then change the light waves that strike them into nerve impulses that are carried along the optic nerve to the visual center of the brain Optic nerve Nerve tissue formed by the axons of the retinal cells Transmits nerve impulses form the retina to the optical centre of the brain Examples of retinal nerve cells: Rods = detect light and dark Cones = detect colour

Visual pathway

What is the role of the brain in vision? It is only when the center for vision in the brain (in the occipital lobe) is stimulated that a person has any visual sensation Therefore, it is not only the eyes alone that allow us to “see” but also the brain.

Match the following words with the correct term Eye Retina Optic Nerve Brain Transformer Analyzer Conductor Receiver

The Chain Reaction Involved in Vision

Recall the blindspot?

Lenses Convex lenses Concave lenses Also called converging Cause light to converge on a focal point This is like the actual lens inside your eye Concave lenses Also called diverging lens Cause light to diverge from a focal point

Eye Disorders Hyperopia (far-sighted): Myopia (near-sighted): The image is focused behind the retina Close objects are blurred Requires CONVEX lenses Myopia (near-sighted): The image is focused in front of the retina Distant objects are blurred Requires CONCAVE lenses Presbyopia : loss of elasticity of the lens (usually in old age) Long eyeball Myopia Short eyeball Hyperopia -Normal vision occurs when light is focused directly on the retina rather than in front or behind it. A person with normal vision can see objects clearly near and faraway. -Nearsightedness results in blurred vision when the visual image is focused in front of the retina, rather than directly on it. It occurs when the physical length of the eye is greater than the optical length. For this reason, nearsightedness often develops in the rapidly growing school-aged child or teenager, and progresses during the growth years, requiring frequent changes in glasses or contact lenses. A nearsighted person sees near objects clearly, while objects in the distance are blurred. -Farsightedness is the result of the visual image being focused behind the retina rather than directly on it. It may be caused by the eyeball being too small or the focusing power being too weak. Farsightedness is often present from birth, but children can often tolerate moderate amounts without difficulty and most outgrow the condition. A farsighted person sees faraway objects clearly, while objects that are near are blurred.

Common visual defects

Normal View Myopia Hyperopia Near Sighted Far Sighted

OPTICAL ILLUSIONS

Your brain has learned certain tricks throughout your life Your brain has learned certain tricks throughout your life. These are “shortcuts” or easier ways to analyze stimuli. It is possible to use these shortcuts to trick your brain. TED Talk

Which line is longer?

Are these lines bent, or straight?

Which man is bigger?

What about these doors?

Also, your brain has learned that things can only be one thing… When something which can be seen as two different things appears out of context, your brain will switch from seeing one, to the other… but not both at the same time.

Your brain fills in certain missing information that is absent because of your blind spot. Sometimes it fills in the wrong information

What`s wrong?

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http://www.hhmi.org/senses/ http://www.nei.nih.gov/education/visionschool/schintro/VISIONSchoolProgram.pdf

Cataract Surgery Video Online http://www.cureblindness.org/cataracts/video.html Lasik eye surgery animation http://www.mayoclinic.com/health/lasik-eye-surgery/MM00607 You tube: http://www.youtube.com/watch?v=Y-TUMw1FTmY

FYI: Nocturnal vision (tapetum)

Nocturnal Vision http://www.pbs.org/wgbh/nova/leopards/nocturnaleye.html http://www.pbs.org/wgbh/nova/leopards/nightvision.html

Visual Acuity Tests & Snellen Chart http://www.mdsupport.org/snellen.html Visual acuity (vision) is determined in each eye using the Snellen Chart. The letters for normal vision (20/20) are 3/8-inch tall, viewed at 20 feet. People with normal vision can read these letters. A refraction test may also be performed where the doctor puts several lenses in front of the eyes to determine if glasses are needed. Visual acuity (vision) is determined in each eye using the Snellen Chart. This chart consists of random letters of different sizes. The letters for normal vision (20/20) are 3/8-inch tall, viewed at 20 feet. People with normal vision can read these letters. A refraction test may also be performed where the doctor puts several lenses in front of the eyes to determine if glasses are needed. To Test Visual Acuity Position the patient 20 feet in front of the Snellen eye chart Have the patient cover one eye at a time with a card. Ask the patient to read progressively smaller letters until they can go no further. Record the smallest line the patient read successfully (20/20, 20/30, etc.) Repeat with the other eye.

Snellen Chart When checking visual acuity, one eye is covered at a time and the vision of each eye is recorded separately, as well as both eyes together. In the Snellen fraction 20/20: the first number represents the test distance, 20 feet. The second number represents the distance that the average eye can see If a person sees 20/40, at 20 feet from the chart that person can read letters that a person with 20/20 vision could read from 40 feet away.