Reasons to Use the Dissection Video and - PowerPoint Presentation

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Reasons to Use the Dissection Video and Accompanying PowerPoint Presentation Reduce the number of specimens used by a class Increase the quality of the dissection for the students Review opportunity, increasing the learning experience for the studentsStudent unable to dissect due to pregnancy or hypersensitivity to the preservatives Student chooses not to dissect due to ethical/moral reasons

Dissection 101:

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Dissection 101:As an educator you are responsible for the implementation of the dissection activity described in the video and PowerPoint. You must have safety procedures and rules established for your classroom and make sure all of the students follow the rules to ensure a safe environment. South Dakota Public Broadcasting and Dakota State University cannot in any way be responsible or liable for any injury as a result of performing the described dissection. Complete the dissection if you feel it is appropriate and safe for your individual class. Have fun and stay safe!

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Safety Considerations

Age appropriate activity for the children in your care

Safety Data Sheet (SDS) available for accident reference

Poison control number/phone readily available

Latex free gloves, eye protection and apron/lab coat

Eyewash station, shower and sink

Sharp instruments (cut away from self and others)

Sharps and specimen(s) disposal

Encourage students to report all accidents

Basic science laboratory rules (strictly enforced)

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Dissection 101:

Cow Eye

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ClickExterior of the Cow Eye External Orientation

Side view

Cornea: Anterior protective covering of the eye; transparent allowing light to enter; appears cloudy due to preservation process

Essential Fat: White/grey in color; provides protection/cushion

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ClickGetting Started

Use a scissors or scalpel to remove the excess fat from the eyeball (capsule); always cut away from yourself

The extrinsic muscles, which are used to move the eye, should also be removed (appear marbled, similar to the look and texture of a raw steak or roast)

Do not remove the optic nerve

Dissection 101:

Cow Eye

Optic nerve

Extrinsic muscles

Student Cuts:

YouTube

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Optic nerve, chord-like structure protruding from the back of the eye; carries nervous signal from the retina to the posterior (occipital) region of the brain

Dissection 101:

Cow Eye

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Dissection 101:

Cow Eye

Continue using a scissors or scalpel to remove the fat, connective tissue and muscle from the back of the eye

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Dissection 101:

Cow Eye

Use the point of a scissors or a scalpel to make an incision through the layers of the eye capsule (similar to figure 1); there are three layers from the exterior: sclera (whitish/grey, continuous with the transparent cornea), choroid (thin dark black layer), and the retina (thin greyish/pink layer)

Use a scissors to dissect the entire circumference of the capsule (see figure 2); do not cut toward the cornea

Figure 1

Figure 2

Student Cuts:

YouTube

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Dissection 101:Cow Eye

Using steady pressure, pull the two sections slowly apart

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Vitreous humor: Jelly-like

material, provides

shape/support for the eyeball; helps hold retina in place

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Dissection 101:Cow Eye

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Many times the greyish/pink retina is attached to the vitreous humor, carefully remove/scrape the retina from the vitreous humor and lay it on the back of the eyeball.

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Vitreous humor removed, retina against the

back of the eye

Student Cuts:

YouTube

Using your finger or a forceps, carefully scrape any of the jelly-like vitreous humor that is attached to the front of the eye

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Dissection 101:Cow Eye

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Retina: Nervous tissue, location of the photo receptors (cones for sharp color vision and rods for night, dark/shaded vision); light energy converted to electrical impulse; the retina is continuous with the optic nerve which leaves the back of the eye carrying the nervous impulse to the brain

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Dissection 101:Cow Eye

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Retina

Optic nerve

Optic disc (blind spot): location on the retina where the retina attaches to the optic nerve, sight does not occur at this location because there are no cones or rods present

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Dissection 101:Cow Eye

Many laboratory books label the fovea centralis/macula, which is the location in eye where the sharpest vision occurs; the fovea centralis/macula is dense with cones and is the location of focus during lighted conditions, like reading (in humans); the fovea centralis/macula appears as a depression in the retina, but it is very difficult to find

(Note: know the function for the quiz, identification is not required )

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Dissection 101:Cow Eye

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Choroid: Dark layer of the eye, rich with blood vessels; reduces scattering of light and provides nourishment for the eye

Choroid shown folded

forward in this image

Many vertebrates like the cow

, deer,

and cat have a tapetum lucidum which is an iridescent, reflective layer found on the choroid; the tapetum lucidum aids in the reflection of light toward the retina, increasing the ability to see at night; the human choroid does not have a tapetum lucidum

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Dissection 101:Cow Eye

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Sclera: Tough protective outer layer of the eye which gives the eyeball its shape; the white part of the human eye; continuous with the transparent cornea; the sclera has blood vessels (may appear bloodshot); the cornea does not have blood vessels

Cornea

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Dissection 101:Cow Eye

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Anterior Identification

Using a dissection probe, carefully remove the lens from the anterior of the eye

Lens

Suspensory ligaments: Hold

the lens in place, attaches

lens to

ciliary

body

Note: Aqueous humor, a transparent fluid produced by the ciliary body is located between the lens and the cornea; the fluid provides shape for and nourishes the cornea and it also provides nourishment for the lens; the fluid will release as the lens is removed

Student Cuts:

YouTube

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Dissection 101:Cow Eye

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Using a dissection probe, carefully remove the choroid,

ciliary

body, and iris from the anterior of the eye; these structures will be removed as one unit

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Dissection 101:Cow Eye

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Cornea: Anterior protective covering of the eye; transparent allowing light to enter; appears cloudy due to preservation process; lacks blood vessels, nourished by aqueous humor; continuous with sclera

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Dissection 101:Cow Eye

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Lens: Biconvex structure that focuses light on the retina through a process called accommodation

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Dissection 101:Cow Eye

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Lens

Lens

Far Object

Close Object

Retina

Retina

Muscles of the ciliary body contract toward the lens (Figure 1), resulting in less pull on the lens. The lens bulges to its natural form resulting in the light rays bending more for closer objects. The muscles of the ciliary body relax pulling away from the lens causing the lens to flatten for distant objects (Figure 2).

Ciliary Body

Iris

Pupil

Figure 2

Figure 1

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Dissection 101:Cow Eye

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Iris: Structure of the eye which controls the size of the opening into the eye which is called the pupil. The pupil gets larger when the radial muscles of the iris contract in dim light.

The circular/sphincter

muscles of the iris contract to reduce the size of the pupil for brighter light. The iris is the colored structure of the human eye.

Pupil: Opening of the eye, allows light to enter. The diameter of the opening is controlled by the iris. The pupil is the dark center of the eye; the pupil is black because light enters but it does not leave.

Ciliary body

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Dissection 101:Cow Eye

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Microscopic View of the Iris, Ciliary Body and Pupil

Anterior view, closest to the cornea

Posterior view, closest to the lens

Ciliary body

Iris

Pupil

Pupil

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Dissection 101:Cow Eye

Retina

Optic nerve

Choroid with tapetum lucidum

Iris

Pupil

Cornea

Sclera

Lens

Vitreous humor

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Review Main Structures

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Dissection 101:

Produced by Dakota State University

and South Dakota Public Broadcasting

Cow Eye