Download Nervous System Dissection Labs BIO 2514 Experiment : Cow Eye

Nervous System Dissection Labs BIO 2514
Experiment : Cow Eye Dissection
Survival depends on the meaningful interpretation of stimuli. The five senses (taste, sight, touch,
sound, smell) are completely dependent on the nervous system. Nearly 70% of the sensory receptors
in the body are found in the eye. Photoreceptors are specialized cells that sense and encode light
patterns, from which the brain can construct images. The cow eye is quite similar to the human eye.
Through this lab, you will gain an understanding of how the eye forms images and communicates with
the brain through dissection and examination of the cow eye.
Definitions
Aqueous Humor: Aqueous fluid that provides shape to the front eye (watery liquid)
Choroid: The middle layer of the eye that contains blood vessels
Cornea: A clear protective layer that refracts light
Fovea Centralis: Contains photoreceptors used for color interpretation
Iris: The colored muscle of the eye that regulate pupil size to protect the retina from light
Lens: Structure that refracts light onto the retina
Optic Nerve: Pathway for impulses to the occipital lobe of the brain
Pupil: Similar to a condenser on a microscope, this muscle allows light into the eye
Retina: Posterior portion of eye that contains photoreceptors (rods and cones)
Sclera: The white, outermost protective part of the eye
Vitreous Humor: A viscous liquid that provides shape to the eye
Materials
Cow eye
Dissection tools
Protective glasses
Face Mask
Protective Gloves
209
Note: In a living creature, the lens is clear and flexible; after preservation, it may have yellowed
and become more rigid.
Procedure
1. Carefully observe the eye and remove any fat or extrinsic muscle with the scalpel. After removing
this tissue, the sclera and optic nerve should be visible.
2. Make an incision with the scalpel in the cornea until the aqueous humor (a clear liquid) is released.
3. Make an incision with the scalpel through the sclera around the middle of the eye so that one
half will have the anterior features of the eye (the cornea, lens, iris, and ciliary body) and the
other half will contain the posterior features (most noticeably where the optic nerve is
attached to the eye).
4. Place posterior half with the cornea on the dissection tray.
5. Using a scalpel, slice through the cornea.
6. Using forceps, remove the iris, located between the cornea and the lens.
7. The anterior half of the eye contains the lens. Notice the vitreous humor, the clear gel that
surrounds the lens.
8. Using the scalpel and forceps, remove the lens from the specimen.
9. Place the lens on a piece of paper with writing on it.
10. Remove the vitreous humor from the anterior half of the eyeball and note the blood vessels on
the anterior wall. This is the retina.
11. Using gloved fingers, move the retina around the eye ball and sense where the optic nerve is
connected to this tissue.
12. Use forceps to gently lift the retina off the inside wall of the eye. You should observe a colorful,
iridescent, shiny tissue – the choroid coat (vascular tunic).
13. Turn the eye over and observe where the nerve enters the eyeball.
210
Experiment : Sheep Brain Dissec1on
The brain is the master control center of the body. This experiment will guide you through a dissection
of a preserved sheep brain in order to familiarize yourself with the structures of the brain.
Materials
Sheep Brain
Dissection Tray
Dissection Tool Set
Protective gloves
Safety Glasses
Face Mask
Procedure
1. Examine the external features of the sheep brain. Compare the areas of the brain (cerebrum,
brain stem, cerebellum). From a lateral view, locate the frontal, parietal, occipital and temporal
lobes.
2. Locate the central sulcus.
3. Place the brain with the ventral side-down for a dorsal view of the organ. Note the pia mater
extending downward into the sulci on the superior and lateral surfaces. Observe the dura mater,
the arachnoid mater, and blood vessels on the surface of the brain. The two cerebral hemispheres
are separate by a longitudinal fissure. Each hemisphere is divided into four major
lobes, as shown in the figure below. The frontal lobes are directly cephalic from the cruciate
fissure (may be difficult to locate). Moving caudally, you will cross the parietal lobe and then
the occipital lobe. A slight bulge superior to the hippocampus gyrus is the temporal lobe,
which is likely ill-defined.
4. Turn the brain over to examine its inferior aspect.
5. View the club-like olfactory bulbs on the inferior surface of the frontal lobes of the cerebral
hemispheres.
6. Locate the optic nerve. Find the optic chiasm, the x-shaped structure where fibers from each
optic nerve cross over to the opposite side.
7. Find the pituitary gland (posterior to the chiasm).
8. Locate the midbrain, pons, and medulla oblongata posterior to the optic chiasm.
9. Place the brain with the ventral side down.
10. Using a scalpel, make a midsagittal cut along the longitudinal fissure and midline of the cerebellum
to create left and right halves. Note the tree-like arrangement of the white matter that
is the cerebellar cortex.
11. Observe the exposed corpus callosum, the prominent collection of axons that extends along
the medial face of the cerebral hemispheres.
12. Just outside the third ventricle is the pineal body.
13. Identify the thalamus and hypothalamus (part of the diencephalon)
14. Slice a small cross section of the spinal cord. Note the classic butterfly-shaped section of the
gray matter and the dorsal and ventral roots on the outside of the spinal cord.
16. Dispose of the brain specimen appropriately and disinfect your work area and dissection tools.
Wash your hands when complete.
UPLOAD PICTURES and LABELS
1.
In your dissection pan, take a picture of the anterior and posterior dissected cow eye cavities
with as many labels as you can identify. Upload this picture to the cow eye dissection upload
area.
2. In your dissection pan, take a picture of the midsagittal half of your sheep brain with the labels:
cerebellum, cerebral hemispheres, corpus callosum, diencephalon, mid brain, medulla
oblongata, and pons. Locate and label spinal cord that you see on your sheep brain. Upload this
picture to the sheep brain dissection upload area.