FREE ESSAY ON DISSECTION AND ISOLATION OF A FROGS CNS

DISSECTION AND ISOLATION OF A FROGS CNS

Dissection of an adult bullfrog's central nervous system (CNS)
Experiment consists of the dissection and analyzation of a bullfrog's nervous system.
Dissection consists of the isolation of the CNS consisting of the brain and spinal cord.
It also consists of analyzing the nervous tissue under the microscope. 
Materials needed: frog, scalpel, razor blade, dissecting tray, pins, forceps, scissors,
microscope, slides, slide covers, water, blue dye, diagram of frog's brain, paper towel.
The bullfrog's CNS is composed of the brain, which is further divided into the olfactory
bulb, cerebrum, optic tract, optic lobe, pituitary gland, and the cerebellum. Also
contained within the CNS is the spinal cord which in contained within the spine The brain
was about an inch in length and ? of an inch in diameter. The spinal cord was about 2.5
inches in length and the diameter of the spine was about 1/8 of an inch. The cerebellum
in the frogs brain is very small in comparison to the rest of the brain and also to the
size of the cerebellum in other animals compared to the size of their brains.
Place the frog in the dissecting tray so the ventral section faces upwards with the head
pointing away from you. This will allow for easier access to the CNS since you don't have
to cut through the skull. Pin each of its legs down to the tray using the pins. Using the
scalpel start the incision at the base of the jaw. This will be a superficial cut just
enough to cut through the skin. Pull the scalpel in a caudal direction towards the tail.
After you've done this make another incision lateral to where you started the first one
and another one where you ended the cut. Pull the skin back and either cut it off or pin
it down. Muscle of the breastbone and abdomen will be exposed. Using the scissors make a
deep cut through this, again cutting in a caudal direction to the tail. Cut off the arms
of the bullfrog and remove all of the muscle mass. You must now remove the lower jaw of
the frog. Using the scissors cut through the area where the jaw connects to the skull.
This will expose a membrane covering the brain. Make a small superficial cut using the
scalpel in this membrane. Using the scalpel, lift up the cut and then use the scissors to
remove all of this membrane. The brain should now be exposed. Now you must remove all the
internal organs. There may or may not be an egg sac, if there is try not to puncture it
when you remove it otherwise it can get messy, but if you do it is ok. Remove all the
internal organs until you can see the spinal cord. Now that you have isolated the nervous
system you can remove pieces of it to view under the microscope. To do this, first
identify the section you are going to remove using a diagram of the brain such as the one
shown in latter pages or one out of a lab manual. Using a razor blade remove a small
section of the brain. Set this on the table and using the blade cut away as thin of a
section as you can. Place a drop or two of water on a slide and place the thin section of
brain tissue on the slide. Place a cover slip over this. Put 1-2 drops of the dye right
next to the cover slip. Place the paper towel on the side opposite where you placed the
dye. This should pull the dye through and stain the tissue. After you've done this place
2-3 drops of water on the same side you placed the dye and pull that through with the
paper towel to remove the excess dye. Place this under the microscope and observe. Any
thin red, squiggly lines are vascular tissue. The stringy bundles of fiber would be the
nerve tracks. After doing all of this you should clean up! Remove the pins and rinse
those off. Throw away the frog and all the large pieces of it. Clean off the tray and let
it air dry. 
The intact, isolated brain matter appeared to be gray, signifying that it was
unmyelinated nerve tissue. It was narrow and each part of the brain was somewhat easily
distinguishable. Under the microscope the tissue had easily distinguishable nerve fibers
and in some cases it contained vascular tissues distinguishable by the small capillaries.
The tissue felt smooth and rubbery. It was somewhat soft yet firm. Based on my
observations from the microscope I saw how the soma and dendrites and axons all went
together to form nervous tissue. 
Bibliography
http://k-2.stanford.edu/creatures/InfoFrames/CNS.1.1.html - various information
http://www.neurocomputing.org/comparative_neuroanatomy.htm - picture of frog's brain