Dissection Frogs Central Nervous System
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 ¾ 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