Download Why dread a bump on the head? June 2012 Lesson 5: What

Why dread a bump on the head?
Lesson 5: What happens to neurons after TBI?
June 2012
Neurobiology Technique #1
ELECTROPHYSIOLOGY
Neurobiology Technique #2
ANIMAL BEHAVIOR
Electrophysiology is a way of observing and recording the electrical
activity of cells. This is a particularly important technique for
neuroscience, since neurons generate electrical signals in order to
pass signals from one part of the body to another, or from one cell
to another. There are many different electrophysiological
techniques for different situations, but a basic technique involves
inserting a very sharp, fine electrode directly into a single cell. This
electrode measures electrical charge inside the cell, and how it
changes over time. If an electrical signal passes through the cell, the
charge measured by the electrode will rapidly change. Electrodes
can also be placed near groups of cells, to measure changes in
charge that happen when all the cells create electrical signals at the
same time. These types of experiments can be done in living
animals during surgical procedures where the skull is opened to give
access to the brain. They can also be performed using slices of brain
tissue that are kept alive for limited amounts of time. As cells in the
slice begin to die, fewer and fewer cells will produce signals; only
living cells will produce normal changes in electrical charge.
Researchers may have many different reasons for observing and
measuring the behavior of animals. Many experimental treatments,
as well as illnesses and conditions, can affect the health and
functioning of the brain. A natural consequence of changes in the
brain is often an alteration in the behavior of the animal.
Researchers can measure simple aspects of behavior, such as
response to odors, lights, sounds, and other stimuli. Animals are
often moved to a test environment where they can be easily
observed or video-recorded. The animal is then exposed to the
stimulus (the light, sound or other experience) and its response
(startling, pricking ears, standing still) is noted. More complex tests
of behavior include studying things like learning; for example, the
animal might be trained to associate a stimulus with a reward of
food, or a frightening event such as an unpleasant noise. The
animal’s ability to respond in a normal way or be able to learn
different associations can tell the researcher about the health of
different regions of the brain, and whether those different regions
are functioning properly.
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Why dread a bump on the head?
Lesson 5: What happens to neurons after TBI?
June 2012
Neurobiology Technique #3
DNA Gel Electrophoresis
Neurobiology Technique #4
Cell Culturing
Researchers use gel electrophoresis to examine the length of DNA
that they extract from biological material including brain tissue. This
research method begins with DNA that has been extracted from a
small piece of tissue that is removed from the organism being
studied. The researcher inserts the DNA sample into holes in one
end of a square block made of Jell-O-like material, called a “gel”. An
electrical current is passed through the gel so it has a negatively
charged side and positively charged side. The DNA, which has a
negative charge, moves from where it starts (the negative side) in
the gel toward the opposite (positive) side of the gel. As the DNA
moves forward in a line through the gel, the fragments of DNA in
the sample separate based on how long they are. After waiting a set
amount of time, the researcher can see how far the fragments of
DNA in the sample have traveled to estimate how long the pieces of
DNA are. The ones that travelled the farthest are the smallest
fragments of DNA. The DNA fragments that stayed nearest where
they started are the longest pieces of DNA. Pieces of similar length
will cluster together and make dark areas, called bands. The bands
of DNA from the tissue sample are compared to bands created by
DNA fragments of known lengths. In this way, the researcher can
determine the lengths of the fragments in the DNA sample that was
taken from the organism’s tissue.
Cell culturing allows researchers to easily view properties of certain
cell types that would be hard to see in a whole living organism or in
pieces of tissue. A piece of tissue must be dissected from the
organism and then processed quickly, so that the cells are not killed
by the stress of being removed from the organism. The piece of
tissue is treated with proteins or chemicals that can break down the
substances that hold tissue together, so that the individual cells
begin to separate out. The cells are then gently swirled so that they
separate completely from each other. All of these steps must be
done carefully, so that the cells are not damaged too much. The
cells can then be transferred to a dish coated with proteins that
help the cells attach to the surface, and a solution called growth
medium is added. The growth medium contains the sugars,
nutrients, oxygen and moisture that the cells would usually get from
the blood, lymph or other fluid in the body needed to survive. The
cultured cells can be kept for days or weeks, and can be examined
and photographed or videotaped using a microscope to monitor any
growth, change in shape, or response to experimental treatments
that are added to the medium. However, even when great care is
taken not to damage the cells during the culturing procedure, and
with careful medium changes, the cells will gradually die, limiting
the length of time during which experiments on these cells can be
performed.
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Why dread a bump on the head?
Lesson 5: What happens to neurons after TBI?
Technique
Claim
June 2012
Evaluating Neurobiology Techniques
Evidence
This technique
WILL / WILL NOT
#1
Provide additional evidence
Electrophysiology
about the occurrence of
apoptosis and necrosis in
brain tissue after TBI.
This technique
WILL / WILL NOT
#2
Animal Behavior
Provide additional evidence
about the occurrence of
apoptosis and necrosis in
brain tissue after TBI.
This technique
#3
DNA Gel
Electrophoresis
WILL / WILL NOT
Provide additional evidence
about the occurrence of
apoptosis and necrosis in
brain tissue after TBI.
This technique
WILL / WILL NOT
#4
Cell Culturing
Provide additional evidence
about the occurrence of
apoptosis and necrosis in
brain tissue after TBI.
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Reasoning