the neuroscience of traumatic brain injury - project … · the neuroscience of traumatic brain...
TRANSCRIPT
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Why dread a bump on the head? The Neuroscience of Traumatic Brain Injury
Lesson 5: What happens to neurons after TBI?
I. Overview In this lesson students learn what happens at the neuronal level after a traumatic brain injury by looking
at two modes of cell death: necrosis and apoptosis. Students begin by studying micrographs of individual
neurons that are undergoing two different types of cell death. They are guided in making key
observations that allow them to identify morphological characteristics of each pathway. Students then
go on to analyze gel electrophoresis results from DNA samples taken from injured brain tissue. Through
this activity, they learn about the “step ladder” pattern of apoptotic DNA that has been systematically
cleaved and the “smear” pattern from necrotic cells in which the DNA degrades more randomly.
Connections to driving question In this lesson students learn about the impact of TBI at the neuronal level. They discover the two
different types of cell deaths that can result from a brain injury.
Connections to previous lessons In in first part of the unit, students learn about the different types of TBI and the consequences of TBI at
the macro level. In the previous lesson, students began to focus in on the cellular level by first learning
about neurons and neuronal communication. This lesson builds on these ideas by discussing how
traumatic brain injury affects the cells that make up the brain.
II. Standards
National Science Education Standards Content Standard C: The Cell
Cell functions are regulated. Regulation occurs both through changes in the activity of the
functions performed by proteins and through the selective expression of individual genes. This
regulation allows cells to respond to their environment and to control and coordinate cell
growth and division. (9-12 C: 1/4)
Benchmarks for Science Literacy
The Human Organism: Basic Functions
The immune system functions to protect against microscopic organisms and foreign substances
that enter from outside the body and against some cancer cells that arise within. (6C/H1*)
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Communication between cells is required to coordinate their diverse activities. Cells may secrete
molecules that spread locally to nearby cells or that are carried in the bloodstream to cells
throughout the body. Nerve cells transmit electrochemical signals that carry information much
more rapidly than is possible by diffusion or blood flow. (6C/H3*)
The human body is a complex system of cells, most of which are grouped into organ systems
that have specialized functions. These systems can best be understood in terms of the essential
functions they serve for the organism: deriving energy from food, protection against injury,
internal coordination, and reproduction. (6C/H6** (SFAA))
The Human Organism: Mental Health
Biological abnormalities, such as brain injuries or chemical imbalances, can cause or increase
susceptibility to psychological disturbances. 6F/H2
III. Learning Objectives
Learning Objective Assessment Criteria Location in Lesson
Explain that traumatic brain injury results in two types of cell death, necrosis and apoptosis.
Students are able to explain that necrotic and apoptotic cell death occur upon impact and after a traumatic brain injury
Throughout lesson
Describe and compare/contrast the major characteristics of a neuron undergoing necrosis and a neuron undergoing apoptosis.
Students can describe:
Characteristics of necrosis: swollen cell bodies, chromatin condensation, random DNA fragmentation, and membrane disintegration.
Characteristics of apoptosis: chromatin condensation, cell shrinkage, systematic DNA fragmentation, and formation of compact, spherical apoptotic bodies.
Activity 2
Compare the causes and results of neuronal necrosis and neuronal apoptosis
Students are able to explain:
Neuronal necrosis is caused by direct trauma/injury to the cells and elicits an inflammatory response.
Apoptosis is a mode of programmed (modulated by the cell) cell death that is initiated by the cell when it receives certain signals and the process does not elicit an inflammatory response.
Activities 2 & 3
Explain the experimental technique of gel electrophoresis and the main principles behind how it works
Student explanations include:
Gel electrophoresis is a technique used to sort DNA fragments by size.
DNA is negatively charged so an electrical current is used to move the DNA through
Activity 3
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the gel.
The fragments of DNA are separated by size because smaller pieces are able to move more easily through the gel whereas larger fragments do not move as far.
The smaller fragments of DNA move the farthest and the larger fragments stay nearest the starting point at the well.
Describe and explain the results of a gel electrophoresis of DNA from necrotic and apoptotic cells
Students can explain:
A gel electrophoresis of DNA from an apoptotic cell shows a “ladder” pattern because the DNA is systematically cleaved at 180 base pairs (and multiples thereof).
Explain that a gel electrophoresis of DNA from a necrotic cell shows a “smear” pattern because the DNA is degraded more randomly.
Activity 3
IV. Adaptations/Accommodations In this lesson, students have many opportunities to think carefully through the science content. If
students have special needs and require more time, consider dedicating more time to these activities.
During discussions, you can ask students to initially write their responses so that they have more time to
think and respond.
Many of the activities within this lesson require students to recall information from other lessons within
the unit and also from other units that they have likely seen previously. If students struggle with this,
consider adding a vocabulary review before each activity or creating a glossary for the lesson as it
progresses.
The homework readings span different Flesch-Kincaid reading levels. "Apoptosis and Cancer" is 12.1,
"Apoptosis in the Immune System" is 12.6, "Apoptosis and Mitosis" is 13.3, and "Apoptosis in
Development" is 13.9. Take students' reading ability into account when assigning readings to each
student. If a student's needs make the readings difficult, then arrange for them to be read to the
student or consider making a recording for the student.
Safety
There are no additional safety concerns associated with this lesson.
V. Timeframe for lesson
Opening of Lesson
Discussion to review previous lesson and introduce this lesson – 10 minutes
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Main Part of Lesson
Activity 1: Micrographs of a typical neuron – 10 minutes
Activity 2: Identifying necrosis and apoptosis morphologies – 25 minutes
Activity 3: Gel electrophoresis and cell death – 30 minutes
Conclusion of Lesson
Whole class discussion connecting cell death and effects on behavior and function – 15 min
VI. Advanced prep and materials
Opening of Lesson
Materials:
Chalkboard, white erase board, or large sheet of paper to write on
Writing utensil
Model Organisms Reading: U4_L5_Reading_ModelOrganisms (Optional)
Preparation:
No preparation required
Make enough copies of the Model Organisms document so each group of 2-4 students has one
OR simply project this document onto the screen and go over it as a class. (This will depend on
how in depth of an explanation of a model organism is preferred.)
Activity 1: Micrographs of a typical neuron
Materials
“Typical Neurons” student sheet: U4_L5_StudentSheet_TypicalNeuron
Preparation:
Print one copy for each student. Have this document ready to be projected onto a screen for the
whole class to see.
Activity 2: Identifying necrosis and apoptosis morphologies
Materials
“Morphologies of Cell Deaths” student sheet: U4_L5_StudentSheet_MorphologiesOfCellDeath
(p.1)
“Recording Observations of Cell Death Morphologies” student sheet:
U4_L5_StudentSheet_MorphologiesOfCellDeath (p.2)
Description of Apoptosis and Description of Necrosis student sheet:
U4_L5_StudentSheet_Apoptosis&Necrosis
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Preparation
Print one copy per every two students of “Morphologies of Cell Deaths”. Have this document
ready to be projected onto a screen for the whole class to see.
Print one copy per student of “Recording Observation of Cell Death Morphologies”
Print one copy per every two students of the document including both descriptions for
apoptosis and necrosis.
Activity 3: Gel electrophoresis and cell death
Materials
Neurobiology Techniques descriptions & “Evaluating Neurobiology Techniques” student
worksheet: U4_L5_StudentSheet_NeurobioTechniques
“Gel Electrophoresis Results” student sheet: U4_L5_StudentSheet_GelElectrophoresisResults
Preparation
Print one copy of each of the four neurobiology techniques per every group of four students
Print one copy per student of the last page of the document, “Evaluating Neurobiology
Techniques”
Print one copy per every two students of the “Gel Electrophoresis Results” student sheet.
Prepare to project “Gel Electrophoresis Results” document onto a screen for the whole class to
see.
Conclusion of Lesson
Materials:
Four student readings on different roles of apoptosis
o “Apoptosis and Mitosis”: U4_L5_Reading_ApoptosisAndMitosis
o “Apoptosis and Cancer”: U4_L5_Reading_ApoptosisAndCancer
o “Apoptosis in Development”: U4_L5_Reading_ApoptosisDevelopment
o “Apoptosis in the Immune System”: U4_L5_Reading_ApoptosisImmuneSystem
"Homework Organizer": U4_L5_StudentSheet_ApoptosisDiscussion
Preparation
Make copies as needed (this will depend on teacher preference)
VII. Resources and references
References
Activity 1 Documents:
“Typical Neuron”: U4_L5_StudentSheet_TypicalNeuron
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1. University of Delaware. Retrieved on July 12, 2012
from: http://www.udel.edu/biology/Wags/histopage/colorpage/cne/cnemnns.GIF
2. Zou, X., Liu, F., Zhang, X., Patterson, T.A., Callicott, R., Liu, S., Hanig, J.P., Paule, M.G.,
Slikker Jr., W., and W. Cheng. (2011). Inhalation anesthetic-induced neuronal damage in
the developing rhesus monkey. Neurotoxicology and Teratology 33: 592-597.
Activity 2 Documents:
“Morphologies of Cell Deaths”: U4_L5_StudentSheet_MorphologiesOfCellDeath
1. Garcia, J.H., Liu, K-F., Ye, Z-R, and Gutierrez, J.A. (1997). Incomplete infarct and delayed
neuronal death after transient middle cerebral artery occlusion in rats. Stroke, 28: 2303-
2310.
2. Li, Y., Chopp, M., Powers, C., and N. Jiang. (1997). Apoptosis and protein expression after
focal cerebral ischemia in rat. Brain Research, 765: 301-312.
3. Martin, L.J., Al-Abdulla, N.A., Brambrink, A.M., Kirsch, J.R., Sieber, F.E., and C. Portera-
Cailliau. (1998). Neurodegeneration in excitotoxicity, global cerebral ischemia, and target
deprivation: A perspective on the contributions of apoptosis and necrosis. Brain Research
Bulletin, 46: 281-309.
4. Wei, L., Han, B.H., Li, Y., Keogh, C.L., Holtzman, D.M., and S.P. Yu. (2006). Cell death
mechanism and protective effect of erythropoietin after focal ischemia in the whisker-
barrel cortex of neonatal rats. Journal of Pharmacology and Experimental Therapeutics,
317: 109-116.
Descriptions of Apoptosis and Necrosis: U4_L5_StudentSheet_Apoptosis&Necrosis
1. Li, Y., Chopp, M., Powers, C., and N. Jiang. (1997). Apoptosis and protein expression after
focal cerebral ischemia in rat. Brain Research, 765: 301-312.
2. Martin, L.J., Al-Abdulla, N.A., Brambrink, A.M., Kirsch, J.R., Sieber, F.E., and C. Portera-
Cailliau. (1998). Neurodegeneration in excitotoxicity, global cerebral ischemia, and target
deprivation: A perspective on the contributions of apoptosis and necrosis. Brain Research
Bulletin, 46: 281-309.
3. Purves, D., Augustine, G.J., Fitzpatrick, D., Hall, W.C., LaMantia, A-S., McNamara, J. O., and
White, L.E. (Eds.). (2008). Neuroscience. Sunderland, MA: Sinauer Associates, Inc.
Activity 3 Documents:
“Gel Electrophoresis Results”: U4_L5_StudentSheet_GelElectrophoresisResults
1. Rink, A., Fung, K-M, Trojanowski, J.Q., Lee, V.M.-Y., Neugebauer, E., and McIntosh, T.K.
(1995). Evidence of apoptotic cell death after experimental traumatic brain injury in the
rat. American Journal of Pathology, 147 (6).
Homework Documents:
“Apoptosis and Mitosis”: U4_L5_Reading_ApoptosisAndMitosis
1. Bowen, I.D., Bowen, S. M., and Jones, A. H. (1998). Mitosis and apoptosis: Matters of
life and death. Chapman & Hall: London.
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2. Guicciardi, M. E. and Goes, G. J. (2011). Regulation of cell death in the gastrointestinal
tract. In John C. Reed and Douglas R. Green (Eds.) Apoptosis: Physiology and pathology.
Cambridge University Press: New York.
3. Saltsman, K. (2005). The last chapter: Cell aging and death. In Inside the Cell. National
Institute of General Medical Sciences.
4. Superstock, Flirt. (2012). Image: 1829-8468. Retrieved from:
http://www.superstock.com/stock-photos-images/1829-8468.
“Apoptosis and Cancer”: U4_L5_Reading_ApoptosisAndCancer
1. National Cancer Institute. (2005). Understanding cancer and related topics [PowerPoint
document]. Retrieved from National Cancer Institute at the National Institutes of Health
Understanding Cancer Series Web Site:
http://www.cancer.gov/cancertopics/understandingcancer/cancer
2. Yang, L. (2005). Disfunction of the apoptotic pathway in cancer cells. In M. Sluyser (Ed.),
Application of Apoptosis to Cancer Treatment (pp. 1-28). The Netherlands: Springer.
3. University of Illinois at Chicago (2012, March 1). Molecule's role in cancer suggests new
combination therapy. ScienceDaily. Retrieved June 27, 2012, from
http://www.sciencedaily.com /releases/2012/03/120301143336.htm
“Apoptosis in Development”: U4_L5_Reading_ApoptosisDevelopment
1. Brill, A., Torchinsky, A., Carp, H., and Toder, V. (1999). The role of apoptosis in normal and
abnormal embryonic development. Journal of Assisted Reproduction and Genetics 16(10):
512-519.
2. Hardy, K. (1999). Apoptosis in the human embryo. Reviews of Reproduction 4: 125-134.
3. Hillis, D.M., Sadava, D., Heller, H.C., and Price, M.V. (2012). Principles of Life. Sunderland,
MA: Sinauer Associates, Inc.
4. Purves, D., Augustine, G.J., Fitzpatrick, D., Hall, W.C., LaMantia, A-S., McNamara, J. O., and
White, L.E. (Eds.). (2008). Neuroscience. Sunderland, MA: Sinauer Associates, Inc.
5. University of New South Wales. (2012). UNSW Embryology. Retrieved from:
http://php.med.unsw.edu.au/embryology/index.php?title=BGDA_Lecture_-
_Development_of_the_Embryo/Fetus_2
“Apoptosis in the Immune System”: U4_L5_Reading_ApoptosisImmuneSystem
1. Everett, H. and McFadden, G. (1999) Apoptosis: An innate immune response to virus
infection. Trends in Microbiology. 7(4): 160-165.
2. Krammer, P.H., Behrmann, I., Daniel, P., Dhein, J., and Debatin, K-M. (1994). Regulation of
apoptosis in the immune system. Current Opinion in Immunology. 6: 279-289.
3. U.S. National Library of Medicine. (2012). Retrieved from:
http://ghr.nlm.nih.gov/handbook/illustrations/apoptosismacrophage
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VIII. Lesson implementation
Opening of Lesson: Begin the lesson by reviewing what students learned in the “How to build a neuron” lesson and by
adding some more information on the cellular components of a neuron. Ask students the following
questions to facilitate a review discussion:
What are some unique structural features of neurons that distinguish them from other cells?
What are three main parts of a typical neuron that make up the whole cell?
What is the soma?
What is contained in the nucleus of all cells including neurons?
Can you name some functions of neurons?
How do neurons communicate with each other?
As students volunteer answers, draw a typical neuron on the board labeling the different parts that are
discussed. Be sure to draw and label the following: soma, dendrites, axon, nucleus, DNA, cell wall,
cytoplasm.
Encourage students to shift their attention to today’s lesson by asking the following question:
What do you think happens to neurons when the brain is injured?
o Students will likely provide a number of different answers such as “they die,” “they
disappear,” “the injured part of the brain goes black,” “they become smushed” etc.
Next, direct students to think forward by asking them the following question:
How do you think scientists investigate this question?
o Possible student answers include: use microscopes, look at brains of people who have
head or brain injury, do experiments on other animals, use brain scans etc.
Explain to students that scientists use several ways to study what happens to the brain after a traumatic
brain injury.
One way is by using different types of brain scans such as a CT scan.
Additionally, in order to study what happens to neuronal cells, scientists prepare slides of brain
tissue that they look at under a microscope. But this requires a piece of brain tissue be removed
from the brain, so it is only done in emergency situations or for biopsies of potentially diseased
brains; tissue sections of whole brains can only be examined after a person has died.
Sometimes, people will give permission for scientists to study their brain post mortem (meaning
after death) to develop an understanding of what happened to the brain at the cellular level.
However, this is not a simple task and studying only human brains would hinder progress of
scientific research on TBI.
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Another important way to research this topic is to use model organisms. Model organisms play a
critical role in advancing understanding of a variety of biological processes.
Explain to students that today they are going to be looking at slices of brain tissue mainly from rats to
try to answer the question, “What happens to neurons when the brain undergoes traumatic brain
injury?”
Teacher Pedagogical Content Knowledge Depending on the level of the class and on whether they have learned about the concept of model organisms before, it may be appropriate to spend more time explaining the role of model organisms in scientific research. The file “Model Organisms” is an informational reading and is a helpful tool in teaching students these ideas. (U4_L5_StudentSheet_ModelOrganisms).
Main Part of Lesson
Activity 1: Micrographs of a typical neuron
Explain to students that they are going to investigate the following question: What happens to neurons
when the brain experiences a traumatic injury? (This question should be written on the board so
students can see it and keep it in mind throughout the lesson.) They are going to use data and findings
from actual published scientific research to figure out and explain the answer to this question.
For the first activity in their investigation, have students work together in groups of 2 to 4 people. To
each group, hand out the worksheet of micrographs that show “typical neurons”
(U4_L5_StudentSheet_TypicalNeuron).
Project the document onto the board from a computer for the whole class to see. This way the
images can be easily pointed at and referred to in order to guide students through the activity.
Explain to students that one method scientists use to study the brain is to look at slides of thin brain
slices under a microscope. The images they will see and use in class, are photos/digital images taken
through a microscope and are called “micrographs.”
The first two images on the student sheet show neurons from normal, uninjured rat brains.
These will be referred to as the “typical” neurons because they are images of what a normal
neuron looks like.
o The first image shows a whole neuron.
o The second image zooms in on the nucleus of a neuron.
Have students identify the following parts of the neuron on the first image: nucleus, nucleolus, soma,
and dendrites (Question 1 on the worksheet).
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Teacher Pedagogical Content Knowledge To give students a sense of the scale they are looking at in these micrographs, one of the following comparisons can be used:
The nucleus of the neuron in this image is one-tenth the width of the average human hair. Or, in other words, 10 nuclei stacked up would equal the same width as a human hair.
If the neuron nucleus were the size of a marble, then the width of your hand would equal half a mile.
Give students time to become familiar with how to look at micrographs of neurons by having them
identify and label the parts on the images.
Walk around and help the groups as they complete question #1. Though they may need some
guidance, students should be able to identify these four parts with little difficulty since they are
visible in the image. The most difficult part to identify is perhaps the dendrites. In this image, if
observed carefully, three projections can be seen extending out from the soma. These are the
neuron’s dendrites.
Ask students to trace around the nucleus, the soma, and the dendrites if it would help them to
better read the image.
Once students have identified parts a–d, either review the answers as a class or if all students seemed to
have understood during the group work, continue to the next question.
Draw students’ attention to the axon and axon terminal, two parts of a neuron that they have discussed
previously but are not readily visible in this micrograph.
Have students draw on their knowledge of what a neuron looks like in order to point out or draw in
where the axon terminal and dendrites might be if they were visible.
Tell the students that the axon also extends from the soma, however it is not visible in this image.
The axon might extend upward or perhaps it is extending out behind the soma; both are
positions that are not visible to us due to the angle at which this image was taken. This neuron’s
axon terminal, which is at the end of an axon, could be a meter away as an axon can be over a
meter long (far out of the frame of this micrograph). However, axon terminals of neurons
providing input to the neuron in the micrograph would be within the frame of this micrograph.
Next, turn students’ attention to the second image. Remind students this image is zoomed in to focus on
the nucleus. The larger, lighter colored circle is the nucleus. Outside of the nucleus, but within the cell
membrane is the cytoplasm, which contains the cell’s organelles.
Ask the following questions to discuss what they can see in this micrograph of the nucleus:
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What do you think the gray-ish stuff inside the nucleus is?
o Students may give responses such as the following: ribosomes, chromosomes,
chromatin, DNA, proteins, amino acids etc. If students say chromosomes, tell them
that’s a great answer but not quite correct. Depending on how much cell biology
students have had previously, the differences between chromosomes, chromatin, and
DNA can be explained to them. The right answer is chromatin, DNA or it can be called
chromatin DNA to indicate the DNA is in its uncondensed state.
What does the chromatin DNA look like here? Is it in a tight chromosome formation like we see
in mitosis? Or is it loose and spread out?
o Students should be able to note that the chromatin or DNA is not gathered tightly and is
loose and spread out throughout the nucleus. That is why it appears very light gray.
Scientific Practices: Analyzing and Interpreting Data In Activity 1, students are introduced to micrograph data which allows for visualization of typical neuron cell. In Activity 2, students draw comparisons between the morphology of a typical neuron with new morphological data of neuronal cells undergoing two different types of cell death. Through these activities, students have an opportunity to make observations, analyze and interpret real images of neurons, and draw conclusions using published scientific data.
Activity 2: Identifying necrosis and apoptosis morphologies
Encourage them to think about how neurons might look after TBI. Ask students the following questions:
Do you think neurons look different if they are affected by a traumatic brain injury?
What do you think the neurons in an injured brain look like? Describe or draw what you might
see.
Give students a few minutes to draw or describe what they might expect to see and have a few students
share their ideas.
Remind students that scientists use model organisms to study what happens to neurons after brain
injury. Tell students that they are now going to look at some real micrographs of brain tissue from rats
that experienced traumatic brain injury in order to investigate their driving question: What happens to
neurons when the brain experiences a traumatic injury?
For this activity, tell students they will be working in their groups again.
Hand out the “Morphologies of Cell Death” sheet (U4_L5_StudentSheet_MorphologiesOfCellDeath, p.1)
1 per student or several per group and the corresponding worksheet “Recording Observations of Cell
Death Morphologies” (U4_L5_StudentSheet_MorphologiesOfCellDeath, p.2) 1 per each student.
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(Also, project the sheet showing the neuron micrographs onto the board from a computer for the whole
class to see. This way the images can be easily pointed at and referred to in order to guide students
through the activity.)
Ask students:
Does anyone know what “morphology” means?
o Answer: “Morphology,” in this case, means the form and/or structure of something.
Explain that they are now going to look at the morphology of a neuron during the process of cell death.
This means that they are going to study the form and structure of the neurons by observing what they
look like in these micrograph images.
Direct students’ attention to look only at the top row of images titled “Morphology of Cell Death Type
1.” These are a sequential set of images showing one type of cell death that has been observed
happening to neurons after TBI.
Tell students that the first image, A, is the nucleus of a typical neuron (like the images on the first
handout). Explain to students that they should use image A as a point of reference to see what changes
take place in the cell as cell death progresses.
Have students work with the other students in their group to observe and identify what is happening in
the first row.
Students should use the top row (the one for “Cell Death Type 1) in the table on the second
worksheet to guide their observations.
In this initial description, students will describe what changes they see happening to the DNA
and the nucleus, and what they see happening to the cell overall in the final stages.
Give students about 10–15 minutes to fill out the top “Cell Death Type 1” row of the table by observing
what is happening in the images.
It can be difficult for the untrained eye to recognize all aspects of what the micrographs are
showing, therefore students will need assistance and scaffolding as they think through this
activity. The teacher answer key version of this worksheet
(U4_L5_StudentSheet_MorphologiesOfCellDeath_ANSWERS) may be helpful while guiding
students.
The following are parts with which students may have difficulty and possible ways to guide
discussion when they come to these points:
o Students may have difficulty describing what happens to the DNA. They will likely be able to
point out that “there are bigger, darker dots in the in the nucleus.” Guide students by asking
questions such as “What do the darker spots indicate is happening to the DNA?” “How is the
state of the DNA changing as compared to its loose, uncondensed, state in the typical
nucleus?” If students have already studied cell biology, mitosis/meiosis, and/or DNA, they
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can be asked to recall what DNA looks like in the early stages of mitosis or meiosis. Is that
similar to what you see here? However, make certain students understand that the DNA is
condensing but it is not forming chromosomes as it does during the cell cycle.
o The second column asks students to observe changes in the nucleus size. Typically, when
cells undergo necrotic cell death, they swell before disintegrating. It is difficult to observe
swelling of the nucleus in these images. Therefore, students can simply be told this or they
can simply only write down what they are able to observe. (A later reading will further
clarify this aspect of the morphology.)
o In the final image, students need to be told that image D is zoomed out and the arrow
points to the whole neuron after it has undergone cell death type 1.
o In the last column, students are asked to note what happens in the final stages of cell death.
Students will be able to make key observations that explain what is happening such as “the
neuron seems to have fallen apart,” “it no longer has the same shape,” and so on. At this
point, encourage students to take their thinking further by asking “What does that imply
would have happened to the membrane?” and “If the membrane broke down, what would
happen to everything that is in the cell?”
Once students have completed the first row of the table, bring the class back together to summarize and
review as a class what they saw happening in this first cell death type.
The main take away points from Cell Death Type 1 that students should discern are the following:
the DNA condenses
the nucleus loses its shape and the nuclear membrane loses its integrity
the whole cell membrane loses its integrity and the contents of the cell spill out
Next, introduce Cell Death Type 2. Explain to students that they have been talking about one kind of cell
death morphology that neurons undergo due to TBI. But scientists have identified another type of cell
death process. This second type is shown by the second row of images.
Ask students to work in their groups again to study the morphology of Cell Death Type 2. While they do
this, they should think not only about the changes the neuron undergoes from the typical neuron state,
but also about how this cell death type is different from the first one they looked at.
Give students 10-15 minutes to complete the second row of their table. Again, students will likely need
support with the following parts:
As before, students will need to make the connection between dark globs in the nucleus and
condensing DNA. Additionally, they will need to be directed to distinguish between, dispersed
clumps of condensed DNA in Type 1 versus the aggregation of condensed DNA in Type 2.
In the final image, image 4 is zoomed out and the arrow is pointing to the whole neuron after it
has undergone cell death type 2.
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o Draw students’ attention to what the arrowhead is pointing at in images 2 and 3. This is
the beginning of the multiple circular bodies they can see in the zoomed out image 4.
This is a process in which the cell is breaking apart into separate bodies containing the
condensed contents of the cell.
Once students have completed describing the morphology of Cell Death Type 2, review their
observations together as a class. The main take away points students should recognize at this point are
the following:
The DNA condenses
The nucleus and the cell shrink and become more rounded and the nuclear membrane stays
more intact in the images.
The neuron cell begins to break down into smaller tightly packed bodies that contain the
contents of the cell.
Explain to students that the next step is to identify the two different types of cell deaths.
Explain that each group will receive two descriptions of two different types of cell death. Based
on the contents of these paragraphs and what they observed in the micrographs, they should
work with their group to match each sequence of images with the correct reading on cell death
type to identify them.
Hand out at least one copy of each of the two description readings to each group: one on Necrosis and
one on Apoptosis (U4_L5_StudentSheet_Apoptosis&Necrosis). Give students about 5–7 minutes to read
the descriptions and begin identifying the matching elements between the readings and the images.
Once students have discussed the readings and matched each sequence of images with the
corresponding description of cell death type, bring the class back together to highlight some of the
major features of each type and the most important differences between the two.
Ask students the following questions to check their understanding of the main take away points of this
activity:
What pieces of information helped you to decide how to match each line of cell morphology
with the correct cell death type from the readings?
What new things did you learn from the readings that you were not able to observe in the
neuron micrographs?
o Apoptosis is initiated due to biochemical signals and is controlled by the cell where as
necrosis is not. Necrosis happens when the cell becomes damaged in some way.
o DNA fragmentation is different in each cell death type. In necrosis DNA is fragmented
randomly. In apoptosis DNA is fragmented in an orderly way into 180bp and multiples of
180bp.
o During necrosis, the cells become swollen.
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o In apoptosis, the cell breaks into circular bodies that are called “apoptotic bodies.”
o Necrosis does elicit an inflammatory response and apoptosis does not.
Activity 3: Gel electrophoresis and cell death
Explain to students that studying the morphology of the neurons after TBI, like they just did, gave
scientists one piece of evidence that TBI resulted in two different types of cell deaths.
Ask students if scientists stop with only one piece of evidence when trying to explain a specific
phenomenon?
Wherever possible, scientists try to collect more evidence to further explain and support their
claims.
Hand out the readings on the four different neurobiology techniques--at least one copy of each reading
to each group (U4_L5_StudentSheet_NeurobioTechniques). Give each student one copy of the
corresponding “Evaluating Neurobiology Techniques” worksheet [last page of the same file).
Explain that described on these sheets are several different techniques used by neurobiologists to study
the brain: 1) electrophysiology, 2) animal behavior, 3) DNA gel electrophoresis, and 4) cell culturing.
Tell students that by using what they know about necrosis and apoptosis to decide which technique
would allow them to collect additional evidence for whether both necrosis and apoptosis are present
after TBI. They should use what they already know about the processes and characteristics of apoptosis
and necrosis (they can refer to the previous handouts) to figure out what technique will give them the
information they need to more fully answer the driving question: What happens to neurons when the
brain experiences a traumatic injury?
Students should review the reading on each technique as a group. For each technique, they must decide
whether it will or will not provide the information they are looking for – additional evidence for the
occurrence of both apoptosis and necrosis in the brain after TBI.
Once they have decided whether the technique will be useful to them or not, in the “Claim” column,
they need to circle “will” or “will not” to reflect their decision. They then need to complete the
“Evidence” and “Reasoning” columns with information about how they made their decision and how
they know it is the right one.
What technique will be useful?
What evidence do they have to support their claim?
What is their reasoning to explain how their evidence supports their claim?
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Scientific Practices: Constructing Explanations Scientists often go through a rigorous thought process in order to define their investigation, consider their options of methodology, and decide on the most appropriate techniques to generate the type of data that will provide valuable insight into their question of inquiry. Similarly, the neurobiology techniques activity above encourages students to think logically about the information they have in order to decide the best ways to acquire the information they need. The claim, evidence, and reasoning approach to this problem scaffolds students’ reasoning processes and their construction of sound explanations.
Once students have completed the CER worksheet on neurobiology techniques, bring all students back
together to review as a class what they decided.
Which techniques did they think would be useful in this case? Why?
Which techniques will not give them useful information? Why not?
Each group should have a chance to respond at least once.
At the end of the discussion, the whole class should have the common understanding that the
Gel Electrophoresis technique will help them find the most informative data for what they are
looking for. This is because it shows size of DNA fragments, which is a distinguishing factor
between apoptosis and necrosis.
Students should also understand that the other techniques—though useful in other ways—
would not be useful in this case because they will not indicate whether the cells died through
apoptosis or necrosis.
Students will now learn about the procedure of conducting a gel electrophoresis and then analyze the
data that results from DNA gel electrophoresis of injured brain tissue.
Begin by showing a short virtual lab video on the procedure of a gel electrophoresis. The Genetics
Science Learning Center at the University of Utah developed an interactive gel electrophoresis virtual
lab. The virtual lab can be found at this link: http://learn.genetics.utah.edu/content/labs/gel/. The first
part of this virtual lab explains the main ideas about gel electrophoresis. This can be projected up on a
screen from a computer for the whole class to see and each step can be expanded on. Through this
section of the virtual lab, students should learn the following:
Gel electrophoresis is used by scientists to sort DNA fragments by size.
The DNA fragments move through a gelatin-like material (the gel) with many bubbles in it that
the DNA must get around. Therefore the smaller pieces move faster and further and the bigger
pieces get stuck more and cannot move as far. Think about a little kid getting through a crowd of
people versus an adult. The small kid will have a much easier time getting around the people
and will get further than the adult in the same amount of time.
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The DNA is moved through the gel using an electrical current. Since DNA has a negative charge it
moves away from the negative end of the gel where it started and toward the positive end.
In the end, large groups of DNA fragments clumped by size can be seen as bands on the gel.
With every gel, one column contains a “standard.” This is a sample of DNA fragments of known
size that is used as a marker to determine the size of the unknown DNA fragments in the other
samples.
DNA is measured in base pairs or “bp” because DNA is made up of links of base pairs. For
example Cytosine (C) links with Guanine (G) and Adenosine (A) links with Thymine (T) to form
base pairs. DNA is long chain of these links. (An example can be drawn on the board so students
can visualize this.)
Pieces of similar length will cluster together and make dark areas, usually called bands. An area
on the gel that is darker indicates that there are more pieces of DNA in that part of the gel that
are all of similar length. (This is not explicitly explained in the virtual lab and therefore, will need
to be explained to students after they complete the virtual lab.)
(Note: If students have already conducted their own gel electrophoresis in an earlier unit or class, this
activity can be replaced with a short review discussion to get them to recall what the procedure looked
like.)
Teacher Pedagogical Content Knowledge The second half of the gel electrophoresis virtual lab gives students an opportunity to run a gel virtually. The lab walks them through each of the steps in the procedure and in the end they identify the sizes of DNA fragments in their unknown sample by comparing the bands to the standards. This is a helpful activity for students who are learning about gel electrophoresis for the first time or are having difficulty grasping the concept of how gel electrophoresis works and the data that it can produce. The activity would take about 20 minutes and would require that students have at least one computer per 2–3 students. This activity is recommended if students need further support in learning the concepts and if the resources are available.
Following the virtual lab and discussion ask students the following questions:
Based on what you just learned about gel electrophoresis, what would you predict to be the
results of the gel electrophoresis if you run a sample of DNA from injured brain tissue?
Students can be asked to draw their own versions of gel results that depict and explain what they might
expect to see.
Then, discuss this question as a class. Students will likely give a number of different answers. Encourage
them to look at the information they have about how the DNA fragments in necrosis versus in apoptosis
to make their prediction. Although students need not provide correct answers, they should be making
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connections between the gel electrophoresis technique and DNA fragmentation in necrosis and
apoptosis.
Explain to students that they will not be doing an actual gel electrophoresis experiment here since
obtaining and preparing brain tissue from an injured rat’s brain is a complicated and highly technical
process. Instead, they will be analyzing results that scientists have published in scientific journals.
Hand out the student sheet of the gel electrophoresis results
(U4_L5_StudentSheet_GelElectrophoresisResults). Also, project this document onto the board from a
computer for the whole class to see. This way the image can be easily pointed at and referred to in order
to guide students through the activity.
Explain to students that the far left column of bands is the standard of DNA fragments of known size.
Help students become oriented to what they are looking at on the gel and how to read it by asking the
following questions:
From where did the samples begin? How do you know?
Can you label each of the bands that appear between 100bp and 600bp?
If a DNA fragment were 300bp long, where would it appear on the gel?
Does each band represent just one piece of DNA or lots of fragments of DNA of the same size?
Now that students have an understanding of how to read the information contained in the gel, allow
students to analyze the results of an experimental gel sample.
Ask students to look at the second column and explain that this sample contains a DNA sample of brain
tissue from a rat experienced moderate brain injury. Ask students the following questions to facilitate
discussion and interpret what they are seeing.
What do you see happening in the second column?
What do you think these areas of large dark bands of DNA indicate?
What do you notice about the approximate sizes of the DNA fragments in these clumped
sections?
What type of cell death does this “ladder” pattern indicate is happening in the neurons of the
injured brain tissue?
Why do you think you see the darker shade all the way down?
How small are the smallest fragments?
What type of cell death do you think this “smear” pattern indicates is happening in the neurons
in the injured brain tissue?
How do you know?
What components of what you predicted are the same and what is different?
Do these data support the data we collected by looking at cell morphology?
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Does this strengthen our conclusion that both necrosis and apoptosis occur in the brain in
response to traumatic brain injury?
Scientific Practices: Analyzing and Interpreting Data Through the Gel Electrophoresis activity students learn about a valuable technique in biology and also have an opportunity to analyze authentic scientific data. In this activity, students apply information from the previous activities in order interpret the gel electrophoresis results and gain more insight into the effects of traumatic brain injury on neuronal cells.
Conclusion of Lesson
Have students answer the lesson’s driving question (What happens to neurons when the brain
experiences a traumatic injury?). Students should answer by explaining apoptosis and necrosis using the
two different types of evidence they collected in this lesson, cell death morphology and gel
electrophoresis.
Tell students that they now need to connect these ideas back to the level of brain anatomy and function
and resulting human function.
Explain to students that they have learned a great deal today about two types of cell death: 1) necrosis
which happens almost immediately due to direct damage to the cells from TBI and 2) apoptosis which
happens as a second wave of cell death due to the signals neurons receive from the damaged cells
around them.
Ask the following questions to get students to think about what this means at the macro level:
What do you think cell death means at the level of brain function?
Does necrosis of neuronal cells affect brain function?
Does apoptosis of neurons affect brain function?
Would these changes have effects on the person’s or animal’s personality and/or behavior?
If apoptosis after TBI could be stopped, would you stop it? Why? Would you not? Why not?
Students need not have specific and accurate answers to these questions. However, they should be able
to draw on their knowledge from this and previous lessons to say that both necrosis and apoptosis
would be detrimental to brain function (which in turn affects personality/behavior) because any time
neurons die (especially in large quantities such as in TBI), the neural networks they are a part of become
disrupted to some extent.
For the final question on whether apoptosis after TBI should be stopped are not, there is no clear
answer that is overwhelmingly agreed upon by the neuroscience community.
Students could answer this question either way as long as they are able to support their claim.
For example, they could answer, yes, apoptosis should be inhibited because it damages more
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neurons, potentially further disrupting cognitive function. They could also respond, no,
apoptosis should not be stopped because as a programmed cell death that does not elicit the
inflammatory response, it helps to contain the damage caused by the TBI. These are both valid
responses in which students have applied the knowledge they have gained thus far in this unit.
For homework or before beginning the next lesson, students should complete Lesson 5 questions in the
Lesson Journal. Students should also read the articles on various roles of apoptosis.
U4_L5_Reading_ApoptosisAndMitosis
U4_L5_Reading_ApoptosisAndCancer
U4_L5_Reading_ApoptosisDevelopment
U4_L5_Reading_ApoptosisImmuneSystem
Depending on the level of the class, students can be required to do all four readings, or each student can
be responsible for one or two readings and which they will share via a jigsaw activity in the following
class.
If a jigsaw approach is preferred, divide the class into 4 groups and assign one reading to each
group of students or divide the class in half and assign two readings to each group (one shorter
one and one longer one). For homework they should read their article and be prepared to share
the information it contains with the rest of the class the next day.
Check for student understanding with a discussion of the articles that students read. You may elect to
use an organizer to help students communicate important points from the readings. The organizer is
found under the filename U4_L5_StudentSheet_ApoptosisDiscussion.
The following questions can be used in the discussion:
How is the process of necrosis different from the process of apoptosis? How are the processes
similar?
What role do apoptosis and necrosis play in TBI?
Besides a response to TBI, what other functions does apoptosis serve in the body?
Similar to some of the functions of apoptosis in the immune system that you read about,
apoptosis can also be initiated in neurons that are dysfunctional or not working properly in a
normal, uninjured brain. What might this be advantageous?
If apoptosis after TBI could be stopped, would you stop it? Why? Would you not? Why not?
Teacher Pedagogical Knowledge This discussion on the apoptosis readings can occur at different times. If time allows, the readings and discussion can be done as a closing to this lesson. Otherwise the readings can be assigned as homework and the jigsaw activity to share information in the readings and the class discussion can take place in the next class. Also, note that different readings have different prerequisite knowledge. The reading on apoptosis in
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development may require additional vocabulary work for students unfamiliar with the concepts. Take care to ensure that the reading assignment is appropriate for each student.
Assessment There are several options for assessment in this lesson. Any of the worksheets completed in this lesson
could be collected and assessed. Also, key discussion questions from each activity can be compiled and
used as an in-class or homework assignment that students can turn in for a grade. Another option is to
use the last question of the lesson’s closing discussion about whether are not to inhibit apoptosis after
TBI as the prompt for an in-class writing assignment. Both responses would be considered equally and
students would need to demonstrate their understanding through the argument they formulate to
support the claim they choose.