Download Leap 2 - Teacher - Teacher Enrichment Initiatives

Making the leap part 2 observing Transmission of
information through neurons
Teacher pages
Activity description:
After making observations and inferences in Making the Leap Part 1,
students will rotate through six stations, each with Station Cards that
explain how nerve impulses are transmitted through neurons. In this way,
information is automatically chunked into small batches for students. Using
the six station cards and a Neuron Graphic Organizer, students will utilize
multiple learning styles to describe, illustrate, explain, and make analogies
as they construct understanding about the electrochemical process of
conducting information through neurons.
Activity Background:
The nervous system is like an electrical network that relays information to
and from the brain and spinal cord, allowing communication among all body
systems and the brain. Sensory information, such as temperature, touch,
vision, taste, and sound is received by the nervous system. It is relayed
through neural networks to the brain or spinal cord, which make up the
central nervous system (CNS). In the CNS, information is interpreted.
Messages are sent from the CNS through specific nerve pathways so the
appropriate body part or
system responds.
dendriTes
nuCleus
There are millions of
nerve cells (neurons)
in the body. They form
Axon
complex nerve pathways
Axon
Tip
between the CNS and
other body systems.
Neurons are especially
designed to transmit
nerve impulses. Neurons
have extensions off of the
Cell Body
cell body called dendrites
and axons (Figure 1).
Figure 1 neuron
Positively Aging®/CAINE
2009© The University of Texas Health Science Center at San Antonio
ConTenT
lesson
neurotransmission: Content lessons
Using a Neuron Graphic Organizer, station cards, and images provided in
this lesson, students will be able to:
n Explain how neurons transmit signals via an electrochemical process
n Compare and contrast their observations and inferences from
Making the Leap Part 1 with information provided in this activity
Activity overview
Activity objectives:
1
When a stimulus begins the transmission of information, an impulse travels
through a single neuron first as an electrical impulse. How does this electrical impulse happen? The stimulus changes the balance of charged particles
in the neurons relative to body tissues around the neurons.
eleCTriCAl energy in A neuron
Important elements and compounds in neurons are sodium, potassium,
calcium, chloride, and some proteins. All of these chemicals can exist as
charged particles called ions. Ions can have either a positive or negative
charge depending upon the numbers of protons and electrons. If there are
more protons than electrons, the charge will be positive. If there are more
electrons than protons, the charge will be negative. Unbalanced positive
and negative charges within neurons cause an impulse to travel through
the neuron.
Table 1 Important Ions in the Nervous System
Ion
sodium
potassium
Calcium
Chloride
protein
Charge
+1
+1
+2
-1
+ or – Charges
possible
Numbers of Extra Protons or Electrons
1 more proton than electrons
1 more proton than electrons
2 more protons than electrons
1 more electron than protons
How do the charged ions make the electrical impulses travel through neurons? Neurons at rest have more negatively charged proteins and chloride
inside them than positively charged particles. This means, at rest, a neuron
has a slightly negative charge as compared to the charge outside of the cell
(Figure 2).
iMpulse in neuron ACTion poTenTiAl
node oF rAnvier
++
++
+++
++
Myelin sheATh
Cell Body (soMA)
Figure 2 negative Charge in neuron
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++
ConTenT
lesson
neurotransmission: Content lessons
How do the impulses begin their journey through the neuron? It all starts
with a stimulus. A stimulus is anything that causes a reaction. A stimulus
can be external, when it occurs outside the body (such as a temperature
change or hitting your arm), or it can be internal, (such as feeling thirsty
when the body needs water).
Activity overview, continued
Dendrites receive impulses and carry them to the cell body. Axons carry
information away from the cell body. “Information” in the nervous system
travels through neurons as electrical impulses.
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If the overall charge of a neuron becomes positive enough to fire off an
impulse, it will travel from its point of origin and ultimately through the
axon. As the impulse travels, it causes a burst of positively charged activity.
As the impulse travels along the axon, it comes to the end of the neuron, also
known as the axon tip or terminal. There is not a direct connection between
the axon tip of one neuron and the dendrite of another neuron. Surprisingly,
a gap (synapse) exists (Figure 3). The impulse is in an electrical form when
it reaches the synapse and cannot cross in that form. What happens to the
electrical impulse? How can it “leap” across the gap between one neuron and
the next? This is where the chemical portion of “electrochemical” comes
into it.
Sending Cell
Vesicle
Transporter
Synapse
Receptor
Molecules
Neurotransmitter
Receiving Cell
Figure 3 synapse
(Adapted from http://www.drugabuse.gov/NIDA_notes/NNvol21N4/Impacts.html)
Chemical Energy in the Neuron: We have all seen energy transformations
when chemical energy is transformed to electrical, then radiant and thermal
energy in a battery powered flashlight. In a neuron, a similar energy transformation takes place, except the electrical energy is transformed to chemical energy at the end of axons (axon terminal). When the electrical impulse
reaches the axon terminal, it causes a special chemical (neurotransmitter) to
be released. The neurotransmitter crosses the synapse, in a chemical form,
to the dendrites of the next neuron. This starts the electrical impulse in the
next neuron.
Positively Aging®/CAINE
2009© The University of Texas Health Science Center at San Antonio
ConTenT
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neurotransmission: Content lessons
If enough sodium ions move in, an impulse will be sent. If not, no impulse
will be sent. It is an “all or none” event. Eventually, potassium ions will
move out of the neuron and sodium stops moving into the cell. This causes
the neuron to return to its negatively charged resting state. Neurons expend
energy to move sodium and potassium in and out of the cell.
Activity overview, continued
When a stimulus occurs, it causes a change in the arrangement of the potassium (+1) and sodium (+1) ions in and around the neurons. Sodium (+1)
ions will begin to move into the neuron. The overall charge of the neuron
begins to change. Sodium ions have a positive charge, so the neuron
becomes less negative as sodium ions move inside.
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The chemical neurotransmitter is no longer needed; it served only to prompt
an electrical signal to travel through the receiving neuron. Four things can
happen to the leftover neurotransmitter as the impulse continues its journey
in electrical form. The neurotransmitter can:
1. diffuse or drift out of the cell
2. be destroyed by chemical reactions that take place in the
“receiving” neuron
3. be destroyed by specialized “clean up” glial cells
4. be reabsorbed back into the “sending” neuron - this reabsorption
will signal cells to STOP releasing additional neurotransmitter, until
the next stimulus occurs.
This signaling to STOP releasing additional neurotransmitter is an example
of a negative feedback loop. In a negative feedback loop, an action will
continue until something tells it to stop. The thermostat on an air conditioner works this way. When the temperature becomes too warm, the air conditioner will start to run. When the thermostat senses that the temperature
has become cooler, it will relay that information to the air conditioner and
the air conditioner will stop making cold air.
Neurotransmitters: There are at least 100 different neurotransmitters, and
they have different functions. The neurotransmitters are synthesized from
the proteins in the food we eat. Table 1 lists common neurotransmitters and
their functions within the body. When the body receives a stimulus, the area
of the brain that processes the stimulus and the resulting response determines which of the neurotransmitters will be activated.
Positively Aging®/CAINE
2009© The University of Texas Health Science Center at San Antonio
ConTenT
lesson
neurotransmission: Content lessons
Remember, neurons are like wires. Similar to the chemicals in a battery in a
flashlight, the chemical itself does not travel along the network or “wires”,
only the impulse does. What happens to the special chemical neurotransmitter once it has reached the next neuron?
Activity overview, continued
Neurotransmitters are stored as molecules in storage areas called vesicles
in the axon terminals of the “sending” neuron. They wait for an electrical
impulse to come. If the impulse is strong enough, it acts as a signal for the
neurotransmitter to leave the vesicle and cross the synapse to the dendrites
of the next neuron, or the “receiving” neuron. The neurotransmitter will
diffuse out of the axon tip or terminal, and be “accepted” by specialized
receptor areas on the dendrite of the next neuron. The receptors are
specialized, so they receive only their “own” neurotransmitter. As the
neurotransmitter is received by the receptor, it triggers electrical impulses
which travel through the neuron to the axon tip at the next synapse and
the process repeats through a network of neurons until the information
reaches its destination.
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Table 1: Common neurotransmitters and Their Functions
Neurotransmitter
Function
We’ve learned that different areas of the brain control intelligence, emotions,
feelings, memory, and physiological functions. The neurotransmitters in the
brain facilitate these functions. No stimulus or response can happen in the
nervous system without the neurotransmitters. The neurotransmitters can
either cause an effect or feeling (excitatory) or prevent an effect or feeling
(inhibitory). These chemical compounds exist in a delicate balance
(equilibrium).
The type of neurotransmitter activated, either inhibitory or excitatory,
is dependent on the activity and the part of the brain involved. Physical
activity, for example, causes release of neurotransmitters called endorphins.
Endorphin release triggers feelings of well being. That is why an individual
generally feels good after exercise. Also, endorphin release will mask feelings of pain. Endorphin release in long distance runners masks the discomfort associated with extreme physical activity, so they are able to keep going.
Feelings of depression are closely related to neurotransmitters, such as
serotonin. Serotonin is often reabsorbed back into the sending neuron after
it has relayed the electrical information to the receiving neuron. Sometimes,
too much serotonin is reabsorbed, and not enough remains in the synapse.
This can cause feelings of depression. Commonly prescribed antidepressants
such as Prozac prevent the “reuptake” of serotonin back into the sending
neuron. This allows more to remain in the synapse and relieving feelings of
depression. Such antidepressants are known as “Selective Serotonin
Reuptake Inhibitors” or SSRIs.
Positively Aging®/CAINE
2009© The University of Texas Health Science Center at San Antonio
ConTenT
lesson
neurotransmission: Content lessons
Fight or flight
Long term memory, hunger, sleep/
wake cycle
dopamine
Pleasure / reward system, movement,
attention, memory
serotonin
Emotions, sleep, satiety
Acetylcholine
Thirst, body temp, short term memory,
motor function
glutamate
Neuron activity (increases it), learning /
cognition memory
endorphins
Emotion, pain, pleasure, appetite.
Released with exercise
gABA (gamma-aminobuyricacid) Neuron activity (slowed), anxiety,
memory, anesthesia
Activity overview, continued
Adrenalin (epinephrine)
norepinephrine (noradrenalin)
5
5 sets of Making the Leap Station Cards
Colored pencils
1 Copy Processing Out Section per student
Activity instructions:
•
•
•
•
•
•
•
Set up six stations so there are five copies of the same Making the
Leap Station Cards at each station.
Divide class into six groups.
Assign each group to a station.
Instruct students to read the station card carefully and to look at the
illustrations on the card. They should re-read the card and then
discuss it in their group.
Individually, students should work on their Making the Leap Flow
Chart, filling in information and diagrams as instructed on the
flow chart.
When most students have completed the station, ask students to
rotate to the next station. Repeat until all stations have been
completed.
Cut out the dice at the end of the activity and use for review.
Management suggestions: Laminate the Making the Leap
Station Cards for durability and reuse. Be sure to circulate among the stations to help direct discussion and answer questions about the flow chart.
suggested Modifications: Visit students needing assistance
more frequently as you circulate through the stations. You might also provide a flow chart that is partially filled to help these students complete their
task and to ensure they have correct information at the end of the activity.
suggested extensions:
Students develop “claymation” videos
showing process of impulse traveling through the nervous system. Examples
can be found on the Internet to give students an idea of what these might
look like. This idea might also be used instead of the stations for high ability
students needing enrichment.
Positively Aging®/CAINE
2009© The University of Texas Health Science Center at San Antonio
ConTenT
lesson
neurotransmission: Content lessons
Materials:
Activity overview, continued
Many different substances and activities can affect the function of neurotransmitters. Some of these include: emotions, physical activity, genetic
makeup, illness, foods consumed, starvation, pain, injury, drugs, and
chemicals in our environment. Remember, all bodily functions and
activities require neurotransmitters. A well-functioning, healthy body
requires the release and synthesis of neurotransmitters. This release and
synthesis must occur in such a way as to maintain optimum balance.
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references used:
Merck manual of diagnosis and therapy - 18th ed. (2006). Section 16 Neurologic disorders and neurotransmission, p 207.
Nervous System. (2009). In Compton’s by Britannica. Retrieved
June 29, 2009, from Encyclopædia Britannica Online School Edition:
http://school.eb.com/comptons/article-205350
Walker, Richard; Parker, Steve; and Winston, Robert. (2007). The Human
Body (Book & DVD). DK Publishing, Inc., 256 pp.
Positively Aging®/CAINE
2009© The University of Texas Health Science Center at San Antonio
ConTenT
lesson
neurotransmission: Content lessons
National Institutes of Health Medline Plus Website accessed from
http://www.nlm.nih.gov/medlineplus/ on July 29, 2009
Activity overview, continued
National Institute on Drug Abuse (NIDA) for Teens. Retrieved June 20, 2009
from http://teens.drugabuse.gov/blog/tag/neurons/
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