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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 Positively Aging®/CAINE 2009© The University of Texas Health Science Center at San Antonio ++ ++ 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. 2 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 lesson 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. 3 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. 4 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. 6 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/ 7 Activity “Administrivia”: Intended Grade Level: 6– 8 process skills utilized in lesson: observation, inference, compare/contrast previous learning Assumed: parts of cell, basic function of nervous system Key Words for Web page: Nervous System axons, synapse Impulse electrochemical, neurotransmitter Stimulus vesicle, receptors Neurons autoreceptors, reuptake, cell body, ions, glial cells, dendrites, energy transformation Positively Aging®/CAINE 2009© The University of Texas Health Science Center at San Antonio ConTenT lesson neurotransmission: Content lessons nerve impulse, electrochemical conduction of nerve impulse, neurotransmitters, structure and function of neuron Relevant TEKS Science, Grade 6, Beginning with School Year 2010-2011. 9.c Force, motion, and energy. The student knows that the Law of Conservation of Energy states that energy can neither be created nor destroyed, it just changes form. The student is expected to demonstrate energy transformations such as energy in a flashlight battery changes from chemical energy to electrical energy to light energy. Science, Grade 7, Beginning with School Year 2010-2011. 7.b Force, motion, and energy. The student knows that there is a relationship among force, motion, and energy. The student is expected to illustrate the transformation of energy within an organism such as the transfer from chemical energy to heat and thermal energy in digestion 12 Organisms and environments. The student knows that living systems at all levels of organization demonstrate the complementary nature of structure and function. The student is expected to: 12.b identify the main functions of the systems of the human organism, including the circulatory, respiratory, skeletal, muscular, digestive, excretory, reproductive, integumentary, nervous, and endocrine systems; 12.c recognize levels of organization in plants and animals, including cells, tissues, organs, organ systems, and organisms; 12.e compare the functions of a cell to the functions of organisms such as waste removal; and 12.f recognize that according to cell theory all organisms are composed of cells and cells carry on similar functions such as extracting energy from food to sustain life. 13 Organisms and environments. The student knows that a living organism must be able to maintain balance in stable internal conditions in response to external and internal stimuli. The student is expected to: 13.a investigate how organisms respond to external stimuli found in the environment such as phototropism and fight or flight; and 13.b describe and relate responses in organisms that may result from internal stimuli such as wilting in plants and fever or vomiting in animals that allow them to maintain balance. science, grade 8, Beginning with school year 2010-2011. (2) Scientific investigation and reasoning. The student uses scientific inquiry methods during laboratory and field investigations. The student is expected to: 2.a plan and implement comparative and descriptive investigations by making observations, asking welldefined questions, and using appropriate equipment and technology 2.b design and implement comparative and experimental investigations by making observations, asking welldefined questions, formulating testable hypotheses, and using appropriate equipment and technology health education, grade 6.2.a Health information. The student recognizes ways that body structure and function relate to personal health throughout the life span. The student is expected to (A) analyze the relationships among the body systems “Administrivia” Key Concepts: 8 Making the leap part 2 Making the leap station Cards (Laminate for re-use) Making the Leap Station 1 Neuron Structure and Function The nervous system is like an electrical network. It relays information to and from the brain and spinal cord, allowing communication among all body systems and the brain. nerve pathways. Neurons are especially designed to transmit nerve impulses. Neurons have branches off of the cell body called dendrites and axons. dendriTes Dendrites receive impulses and carry nuCleus them to the cell body. Axons carry information away from the cell body. Axon “Information” in the nervous Axon Tip system travels through neurons as electrical impulses. Cell Body Think Point: (Write your answer on the Neuron Graphic Organizer) Nerve cells are very different from other cells. How are they especially designed to do their job? Positively Aging®/CAINE 2009© The University of Texas Health Science Center at San Antonio Positively Aging®/CAINE 2009© The University of Texas Health Science Center at San Antonio 1 ConTenT lesson neurotransmission: Content lessons There are millions of nerve cells (neurons) in the body and they form complex 9 Making the Leap Station 2: Stimulus Happens A stimulus starts the transmission of information through neurons. This transmission is called an impulse. The impulse travels through a single neuron first as an electrical impulse. This first neuron is the “sending neuron”. The next neuron to transmit the information is the “receiving neuron”. The impulse continues like this from one neuron to the next until it reaches its destination. sending neuron dendriTe reCeiving neuron Axon Axon nerve iMpulse dendriTe Think Point: (Write your answer on the Neuron Graphic Organizer) How is transmitting information in the nervous system like a relay race? Be sure to include the start of the race, the work of each “runner”, and the cooperation among runners in your answer. Positively Aging®/CAINE 2009© The University of Texas Health Science Center at San Antonio Positively Aging®/CAINE 2009© The University of Texas Health Science Center at San Antonio 2 ConTenT lesson neurotransmission: Content lessons 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). A stimulus can also be internal, (such as feeling thirsty when the body needs water). 10 Making the Leap Station 3: Positive Ions Flood Inside of Neuron Neurons at rest have a negative charge compared to the body tissue around them. When a stimulus occurs, it causes a change in the arrangement of the potassium and sodium ions in and around the A CTion neurons. Sodium ions iMpulse in neuron poTenTiAl (+1) will begin to move node oF into the neuron. The overrAnvier + + ++ all charge of the neuron ++ +++ begins to change. Sodium ions have a positive ++ + + charge, so the neuron Myelin becomes less negative as sheATh sodium ions move inside. Cell Body (soMA) 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. Think Points: (Write your answer on the Neuron Graphic Organizer) How do ions make the electrical impulses travel through neurons? What happens if there are not enough sodium ions moving into a neuron after a stimulus? Positively Aging®/CAINE 2009© The University of Texas Health Science Center at San Antonio Positively Aging®/CAINE 2009© The University of Texas Health Science Center at San Antonio 3 ConTenT lesson neurotransmission: Content lessons Important chemical elements in neurons are sodium, chloride, and potassium. These elements 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. Sodium and potassium ions have a positive 1 (+1) charge. Chloride ions have a negative 1 (-1) charge. 11 Making the Leap Station 4: Neurotransmitter Crosses Synapse There is not a direct connection between the axon tip of a sending neuron and the dendrite of a receiving neuron. Surprisingly, a gap or space called a synapse exists. The impulse is in an electrical form when it reaches the synapse and cannot cross in that form. When the electrical impulse reaches the end of the axon, it causes a special chemical (neurotransmitter) to be released. The neurotransmitter Vesicle (Neurotransmitter inside) crosses the synapse, in a chemical form, to the dendrites of the next neuron. This, in turn, starts the Transporter Synapse electrical impulse in the receiving neuron. Receptor Molecules Neurotransmitter Receiving Cell Think Point: 4 (Write your answer on the Neuron Graphic Organizer) How does an impulse make the leap across a synapse? Positively Aging®/CAINE 2009© The University of Texas Health Science Center at San Antonio Positively Aging®/CAINE 2009© The University of Texas Health Science Center at San Antonio ConTenT lesson neurotransmission: Content lessons Sending Cell 12 Making the Leap Station 5 Neurotransmitter Arrives at Receiving Neuron The neurotransmitter will spread (diffuse) out of the axon tip of the sending cell, and be “accepted” by specialized receptor areas on the receiving neuron. The receptors are specialized so they receive only their “own” neurotransmitter. receptor, it triggers electrical impulses to be sent through the receiving cell. This Sending Cell process will happen over and over, relay style, through multiple neurons Vesicle (Neurotransmitter inside) until the “message” arrives at its destination. Transporter Synapse Receptor Molecules Neurotransmitter Receiving Cell Think Point: (Write your answer on the Neuron Graphic Organizer) Why are neurotransmitters required before the message can be carried by the next neuron? Positively Aging®/CAINE 2009© The University of Texas Health Science Center at San Antonio Positively Aging®/CAINE 2009© The University of Texas Health Science Center at San Antonio 5 ConTenT lesson neurotransmission: Content lessons As the neurotransmitter is received by the 13 Making the Leap Station 6 Neurotransmitter Negative Feedback Loop Once the electrical impulse has begun in the receiving neuron, the chemical neurotransmitter is no longer needed. Four things can happen to the leftover neurotransmitter. The neurotransmitter can: This signaling to STOP releasing more neurotransmitter is an example of a negative feedback loop. In a negative feedback loop, an action will continue until something tells it to stop. ∂ impulse Sending Cell Vesicle (Neurotransmitter inside) ∑ neurotransmitter released across synapse ∏ impulse sent π when neurotransmitter Transporter Receptor Molecules is reabsorbed, impulse Receiving Cell formation sTops Think Point: (Write your answer on the Neuron Graphic Organizer) Why is the negative feedback loop important? Positively Aging®/CAINE 2009© The University of Texas Health Science Center at San Antonio Positively Aging®/CAINE 2009© The University of Texas Health Science Center at San Antonio 6 ConTenT lesson neurotransmission: Content lessons 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 14 Making the leap Flow Chart processing out Think Point 1 _________________________________________________ Label _________________________________________________ _________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ Label ______________________________________________________________________ Label Think Point 2 _________________________________________________ _________________________________________________ _________________________________________________ ______________________________________________________________________ ______________________________________________________________________ Label Think Point 3 _________________________________________________ ______________________________________________________________________ ______________________________________________________________________ _________________________________________________ Think Point 4 _________________________________________________ _________________________________________________ ______________________________________________________________________ _________________________________________________ ______________________________________________________________________ _________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ Think Point 5 _________________________________________________ _________________________________________________ _________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ Think Point 6 _________________________________________________ _________________________________________________ _________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ Positively Aging®/CAINE 2009© The University of Texas Health Science Center at San Antonio ConTenT lesson 15 evaluation dice Think point 1 How is a neuron designed to do its job? Think point 2 Synapse Think point How do ions make the electrical impulses travel through neurons? 6 3 5 Why are neurotransmitters required before the message can be carried by the next neuron? Think point Think point How is transmitting information in the nervous system like a relay race? Positively Aging®/CAINE 2009© UTHSCSA Think point 4 How does an impulse make the leap across a synapse? Positively Aging®/CAINE 2009© The University of Texas Health Science Center at San Antonio ConTenT lesson 16