ALA-Neurons

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Apr 3, 2024

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ALA–Neurons Be sure to DOWNLOAD AND SAVE this file BEFORE you enter responses—so that you can navigate to the correct file and avoid uploading a blank document when uploading your completed assignment. IMPORTANT—YOU MAY SUBMIT THIS ALA AS INDIVIDUALS, OR AS GROUPS LIKE NORMAL! You can also have two students work together and submit as the “trio” and the third student can submit as an individual---whatever you prefer. Please enter the following: Class Time: 11:00-12:15 Team (Table) No. 5 Trio letter (A, B, or C) B If submitting as a trio like normal: Enter the names of group members below who helped with completing this ALA and therefor deserve credit. If submitting as an individual: Enter your name below as the “Recorder” and submit separately from your other trio members. Also note the explanation of contributions on the last page. Be sure to enter FIRST AND LAST NAMES. Student #1 (Recorder) Onalee Shogren Student #2 Sadie Shippee Student #3 River Soto Student #4 (most teams will only have three students) ALA Reminders:  Save file to desktop (or somewhere you can locate) , then upload when submitting your assignment.  Submit completed assignment as either a Word or PDF file ( not as a google doc or “Pages” file common on Macs ).  You must make notable contributions to the completed assignment and your name must be on the assignment to receive credit. It is up to you to make sure the "recorder" enters your name before submitting.  You may use your book, internet, or any other resources you wish to answer these questions. Be sure to ask Dr. C if you need help! STOP! If you are at all unsure about how to prevent a submission of a blank file, do a quick test run before you proceed any further. Save this file with info entered above locally on your device then submit through blackboard. Then, check your submission to make sure it does indeed show the correct version. 1

HOW DO NEURONS WORK? A neuron at rest maintains a resting potential. Although several types of ions and other molecules play a part in establishing a resting potential, a resting neuron has an overall negative charge relative to its surrounding environment (~ -70 mV) and there is a high concentration of Na + outside the neuron and a high concentration of K + inside the neuron (due to active transport by the Na/K pump). In addition to the Na/K pump, the cell membrane of neurons also contains voltage-gated Na + and K + channels. These are proteins that remain “closed” when the membrane is polarized (a neuron at rest), but “open” when the membrane becomes depolarized. When the gates are open, they allow Na + or K + to move across the membrane (therefore, these voltage-gated channels play a role in facilitated diffusion). 1. Consider the images above, which illustrate voltage-gated Na + gates in the membrane of a neuron. Does “A” represent a neuron at rest or one that is transmitting an action potential? At rest 2. Consider image “B”. Will the neuron become MORE polarized or DEPOLARIZED as the voltage-gated channel opens (i.e., would the overall charge of the neuron become more negative or positive compared to its resting potential)? Depolarized 3. If a K + gated channel located in a neuron membrane were to open, would the neuron become MORE polarized or DEPOLARIZED (i.e., would the overall charge of the neuron become more negative or more positive compared to its resting potential)? More polarized Most neurons will “fire” (i.e., they will send an action potential) once their membranes are depolarized to a certain level (the “threshold” level). Under most circumstances, once an axon’s membrane potential reaches threshold (about -55 mV in mammals), an action potential is automatically triggered. The graph below shows the changes in membrane potential that occur in an axon membrane that is initially at resting potential. 2

Match the descriptions below with regions “A” – “E” in the graph above. 4. Na+ channels fully open and K+ channels closed. Na+ rapidly enters the cell. C 5. Na+ channels closed and K+ channels open. K+ rapidly leaves the cell. D 6. Na+ channels closed and K+ channels closed. Na/K pump is working. A and E 7. Na+ channels begin to open (but only slightly). B How fast can an action potential travel? You were asked to conduct an experiment to address this question with materials available in class! Answer the questions below based on your in-class experiment. 8. Describe your experimental procedure below. Include a brief discussion of the constraints, limitations, or sources of potential error in your experiment. We tested someone’s reflexes by dropping a pencil and seeing how long it took them to catch it. We also measured the distance the pencil had fallen when they caught it. There was definitely potential error in stopping the time exactly when the pencil was caught, as well as the chances of the participants hand dropping to catch the pencil. This would have skewed the measurement. 9. Report your result in meters/second, then convert to miles/hour. Show all of your calculations and conversions! 0.775m/s and 1.73 mi/hr. 10. Do some research online. What is the maximum action potential velocity you can find? 100 m/sec (580/hr.) to less than 0.22 mi/hr. 3

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What happens once the action potential reaches the end of the axon (i.e., the terminal branches)? Neurons are in constant communication with adjacent neurons via synapses. Synapses are regions where the terminal branches of one neuron (the presynaptic neuron) release neurotransmitters that interact with the dendrites or cell body of another neuron (the postsynaptic neuron). Depending on the events that occur, the postsynaptic neuron is either stimulated to produce an action potential (an Excitatory Post Synaptic Potential, or EPSP), or, is inhibited from producing an action potential (an Inhibitory Post Synaptic Potential, or IPSP). 11. The list below indicates the events that occur at a synapse, but they are not listed in the correct order. Indicate the correct sequence of these events below (you can simply place the appropriate letter on the red lines below). A. Vesicles release neurotransmitters into synapse. B. Neurotransmitter is either broken down by an enzyme or transported back into the presynaptic cell via re-uptake transporters C. Neurotransmitter binds with ligand-gated channel. D. Receptors open allowing diffusion of ions (e.g., Na + or K + ) across membrane. This will cause either an excitatory post-synaptic potential (EPSP) or an inhibitory post-synaptic potential (IPSP) depending on which ions move across membrane. E. Action potential arrives at terminal branch. First = E Second = A Third = D Fourth= C Fifth = B 4

Consider the post-synaptic responses below. 12. Does “A” represent an EPSP or IPSP? EPSP 13. Which ligand-gated channel (receptor) would be most likely to induce the response in “A” if it were to open? (Na + or K + ). Na+ 14. Does “B” represent an EPSP or IPSP? IPSP 15. Which ligand-gated channel (receptor) would be most likely to induce the response in “B” if it were to open? (Na + or K + ). K+ 16. “C” illustrates what happens when two presynaptic neurons interact with one postsynaptic neuron at the same time (specifically when the signal in “A” and “B” arrive at a postsynaptic neuron). What can you conclude? A and B would cancel each other out. CASE STUDY: How can a frog kill with its skin? Certain species of frogs in the genus Phyllobates have a powerful defensive adaptation—their skin can secrete a milky fluid that contains an extremely toxic compound called batrachotoxin (BTX). These frogs, which are found in Colombia, are known as poison dart frogs because some indigenous Colombian hunters coat the tips of their blowgun darts with the frogs’ skin secretions. An animal hit by one of these darts dies quickly. What is the mechanism of action of BTX? 5

The graph below shows the effect of BTX on the membrane potential of an axon. Source: Narahashi, T., E. X. Albuquerque, and D. Deguchi. 1971. The Journal of General Physiology 58: 54– 70. 17. Which of the following is the most likely explanation for the effect of BTX on the axon? Highlight your answer in red . a. Inactivation of Na + /K + -ATPase(the sodium/potassium pump) b. Closing of sodium channels c. Opening of sodium channels d. Opening of potassium channels 18. As shown by the graph above, BTX depolarizes the membrane and prevents repolarization. What effect would this have on electrical signaling by the nervous system? How could this result in death? The BTX stops the production of the action potential, and this causes signals to stop production. This could result In death because the BTX causes irreversible damages to the cells of the nervous system, which would lead to cardiac failure. The remaining questions are modified from, “The Case of the Malfunctioning Neuron: When Cellular Processes Go Wrong,” by Kirsten L. Hokeness Part I – The Nervous System Joyce was sitting in her freshman biology class trying to connect the moving parts of protein synthesis. She couldn’t concentrate however, and was particularly distracted. She had just been home for a long weekend to visit her parents and had noticed some peculiar things going on with her mom. When she and her mom were out shopping, her mom had been walking a bit funny. Her foot kept slapping against the ground. Joyce also had noticed that her mom was talking with a slight slur, something she had never heard before. At first, Joyce found it amusing. But this continued throughout the day and during her entire visit home. Joyce also noticed some twitching in her mother’s forearms. Being a “pre-health” biology major, she started to wonder what was going on. Joyce went up to her dorm room, opened up her textbook, and turned to the chapter on the brain. She read about how the brain is made up of billions of neurons, which are the basic 6

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cellular units of the brain. These neurons help people to think, respond to the environment around them, maintain homeostasis, and move. “Aha!” Joyce said to herself. Maybe her mom’s strange walking and speech had to do with how her neurons were working. Joyce decided to ask her teacher after her next class how neurons communicated with each other and with muscles. Her teacher eventually directed her to a brief video on how neurons function:  Video 1: 2-Minute Neuroscience: The Neuron, 2014: < https://youtu.be/6qS83wD29PY > After examining neuron function, Joyce spent some time searching on the internet and came across a documentary video about a woman whose mom was diagnosed with a disease called Amyotrophic Lateral Sclerosis, or ALS:  Video 2: A Personal Story of ALS, 2017: < https://youtu.be/_OL2YOTTp_k > Joyce then did some research on what ALS is and watched a video about it:  Video 3: 2-Minute Neuroscience: Amyotrophic Lateral Sclerosis (ALS) , 2017. < https://youtu.be/kOnk9Hh20eg > 19. Draw a normal motor neuron in the space below (or insert a picture of your drawing) and label the major parts of that neuron. Labels on the figure should include dendrites, cell body, axons, myelin sheath, and the neuromuscular junction. In comparison, describe or diagram what a neuron might look like in a person diagnosed with ALS. Neurons in patients with ALS generally cause loss of control in muscles as neurons begin to die (degenerate). This is because ALS is called “movement-initiating nerve cells.” 7

Part 2 – When Things Go Wrong Joyce understood that DNA contains the information that codes for proteins. In addition, the segments of DNA that do code for particular proteins are called genes. Proteins are made by ribosomes based on the information given to them by the DNA, which is transcribed to mRNA for travel to the ribosomal site. The last step of protein synthesis is protein folding. The protein is folded precisely into a three-dimensional structure that is based on the order of the amino acids and can now play the correct biological role within the cell (Creighton, 1990). Mutations, which are changes to the DNA or the genetic sequence within a cell, can occur. Mutations may have no impact on protein production or they can have devastating consequences to the protein depending on which bases and the number of bases affected by the mutation (University of Utah, Genetic Science Learning Center, n.d.). Joyce wondered if mutations could play a role in the development of ALS and did some searching for possible causes of ALS (Muscular Dystrophy Association, n.d.). She found that there are in fact a large number of genes that have been identified as possible contributors to the development and progression of the disease. She also remembered from the video she watched that described ALS that patients displayed protein aggregates or clumps of irregular proteins in and around the neurons. One of the first mutations to be described in ALS patients was traced to mutations in the gene SOD-1 (Bunton- Stasyshyn, 2015). One of the functions of SOD-1 is to act as a sponge to a neurotransmitter called glutamate. Glutamate is a chemical released at the synaptic gap and is used to send a signal to the next neuron. Glutamate plays an important role in keeping the signals in the brain going. The bad part of glutamate is that it can be toxic if it accumulates to high levels at the synaptic gap. Research has shown that in addition to SOD-1 being mutated, ALS patients also display higher levels of glutamate in the fluid that bathes the brain and in the spinal cord when compared to controls (ALS Association: Disease Mechanisms, n.d.). If this excess glutamate builds up to high levels and the neurons get damaged, they may not be able to signal to the muscles, which can lead to the atrophy or destruction of the muscles that is seen in patients with ALS (Foran et al., 2009; Van Damme, et al., 2005). 20.What is the role of DNA in protein synthesis? The role of DNA in protein synthesis is to create a guideline for coding the proteins. 21.Explain why it is so critical that protein production occurs properly in cells. Include a discussion of how mutations can affect this process in your answer. It is critical that protein production occurs properly in cells because they are important to control cell division, metabolism, and flow of materials/information. Proteins are essential to cellular functions and even to create enzymes. Without proteins or a mistake can create diseases such as cancer. Therefore, it is important for synthase to be correct during protein production in order to prevent mutations from occurring which can affect one’s DNA. In the space below, briefly indicate how each trio member listed on page one contributed to the assignment. What contributions did each trio member make to the ALA? 8

Student #1 (Recorder) Write the answers and contribute ideas/answers Student #2 Contribute ideas/answers Student #3 Contribute ideas/answers Student #4 (most teams will only have three students) DON’T FORGET TO ENTER NAMES AT THE TOP OF PAGE 1! Recorder: Save completed assignment to your computer as a Word or PDF file then upload to Blackboard before leaving class today (ask if you need assistance uploading files to blackboard). 9

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