Action Potentials Extended
LABORATORY ONE
Action Potentials Extended In this lab you will work in pairs to experimentally manipulate simulated neurons to determine how membrane potentials and action potentials are generated.
Objectives of This Lab
Explain that action potential firing rate reflects stimuli intensity.
Explain that neurons have stimulus thresholds for producing action potentials.
Explain that transmission between neurons usually uses chemical neurotransmitter.
Explain that diffusion is the net movement of particles from a region of high concentration to a region of low concentration based on the random motion particles.
Predict and explain ion movement in response to diffusion and electric forces including application of the concept of the equilibrium potential (potential at which diffusion and electric forces are in balanced opposition, resulting in no net flow of ions).
Predict and explain changes in membrane potential based on membrane conductance to Na+ and K+ and ion movement.
Predict and explain changes in membrane potential based on concentrations of Na+ and K+ and ion movement.
Science Processes in This Lab
Predicting, Interpreting, Explaining and Applying.
I. Introduction Think back to the shower example from last week. Now that you know more about how neurons work via ions movement, we can go into more detail. Refer to the figure on page 1.2 throughout this more detailed description. Imagine you are about to take a shower in the morning before going to school. You have turned on the faucet to start the water as you prepare to get in the shower. After a few minutes, you expect the water to be a temperature that will be comfortable to enter. So you put your hand out into the spray of water. What happens next depends on how your nervous system interacts with the stimulus of the water temperature and what you do in response to that stimulus. Found in the skin of your fingers or toes is a type of sensory receptor that is sensitive to temperature, called a thermoreceptor. When you place your hand under the shower, the cell membrane of the thermoreceptors changes its electrical state (voltage) via the opening of ion channels. The amount of change is dependent on the strength of the stimulus (how hot the water is). This is called a graded potential. If the stimulus is strong, the voltage of the cell membrane will change enough to generate an electrical signal that will travel down the axon. The voltage at which such a signal is generated is called the threshold, and the resulting electrical signal is called an action potential. In this example, the action potential travels—a process known as propagation— along the axon from the axon hillock to the axon terminals and into the synaptic end bulbs. When this signal reaches the end bulbs, it causes the release of a signaling molecule called a neurotransmitter. The neurotransmitter diffuses across the short distance of the synapse and binds to a receptor protein of the target neuron. When the molecular signal binds to the receptor, the cell membrane of the target neuron changes its electrical state and a new graded potential begins. If that graded potential is strong enough to reach threshold, the second neuron generates an action potential at its axon hillock. The target of this neuron is another neuron in the thalamus of the brain, the part of the Neural Pathways adapted from The Function of Nervous Tissue. Download for free at http://cnx.org/contents/606c718b-c8b9-4091-b202-0a563fcc423c@5. B I O L O G Y 2 2 0 © J E N N I F E R D
2.1 O H E R T Y
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CNS that acts as a relay for sensory information. At another synapse, neurotransmitter is released and binds to its receptor. The thalamus then sends the sensory information to the cerebral cortex, the outermost layer of gray matter in the brain, where conscious perception of that water temperature begins. Within the cerebral cortex, information is processed among many neurons, integrating the stimulus of the water temperature with other sensory stimuli, with your emotional state (you just aren't ready to wake up; the bed is calling to you), memories (perhaps of the lab notes you have to study before a quiz). Finally, a plan is developed about what to do, whether that is to turn the temperature up, turn the whole shower off and go back to bed, or step into the shower. To do any of these things, the cerebral cortex has to send a command out to your body to move muscles. A region of the cortex is specialized for sending signals down to the spinal cord for movement. The upper motor neuron starts in this region and extends all the way down the spinal cord. At the level of the spinal cord this neuron synapses with the lower motor neuron. This second motor neuron is responsible for causing muscle cells to contract. Neural pathways adapted from The Function of Nervous Tissue. Download for free at http://cnx.org/contents/606c718b-c8b9-4091-b202-0a563fcc423c@5.
II. Logistics We will use a neuron simulation software for this lab. For the prelab assignment you will need to download and install the computer program at home. You will do the Pre-assessment and Section 1 as your pre-lab at home, due at the normal time Tuesday at 8 am. On Tuesday, we will sync Canvas with SimUText. Before Tuesday, you will not see your pre-lab points in Canvas. You will do Sections 2 and 3 in lab with your classmates. After lab you will do the Post-assessment at home. You do not have to do Sections 4 and 5. You may want to do Section 5 to practice. You can also choose to revisit Sections 2 and 3 at home to study. To create an account and download and install SimUText do the following. 1. Go here and create an account: https://www.simutext2.com/student/register.html#/key/UeE4gS7C-EqYR-sNvD-TTkH 2. You must use your UW email and UW student number (see example below) in your account. If you do not use this format you will not receive any credit. UW has paid for one SimUText account for each student. You need that account to be with your UW NetID to get points. If you do not use your NetID do NOT make another account, this costs money. Just change your login/username in settings. Login/Email: [email protected] Student ID: 1234567 3. Click the Create Account button. 4. Click the Continue button. 5. Agree to the license agreement. 6. Click Submit and Continue. Your copy of SimUText is paid for by UW. 7. Click Finish Registration. 8. Respond to the SimUText research statement. You can choose yes or no, it doesn’t impact your experience in this course. 9. Once you complete your registration, you must download and install the SimUText application. You will need the account information you created when you registered to log in to the SimUText System. 10. If you want to do your home assignments at a computer lab, you can run SimUText in a computer lab by using the following: Windows version: https://4562a2fe965fc513c93f63ec4fd6424632b65c1798e6fa5629ca.ssl.cf2.rackcdn.com/SimUText_20162017_Win_Setup_20161230.msi Mac OS X version: B I O L O G Y 2 2 0 © J E N N I F E R D
2.2 O H E R T Y
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https://4562a2fe965fc513c93f63ec4fd6424632b65c1798e6fa5629ca.ssl.cf2.rackcdn.com/SimUText_20162017_Mac_Installer_20161230.dmg Problems or questions? Visit SimUText Support (http://simbio.com/support/simutext) should you encounter problems, you may need your course-specific Access Key. It is: UeE4-gS7C-EqYRsNvD-TTkH After you have completed the subscription process, if you ever need to download the SimUText application installers again, you will be able to access them by logging into the SimUText Student Portal (https://www.simutext2.com/student).
III. Board Work Exercise 1: All eukaryotic cells have resting membrane potentials, not just animal cells and not just nerves. Imagine you have alive and functioning mammalian liver cells in three separate Petri dishes incubating at 37ºC. Each Petri dish contains a solution with a potassium concentration of 5 mM and each cell has an internal potassium concentration of 150 mM. You place a special electrode in each cell so you can manipulate the cell’s membrane potential. So, you can change the membrane potential, but not concentrations of K+. Make three flux thought organizers (i.e., include the concentrations given, membrane potential and an arrow for both driving forces) for the net movement of potassium in three conditions: A) When there is no net movement of K+ into or out of the cell. B) When net movement of K+ is out of the cell. C) When net movement of K+ is into the cell. Hint: The Nernst equation is what? Exercise 2: Your TA will assign you one of the three neuronal detective cases at the end of section 3. First, draw the standard action potential. Then, in another color, draw how the membrane potential was different for your case. Finally, make a diagram of a neuron (including channels and ion concentrations) and explain why the toxin, drug etc. had the impact on the neuron it did.
B I O L O G Y 2 2 0 © J E N N I F E R D
2.3 O H E R T Y
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Action Potentials Extended In this lab you will work in pairs to experimentally manipulate simulated neurons to determine how membrane potentials and action potentials are generated.
Objectives of This Lab
Explain that action potential firing rate reflects stimuli intensity.
Explain that neurons have stimulus thresholds for producing action potentials.
Explain that transmission between neurons usually uses chemical neurotransmitter.
Explain that diffusion is the net movement of particles from a region of high concentration to a region of low concentration based on the random motion particles.
Predict and explain ion movement in response to diffusion and electric forces including application of the concept of the equilibrium potential (potential at which diffusion and electric forces are in balanced opposition, resulting in no net flow of ions).
Predict and explain changes in membrane potential based on membrane conductance to Na+ and K+ and ion movement.
Predict and explain changes in membrane potential based on concentrations of Na+ and K+ and ion movement.
Science Processes in This Lab
Predicting, Interpreting, Explaining and Applying.
I. Introduction Think back to the shower example from last week. Now that you know more about how neurons work via ions movement, we can go into more detail. Refer to the figure on page 1.2 throughout this more detailed description. Imagine you are about to take a shower in the morning before going to school. You have turned on the faucet to start the water as you prepare to get in the shower. After a few minutes, you expect the water to be a temperature that will be comfortable to enter. So you put your hand out into the spray of water. What happens next depends on how your nervous system interacts with the stimulus of the water temperature and what you do in response to that stimulus. Found in the skin of your fingers or toes is a type of sensory receptor that is sensitive to temperature, called a thermoreceptor. When you place your hand under the shower, the cell membrane of the thermoreceptors changes its electrical state (voltage) via the opening of ion channels. The amount of change is dependent on the strength of the stimulus (how hot the water is). This is called a graded potential. If the stimulus is strong, the voltage of the cell membrane will change enough to generate an electrical signal that will travel down the axon. The voltage at which such a signal is generated is called the threshold, and the resulting electrical signal is called an action potential. In this example, the action potential travels—a process known as propagation— along the axon from the axon hillock to the axon terminals and into the synaptic end bulbs. When this signal reaches the end bulbs, it causes the release of a signaling molecule called a neurotransmitter. The neurotransmitter diffuses across the short distance of the synapse and binds to a receptor protein of the target neuron. When the molecular signal binds to the receptor, the cell membrane of the target neuron changes its electrical state and a new graded potential begins. If that graded potential is strong enough to reach threshold, the second neuron generates an action potential at its axon hillock. The target of this neuron is another neuron in the thalamus of the brain, the part of the Neural Pathways adapted from The Function of Nervous Tissue. Download for free at http://cnx.org/contents/606c718b-c8b9-4091-b202-0a563fcc423c@5. B I O L O G Y 2 2 0 © J E N N I F E R D
2.1 O H E R T Y
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U
N I V E R S I T Y
O F
W
A S H I N G T O N
A U T U M N ,
2 0 1 6
2 0 1 6
CNS that acts as a relay for sensory information. At another synapse, neurotransmitter is released and binds to its receptor. The thalamus then sends the sensory information to the cerebral cortex, the outermost layer of gray matter in the brain, where conscious perception of that water temperature begins. Within the cerebral cortex, information is processed among many neurons, integrating the stimulus of the water temperature with other sensory stimuli, with your emotional state (you just aren't ready to wake up; the bed is calling to you), memories (perhaps of the lab notes you have to study before a quiz). Finally, a plan is developed about what to do, whether that is to turn the temperature up, turn the whole shower off and go back to bed, or step into the shower. To do any of these things, the cerebral cortex has to send a command out to your body to move muscles. A region of the cortex is specialized for sending signals down to the spinal cord for movement. The upper motor neuron starts in this region and extends all the way down the spinal cord. At the level of the spinal cord this neuron synapses with the lower motor neuron. This second motor neuron is responsible for causing muscle cells to contract. Neural pathways adapted from The Function of Nervous Tissue. Download for free at http://cnx.org/contents/606c718b-c8b9-4091-b202-0a563fcc423c@5.
II. Logistics We will use a neuron simulation software for this lab. For the prelab assignment you will need to download and install the computer program at home. You will do the Pre-assessment and Section 1 as your pre-lab at home, due at the normal time Tuesday at 8 am. On Tuesday, we will sync Canvas with SimUText. Before Tuesday, you will not see your pre-lab points in Canvas. You will do Sections 2 and 3 in lab with your classmates. After lab you will do the Post-assessment at home. You do not have to do Sections 4 and 5. You may want to do Section 5 to practice. You can also choose to revisit Sections 2 and 3 at home to study. To create an account and download and install SimUText do the following. 1. Go here and create an account: https://www.simutext2.com/student/register.html#/key/UeE4gS7C-EqYR-sNvD-TTkH 2. You must use your UW email and UW student number (see example below) in your account. If you do not use this format you will not receive any credit. UW has paid for one SimUText account for each student. You need that account to be with your UW NetID to get points. If you do not use your NetID do NOT make another account, this costs money. Just change your login/username in settings. Login/Email: [email protected] Student ID: 1234567 3. Click the Create Account button. 4. Click the Continue button. 5. Agree to the license agreement. 6. Click Submit and Continue. Your copy of SimUText is paid for by UW. 7. Click Finish Registration. 8. Respond to the SimUText research statement. You can choose yes or no, it doesn’t impact your experience in this course. 9. Once you complete your registration, you must download and install the SimUText application. You will need the account information you created when you registered to log in to the SimUText System. 10. If you want to do your home assignments at a computer lab, you can run SimUText in a computer lab by using the following: Windows version: https://4562a2fe965fc513c93f63ec4fd6424632b65c1798e6fa5629ca.ssl.cf2.rackcdn.com/SimUText_20162017_Win_Setup_20161230.msi Mac OS X version: B I O L O G Y 2 2 0 © J E N N I F E R D
2.2 O H E R T Y
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N I V E R S I T Y
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A S H I N G T O N
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https://4562a2fe965fc513c93f63ec4fd6424632b65c1798e6fa5629ca.ssl.cf2.rackcdn.com/SimUText_20162017_Mac_Installer_20161230.dmg Problems or questions? Visit SimUText Support (http://simbio.com/support/simutext) should you encounter problems, you may need your course-specific Access Key. It is: UeE4-gS7C-EqYRsNvD-TTkH After you have completed the subscription process, if you ever need to download the SimUText application installers again, you will be able to access them by logging into the SimUText Student Portal (https://www.simutext2.com/student).
III. Board Work Exercise 1: All eukaryotic cells have resting membrane potentials, not just animal cells and not just nerves. Imagine you have alive and functioning mammalian liver cells in three separate Petri dishes incubating at 37ºC. Each Petri dish contains a solution with a potassium concentration of 5 mM and each cell has an internal potassium concentration of 150 mM. You place a special electrode in each cell so you can manipulate the cell’s membrane potential. So, you can change the membrane potential, but not concentrations of K+. Make three flux thought organizers (i.e., include the concentrations given, membrane potential and an arrow for both driving forces) for the net movement of potassium in three conditions: A) When there is no net movement of K+ into or out of the cell. B) When net movement of K+ is out of the cell. C) When net movement of K+ is into the cell. Hint: The Nernst equation is what? Exercise 2: Your TA will assign you one of the three neuronal detective cases at the end of section 3. First, draw the standard action potential. Then, in another color, draw how the membrane potential was different for your case. Finally, make a diagram of a neuron (including channels and ion concentrations) and explain why the toxin, drug etc. had the impact on the neuron it did.
B I O L O G Y 2 2 0 © J E N N I F E R D
2.3 O H E R T Y
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