Human physiology an integrated approach 7th edition by silverthorn test bank

Human Physiology: 7th Edition Test Bank – Silverthorn Sample Chapter Neurons: Cellular and Network Properties 1) The portions of a neuron that extend off of the roughly spherical cell body are usually collectively called A) protrusions B) processes C) prostheses D) projections Answer: B Section: Cells of the Nervous System Learning Outcome: 8.2 Bloom’s Taxonomy: Knowledge 2) Detailed understanding of the cellular basis of signaling in the nervous system has led to good understanding of consciousness, intelligence, and emotion A) True B) False Answer: B Section: Organization of the Nervous System Learning Outcome: 8.1 Bloom’s Taxonomy: Knowledge 3) Neurotransmitter is stored and released from A) axon terminals only B) axon varicosities only C) dendritic spines only D) cell bodies only E) axon terminals and axon varicosities Answer: E Section: Cells of the Nervous System Learning Outcome: 8.2 Bloom’s Taxonomy: Knowledge 4) Information coming into the central nervous system is transmitted along neurons A) afferent B) sensory C) efferent D) afferent and sensory E) sensory and efferent Answer: D Section: Organization of the Nervous System Learning Outcome: 8.1 Bloom’s Taxonomy: Knowledge 5) The afferent and efferent axons together form the A) central nervous system B) autonomic division system C) somatic motor division of the nervous system D) peripheral nervous system E) visceral nervous system Answer: D Section: Organization of the Nervous System Learning Outcome: 8.1 Bloom’s Taxonomy: Knowledge 6) The brain and spinal cord together compose the A) central nervous system B) autonomic division system C) somatic motor division of the nervous system D) peripheral nervous system E) visceral nervous system Answer: A Section: Organization of the Nervous System Learning Outcome: 8.1 Bloom’s Taxonomy: Knowledge 7) Exocrine glands, smooth muscles, and cardiac muscles are controlled by the A) central nervous system B) autonomic nervous system C) somatic motor division D) peripheral nervous system E) enteric nervous system Answer: B Section: Organization of the Nervous System Learning Outcome: 8.1 Bloom’s Taxonomy: Knowledge 8) Autonomic motor neurons are subdivided into the A) visceral and somatic divisions B) sympathetic and parasympathetic divisions C) central and peripheral divisions D) visceral and enteric divisions E) somatic and enteric divisions Answer: B Section: Organization of the Nervous System Learning Outcome: 8.1 Bloom’s Taxonomy: Knowledge 9) The enteric nervous system is a network of neurons that function in controlling A) reproduction B) digestion C) excretion, particularly urination D) the skeletal system E) the endocrine system Answer: B Section: Organization of the Nervous System Learning Outcome: 8.1 Bloom’s Taxonomy: Knowledge 10) In general, the nervous system is composed of which two types of cells? motor neurons sensory glial associative A) and B) and C) and D) and 10 E) and Answer: C Section: Cells of the Nervous System Learning Outcome: 8.1 Bloom’s Taxonomy: Knowledge 11) The cell body of neurons is generally A) 90% of the cell volume B) 50% of the cell volume C) 10% of the cell volume D) found in the same position on every neuron Answer: C Section: Cells of the Nervous System Learning Outcome: 8.2 Bloom’s Taxonomy: Knowledge 12) Interneurons are found A) only in the brain B) only in the spinal cord C) only in the CNS D) throughout the nervous system E) only in spinal nerves Answer: C Section: Cells of the Nervous System Learning Outcome: 8.1 Bloom’s Taxonomy: Knowledge 13) The multiple thin, branched structures on a neuron whose main function is to receive incoming signals are the A) cell bodies B) axons C) dendrites D) somata E) None of the answers are correct Answer: C Section: Cells of the Nervous System Learning Outcome: 8.3 Bloom’s Taxonomy: Knowledge 14) The collection of axons that carries information between the central nervous system and the peripheral effectors is called the A) axon hillock B) varicosity C) axon D) dendrite E) nerve Answer: E Section: Cells of the Nervous System Learning Outcome: 8.2 Bloom’s Taxonomy: Knowledge 15) The region where the axon terminal meets its target cell is called the A) collateral B) hillock C) synapse D) nerve E) dendrites Answer: C Section: Cells of the Nervous System Learning Outcome: 8.3 Bloom’s Taxonomy: Knowledge 16) The axon is connected to the cell body by the A) myelin sheath B) axon terminal C) collaterals D) axon hillock E) synapse Answer: D Section: Cells of the Nervous System Learning Outcome: 8.2 Bloom’s Taxonomy: Knowledge 17) Branches that sometimes occur along the length of an axon are called A) dendrites B) axon terminals C) collaterals D) axon hillocks E) synapses Answer: C Section: Cells of the Nervous System Learning Outcome: 8.2 Bloom’s Taxonomy: Knowledge 18) Neurotransmitters are released from the A) dendrites B) axon terminals C) collaterals D) axon hillock E) synapse Answer: B Section: Cells of the Nervous System Learning Outcome: 8.3 Bloom’s Taxonomy: Knowledge 19) The term axonal transport refers to A) the release of neurotransmitter molecules from the axon B) the transport of microtubules to the axon for structural support C) vesicle transport of proteins and organelles down the axon D) the movement of the axon terminal to synapse with a new postsynaptic cell E) None of the answers are correct Answer: C Section: Cells of the Nervous System Learning Outcome: 8.2 Bloom’s Taxonomy: Knowledge 20) Anterograde and retrograde axonal transport are forms of transport A) fast B) slow C) Neither of these Answer: A Section: Cells of the Nervous System Learning Outcome: 8.2 Bloom’s Taxonomy: Knowledge 21) Clusters of nerve cell bodies in the peripheral nervous system are called A) microglia B) neuroglia C) glia D) ganglia E) nodes Answer: D Section: Organization of the Nervous System Learning Outcome: 8.1 Bloom’s Taxonomy: Knowledge 22) Glial cells A) only provide structural and metabolic support B) only guide neurons during growth and repair C) only help maintain homeostasis of the brain’s extracellular fluid D) provide structural and metabolic support and help maintain homeostasis of the brain’s extracellular fluid E) All of the answers are correct Answer: E Section: Cells of the Nervous System Learning Outcome: 8.4 Bloom’s Taxonomy: Knowledge 23) Glial cells communicate primarily using A) electrical signals only B) chemical signals only C) neurotransmitters only D) neuromodulators only E) electrical signals and chemical signals Answer: B Section: Cells of the Nervous System Learning Outcome: 8.4 Bloom’s Taxonomy: Knowledge 24) Myelin is formed by A) axons only B) Schwann cells only C) oligodendrocytes only D) Schwann cells and oligodendrocytes Answer: D Section: Cells of the Nervous System Learning Outcome: 8.4 Bloom’s Taxonomy: Knowledge 25) These glial cells act as scavengers A) Schwann cells B) astrocytes C) microglia D) oligodendrocytes E) ependymal cells Answer: C Refractory periods also explain why action potentials cannot move backward (See Fig 8.15.) The part of the axon experiencing the action potential has open Na+ channels An increase in Na+ inside the cell causes depolarization and perpetuates the action potential toward the axon terminal due to local current flow The area of the axon toward the trigger zone, where the action potential (AP) occurred a moment earlier, is in the absolute refractory period and will not experience another action potential even with a depolarization Section: Electrical Signals in Neurons Learning Outcome: 8.8, 8.9 Bloom’s Taxonomy: Comprehension 198) Explain the two reasons why graded potentials lose strength as they move through the cell Why don’t action potentials lose strength? Answer: As a depolarization wave moves through the cell, some of the positive charge is lost to the extracellular fluid through leak channels Additionally there is cytoplasmic resistance Action potentials not lose strength because they are regenerated in each patch of membrane Section: Electrical Signals in Neurons Learning Outcome: 8.7 Bloom’s Taxonomy: Comprehension 199) Compare and contrast the EPSP, IPSP, and action potential as to ions involved, all-or-none law application, specific cellular locations, and specific cell types involved Answer: EPSPs and IPSPs are graded potentials in postsynaptic cells resulting from the action of neurotransmitters at synapses, which are usually on dendrites of multipolar neurons, but could also be on the synaptic region of any target cell EPSPs increase the probability that a postsynaptic action potential will result, because they involve an influx of sodium, which depolarizes the membrane potential, bringing it closer to threshold IPSPs decrease the probability that a postsynaptic action potential will result, because they involve either an influx of chloride or an efflux of potassium, either of which hyperpolarizes the membrane potential, moving it farther from threshold Action potentials occur in axons of neurons, or in muscle cell membranes They may result from PSPs or in the case of sensory neurons, specific stimuli such as sound or odor, which cause a type of graded potential called a receptor potential Action potentials begin when graded potentials depolarize the membrane potential to threshold The rising phase of an action potential results from sodium influx, and the falling phase from potassium efflux Action potentials, but not graded potentials, are an all-or-none phenomenon Section: Integration of Neural Information Transfer Learning Outcome: 8.14 Bloom’s Taxonomy: Comprehension 200) Define temporal and spatial summation Where does the summation occur? Are these processes mutually exclusive, or can they occur at the same time in a typical multipolar neuron? What key property of neurons these forms of summation demonstrate? Answer: See Figs 8.24 and 8.25 in the chapter Temporal summation is the addition of graded potentials that overlap in time; that is, a second potential arrives before the first one from that source has finished Spatial summation occurs when there is simultaneous arrival of graded potentials originating from more than one synaptic input Summation occurs at the trigger zone Typically a multipolar neuron has many active synapses at a given time, with multiple potentials being produced at each Summation demonstrates postsynaptic integration Section: Integration of Neural Information Transfer Learning Outcome: 8.15 Bloom’s Taxonomy: Comprehension 201) Your study partner has concluded that a single action potential, once initiated, spreads down the length of an axon, non-decrementally; similarly, a single graded potential spreads down the length of a dendrite, but with decrement Is she completely correct? Explain How can the mechanism of decremental and non-decremental conduction help her sort this out? How is the process different in myelinated vs unmyelinated neurons? How may the dominoes analogy help her to understand signal propagation? Answer: While she is correct about graded potentials, she is incorrect about action potentials A GP is initiated at a synapse, for example, and spreads in all directions but loses strength as the ions diffuse; no additional ions are crossing the membrane to boost this signal An AP is initiated at a trigger zone, then a second, identical AP is triggered in the next patch of membrane as more ions enter the cell; thus, there was no decrement of the AP Between membrane patches, the signal is decremental for the same reasons that GPs decrease with spread, but sufficient to stimulate the next AP In myelinated axons, the subsequent APs are farther apart than in unmyelinated axons A row of dominoes, if spaced appropriately, can be felled by pushing on just the first one That domino falls and does not spread to the end of the row, but it causes its neighboring, identical domino to fall, and so on Section: Electrical Signals in Neurons Learning Outcome: 8.7 Bloom’s Taxonomy: Analysis 202) Polio is an uncommon disease in most developed countries, but prior to widespread use of the polio vaccine, it was very common Polio is caused by a virus that infects somatic motor neurons and destroys them From this information, would you expect a polio victim to lose sensation, motor control, other organ function, and/or cognitive function? Explain While most victims of polio survive, some not What is the most likely cause of death? Answer: If only motor neurons are affected, the primary result should be paralysis or inability to control skeletal muscles Because respiration involves skeletal muscles, some victims die of suffocation Section: Organization of the Nervous System Learning Outcome: 8.1 Bloom’s Taxonomy: Analysis 203) In a laboratory situation, a nerve can be stimulated by applying voltage from a stimulator If a stimulus was applied in the middle of a nerve roughly halfway between the cell bodies and the axon terminals, would resulting action potentials travel only from the stimulus point to the axon terminal? Why or why not? How is this similar to or different from the basic characteristics of an action potential discussed in this chapter? What does this tell you about the nature of the axon? Answer: Action potentials would travel in both directions from the stimulus point, simultaneously toward the cell bodies and toward the axon terminals This is because the axon segments on each side of the stimulus point are presumably not refractory when the stimulus is delivered, thus there is nothing to prevent the action potentials from traveling in both directions In normal transmission, the action potential begins where the axon starts, and travels only away from that point, not toward, because the membrane becomes refractory for a period of time after the action potential occurs Thus, the axon is quite capable of transmitting action potentials in either direction, even though normally it is prevented from doing so Section: Electrical Signals in Neurons Learning Outcome: 8.9 Bloom’s Taxonomy: Application 204) Dr Zoydburger has discovered a toxin produced in the venom of a poisonous marine invertebrate Tests on lab mammals indicate that this toxin prevents sodium channel inactivation How would this affect the action potentials produced in the neurons of a poisoned mammal? Answer: Without sodium channel inactivation, the action potential would not repolarize as quickly, thus any function dependent upon the action potential would be prolonged, including neurotransmitter release and postsynaptic response Also, the refractory period would not exist, thus action potentials would travel back up the axon, and down again, repeatedly Section: Electrical Signals in Neurons Learning Outcome: 8.8, 8.9 Bloom’s Taxonomy: Application 205) Your study partner in your physiology class insists that axons conduct graded potentials, and that they play a vital role in production of the action potential Do you agree or disagree? Defend your answer Answer: Your study partner is correct This is easiest to explain in the context of the myelinated axon Voltage-regulated ion channels, which produce the action potential, are located only at nodes of Ranvier This means that the intervening regions not generate action potentials After an action potential is produced at one node, the ions diffuse from this node to the next in a decremental manner, but produce sufficient depolarization at the next node to produce an action potential there Section: Electrical Signals in Neurons Learning Outcome: 8.7 Bloom’s Taxonomy: Application 206) A compound action potential is recorded using electrodes on a nerve How does a nerve differ from an axon? Amplitude and duration of a compound action potential vary according to the stimulus intensity applied to the nerve Given that there is no such variation in the action potential of a single axon, how can you explain this? Answer: A nerve consists of many axons A regular action potential is produced by a single axon, whereas a compound action potential is recorded by equipment from a nerve when multiple axons are producing action potentials, and the voltages add together Increasing stimulus intensity increases the number of axons contributing to the compound action potential This is because different axons have different threshold voltages, so increasing the voltage stimulates a larger number of axons Section: Electrical Signals in Neurons Learning Outcome: 8.2, 8.8 Bloom’s Taxonomy: Analysis 207) Explain the processes that lead to the exocytosis of neurotransmitter from a presynaptic cell Which components are recycled? Which ion is important in triggering exocytosis? Answer: Action potential arrives in synaptic terminal, and stimulates opening of voltageregulated calcium channels The resulting calcium influx triggers exocytosis of synaptic vesicle contents The phospholipids of the vesicle membranes are recycled, either from fusion of vesicles then later formation of new vesicles from the same molecules; or from the kiss-and-run model, in which the vesicle phospholipids are not incorporated into the membrane at all, but remain as vesicles that can be refilled with neurotransmitter Section: Cell-to-Cell Communication in the Nervous System Learning Outcome: 8.13 Bloom’s Taxonomy: Comprehension 208) How the following relate to nervous system development and/or healing? Synaptic plasticity, neuroglia, neurotrophic factors Answer: Synaptic plasticity is the changeability of synapses, necessary for development and continued learning in the nervous system Neuroglia play an important role in healing of damaged neural tissue Schwann cells in the PNS facilitate regrowth of severed axons CNS glia seal off and scar a damaged region Neurotrophic factors are important in maintaining active synapses Section: Organization of the Nervous System Learning Outcome: 8.1 Bloom’s Taxonomy: Application 209) The disease rabies is caused by a virus that attacks the central nervous system The virus is normally introduced when an infected animal bites another, breaking the surface of the skin and allowing the entry of saliva containing the virus Since the virus cannot move by itself, how does it get to neurons in the central nervous system? Answer: Circulation of the lymph may spread the virus throughout the body Retrograde axonal transport brings the viral particles to the nerve cell bodies in the spinal cord Section: Cells of the Nervous System Learning Outcome: 8.2 Bloom’s Taxonomy: Application 210) In multiple sclerosis, there is progressive and intermittent damage to the myelin sheath of central axons One symptom is poor motor control of the affected area Why does destruction of the myelin sheath affect motor control? Answer: Loss of myelin slows or stops impulse conduction, preventing descending tracts from regulating spinal motor neurons, and leading to loss of coordination and the ability to correct for gravity, movement, and so on Section: Electrical Signals in Neurons Learning Outcome: 8.10 Bloom’s Taxonomy: Comprehension 211) Multiple sclerosis (MS) is one of the better known diseases resulting from demyelination of axons (in MS, only CNS axons are affected) Some of the earliest symptoms of the disease are difficulty in focusing the eyes, such as in reading, and difficulty in maintaining balance, and frequently not being able to make adjustments in posture to avoid falling How these symptoms “fit” with what you know about nerve impulses, myelin sheaths, and the location of gated ion channels in the membranes of axons? Answer: Symptoms listed all involve loss of motor control The CNS axons involved in initiating and controlling movement are generally myelinated, thus loss of myelination slows or eliminates conduction of action potentials in these cells Early on, many signals arrive normally at spinal motor neurons to produce movement, but enough signals are missing to cause noticeable alterations in motor control In other words, loss of myelin slows or stops impulse conduction and leads to loss of coordination and the ability to correct for gravity, movement, and so on Gated ion channels should be intact at the nodes of Ranvier, but missing elsewhere along the axon Nodes are generally far enough apart that without myelin, sufficient positive current from one active node does not arrive at the next node to bring it to threshold as quickly as normal or at all, and impulse conduction slows or stops Section: Electrical Signals in Neurons Learning Outcome: 8.10 Bloom’s Taxonomy: Application 212) What factors determine the maximum frequency of action potentials conducted by an axon? Answer: Maximum frequency is mostly dependent upon the duration of the absolute refractory period, which determines the upper limit The diameter of the axon, amount of myelination present, and the magnitude of the Na+ and K+ gradients across the axonal membrane all affect action potential velocity may also play a secondary role Section: Electrical Signals in Neurons Learning Outcome: 8.4 Bloom’s Taxonomy: Knowledge 213) Compare and contrast the communication mechanisms between the nervous and endocrine systems In other words, how neurons and neurotransmitters signal to their postsynaptic cells, compared to the way endocrine glands and hormones communicate with their target cells? Answer: (Note to instructor: Students must have already completed the endocrine chapter(s) in order to answer this.) Neurotransmitters usually not enter the cell, thus must combine with receptors on the membrane, using mechanisms similar to the amino acid-derivative hormones Similarities include opening channels in the postsynaptic cell membrane, leading to depolarization of the neuron In endocrine target cells, the arrival of the stimulus begins a different sequence of events, such as triggering an enzyme cascade, and second messenger systems Section: Cell-to-Cell Communication in the Nervous System Learning Outcome: 8.13 Bloom’s Taxonomy: Application 214) You and your lab partner have prepared a frog nerve for gathering data on action potentials You connect an electronic stimulator to the nerve and ask your partner to gradually increase the voltage until you see an action potential Your partner says that the voltage knob is stuck, that is, it will not increase the voltage Is there another way to trigger action potentials using this stimulator? If so, what you tell your partner to do? Answer: Your lab partner can increase the stimulus frequency instead A higher frequency of stimuli can result in temporal summation of graded potentials such that the lower voltages sum to threshold Section: Integration of Neural Information Transfer Learning Outcome: 8.15 Bloom’s Taxonomy: Comprehension 215) A lab technician has inadvertently substituted lithium for sodium in a solution of saline for use by students in neurophysiology labs If a frog nerve was bathed in this solution, what would happen upon stimulation of the nerve? Answer: Assuming the specificity of the voltage-regulated sodium and potassium channels is absolute, the axons will be unable to generate action potentials The sodium channels will open and close, but there will be no ionic current through them The students will still see hyperpolarization, as the potassium efflux should be unaffected by lithium Section: Electrical Signals in Neurons Learning Outcome: 8.8 Bloom’s Taxonomy: Analysis 216) Explain the differences in axon regeneration in the CNS and PNS, and the implications for recovery from injury What experiments might scientists try based on these differences? Answer: Schwann cells, present in the PNS but not the CNS, facilitate regrowth of severed axons This means that people not recover as well from CNS injury compared to PNS injury It is possible that there is something fundamentally different in CNS axons compared to PNS axons that accounts for this effect To test for this, Schwann cells could be transplanted into the spinal cord or brain and CNS axons observed for regrowth Such experiments have been done, and it is the case that CNS axons are capable of regrowth in the presence of Schwann cells Identification of chemical or physical factors in the Schwann cells would advance this field of research Section: Cells of the Nervous System Learning Outcome: 8.4 Bloom’s Taxonomy: Application 217) Create diagrams (of the cells) and graphs (of the potentials) to illustrate the two different situations described below in a multipolar neuron with a threshold voltage of 15 mV above resting potential In each, indicate decrement of graded potentials (by drawing the same GP at different points as it spreads along the neuron), as well as summation Situation 1: There are three simultaneously active synapses on the multipolar neuron, two producing EPSPs and one an IPSP At least one of the EPSPs is larger than 15 mV at the synapse The neuron does NOT generate an action potential Situation 2: There are two simultaneously active synapses, one producing an EPSP and the other an IPSP The neuron generates an action potential Answer: (Note to instructor: It is best to have demonstrated this in class or on a handout at some time prior to the exam.) Diagrams and graphs should resemble those in Figure 8.7 in the chapter, except that the number of synaptic inputs shown will be greater (see Fig 8.24), and a set of graphs should be drawn for each input Diagrams of a multipolar neuron with the different synapses indicated should be produced There should be a total of three to five synapses, depending on whether or not the student assumes the three synapses described for situation are different from those for situation The graph of summation should resemble Figure 8.24c,d In situation 1, the student should choose amplitudes that sum to a value below +15 mV (the PSP that was 15 mV at the synapse is smaller when it reaches the trigger zone) In situation 2, the student should choose amplitudes that sum to a value equal to or above +15 mV Section: Integration of Neural Information Transfer Learning Outcome: 8.14 Bloom’s Taxonomy: Application 218) We have finally discovered life on Venus NASA scientists are investigating a newly discovered life form: a single-celled organism found in the swampy canals You have been contracted by NASA to perform an electrophysiology study Using intracellular electrodes to measure the electrical charge inside the cell, you find it has a resting membrane potential of -45 mV when the outside fluid is arbitrarily set to mV Additionally, you have determined ion concentrations and listed them below [ ] in mOsm/L K+ Na+ Cl- Cell Swamp 15 40 150 175 40 For fun, you have used new molecular biology techniques to insert protein channels into the cell membrane that allow only Na+ and Cl- to pass Predict which ion(s) will move Tell what direction it (they) will move and what force(s) is/are acting on it (them) Answer: K+ cannot move because, without potassium channels, the membrane is not permeable to it Na+ will move into the cell because both its chemical and electrical gradients favor movement in Cl- leaves the cell due to the electrical gradient (the negative resting potential repels it) Section: Electrical Signals in Neurons Learning Outcome: 8.8 Bloom’s Taxonomy: Analysis 219) Use the Nernst equation to predict the membrane potential for each ion Answer: EK+ = 61 log 150/5 = 90.10 mV, ENa+ = 61 log 175/15 = 65.08 mV, ECl- = -61 log 40/40 = m Section: Electrical Signals in Neurons Learning Outcome: 8.5 Bloom’s Taxonomy: Application 220) If an axon has an absolute refractory period of msec, what is the maximum frequency of action potential (AP) production in that neuron? Answer: X AP/2 msec × 1000 msec/1 sec = 500 APs per second Section: Electrical Signals in Neurons Learning Outcome: 8.4 Bloom’s Taxonomy: Analysis 221) Draw and label an action potential, in the form of a graph Answer: Graph should be similar to Figure 8.9 in the chapter Section: Electrical Signals in Neurons Learning Outcome: 8.8 Bloom’s Taxonomy: Comprehension 222) Draw a graph showing change in membrane permeability (don’t worry about including the units of permeability) to sodium and potassium during the course of an action potential For reference, superimpose a graph of the action potential Answer: Graph should resemble Figure 8.9 in the chapter Section: Electrical Signals in Neurons Learning Outcome: 8.8 Bloom’s Taxonomy: Comprehension 223) Draw a graph showing what would happen to resting membrane potential over time, if the sodium/potassium pump were not functioning How would this affect a neuron’s ability to produce action potentials? What does this imply about the quantity of ions that normally cross the membrane during the course of an action potential? Answer: It would be appropriate for the student to draw action potentials on the graph beginning at the point where the resting potential drifts up to threshold, and decreasing in frequency as the resting potential approaches Very gradually, a cell’s resting membrane potential would increase until it reached and stabilized there At that point the ions would be in equilibrium, and no further net flow of charge would occur There would be no effect on ability to generate action potentials initially, but with the disappearance of the differential distribution of sodium and potassium upon which the action potential depends, action potentials would gradually come to a stop This points out the fact that during any single action potential, so few ions cross the membrane that there is no significant change in ion concentrations Thousands of action potentials would be required before the absence of the sodium-potassium pumps would be noticeable Section: Electrical Signals in Neurons Learning Outcome: 8.8 Bloom’s Taxonomy: Application 224) The amplitude of an action potential depends in part on the amount of sodium in the extracellular fluid Stanley Student has carefully impaled a neuron with an intracellular electrode He tests the role of extracellular sodium by changing the concentration in the bathing fluid and recording an action potential after each change The data he generated are shown in the table, where amplitude listed is the peak amplitude of the action potential; make an appropriate graph Conc Sodium (mOsM) 100 120 140 160 180 200 Amp (mV) 90 91 92 94 96 10 Answer: Section: Electrical Signals in Neurons Learning Outcome: 8.4 Bloom’s Taxonomy: Application 225) Draw graphs showing the effects of hypokalemia and hyperkalemia on action potential production Don’t worry about exact millivolt values — the point is to show that you understand the effects of these conditions relative to normal Answer: Graphs should resemble Figure 8.17 in the chapter Section: Electrical Signals in Neurons Learning Outcome: 8.10 Bloom’s Taxonomy: Application 226) In the graphs below, identify normokalemia, hyperkalemia, and hypokalemia Answer: See Figure 8.17 in the chapter Section: Electrical Signals in Neurons Learning Outcome: 8.10 Bloom’s Taxonomy: Comprehension 227) Draw graphs showing the effect on action potentials in a cell following effective doses of each of the listed neurotoxins Assume that the cell is normally brought to threshold by an electrical stimulus applied to it, so that any abnormality is due to the toxin Precise values for voltage and duration are not important, just a general trend in how the action potential may be different from normal puffer fish poison (blocks voltage-gated sodium channel activation) tetraethylammonium (blocks voltage-gated potassium channels) ouabain (blocks sodium-potassium pumps) sea anemone toxin (blocks voltage-gated sodium channel inactivation) Answer: no action potential; membrane potential would show a stimulus pulse that reaches threshold, however prolonged action potential, as repolarization is slowed in absence of potassium efflux; peak may be higher as well normal action potential prolonged action potential, as sodium influx lasts longer; peak may be higher as well Section: Cell-to-Cell Communication in the Nervous System Learning Outcome: 8.4 Bloom’s Taxonomy: Application 228) Draw graphs showing the effects on action potentials in a postsynaptic cell of effective doses for each of the listed toxins Assume that the cell is normally brought to threshold by the stimuli applied to its inputs, so that any abnormality is due to the toxin curare (prevents receptor from binding neurotransmitter) botulinum toxin (prevents neurotransmitter release) Answer: In both cases, action potential is prevented, because the postsynaptic potential is blocked Membrane potential would remain at resting potential, because even a subthreshold postsynaptic potential fails to appear in the absence of neurotransmitter action Section: Cell-to-Cell Communication in the Nervous System Learning Outcome: 8.6 Bloom’s Taxonomy: Application 229) Explain the roles that the AMPA and NMDA receptors play in long-term potentiation Answer: Both AMPA and NMDA receptors are located on the postsynaptic cells (dendrites) and require binding of the excitatory neurotransmitter glutamate for activation When glutamate binds to the AMPA receptor, the channel opens and Na enters the cell This causes depolarization of the immediate postsynaptic cell or dendrite This depolarization causes Mg2+ ions to be “kicked out” of the NMDA receptor channel; hence, Mg2+ is no longer acting as a channel blocker If at the same time glutamate is bound to the NMDA receptor then the channel gate is open and Ca2+ enters the cell The entry of Ca2+ triggers 2nd messenger pathways that result in an increase in the number of glutamate receptors inserted into the post-synaptic membrane This increases the probability of an increase in the postsynaptic response or depolarization to glutamate that is referred to as long-term potentiation Section: Integration of Neural Information Transfer Learning Outcome: 8.9 Bloom’s Taxonomy: Comprehension