Biology/ANNB 261 Exam 1 Spring, 2006

Transcription

1 Biology/ANNB 261 Exam 1 Spring, 2006 Name * = correct answer Multiple Choice: 1. Axons and dendrites are two types of a) Neurites * b) Organelles c) Synapses d) Receptors e) Golgi cell components 2. The three components of the cytoskeleton of a neuron are a) Actin, myosin, troponin b) Microtubules, neurofilaments, neurofibrillaries c) Neurofilaments, actin, microtubules * (microfilaments are made of actin molecules) d) Golgi apparatus, neurofilaments, neurotubules e) neurofilaments, neurotubules, microfilaments 3. This organelle is a major site of synthesis of proteins destined for the plasma membrane. a) Rough ER * b) Smooth ER c) Golgi apparatus d) Mitochondrion e) Nucleolus 4. Which of the following cells would be likely to myelinate an axon in your leg? a) Microglia b) Astrocytes c) Schwann cell * d) Oligodendroglia e) Golgi Type II glial cell 5. Some sensory neurons consist only of a soma and two neurites or processes. We might classify such neurons as a) Unipolar b) Bipolar * c) Multipolar d) Interneuron e) Efferent 6. Which of the following is a violation of the neuron doctrine as it was originally stated? a) Dendritic spines b) Gap junctions *

2 c) Synapses d) Second messenger systems e) B and C 7. Horseradish peroxidase is injected into your calf muscle, and it is transported from the terminals of the motor neurons to the cell bodies of the motor neurons in your spinal cord. This is an example of transport, which involves the movement of dynein along in the axons of the motor neurons. a) Anterograde; microfilaments b) Anterograde; microtubules c) Retrograde; microfilaments d) Retrograde; microtubules * e) Anterograde: neurofilaments 8. Postmortem examination of the brain of an Alzheimer s disease patient reveals the presence of neurofibrillary tangles in certain areas. These are believed to be caused by a) Entanglements of rough ER b) Neurofilament degradation c) Degeneration of microfilaments d) Disregulation of beta-amyloid e) Disregulation of a microtubule-associated protein (MAP) * 9. Which of the following is NOT thought to be a function of astrocytes? a) Phagocytosis b) Metabolic transport of nutrients necessary for normal neuronal function c) A component of the blood brain barrier d) Regulation of Ca 2+ concentrations around the synapse e) Transportation of neurotransmitter through the blood brain barrier * 10. Which of the following is true about microglia a) They regulate the chemical content of the extracellular space surrounding neurons b) They are responsible for myelinating axons c) They are able to perform phagocytosis within the CNS * d) They are important for providing structural support for neurons e) Actually, research has not been able to reveal their functions yet. 11. Suppose a neuron was selectively permeable only to Na + ions. What would happen to the membrane potential of this cell if K + channels then opened? a) V m would depolarize b) V m would hyperpolarize * c) The cell would fire an action potential d) Nothing would happen to the membrane potential e) None of the above 12. All of the following are true about the equilibrium potential of an ion EXCEPT ## Because of the wording of this question, I accepted c-e as the correct answer. a) It depends on the concentration of the ion inside and outside the neuron

3 b) It is the voltage at which diffusional and electrical forces on the ion are equal yet opposite c) It depends upon the permeability of the channel for potassium or sodium. d) It depends on the membrane conductance to that ion * e) There are no exceptions; all of the above are true 13. If you instantly destroyed all of the sodium/potassium pumps in your neurons, a) They could fire action potentials for a while but would eventually depolarize and die * b) They would depolarize and die within seconds c) They could no longer fire action potentials d) They would be unaffected e) They would become locked into the resting membrane potential 14. In a neuron at rest, a) Membrane is more permeable to potassium than it is to sodium b) Membrane potential is closer to the equilibrium potential for potassium than it is to the equilibrium potential for sodium c) Membrane is not permeable to sodium d) Membrane is not permeable to potassium e) A and b of the above are correct * 15. All of the following will increase the speed with which an axon conducts action potentials EXCEPT a) Having greater distance between the nodes of Ranvier b) Increasing the diameter of the axon c) Myelinating the axon d) Increasing the number of voltage-gated Na + channels e) There are no exceptions; all of the above are correct * 16. Enough positive current is injected into a neuron to depolarize the membrane to threshold. Which of the following would occur? a) Voltage-gated K + channels would open, K + ions would flow into the cell down their electrochemical gradient, and an action potential would be generated b) The injected current will flow back out of the cell until Vm has returned to the resting state c) The membrane potential is not affected by any kind of injected current d) Voltage-gated Na + channels would open, Na + ions would flow into the cell down their electrochemical gradient, and an action potential would be generated * e) Vm becomes clamped at a specific value 17. A person ingests a drug that alters voltage-gated sodium channels such that they no longer inactivate. What would be the consequences of being exposed to such a drug? a) The threshold for firing action potentials would decrease b) The threshold for firing action potentials would increase c) Action potentials would occur at a higher frequency d) The membrane would not repolarize rapidly after an action potential * e) The threshold of voltage-activated potassium channel is reached faster 18. If an axon at resting membrane potential was exposed to tetrodotoxin (TTX), the result would be

4 a) An action potential b) A very slow depolarization c) A rapid hyperpolarization d) TTX will have little or no effect on the resting membrane potential * e) No undershoot after the action potential 19. Cation M + is at electrochemical equilibrium when the membrane potential is at 45 mv. Which of the following is true? a) M + is more concentrated inside the cell * b) There is an equal concentration of M + on both sides of the cell membrane c) The membrane is impermeable to M + d) M + is more concentrated outside the cell e) A cation such as M + cannot have an electrochemical equilibrium as low as -45 mv. 20. The undershoot of an action potential is a direct result of a) Deinactivation of the voltage-gated sodium channels b) The action of the Na + /K + pump c) The opening of delayed rectifier K + channels * d) Na + leaving the cell e) An increase in sensitivity of the membrane to the effects of sodium influx 21. If delayed rectifier K + channels did not exist, the membrane would a) Never repolarize after an action potential b) Repolarize at a faster rate after an action potential c) Repolarize at a slower rate after an action potential * d) Require a voltage-activated Ca 2+ gate to repolarize the membrane e) Depolarize until the membrane reached 0 mv. 22. If V m = E K, then a) I k is zero * b) g k is zero c) E Na is negative d) V m = resting membrane potential e) Nernst equation is inapplicable 23. You discover an ion channel that, when open, is permeable to all ions. This channel lacks a) Gating b) Selectivity * c) Quaternary structure d) An alpha subunit e) A voltage sensing domain 24. What does an axon that conducts action potentials via saltatory conduction have that is unique from axons that do not conduct via saltatory conduction? a) Voltage-gated sodium channels b) Myelin *

5 c) Delayed rectifier channels d) Chemical synapses e) An axon hillock 25. You observe an action potential from a typical neuron; then you apply a toxin that blocks delayed rectifier voltage-gated potassium channels and observe the effects. What characteristics of the action potential would be changed? a) Duration of the action potential b) Undershoot (afterhyperpolarization) c) Resting membrane potential d) Both a and b * e) a, b, and c are all correct 26. Why is I K greater at the height of an action potential than at the resting membrane potential? # Corrected error in key a) Because delayed rectifier channels are open b) Because V m E K is greater at the height of an action potential * c) Because E K is greater d) Because I L has been activated e) a and b are correct but not c or d 27. The I A current differs from the I K current in that a. I A is a calcium current rather than a potassium current b. I A is activated after the I K current c) I A has a longer duration than I K when the membrane remains depolarized d) Compared to I K, I A adds only modestly to repolarization during the relative refractory period e) I A hyperpolarizes the membrane before the action potential rather than after * 28. An important characteristic of the I M current is that a) It can be regulated by synaptic transmitter activity * b) It hyperpolarizes the membrane before the action potential, slowing the onset of the action potential c) It is a short-duration current because of an inactivation gate d) It decreases the duration of the action potential e) It is based on a Ca 2+ activated channel 29. The I AHP current is a) a sodium current rather than a potassium current b) able to delay the onset of the action potential c) a slowly-developing Ca 2+ -activated potassium current * d) able to increase the number of action potentials evoked by a stimulus e) unaffected by synaptic neurotransmitter activity

6 30. How could you increase the length constant of a dendrite? a) Open up potassium channels in the membrane of the dendrite b) Close potassium channels in the membrane of the dendrite * c) Decrease the diameter of the dendrite d) Shorten the length of the dendrite e) Add an autoreceptor to the membrane 31. When a ligand binds to a receptor, the ligand a) Forms a complex with the receptor that can activate a kinase directly b) Phosphorylates the receptor c) Causes a conformational change in the receptor * d) Passes through the receptor to the inside of the cell e) Is responsible for the selectivity of the channel 32. The molecule that catalyzes the conversion of ATP to camp is a) Phospholipase C b) Adenylyl cyclase * c) Endonuclease d) Protein kinase e) The βγ complex of the G-protein 33. A presynaptic neuron fires at 10 action potentials (APs) per second, and the postsynaptic cell does not fire an AP. When the same presynaptic neuron fires at 20 APs per second, however, the postsynaptic cell fires. This is an example of a) Temporal summation * b) Spatial summation c) Shunting inhibition d) Axonal summation e) Quantal release 34. If a neuron lacked synapsin, what function would be disrupted? a) Generation of EPSPs b) Release of synaptic vesicles * c) Action potential propagation d) Calcium entry into the presynaptic terminal e) Endocytosis 35. Synaptic transmission involving G-protein-coupled receptors, compared with transmission involving ligand-gated ion channels, is a) Slower and involves more local postsynaptic changes b) Slower and involves more widespread postsynaptic changes * c) Slower and involves more efficient summation of the synaptic potentials d) Faster and involves more local postsynaptic changes e) Faster and involves more widespread postsynaptic changes

7 36. Inhibitory postsynaptic potentials (IPSPs) a) Keep a neuron away from threshold * b) Occur only at the soma c) Do not spatially summate d) Are always due to the opening of potassium channels e) Also occur on the presynaptic membrane 37. Which of the following acts as a second messenger in the cascade initiated by norepinephrine β receptors? # Corrected error in key a) Adenylyl cyclase b) Α subunit of the G-protein c) Protein kinase A d) GTP e) camp * 38. Shunting inhibition is characterized by a) Outward flow of chloride ions b) Influx of sodium current c) An increase in the threshold of the voltage-activated sodium gates d) A decrease in the membrane resistance * e) A decrease in the size of the action potential 39. Neurotransmitter desensitization occurs when a) Diffusion of the neurotransmitter occurs b) The neurotransmitter is removed by a glial cell c) An enzyme cleaves the neurotransmitter into parts d) Stays in the synapse for an extended time * e) a, b, and c are correct 40. In postsynaptic receptors that bind ACh, ion current flows when Vm is below the reversal potential of ACh, whereas current flows when Vm is above the reversal potential. a) into the cell, out of the cell * b) out of the cell, into the cell c) into the cell, outward because Cl - now contributes to the current d) out of the cell, into the cell because Cl - now contributes to the current e) in neither direction because the influx of Na + ions is equal to the efflux of K +

8 Exam 1 Short answer Name Briefly define or describe 3 of the following 5 (4 points each): 1. PSE (give me the name and function) (lecture) Presynaptic excitation - synaptic depolarization which leads to increased Ca2+ influx and more exocytosis of neurotransmitter. Can be result of depolarization at axoaxonic synapse. 2. Neuromodulator (p 129) Does not produce a synaptic potential by itself but modifies synaptic potentials produced by neurotransmitters 3. Kiss-and-run endocytosis (lecture) During exocytosis, the vesicle does not completely integrate itself into the plasma membrane, rather releases NT and then reforms into vesicle. Occurs with low to normal rates of AP. 4. SNARE (text and lecture) SNAREs (SNAP receptors which are Soluble NSF-attachment proteins. Synaptobrevin: in membrane of vesicle ( v-snare ) Syntaxin and SNAP-25 are in plasma membrane ( t-snare for target membrane) These SNARE proteins form a macromolecular complex that binds the vesicle to the plasma membrane 5. Nernst equation (text and lecture) Formula or math relationship which allows one to compute the ionic equilibrium potential. Based on log ratio of concentrations of the ion on both sides of the membrane and several variables such as the valence and charge of the ion and the gas constant. Best if you gave the formula. Essay (15 points): You have discovered a new neuron and you need to determine which ions are responsible for its resting membrane state. You decide to use the voltage clamp method for your experiments. (text and lecture) 1) What is the voltage clamp method and what does it tell you? Method in which the experimenter can clamp or hold the Vm constant and measure changes in membrane conductance/ currents at different voltages. This based on the relationship described by Ohm s Law (Vm = Iion*Resistance or its variations) 2) How would you use this method to determine if Na + or K + is contributing to the resting membrane potential? This answer could be approached several ways. Most likely you would step Vm in (e.g.,) 20 mv increments from some very hyperpolarized point (-100 mv) to some very depolarized point (e.g., +160 mv) while manipulating either concentrations of each ion or the conductance of Na+ or K+ channels. E.g. In the simplest acceptable method, you could either increase or decrease the concentration of each ion while holding the concentration of the other ion constant. Answer to part 3 then had to be consistent with this approach. (For this to work, you would want to also add TTX to stop the voltage-activated Na+ gates and an Action Potential but I did not require that as part of the answer.)

9 You could also use either substitute ions (substituting 1 at a time) that will not go through the channels but will maintain the electrical gradient or you could use a poison or a drug that blocks conductance of one of the two types of channels, while measuring the remaining current flow. 3) What results would you expect to see if either of these two ions are contributing to the RMP? For the first method in #2, you have to make it real clear that you are making assumptions that Na+ and K+ are present in normal concentrations inside and outside your new neuron (likely to be true) and that you expect to see an inward current at low Vm due to greater influx of Na+ than K+ efflux. This current reverses to an outward current around 0 mv, which is due to Na+ influx weakening and K+ efflux becoming the stronger current. If your new neuron is similar to a typical neuron, you will find that the K+ current is more important for RMP and that the K+ current will be stronger impact on RMP than the Na+ current when you change the concentrations of each ion because the K+ channels are much more permeable than the Na+ current. For another set of potential methods for #2: Blocking K+ leaves only the Na+ current. You would expect that there would be an inward current which gets weaker as Vm gets closer to Na+ Eq some point above 0 mv. Blocking Na+ channels leaves K+ current. You would expect an outward current which gets stronger as Vm becomes more depolarized (further away from E K ). While it would not be expected for a RMP of a typical neuron, you will get extra credit if you also checked for an inactivation gate but you needed to explain what you expect as a result. You would get additional credit if you also considered what would happen if concentrations of each ion were DIFFERENT from the normal neuron but you needed to be real clear about this situation and what you expected to find.