PHSL 3061/ 3071/ 5061 - Fall 2003 - Study Questions:

The following values may be useful:
The gas constant = 8.314 joules/(mole^.° K)
The Faraday = 96,500 coulombs/mole
Plank’s constant = 6.625 x 10^-34 joule/sec
Boltzman’s constant = 1.389 x 10^-23 joule/° K
Avagadro’s number = 6.23 x 10^-23 molecules/mole

The following constants may be useful:
R = 8.314 V*coul
F = 96,500 coul
T ^oK = 273 + ^oC
ln x = 2.303 log x

Kathleen Zahs

1. In the year 3001, a neurophysiologist traveling on the starship Enterprise lands on the planet Xylon. He discovers that glial cells of the creatures on Xylon are exclusively permeable to lithium ions (Li⁺). The extracellular concentration of Li⁺ is 1.2 mM and the intracellular concentration of Li⁺ is 120 mM. What is the membrane potential of a glial cell on Xyon? (Assume that the temperature of the Xylonites is 37° C and that the same laws of physics and chemistry that we have here on Earth also apply on Xylon.)
1. -100 mV
2. -123 mV
3. + 100 mV
4. +123 mV
5. None of the above

2. Which of the following statements is TRUE regarding a typical neuron on Earth?
1. The resting membrane potential is exactly equal to the equilibrium potential for K⁺.
2. The resting membrane potential is exactly equal to the equilibrium potential for Na⁺.
3. The resting membrane potential is exactly halfway between the equilibrium potential for K⁺ and the equilibrium potential for Na⁺.
4. The Na⁺-K⁺ ATPase actively pumps Na⁺ out of the cell and K⁺ into the cell.
5. None of the above

3. A tract is a bundle of axons:
1. in the peripheral nervous system.
2. in the central nervous system.
3. that carry information to the central nervous system.
4. that carry information away from the central nervous system.

4. Increasing the number of leak channels in a membrane will have what effect on the time constant?
1. increase the time constant
2. decrease the time constant
3. have no effect on the time constant

5. Increasing the number of leak channels in a membrane will have what effect on the space constant?
1. increase the space constant
2. decrease the space constant
3. have no effect on th+e space constant

6. You are a neurophysiologist recording from the axon of a giant squid. You place a stimulating electrode in the axon, about halfway along its length. Using this electrode, you then apply a large depolarizing current to the axon. (Your stimulus is sufficient to bring the axon to threshold for firing action potentials.) As a result of this stimulus, action potentials will propagate along the axon:
1. in both directions, away from the stimulus.
2. only in one direction: from the stimulus towards the axon terminal.
3. only in one direction: from the stimulus towards the axon hillock/initial segment.
4. in one direction or the other, determined randomly.

7. Myelin affects the membrane space constant and the membrane time constant because it:
1. decreases membrane resistance.
2. increases membrane resistance.
3. decreases membrane capacitance.
4. (1) and (3)
5. (2) and (3)

8. Which of the following statements is/are TRUE?
1. Chemical synapses are faster than electrical synapses.
2. Chemical synapses are formed by gap junction channels.
3. Chemical synapses can amplify the signal passing from the pre-synaptic cell to the post-synaptic cell.
4. All of the above
5. None of the above

9. Which of the following inhibitory synapses will be the most effective in preventing a neuron from firing action potentials? (Assume that the ipsps generated by the synapses are of equal size.)

1. A
2. B
3. C
4. The synapses are equally effective in preventing a neuron from firing action potentials.

10. Which of the following statements is/are TRUE?
1. An inhibitory synapse always causes a hyperpolarization of the membrane potential of the post-synaptic cell.
2. Ca²⁺ entry into the pre-synaptic terminal is not required for exocytosis (release of neurotransmitter from synaptic vesicles).
3. A given neurotransmitter always evokes the same type of post-synaptic response (either inhibitory or excitatory), regardless of the type of receptor on the post-synaptic cell.
4. After exocytosis, synaptic vesicles in the pre-synaptic terminal are recycled.

11. Consider the following experimental situation: You are a neurophysiologist studying mechanisms of synaptic plasticity. You are using neurons grown in culture as your model system. In this culture, cell A is pre-synaptic to cell B. You use an electrode to stimulate the axon of cell A at high frequency, and a second electrode to record the membrane potential of cell B. You observe that every action potential in the pre-synaptic cell is followed by an action potential in the post-synaptic cell. If the synapse between cell A and cell B behaves according to Hebb’s Rule, what will happen?
1. The experimental manipulation will not affect synaptic strength.
2. The synapse between cell A and cell B will be strengthened.
3. The synapse between cell A and cell B will be weakened.

12. Which of the following statements is FALSE?
1. NMDA receptor antagonists will prevent long-term potentiation.
2. Activation of glutamate receptors on the post-synaptic cell is required for the acquisition of long-term potentiation.
3. Activation of glutamate receptors on the post-synaptic cell is required for the acquisition of long-term depression.
4. Ca²⁺ influx into the post-synaptic cell is necessary for the acquisition of long-term potentiation but not for the acquisition of long-term depression.

13. Which of the following events is/are necessary for Ca²⁺ influx through the NMDA receptor?
1. binding of glutamate to the NMDA receptor
2. depolarization of the post-synaptic cell
3. activation of a metabotropic purinergic (ATP) receptor
4. both A and B
5. both B and C

14. Which of the following statements is FALSE?
1. Astrocytes can release neurotransmitters.
2. Astrocytes contain synaptic vesicle proteins.
3. Release of glutamate from astrocytes is via a Ca²⁺-dependent mechanism.
4. It is well-established that astrocytes release glutamate from synaptic vesicles like those found in neurons.

15. Intercellular Ca²⁺ waves between astrocytes may be propagated by the diffusion of extracellular ATP. By which of the following mechanisms is ATP thought to be released from astrocytes?
1. the action of the Na⁺-K⁺ ATPase running in the "forward" direction
2. reversal of the Na⁺-K⁺ ATPase
3. exit of intracellular ATP through gap junction hemi-channels
4. generation of ATP from the break down of membrane phospholipids, catalyzed by phospholipase C

16. The passage of an intercellular Ca²⁺ wave through astrocytes has been observed to be
correlated with which of the following responses in neighboring neurons?
1. a decrease in intracellular Ca²⁺ in the neurons
2. closure of gap junctions between neurons
3. an increase in the rate of firing of action potentials by the neurons
4. no effects on neuronal physiology have been observed

ANSWERS:

Vincent Barnett

19. In class we discussed three types of reflex arcs. A stretch stimulated reflex, a force stimulated reflex and a pain-stimulated reflex. The stretch reflex involves the response of sensors that are coupled to:
1. Extrafusal muscle fibers
2. Intrafusal muscle fibers
3. Golgi-tendon organs
4. flexor motor units
5. extensor motor units

20. At the neuromuscular junction, the duration of the stimulation due to the nerve signal is dependent on the action of __________ on the muscle cell membrane.
1. voltage-gated sodium channels
2. voltage-gated potassium channels
3. voltage-gated calcium channels
4. acetylcholine receptors
5. acetylcholine esterase

21. Muscle cell action potentials activate the entire cell rapidly by taking the electrical properties of the:
1. sarcoplasmic reticulum
2. neuromuscular junction
3. the transverse tubules
4. the motor end-plate
5. the endoplasmic reticulum

22. Skeletal muscles have a highly organized internal structure. Each muscle group, for example the psoas muscle of the back, is a parallel bundle of muscle cells. The contractile subunits in psoas muscle cells that are aligned end-to-end are known as __________.
1. sarcomeres
2. myofibrils
3. myosin filaments
4. actin filaments
5. A-bands

23. The relaxation of skeletal muscle is regulated by the internal calcium concentration. The uptake of calcium during relaxation is due to __________ in the __________ .
1. calcium release channels; sarcoplasmic reticulum
2. calcium release channels; sarcolemma
3. calcium pumps; sarcolemma
4. calcium pumps; sarcoplasmic reticulum

24. The calcium sensor that triggers muscle force production is __________.
1. tropomyosin
2. titin
3. troponin
4. t-tubular
5. testosterone

25. The nucleotide, adenosine-triphosphate (ATP), provides the energy for muscle contraction. During exercise, a Type I muscle cell relies primarily on __________ for ATP production.
1. oxidative phosphorylation
2. creatine kinase
3. creatine phosphorylation
4. glycolysis
5. gluconeogenesis

26. The shortening velocity of a muscle cell can produce depends on the load that it is working under. At zero load the shortening velocity is __________.
1. negative
2. maximum
3. half maximum
4. one-third maximum
5. zero

27. During muscle contraction the width of the __________ shortens.
1. thick filaments
2. thin filaments
3. A-bands
4. I-bands
5. Z-lines

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