Question 1

Use the Nernst equation to predict the membrane potential for each ion.

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Question 2

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?

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Question 3

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?

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Question 4

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?

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Question 5

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?

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Question 6

How do the following relate to nervous system development and/or healing? Synaptic plasticity, neuroglia, neurotrophic factors.

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Question 7

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 do you tell your partner to do?

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Question 8

If an axon has an absolute refractory period of 2 msec, what is the maximum frequency of action potential (AP)production in that neuron?

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Question 9

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.

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Question 10

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 do not.What is the most likely cause of death?

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Question 11

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?

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Question 12

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?

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Question 13

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?

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Question 14

What factors determine the maximum frequency of action potentials conducted by an axon?

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Question 15

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?

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Question 16

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.

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Question 17

Compare and contrast the communication mechanisms between the nervous and endocrine systems.In other words, how do neurons and neurotransmitters signal to their postsynaptic cells, compared to the way endocrine glands and hormones communicate with their target cells?

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Question 18

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 do these symptoms "fit" with what you know about nerve impulses, myelin sheaths, and the location of gated ion channels in the membranes of axons?

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Question 19

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?

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Question 20

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 0 mV.Additionally, you have determined ion concentrations and listed them below.
 $$\begin{array} { | l | l | l | } 
\hline \begin{array} { l } 
{ [  ]\text { in } } \
\text { mOsm/L }
\end{array} & \text { Cell } & \text { Swamp } \
\hline \mathrm { K } ^ { + } & 5 & 150 \
\hline \mathrm { Na } ^ { + } & 15 & 175 \
\hline \mathrm { Cl } - & 40 & 40 \
\hline
\end{array}$$ 
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).

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Quiz 8: Neurons: Cellular and Network Properties