Term Paper: Nerve Cells and Nerve Impulses Synapses and Anatomy of the Nervous System

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¶ … heroin and morphine are similar in many ways, heroin exerts faster effects on the brain. What can we infer about those drugs with regard to the blood -- brain barrier?

Heroin and morphine are obviously similar since they're both in the opiate class of drugs but the different forms opiates take obviously leads to differences in how quickly the drugs affect the brain. Heroin obviously shoots to the brain, so to speak, much quicker and that is certainly the intent of a heroin user. Obviously, the timeline it takes for heroin is shorter due to things like purity, potency and how quickly they progress through the body, as opposed to pill-based or other medically-accepted forms of opiates like Percocet and the like.

Suppose the threshold of a neuron were the same as its resting potential. What would happen? At what frequency would the cell produce action potentials?

The threshold is the value at which the membrane potential, if reached, leads to an all or nothing sort of proposition as it relates to action potential, so the "all" phase would kick in. The action potential is initiate when the threshold is reached, so that is the frequency. The threshold represents a depolarization effect is what is used to measure threshold.

3. In the laboratory, researchers can apply an electrical stimulus at any point along the axon, making action potentials travel in both directions from the point of stimulation. An action potential moving in the usual direction, away from the axon hillock, is said to be traveling in the orthodromic direction. An action potential traveling toward the axon hillock is traveling in the antidromic direction. If we started an orthodromic action potential at the axon hillock and an antidromic action potential at the opposite end of the axon, what would happen when they met at the center? Why?

Nothing would happen and it's because of the refractory period whereby there is an amount of time and effort (that is not easy) where another action potential would be required but hard to pull off.

4. If a drug partly blocks a membrane's potassium channels, how does it affect the action potential?

The neuron could still fire but it would not be able to fire again because it has been depolarized and that would inhibit or even prevent the neuron from firing again until the potassium channels are unblocked at least to some degree.

1. When Sherrington measured the reaction time of a reflex (i.e., the delay between stimulus and response), he found that the response occurred faster after a strong stimulus than after a weak one. Can you explain this finding? Remember that all action potentials -- whether produced by strong or weak stimuli -- travel at the same speed along a given axon.

The gravity of the stimulus probably has a lot to do with how quickly (if at all) the subject would react. I guess one could compare it to the frog in the pot. If the heat is turned up right away, the frog leaves immediately. However, if it's done progressively, the frog may very well cook to death. In short, just because there's a stimulus that is slight does not mean a reaction will be visible. It could happen but it might not…even though the path of stimulus to reaction is the same amount of time. It all depends on what the stimulus is and what kind of reaction is customary. Slightly raising heat for example may or may not give a reaction but a sharp increase would almost certainly to do. Same time to react and see what is happening but there is less likelihood of a response to a lesser amount of shift in stimulus.

2. A pinch on an animal's right hind foot excites a sensory neuron that excites an interneuron that excites the motor neurons to the flexor muscles of that leg. The interneuron also inhibits the motor neurons connected to the extensor muscles of the leg. In addition, this interneuron sends impulses that reach the motor neuron connected to the extensor muscles of the left hind leg. Would you expect the interneuron to excite or inhibit that motor neuron? (Hint: The connections are adaptive. When an animal lifts one leg, it must put additional weight on the other legs to maintain balance.)

I guess it would depend on how much of a pinch is done. Using the answer from the last question as a guide, if the pinch was slight the reaction may be slight but if the pinch is harsh, the animal is much more likely to react and in a major way and use the other legs to compensate for what is happening with the leg that has to be freed from the pinch. It would all depend on the amount of the stimulus and whether the body or the mind feel there is a reaction that is necessary or not.

3. Suppose neuron X has a synapse onto neuron Y, which has a synapse onto Z. Presume that no other neurons or synapses are present. An experimenter finds that stimulating neuron X causes an action potential in neuron Z. after a short delay. However, she determines that the synapse of X onto Y is inhibitory. Explain how the stimulation of X might produce excitation of Z.

It would depend on how high the signal is at the start of the chain. If the initial signal is rather high, there could absolutely be an excitation in Z. But if that is not the case, there is a chance that this would not occur. A neuron is excitatory if it makes other neurons more likely to fire and inhibitory if it's less likely to make or allow them to fire.

4. Suppose axon a enters a ganglion (cluster of neurons) and axon B. leaves on the other side. An experimenter who stimulates a shortly thereafter records an impulse traveling down B. We want to know whether B. is just an extension of axon a or whether a formed an excitatory synapse on some neuron in the ganglion, whose axon is axon B. How could an experimenter determine the answer? You should be able to think of more than one good method. Presume that the anatomy within the ganglion is so complex that you cannot simply trace the course of an axon through it.

One way would be to test the supposed connection in reverse to see if the path is the same or not. Another dimension would be to fire at different levels of intensity (and from both sides) to see if there is consistency. This would then yield, of analyzed correctly, whether it's one part or multiple parts that is in play here. The way each pathway works back and forth would make clear if they were two different parts connected or if they were all one piece.

5. People who take methylphenidate (Ritalin) for control of attention-deficit disorder often report that, although the drug increases their arousal for a while, they feel a decrease in alertness and arousal a few hours later. Explain.

The drug (as opposed to the extended release version commonly known as Concerta) is quick release and is not metered to the body over time through its other ingredients. As such, there is an initial rush to the body and then it dies down as the medicine is consumed by the body. If an extended pill was taken, the arousal would still happen but would be more tempered and would remain even over the course of the dose.

6. The research on sensitization of the nucleus accumbens has dealt with addictive drugs, mainly cocaine. Would you expect a gambling addiction to have similar effects? How could someone test this possibility?

It is possible but not a certainty that it would happen with the same regularity given that cocaine is an external chemical with obvious effects whereas the urge to gamble is internalized. However, a quick Google search reveals that there is indeed perceived to be a connection between nucleus accumbens and gambling. As to whether they are similar, the method to test that would be to have a control group that is neither gambling addicted or cocaine-using and then have two more groups that have one each of the maladies. The control group's behavior could then be compared to that of the cocaine users and the gamblers to see how they are different from the control group and whether those differences are manifested the same way.

1. The drug phenylephrine is sometimes prescribed for people suffering from a sudden loss of blood pressure or other medical disorders. It acts by stimulating norepinephrine synapses, including those that constrict blood vessels. One common side effect of this drug is goose bumps. Explain why. What other side effects might be likely?

Because the receptors affected by the drug also control the piloerectors and this causes the goosebumps when the blood vessels constrict. The drug is also used for colds… [END OF PREVIEW]

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