CHAPTER 29 Test Your Knowledge
DRIVING QUESTION 1
How is the nervous system organized?
By answering the questions below and studying Infographics 29.2 and 29.5, you should be able to generate an answer for the broader Driving Question above.
KNOW IT
For each of the following, indicate whether it is a part of the CNS or of the PNS.
Light-detecting receptor in the eye______
Amygdala______
Pain receptor in the skin______
Spinal cord______
Thalamus______
light-detecting receptor in the eye (PNS); amygdala (CNS); pain receptor in the skin (PNS); spinal cord (CNS); thalamus (CNS)
Which part of the brain coordinates movement? Which part of the brain maintains body temperature?
movement—cerebellum; body temperature—hypothalamus (diencephalon)
Rank the complexity of the cerebrums of the following vertebrates from 1 (most complex) to 4 (least complex).
Bird________
Chimpanzee________
Salamander (an amphibian)________
Fish________
(1) chimpanzee; (2) bird); (3) salamander; (4) fish
USE IT
Is information flow in the spinal cord one way or two way? Explain your answer.
Two way: the spinal cord helps the CNS receive information from the PNS and send information from the CNS to the PNS.
How does multiple sclerosis cause muscle weakness? Does multiple sclerosis directly affect muscles? Which part of the nervous system is affected?
Multiple sclerosis causes muscle weakness through the destruction of myelin. When myelin is destroyed, action potentials don’t arrive at axon terminals at full strength. Demyelination can impair the communication between neurons and muscles, and muscles will not contract properly.
A brain injury (caused by a blow to the head, for example) that results in the loss of the ability to speak most likely affected the
a. cerebellum.
b. cerebrum.
c. diencephalon.
d. brain stem.
e. hypothalamus.
b
DRIVING QUESTION 2
How do cells in the nervous system transmit signals?
By answering the questions below and studying Infographics 29.3, 29.4, and 29.6, you should be able to generate an answer for the broader Driving Question above.
KNOW IT
Neurons receive information through their
a. axons.
b. axon terminals.
c. cell bodies.
d. dendrites.
e. nuclei.
d
Action potentials are a type of________signaling that relies on________.
a. electrical; neurotransmitters
b. electrical; charged ions
c. electrical; electrons
d. chemical; neurotransmitters
e. chemical; charged ions
b
Neurons release neurotransmitters from their
a. cell bodies.
b. dendrites.
c. axon terminals.
d. all of the above
e. b and c
c
What happens when a neurotransmitter is released into a synaptic cleft?
The neurotransmitter diffuses from the signaling cell (the pre-synaptic cell) to the receiving cell (the post-synaptic cell). It then binds receptors on the post-synaptic cell.
Compare and contrast electrical and chemical signaling by neurons.
Electrical signaling takes place along the length of axons, and involves the movement of sodium and potassium ions across the membrane of axons. Chemical signaling involves the release of chemical signaling molecules (neurotransmitters) into synapses, where they communicate information between neurons and their effector cells (other neurons, glands, muscles).
USE IT
Gatorade and other sports drinks contain replacement electrolytes (ions necessary to enable muscles to continue to contract, especially the ions lost during sweating). Gatorade contains sodium and potassium ions. Other than in the muscle, where else might these ions be crucial during sustained exercise?
Because the neuron that communicates with the muscle does so by firing an action potential and then releasing a neurotransmitter onto the muscle (which in turn causes the contraction), sodium and potassium ions are required for the neuron to continue to fire.
Botox is a chemical treatment injected into skin to prevent wrinkling. It is primarily a bacterial toxin that prevents certain neurons from releasing the neurotransmitter acetylcholine. Acetylcholine is normally released by motor neurons to signal muscles to contract. Does Botox paralyze muscles in a relaxed state or a contracted state?
Botox prevent release of the neurotransmitter that signals muscles to contract. BoTox therefore causes flaccid (that is, relaxed) paralysis.
Is more or less of the neurotransmitter acetylcholine released by the axon terminals of neurons in patients with multiple sclerosis compared to those in people who do not have multiple sclerosis? Explain your answer.
In multiple sclerosis, less neurotransmitter is released by the axon terminals that communicate with muscles. This is because the action potential weakens in the absence of myelin. When less neurotransmitter is released into the synapse, there is not enough signal to initiate contraction in the muscle.
DRIVING QUESTION 3
Why are some drugs (and some behaviors) addictive?
By answering the questions below and studying Infographics 29.1, 29.5, 29.7, and 29.8, you should be able to generate an answer for the broader Driving Question above.
KNOW IT
Addictive substances confer a sense of pleasure because they
a. decrease the amount of dopamine in synaptic clefts.
b. increase the amount of dopamine in synaptic clefts.
c. increase the number of dopamine receptors on the axon terminals of cells that release dopamine.
d. increase the number of dopamine receptors on dendrites of cells that release dopamine.
e. c and d
b
Why do drug users need to take ever-increasing amounts of drugs to get the same high?
Because of the initial surge of dopamine, receptors respond by down-regulating—that is, reducing their numbers. With fewer receptors, the drug cannot elicit excessive feelings of pleasure unless more drug is ingested to overcome the effect of down-regulation.
USE IT
Cocaine prevents dopamine from being removed from the synapse. Why does this cause feelings of pleasure?
Dopamine in the synapse binds to receptors on target cells, leading to feelings of pleasure. If cocaine prevents dopamine from being removed from the synapse, more dopamine will persist in the synapse, enhancing the feelings of pleasure.
Would you expect a person born with a relatively low number of dopamine receptors to be happier or sadder than the average? Explain your answer.
Probably sadder. If there are fewer than normal dopamine receptors, then even normal amounts of dopamine will not elicit normal feelings of pleasure, leading to a possible perception of sadness.
MINI CASE
Parkinson disease is caused primarily by a gradual loss of dopamine-producing neurons in the brain. Why is depression often among the debilitating symptoms of Parkinson disease? There are a variety of medications available to treat people with Parkinson disease. Do some internet research to match each medication listed below with its probable mechanism of action.
Mirapex binds to and activates dopamine receptors; Eldepryl inhibits an enzyme that breaks down dopamine; levodopa can be used by neurons to make dopamine.
While these drugs have different mechanisms at the cellular and molecular level, they all act to increase the levels of dopamine. As dopamine loss is the underlying cause of Parkinson disease, increasing dopamine levels will help treat the symptoms of the disease, (although they do not cure it).
How can drugs with different mechanisms of action all help treat Parkinson disease? (Hint: What do all the underlying mechanisms have in common in terms of their effect?)
INTERPRETING DATA
Study Infographic 29.8.
a. What are the independent and dependent variables in each experiment?
b. The performances of 14 participants are plotted in each graph. Calculate the average time (in seconds) these participants took to walk the straight line, and the average number of words recalled by these participants.
a: In both studies, the independent variable is dopamine receptor availability. In the graph on the left, the dependent variable is the time it takes to walk a straight line (that is, the time it takes to complete the motor skills test), and in the graph on the right, the dependent variable is the number of words that can be recalled after a distraction. b: The average motor skills time is ~10.1 seconds; the average number of words recalled is ~9.6. c: The outlier in the lower left of the right-hand graph is recalling fewer words than would have been predicted based on this participant’s dopamine receptor availability. Someone with ~1.3 dopamine availability would have been predicted to recall 8 words, and this outlier is recalling only 4 words. d: The top right outlier on the right-hand graph is recalling more words than would have been predicted. This participant would have been predicted to recall 12 words but was able to recall 14 words.
In the right-hand graph in Infographic 29.8, you will note that there are a few outliers (two are circled in red in the copy of the graph shown below).
c. For the outlier above, is this participant recalling more or fewer words than would be predicted based on his or her availability of dopamine receptors? Explain your answer.
d. For the outlier on the top right, is this participant recalling more or fewer words than would be predicted based on his or her availability of dopamine receptors? Explain your answer.
BRING IT HOME
Replicate the motor skills experiments shown in Infographic 29.8 with some students. On a flat surface, set up a start line and, 10 yards away, a finish line. Instruct each subject to walk in a straight line from the start to the finish and back as fast as they can without running. Start timing when they cross the start line, and stop timing when they cross the start line again at the end of the trial. Have each participant do the trial three times, and record the average of the three trials as the participant’s final time. Now calculate the average time in your set of participants. How does this compare to the 14 methamphetamine users whose performances are plotted in Infographic 29.8?
Answers will depend on the data generated.
SOURCE: Method from Robertson, K. R., et al. (2006) Timed gait test: normative data for the assessment of the AIDS dementia complex. Journal of Clinical and Experimental Neuropsychology 28:1053–1064.