23.1–23.3 What is the nervous system?
Nervous systems are found in all multicellular animals other than sponges.
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Question 23.23
In a neuron, the cell body:
- a) contains the nucleus, mitochondria, and other cell organelles.
- b) does not contain a nucleus.
- c) has a membrane that is impermeable to water and intracellular solutes.
- d) is highly modified and coated in a fatty myelin sheath.
- e) is considered the primary structure of the “central” nervous system.
Question 23.24
Dendrites:
- a) conduct action potentials away from the cell body.
- b) are present in mammalian nervous systems but not in the nervous systems of other vertebrates.
- c) receive information from other neurons or from the external environment.
- d) are coated in a fatty substance called the myelin sheath, which speeds up the rate at which signals are conducted.
- e) are bundles of axons.
Question 23.25
In individuals with multiple sclerosis (MS), myelin is gradually lost. What symptoms would you expect these individuals to exhibit?
- a) Their cell membranes have reduced numbers of sodium channels.
- b) Their sensory neurons lose the ability to initiate action potentials.
- c) Their brain becomes smaller.
- d) They are able to continue athletic activity long after pain would cause most individuals to stop.
- e) Their neurons gradually lose their ability to conduct electrical impulses.
Question 23.26
Which of the choices below properly describes the difference between the gray and white matter of the nervous system?
- a) The white matter is composed of non-
myelinated fibers, and the gray matter is composed of myelinated fibers. - b) The white matter is composed of neuron bodies, and the gray matter is composed of axons and dendrites.
- c) The white matter is composed of sensory neurons, and the gray matter is composed of motor neurons.
- d) The white matter is composed of myelinated fibers, and the gray matter is composed of non-
myelinated fibers. - e) None of the above are correct
