23.1–23.3
23.1–What is the nervous system?
Nervous systems are found in all multicellular animals other than sponges.
965
Q
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.
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.
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.
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
