Respond appropriately to each statement below either by completing the statement or by answering the question raised.

1. The cellular unit of the nervous system is the neuron. What is the major function of this cell type?

2 and 3. What characteristics are highly developed to allow the neuron to perform this function? (hint two)

4. Would a substance that decreases membrane permeability to sodium increase or decrease the probability of generating a nerve impulse?

5. Why don't the terms depolarization and action potential mean the same thing? (Hint: under which conditions will a local depolarization not lead to the action potential?)

6. A nerve generally contains many thickly myelinated fibers that typically exhibit nodes of Ranvier. An action potential is generated along these fibers by "saltatory conduction." Use an appropriate reference to explain how saltatory conduction differs from conduction along unmyelinated fibers.

Using the key match each ot the terms to the appropriate definition. More than one may apply. (example: a or a, b)

a. action potential d. relative refractory period

b. absolute refractory period e. repolarization

c. depolarization f. sodium-potassium pump

7. period of depolarization of the neuron membrane during which it cannot respond to a second stimulus

8. reversal of the resting potential owing to an influx of sodium ions

9. period during which potassium ions diffuse out of the neuron owing to a change in membrane permeability

10. self-propagated transmission of the depolarization wave along the neuronal membrane

11. mechanism in which ATP is used to move sodium out of the cell and potassium into the cell; restores the resting membrane voltage and intracellular ionic concentrations