Chapter 8 Concept Check Questions

Question 1

Organize the following terms describing functional types of neurons into a map or outline: afferent, autonomic, brain, central, efferent, enteric, parasympathetic, peripheral, sensory, somatic motor, spinal, and sympathetic.

Answer 1

figure 8.1

Question 2

Where do neurons that secrete neurohormones terminate?

Answer 2

Neurons that secrete neurohormones terminate close to blood vessels so that the neurohormones can enter the circulation.

Question 3

What is the difference between a neuron and a nerve?

Answer 3

A neuron is a single nerve cell.
A nerve is a bundle of axons from many

Question 4

Draw a chain of three neurons that synapse on one another in sequence. Label the presynaptic and postsynaptic ends of each neuron, the cell bodies, dendrites, axons, and axon terminals.

Answer 4

8.2 figure

Question 5

Schwann Cells and Oligodendrocytes

Answer 5

Schwann cells in PNS and oligodendrocytes in the CNS support and insulate axons by forming myelin.

Question 6

What is the primary function of each of the following: myelin, microglia, ependymal cells

Answer 6

Myelin insulates axon membranes.
Microglia are scavenger cells in the CNS.
Ependymal cells form epithelial barriers between fluid compartments of the CNS.

Question 7

Name the two glial cell types that form myelin. How do they differ from each other?

Answer 7

Schwann cells are in the PNS and each Schwann cell forms myelin around a small portion of one axon. Oligodendrocytes are in the CNS, and one oligodendrocyte forms myelin around the axons of several neurons.

Question 8

Given the values in Table 8.2, use the Nernst equation to calculate the equilibrium potential for
Express the concentrations as powers of 10 and use your knowledge of logarithms[p. A-38] to try the calculations without a calculator.

Answer 8

(61 *4) / (+2) = 122 mV

Question 9

Would a cell with a resting membrane potential of -70 mV depolarize or hyperpolarize in the following cases? (You must consider both the concentration gradient and the electrical gradient of the ion to determine net ion movement.)

a. Cell becomes more permeable to Ca+2

b. Cell becomes less permeable to K+

Answer 9

a. depolarize

b. depolarize

Question 10

Would the cell membrane depolarize or hyperpolarize if a small amount of Na+ leaked into the cell?

Answer 10

depolarize

Question 11

Ohm’s law

Answer 11

current flow (I) is directly proportional to the electrical difference (in volts, V) between two points and inversely proportional to the resistance (R) of the system to current flow: I = V x 1 / R or
I = V / R

Question 12

Match each ion’s movement with the type of graded potentialitcreates.
a. Na+ entry
b. Cl- entry
c. K+ exit
d. Ca+2 entry

1. depolarizing
2. hyperpolarizing

Answer 12

a. depolarizing
b. hyperpolarizing
c. hyperpolarizing
d. depolarizing

Question 13

Identify the trigger zones illustrated in figure 8.2 if possible

Answer 13

look at figure 8.2

Question 14

Trigger zone

Answer 14

Graded potentials that are strong enough eventually reach the region of the neuron known as the ___________.

Question 15

What is the difference between conductance and conduction in neurons?

Answer 15

Conductance refers to the movement of ions across a cell membrane.

Conduction is the rapid, undiminished movement of an electrical signal down the axon of a neuron.

Question 16

If you put ouabain, an inhibitor of the
pump, on a neuron and then stimulate the neuron repeatedly, what do you expect to happen to action potentials generated by that neuron?

Answer 16

There is no immediate effect, but they diminish with repeated stimulation and eventually disappear

Question 17

The pyrethrin insecticides, derived from chrysanthemums, disable inactivation gates of channels so that the channels remain open. In neurons poisoned with pyrethrins, what happens to the membrane potential? Explain your answer.

Answer 17

The membrane potential depolarizes and stays depolarized

Question 18

When Na+ channel gates are resetting, is the activation gate opening or closing? Is the inactivation gate opening or closing?

Answer 18

During resetting, the activation gate is closing, and the inactivation gate is opening

Question 19

If you place an electrode in the middle of an axon and artificially depolarize the cell above the threshold, in which direction will an action potential travel:

Answer 19

The action potential will go in both directions because the Na+ channels around the stimulation site have not been inactivated by a previous depolarization.

Question 20

Place the following neurons in order of their speed of conduction, from fastest to slowest:

(a) myelinated axon, diameter 20@mm
(b) unmyelinated axon, diameter 20@mm
(c) unmyelinated axon, diameter 200@mm

Answer 20

(a), (c), (b)

Question 21

Hypokalemia

Answer 21

If blood K+ concentration falls too low – a condition known as hypokalemia – the resting membrane potential of cells hyperpolarizes, moving farther from the threshold.

Question 22

When pharmaceutical companies design drugs, they try to make a given drug as specific as possible for the particular receptor subtype they are targeting. For example, a drug might target adrenergic b1-receptors rather than all adrenergic a- and b-receptors. What is the advantage of this specificity?

Answer 22

Because different receptor subtypes work through different signal transduction pathways, targeting drugs to specific receptor subtypes decreases the likelihood of unwanted side effects.

Question 23

Which organelles are needed to synthesize proteins and package them into vesicles?

Answer 23

Proteins are synthesized on the ribosomes of the rough endoplasmic reticulum; then the proteins are directed into the Golgi apparatus to be packaged into vesicles.

Question 24

What is the function of mitochondria in a cell?

Answer 24

Mitochondria are the primary sites of ATP synthesis.

Question 25

How do mitochondria get to the axon terminals?

Answer 25

Mitochondria reach the axon terminal by fast axonal transport along microtubules

Question 26

One class of antidepressant drugs is called selective serotonin reuptake inhibitors (SSRIs). What do these drugs do to serotonin activity at the synapse?

Answer 26

SSRIs decrease reuptake of serotonin into the axon terminal, thereby increasing the time serotonin is active in the synapse

Question 27

How does the axon terminal make acetyl CoA for acetylcholine synthesis?(Hint: see p. 107.)

Answer 27

Acetyl CoA is made from pyruvate, the end product of glycolysis, and CoA.

Question 28

Is Na+-dependent neurotransmitter reuptake facilitated diffusion, primary active transport, or secondary active transport? Explain your reasoning.

Answer 28

Neurotransmitter uptake is secondary active transport because it uses energy stored in the Na+ concentration gradient to concentrate neurotransmitters inside the axon terminal.

Question 29

In Figure 8.24e, assume the postsynaptic neuron has a resting membrane potential of -70 mV and a of -55 mV. If the inhibitory presynaptic neuron creates an IPSP of -5 mV and the two excitatory presynaptic neurons have EPSPs of 10 and 12 mV, will the postsynaptic neuron fire an action potential?

Answer 29

The postsynaptic neuron will fire an action potential because the net effect would be a 17 mV depolarization to -70 - (-17) = -53 mV, which is just above the threshold of -55 mV.

Question 30

In the graphs of Figure 8.24a, b, why doesn’t the membrane potential change at the same time as the stimulus?

Answer 30

The membrane potential does not change at the same time as the stimulus because the depolarization must travel from the point of
the stimulus to the recording point.

Question 30

Why are axon terminals sometimes called “biological transducers”?

Answer 30

Axon terminals convert (transduce) the electrical action potential signal into a chemical neurotransmitter signal.

Question 31

Why would depolarization of the membrane drive
Mg 2+ from the channel into the extracellular fluid?

Answer 31

Membrane depolarization makes the inside of the membrane more positive than the outside. Like charges repel one another, so the more positive membrane potential tends to repel Mg2 +.