2. Nerve Cells and Nerve Impulses

Question 1

1. Santiago Ramón y Cajal was responsible for which of these discoveries?

a. The human cerebral cortex has many specializations to produce language.
b. The brain’s left and right hemispheres control different functions.
c. The nervous system is composed of separate cells.
d. Neurons communicate at specialized junctions called synapses.

Answer 1

c.The nervous system is composed of separate cells.

Question 2

<p>2.What does an afferent axon do?
<br></br>a.It controls involuntary behavior.
<br></br>b.It controls voluntary behavior.
<br></br>c.It carries output from a structure.
<br></br>d.It brings information into a structure.</p>

Answer 2

<p>d.It brings information into a structure.</p>

Question 3

<p>3.Of these species, which probably has the longest axons?
<br></br>a.Humans
<br></br>b.Chimpanzees
<br></br>c.Cheetahs
<br></br>d.Giraffes</p>

Answer 3

<p>d.Giraffes</p>

Question 4

<p>4.Which of the following is NOT one of the four major structures that compose a neuron?
<br></br>a.Dendrites
<br></br>b.Glia
<br></br>c.Soma
<br></br>d.Axon
<br></br>e.Presynaptic terminal</p>

Answer 4

<p>b.Glia</p>

Question 5

<p>.Which of the following is something that glia do NOT do?
<br></br>a.Synchronize activity of a group of axons
<br></br>b.Remove waste material
<br></br>c.Dilate blood vessels to increase blood flow to the most active brain areas
<br></br>d.Conduct action potentials</p>

Answer 5

<p>d.Conduct action potentials</p>

Question 6

<p>6.An advantage of the blood–brain barrier is that it keeps out most \_\_\_\_\_\_. A disadvantage is that it also keeps out \_\_\_\_\_\_.
<br></br>a.viruses . . . most nutrients
<br></br>b.small molecules . . . fat-soluble molecules
<br></br>c.harmful gases . . . oxygen
<br></br>d.waste products . . . water</p>

Answer 6

<p>a.viruses . . . most nutrients</p>

Question 7

<p>7.Which of these chemicals cross the blood–brain barrier by active transport?
<br></br>a.Oxygen, water, and fat-soluble molecules
<br></br>b.Glucose and amino acids
<br></br>c.Proteins
<br></br>d.Viruses</p>

Answer 7

<p>b.Glucose and amino acids</p>

Question 8

<p>8.What makes brain cancers so difficult to treat?
<br></br>a.Nearly all chemotherapy drugs fail to cross the blood–brain barrier.
<br></br>b.Brain cancers spread more rapidly than other cancers.
<br></br>c.The brain includes more pain receptors than other organs.
<br></br>d.The brain has a very low metabolic rate.</p>

Answer 8

<p>a.Nearly all chemotherapy drugs fail to cross the blood–brain barrier.</p>

Question 9

<p>9.What is the brain’s main source of fuel?
<br></br>a.Glucose
<br></br>b.Glutamate
<br></br>c.Thiamine
<br></br>d.Proteins</p>

Answer 9

<p>a.Glucose</p>

Question 10

<p>When the neuron’s membrane is at rest, sodium ions are more concentrated \_\_\_\_\_\_ the cell, and potassium ions are more concentrated \_\_\_\_\_\_.
<br></br>a.inside . . . outside
<br></br>b.inside . . . inside
<br></br>c.outside . . . inside
<br></br>d.outside . . . outside</p>

Answer 10

<p>c.outside . . . inside</p>

Question 11

<p>When the membrane is at rest, the concentration gradient tends to draw potassium ions \_\_\_\_\_\_ the cell, and the electrical gradient draws them \_\_\_\_\_\_ the cell.
<br></br>a.into . . . out of
<br></br>b.into . . . into
<br></br>c.out of . . . into
<br></br>d.out of . . . out of</p>

Answer 11

<p>c.out of . . . into</p>

Question 12

<p>When the membrane is at rest, the concentration gradient tends to draw sodium ions \_\_\_\_\_\_ the cell, and the electrical gradient draws them \_\_\_\_\_\_ the cell.
<br></br>a.into . . . out of
<br></br>b.into . . . into
<br></br>c.out of . . . into
<br></br>d.out of . . . out of</p>

Answer 12

<p>b.into . . . into</p>

Question 13

<p>The sodium–potassium pump moves sodium ions \_\_\_\_\_\_ and moves potassium ions \_\_\_\_\_\_.
<br></br>a.into the cell . . . out of the cell
<br></br>b.into the cell . . . into the cell
<br></br>c.out of the cell . . . into the cell
<br></br>d.out of the cell. . . out of the cell</p>

Answer 13

<p>c.out of the cell . . . into the cell</p>

Question 14

<p>Suppose a neuron has a resting potential of −70 mV. If the potential goes to −80 mV, the change would be a \_\_\_\_\_\_.
<br></br>a.depolarization
<br></br>b.hyperpolarization</p>

Answer 14

<p>b.hyperpolarization</p>

Question 15

<p>Under what conditions does an axon produce an action potential?
<br></br>a.Whenever the membrane is hyperpolarized
<br></br>b.Whenever the membrane’s potential reaches the threshold
<br></br>c.Whenever the membrane is depolarized
<br></br>d.Whenever the membrane’s potential reaches zero</p>

Answer 15

<p>b.Whenever the membrane’s potential reaches the threshold</p>

Question 16

<p>During the rising portion of the action potential, which ions are moving across the membrane and in which direction?
<br></br>a.Sodium ions move out.
<br></br>b.Sodium ions move in.
<br></br>c.Both sodium and potassium ions move in.
<br></br>d.Potassium ions move in.</p>

Answer 16

<p>b.Sodium ions move in.</p>

Question 17

<p>After the action potential reaches its peak, the potential across the membrane falls toward its resting level. What accounts for this recovery?
<br></br>a.The sodium–potassium pump removes the extra sodium.
<br></br>b.Potassium ions move out because their channels are open and the electrical gradient pushes them out.
<br></br>c.Potassium ions move out because their channels are open and the concentration gradient pushes them out.
<br></br>d.Potassium ions move in.</p>

Answer 17

<p>c.Potassium ions move out because their channels are open and the concentration gradient pushes them out.</p>

Question 18

<p>.Which of the following is one way of stating the all-or-none law?
<br></br>a.The amplitude of the action potential in one axon is the same as that in another axon.
<br></br>b.At a given time, either all axons produce action potentials, or none do.
<br></br>c.All stimuli that exceed the threshold produce equivalent responses in the axon.
<br></br>d.During an action potential, all sodium channels open at the same time.</p>

Answer 18

<p>c.All stimuli that exceed the threshold produce equivalent responses in the axon.</p>

Question 19

<p>To which part or parts of a neuron does the all-or-none law apply?
<br></br>a.Axons
<br></br>b.Dendrites
<br></br>c.Both axons and dendrites</p>

Answer 19

<p>a.Axons</p>

Question 20

<p>What does the myelin sheath of an axon accomplish?
<br></br>a.It enables an axon to communicate with other axons.
<br></br>b.It enables action potentials to travel both directions along an axon.
<br></br>c.It enables nutrients to enter the axon.
<br></br>d.It enables action potentials to travel more rapidly.</p>

Answer 20

<p>d.It enables action potentials to travel more rapidly.</p>

Question 21

<p>Is it true that we use only 10 percent of our brain? If so, what does that mean?
<br></br>a.At any moment, only 10 percent of brain cells are active.
<br></br>b.You could lose 90 percent of your brain and still do what you are doing now.
<br></br>c.About 90 percent of the brain’s neurons are immature and not yet functional.
<br></br>d.No, the statement is false and nonsensical.</p>

Answer 21

<p>d.No, the statement is false and nonsensical.</p>

Question 22

<p>What are the widely branching structures of a neuron called? And what is the long, thin structure that carries information to another cell called?</p>

Answer 22

<p>The widely branching structures of a neuron are called dendrites, and the long thin structure that carries information to another cell is called an axon.</p>

Question 23

<p>Which animal species would have the longest axons?</p>

Answer 23

<p>The longest axons occur in the largest animals. For example, giraffes and elephants have axons that extend from the spinal cord to the feet, nearly 2 meters away.</p>

Question 24

<p>Identify the four major structures that compose a neuron.</p>

Answer 24

<p>Dendrites, soma (cell body), axon, and presynaptic terminal.</p>

Question 25

<p>Which kind of glia cell wraps around the synaptic terminals of axons?</p>

Answer 25

<p>Astrocytes.</p>

Question 26

<p>Identify one major advantage and one disadvantage of having a blood–brain barrier.</p>

Answer 26

<p>The blood–brain barrier keeps out viruses (an advantage) and also most nutrients (a disadvantage).</p>

Question 27

<p>Which chemicals cross the blood–brain barrier passively?</p>

Answer 27

<p>Small, uncharged molecules such as oxygen, carbon dioxide, and water cross the blood–brain barrier passively. So do chemicals that dissolve in the fats of the membrane.</p>

Question 28

<p>Which chemicals cross the blood–brain barrier by active transport?</p>

Answer 28

<p>Glucose, amino acids, purines, choline, certain vitamins, iron, and a few hormones.</p>

Question 29

<p>When the membrane is at rest, are the sodium ions more concentrated inside the cell or outside? Where are the potassium ions more concentrated?</p>

Answer 29

<p>Sodium ions are more concentrated outside the cell, and potassium is more concentrated inside.</p>

Question 30

<p>When the membrane is at rest, what tends to drive the potassium ions out of the cell? What tends to draw them into the cell?</p>

Answer 30

<p>When the membrane is at rest, the concentration gradient tends to drive potassium ions out of the cell, and the electrical gradient draws them into the cell. The sodium–potassium pump also draws them into the cell.</p>

Question 31

<p>What is the difference between a hyperpolarization and a depolarization?</p>

Answer 31

<p>A hyperpolarization is an exaggeration of the usual negative charge within a cell (to a more negative level than usual). A depolarization is a decrease in the amount of negative charge within the cell.</p>

Question 32

<p>What is the relationship between the threshold and an action potential?</p>

Answer 32

<p>A depolarization that passes the threshold produces an action potential. One that falls short of the threshold does not produce an action potential.</p>

Question 33

<p>During the rise of the action potential, do sodium ions move into the cell or out of it? Why?</p>

Answer 33

<p>During the action potential, sodium ions move into the cell. The voltage-dependent sodium gates have opened, so sodium can move freely. Sodium is attracted to the inside of the cell by both an electrical and a concentration gradient.</p>

Question 34

<p>As the membrane reaches the peak of the action potential, what brings the membrane down to the original resting potential?</p>

Answer 34

<p>After the peak of the action potential, potassium ions exit the cell, driving the membrane back to the resting potential. Important note: The sodium–potassium pump is NOT responsible for returning the membrane to its resting potential. The sodium–potassium pump is too slow for this purpose.</p>

Question 35

<p>State the all-or-none law.</p>

Answer 35

<p>According to the all-or-none law, the size and shape of the action potential are independent of the intensity of the stimulus that initiated it. That is, every depolarization beyond the threshold of excitation produces an action potential of about the same amplitude and velocity for a given axon. </p>

Question 36

<p>Does the all-or-none law apply to dendrites? Why or why not?</p>

Answer 36

<p>The all-or-none law does not apply to dendrites because they do not have action potentials. </p>

Question 37

<p>Suppose researchers find that axon A can produce up to 1,000 action potentials per second (at least briefly, with maximum stimulation), but axon B can never produce more than 100 per second (regardless of the strength of the stimulus). What could we conclude about the refractory periods of the two axons?</p>

Answer 37

<p>Axon A must have a shorter absolute refractory period, about 1 ms, whereas B has a longer absolute refractory period, about 10 ms.</p>

Question 38

<p>In a myelinated axon, how would the action potential be affected if the nodes were much closer together? How might it be affected if the nodes were much farther apart?</p>

Answer 38

<p>If the nodes were closer, the action potential would travel more slowly. If they were much farther apart, the action potential would be faster if it could successfully jump from one node to the next. When the distance becomes too great, the current cannot diffuse from one node to the next and still remain above threshold, so the action potentials would stop.</p>

Question 39

What are the widely branching structures of a neuron called? And what is the long, thin structure that carries information to another cell called?

Answer 39

widely branching structures of a neuron called Dendrites And what is the long, thin structure that carries information to another cell called Axon

Question 40

Which animal species would have the longest axons?

Answer 40

Which animal species would have the longest axons?