Chapter 1: Nerve Cells & Nerve Impulses

Question 1

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 1

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

Question 2

Which animal species would have the longest axons?

Answer 2

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

Question 3

Compared to other neurons, would an interneuron’s axon be relatively long, short, or about the same?

Answer 3

Because an interneuron is contained entirely within one part of the brain, its axon is short.

Question 4

What are the four major structures that compose a neuron?

Answer 4

Dendrites, soma (cell body), axon, and presynaptic terminal

Question 5

Which kind of glia cell wraps around the synaptic terminals of axons?

Answer 5

Astrocytes.

Question 6

Identify one major advantage and one disadvantage of having a blood–brain barrier.

Answer 6

The blood–brain barrier keeps out viruses (an advantage) and also keeps out most nutrients (a disadvantage)

Question 7

Which chemicals cross the blood–brain barrier passively?

Answer 7

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.

Question 8

Which chemicals cross the blood–brain barrier by active transport?

Answer 8

Glucose, amino acids, purines, choline, certain vitamins, and iron.

Question 9

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

Answer 9

Sodium ions are more concentrated outside the cell, and potassium is more concentrated inside

Question 10

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?

Answer 10

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.

Question 11

What is the difference between a hyperpolarization and a depolarization?

Answer 11

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.

Question 12

What happens if the depolarization does or does not reach the threshold?

Answer 12

If the depolarization reaches or passes the threshold, the cell produces an action potential. If it is less than threshold, no action potential arises.

Question 13

State the all-or-none law.

Answer 13

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

Question 14

Does the all-or-none law apply to dendrites? Why or why not?

Answer 14

The all-or-none law does not apply to dendrites, because they do not have action potentials.

Question 15

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

Answer 15

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.

Question 16

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

Answer 16

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.

Question 17

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?

Answer 17

If the nodes were closer, the action potential would travel more slowly. If they were much farther apart, the action potential would travel 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.

Question 18

Alicia is studying for a quiz on the parts of the neuron. She is having trouble remembering that the part(s) of the neuron that receive(s) the incoming message is/are called _____, which are considered part of the postsynaptic side of the neuron.
a. axons
b. ribosomes
c. soma
d. dendrites

Answer 18

Dendrites

Correct. The dendrites are a tree-looking structure that protrudes from the soma of the neuron. The role of the dendrites is to receive incoming message from other neurons. With regard to a synapse, the dendrites are on the postsynaptic side.

Question 19

Brian is playing a neuroscience trivia game. He is trying to figure out which neuron has its soma in the spinal cord and receives excitation through its dendrites and conducts impulses along its axon to a muscle. What should he guess?
a. motor neuron
b. interneuron
c. sensory neuron
d. glianeuron

Answer 19

Motor neuron

Question 20

Pho is doing a dissection of a sheep brain in her physiology class. Her assignment is to dissect and then sketch pictures of the oligodendrocytes doing their job. What will she be drawing pictures of in her lab notebook?
a. Glial cells that have acted as part of the immune system.
b. Glial cells that have myelinated axons in the brain.
c. Glial cells that have helped neurons migrate during embryonic development.
d. Schwann cells that have caused scar tissue in the brain.

Answer 20

Glial cells that have myelinated axons in the brain

Correct. Oligodendrocytes are responsible for the formation of myelin sheath in the brain (because Pho is dissecting a brain and not the whole body). The glial cells extend out a fatty substance that is wrapped around the axons of neurons in the CNS. The Schwann cells perform a similar function in the PNS.

Question 21

Dr. Pestis is in the lab measuring the voltage changes in neurons during an action potential. Before she begins, she checks to make sure the resting potential is normal. She should measure the voltage as ____ mV.
a. -40
b. 70
c. -70
d. 40

Answer 21

-70 mV
Correct. The resting potential of the neuron is approximately -70mV. The neuron’s interior is more negative compared to the external environment. Dr. Pestis likely measured the voltage with a microelectrode.

Question 22

The ______ law states that the amplitude and velocity of an action potential are independent of the intensity of the stimulus that initiated, provided that the stimulus reaches _____.
a. all-or-none; threshold
b. all-or-none; potential
c. all-or-none; hyperpolarization
d. saltatory conduction law; threshold

Answer 22

Correct. The all-or-none law suggests that assuming a stimulus has reached threshold, it will fire an action potential that will progress down the entire length of the axon. This is true if the stimulus barely reaches threshold or significantly passes threshold.

Question 23

When attempting to produce an action potential in the cells in the lab, Jane measured the membrane potential to be -80mV. In this case, her cells had somehow become _____.
a. depolarized
b. immobilized
c. hyperpolarized
d. repolarized

Answer 23

hyperpolarized

Correct. The normal resting membrane potential of a neuron is around -70mV. When a cell is made to be more negative (like the -80mV in Jane’s cells), it is said to have become hyperpolarized. She should check the cells to determine what is causing the hyperpolarization before continuing her experiment.