Download Answers to End-of-Chapter Questions – Brooker et al ARIS site

Answers to End-of-Chapter Questions – Brooker et al ARIS site
Chapter 43
Test Yourself Questions
1. In vertebrates, the brain and the spinal cord are parts of
a. the peripheral nervous system.
b. the enteric nervous system.
c. the central nervous system.
d. the autonomic nervous system.
e. the endocrine system.
Answer: c. The brain and spinal cord make up the central nervous system.
2. The structures of a neuron that function mainly in receiving signals from other neurons are
a. the myelin sheaths.
b. the axons.
c. the nerve termini.
d. the dendrites.
e. the K+ channels.
Answer: d. Dendrites are structures of the neurons that receive signals from other neurons.
3. The glial cells that form the myelin sheath in the peripheral nervous system are called
a. astrocytes.
b. oligodendrocytes.
c. microglia.
d. neurons.
e. Schwann cells.
Answer: e. Schwann cells form myelin sheets around axons that are located in the peripheral nervous
system.
4. Neurons that function mainly in connecting other neurons in the central nervous system are
a. sensory neurons.
b. efferent neurons.
c. motor neurons.
d. afferent neurons.
e. interneurons.
Answer: e. Interneurons make connections between cells of the central nervous system.
5. The difference of charges across the plasma membrane of an unstimulated cell is called
a. the membrane potential.
b. the resting potential.
c. homeostasis.
d. the graded potential.
e. the action potential.
Answer: b. The resting potential is the difference of charges across the plasma membrane in an
unstimulated cell.
6. Which of the following influences the resting potential of a membrane?
a. negatively charged molecules or ions inside the cell
b. active transport of ions across the membrane
c. concentration of Na+ and K+ inside and outside of the cell
d. all of the above
e. b and c only
Answer: d. The resting potential is influenced by the concentration of negatively charged ions and
molecules inside the cell, the concentration of Na+ and K+ inside and outside of the cell, as well as the
activity of ion pumps that maintain resting concentrations of ions.
7. A cell has reached a threshold potential when it has depolarized to the point where voltage-gated
a. K+ channels open.
b. Na+ channels open.
c. K+ channels close.
d. Na+ channels close.
e. both b and d.
Answer: b. A cell has reached threshold when it has depolarized to the point where voltage-gated Na+
channels open.
8. The speed of transmission of an action potential along an axon is influenced by
a. the presence of myelin.
b. an increased concentration of Ca2+.
c. the diameter of the axon.
d. all of the above.
e. a and c only.
Answer: e. The speed of an action potential is influenced by the presence of myelin and the axon
diameter.
9. Gap junctions are characteristic of
a. electrical synapses.
b. chemical synapses.
c. acetylcholine synapses.
d. GABA synapses.
e. c and d only.
Answer: a. Electrical synapses are formed when the membranes of two neurons are connected by gap
junctions.
10. The response of the postsynaptic cell is determined by
a. the type of neurotransmitter released at the synapse.
b. the type of receptors the postsynaptic cell has.
c. the number of Na+ channels in the postsynaptic membrane.
d. the number of K+ channels in the postsynaptic membrane.
e. all of the above.
Answer: a. The response of the postsynaptic cell is determined by the type of receptor it has.
Conceptual Questions
1.
Distinguish between neurons and glial cells and give an example of a glial cell.
Answer:
neuron - A highly specialized cell that communicates with another cell of its kind and with other types of
cells by electrical or chemical signals.
glia - Cells that surround the neurons; a major class of cells in nervous systems that perform various
functions.
Schwann cells are glial cells that form myelin around axons.
2. Describe the difference between a graded potential and an action potential.
Answer: In a graded potential, a weak stimulus causes a small change in the membrane potential while
a strong stimulus can produce a greater change. Graded potentials occur along the dendrites and cell
body. If a graded potential reaches the threshold potential at the axon hillock, this results in an action
potential. This is a change in the membrane potential that is of a constant value, and is propagated from
the axon hillock to the nerve terminus.
3.
Explain how the transmission of an impulse occurs across a chemical synapse.
Answer: The presynaptic nerve terminal of a chemical synapse has vesicles that contain molecules of
neurotransmitter. When an action potential arrives at the nerve terminal, voltage-gated calcium channels
in the membrane open, allowing calcium ions to diffuse down their electrochemical gradient into the cell.
Calcium triggers the exocytosis of vesicles at the presynaptic membrane, where they release their
neurotransmitter into the synaptic cleft. Once the neurotransmitter has been released, it diffuses across
the synaptic cleft and binds to channels or receptors in the postsynaptic membrane. This binding
initiates a response in the postsynaptic cell, changing the membrane potential.
Experimental Questions
1. What observations led Loewi to develop his hypothesis of how nerves stimulate muscle
contractions?
Answer: Loewi was aware that electrical stimulation of the nerves of frog leg muscles would cause
muscle contractions. Also, he had observed that electrical stimulation of the different nerves associated
with the frog heart did not have the same results. He observed that electrically stimulating one nerve
caused an increase in the rate of muscle contraction in the heart, but electrically stimulating a different
nerve caused a decrease in the rate of muscle contraction.
2. What was Loewi's hypothesis to explain the observations of changes in the rate of contraction of the
frog heart muscle? Describe his experimental design to test his hypothesis. Why did he use two hearts?
Answer: Loewi suggested that the neurons release chemical substances that influence the activity of the
muscle and other neurons. The chemical substances, however, influence the activity of heart muscle
cells in different ways.
Loewi placed two hearts in separate chambers. The chambers, however, were connected, allowing the
saline solutions of the two containers to mix. He stimulated the vagus nerve of one of the hearts and
wanted to observe whether it would have an effect on both hearts. Because Loewi hypothesized that the
neurons release chemical substances, the chemical substance would be released into the extracellular
fluid and diffuse into the saline solution surrounding the hearts. He used two hearts to determine if
chemical substances released by the heart that was electrically stimulated could influence the activity of
the other heart.
3. What were the results of Loewi's experiment? Did the results support his hypothesis?
Answer: When the vagus nerve of one heart was stimulated, the rate of contraction in both hearts was
decreased. This suggested that something was released into the saline solution following the electrical
stimulation that caused the cardiac muscle to slow its rate of contraction. The results did support
Loewi's hypothesis.
Collaborative Questions
1. Discuss the organization of nervous systems in animals.
Answer: The nervous system of more complex animals is divided into the central nervous system and
the peripheral nervous system. The central nervous system is composed of the brain and spinal cord.
The function of the brain is to receive and interpret stimuli from all parts of the body. Once the stimulus
is interpreted, the brain also determines what response is necessary. The peripheral nervous system
consists of neurons that are outside of the central nervous system but connect to it. The peripheral
nervous system receives stimuli from the body and conveys it to the central nervous system for
interpretation. In addition to receiving stimuli, the peripheral nervous is what allows the animal to
respond to stimuli if a response is necessary.
2. Discuss the parts of a neuron.
Answer:
The cell body - This is the part of the neuron which contains the nucleus and other organelles that are
required to keep the cell alive. It is also the central portion of the cell
The dendrites - These are usually branched like a tree. They receive chemical messages from other
neurons and send it to the cell body.
The axon - This is the part of the neuron that sends the electrical information away from the cell body
and sends it to the next cell. It can range in size from a few millimeters in small animals to several
meters in larger ones. Most neurons have a single axon but it may have branches.
Myelin sheath - This is an insulating layer that surrounds the axon in the neurons of vertebrates. This
myelin sheath increases the speed of electrical impulses as they pass down the axon.