Question 1

Why are action potentials usually conducted in one direction?

Accepted Answer

A)  The nodes of Ranvier conduct potentials in one direction. 
B)  The brief refractory period prevents reopening of voltage-gated sodium channels. 
C)  The axon hillock has a higher membrane potential than the terminals of the axon. 
D)  Voltage-gated channels for both Na⁺ and K⁺ open in only one direction. 
A)  The nodes of Ranvier conduct potentials in one direction. 
B)  The brief refractory period prevents reopening of voltage-gated sodium channels. 
C)  The axon hillock has a higher membrane potential than the terminals of the axon. 
D)  Voltage-gated channels for both Na⁺ and K⁺ open in only one direction.

Question 2

A neurophysiologist is investigating nerve reflexes in two different animals: a crab and a fish. Action potentials are found to pass more rapidly along the fish's neurons. What is the most likely explanation?

Accepted Answer

A)  The fish's axons are smaller in diameter; small axons transmit action potentials faster than large axons do. 
B)  Unlike the crab, the fish's axons are wrapped in myelin. 
C)  There are more ion channels in the axons of the crab compared with fish axons. 
D)  Unlike the crab, the fish's axons are wrapped in myelin, and the fish's axons are smaller in diameter; small axons transmit action potentials faster than large axons do. 
A)  The fish's axons are smaller in diameter; small axons transmit action potentials faster than large axons do. 
B)  Unlike the crab, the fish's axons are wrapped in myelin. 
C)  There are more ion channels in the axons of the crab compared with fish axons. 
D)  Unlike the crab, the fish's axons are wrapped in myelin, and the fish's axons are smaller in diameter; small axons transmit action potentials faster than large axons do.

Question 3

The heart rate of a vertebrate will decrease in response to the arrival of ________.

Accepted Answer

A)  acetylcholine 
B)  endorphin 
C)  nitric oxide 
D)  gamma-aminobutyric acid (GAB
A)  
A)  acetylcholine 
B)  endorphin 
C)  nitric oxide 
D)  gamma-aminobutyric acid (GAB
A)

Question 4

The amino acid that operates at most inhibitory synapses in the brain is ________.

Accepted Answer

A)  acetylcholine 
B)  endorphin 
C)  nitric oxide 
D)  gamma-aminobutyric acid (GAB
A)  
A)  acetylcholine 
B)  endorphin 
C)  nitric oxide 
D)  gamma-aminobutyric acid (GAB
A)

Question 5

A chemical that affects neuronal function but is not stored in presynaptic vesicles is ________.

Accepted Answer

A)  acetylcholine 
B)  epinephrine 
C)  nitric oxide 
D)  gamma-aminobutyric acid (GAB
A)  
A)  acetylcholine 
B)  epinephrine 
C)  nitric oxide 
D)  gamma-aminobutyric acid (GAB
A)

Question 6

What happens when a resting neuron's membrane depolarizes?

Accepted Answer

A)  There is a net diffusion of Na⁺ out of the cell. 
B)  The equilibrium potential for K⁺ (EK) becomes more positive. 
C)  The neuron's membrane voltage becomes more positive. 
D)  The cell's inside is more negative than the outside. 
A)  There is a net diffusion of Na⁺ out of the cell. 
B)  The equilibrium potential for K⁺ (EK) becomes more positive. 
C)  The neuron's membrane voltage becomes more positive. 
D)  The cell's inside is more negative than the outside.

Question 7

Of those listed, which event occurs first following a depolarizing stimulus applied to the presynaptic membrane of an axon terminal?

Accepted Answer

A)  Voltage-gated calcium channels in the membrane open. 
B)  Synaptic vesicles fuse with the membrane. 
C)  The postsynaptic cell produces an action potential. 
D)  Ligand-gated channels open, allowing neurotransmitters to enter the synaptic cleft. 
A)  Voltage-gated calcium channels in the membrane open. 
B)  Synaptic vesicles fuse with the membrane. 
C)  The postsynaptic cell produces an action potential. 
D)  Ligand-gated channels open, allowing neurotransmitters to enter the synaptic cleft.

Question 8

Why do Na⁺ ions enter the cell when voltage-gated Na⁺ channels are opened in neurons?

Accepted Answer

A)  because the Na⁺ concentration is much lower outside the cell than it is inside 
B)  because the Na⁺ ions are actively transported by the sodium-potassium pump into the cell 
C)  because the Na⁺ concentration is much higher outside the cell than it is inside, and the Na⁺ ions are attracted to the negatively charged interior 
D)  because the Na⁺ concentration is much higher outside the cell than it is inside, and the Na⁺ ions are actively transported by the sodium-potassium pump into the cell 
A)  because the Na⁺ concentration is much lower outside the cell than it is inside 
B)  because the Na⁺ ions are actively transported by the sodium-potassium pump into the cell 
C)  because the Na⁺ concentration is much higher outside the cell than it is inside, and the Na⁺ ions are attracted to the negatively charged interior 
D)  because the Na⁺ concentration is much higher outside the cell than it is inside, and the Na⁺ ions are actively transported by the sodium-potassium pump into the cell

Exam 48: Neurons, Synapses, and Signaling

Why are action potentials usually conducted in one direction?

A neurophysiologist is investigating nerve reflexes in two different animals: a crab and a fish. Action potentials are found to pass more rapidly along the fish's neurons. What is the most likely explanation?

The heart rate of a vertebrate will decrease in response to the arrival of ________.

The amino acid that operates at most inhibitory synapses in the brain is ________.

A chemical that affects neuronal function but is not stored in presynaptic vesicles is ________.

What happens when a resting neuron's membrane depolarizes?

Of those listed, which event occurs first following a depolarizing stimulus applied to the presynaptic membrane of an axon terminal?

Why do Na⁺ ions enter the cell when voltage-gated Na⁺ channels are opened in neurons?

Evolution, the Themes of Biology, and Scientific Inquiry

The Chemical Context of Life

Water and Life

Carbon and the Molecular Diversity of Life

The Structure and Function of Large Biological Molecules

A Tour of the Cell

Membrane Structure and Function

An Introduction to Metabolism

Cellular Respiration and Fermentation

Photosynthesis

Cell Communication

The Cell Cycle

Meiosis and Sexual Life Cycles

Mendel and the Gene Idea

The Chromosomal Basis of Inheritance

The Molecular Basis of Inheritance

Gene Expression: From Gene to Protein

Regulation of Gene Expression

Viruses

DNA Tools and Biotechnology

Genomes and Their Evolution

Descent with Modification: A Darwinian View of Life

The Evolution of Populations

The Origin of Species

The History of Life on Earth

Phylogeny and the Tree of Life

Bacteria and Archaea

Protists

Plant Diversity I: How Plants Colonized Land

Plant Diversity II: The Evolution of Seed Plants

Fungi

An Overview of Animal Diversity

An Introduction to Invertebrates

The Origin and Evolution of Vertebrates

Vascular Plant Structure, Growth, and Development

Resource Acquisition and Transport in Vascular Plants

Soil and Plant Nutrition

Angiosperm Reproduction and Biotechnology

Plant Responses to Internal and External Signals

Basic Principles of Animal Form and Function

Animal Nutrition

Circulation and Gas Exchange

The Immune System

Osmoregulation and Excretion

Hormones and the Endocrine System

Animal Reproduction

Animal Development

Nervous Systems

Sensory and Motor Mechanisms

Animal Behavior

An Introduction to Ecology and the Biosphere

Population Ecology

Community Ecology

Ecosystems and Restoration Ecology

Conservation Biology and Global Change

Filters