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Ch. 43 - Animal Nervous Systems
Freeman - Biological Science 7th Edition
Freeman7th EditionBiological ScienceISBN: 9783584863285Not the one you use?Change textbook
All textbooksFreeman 7th EditionCh. 43 - Animal Nervous SystemsProblem 11a
Chapter 43, Problem 11a

Certain species of frogs in the genus Phyllobates have a powerful defensive adaptation—their skin can secrete a milky fluid that contains an extremely toxic compound called batrachotoxin (BTX). These frogs, which are found in Colombia, are known as poison dart frogs because some indigenous Colombian hunters coat the tips of their blowgun darts with the frogs' skin secretions. An animal hit by one of these darts dies quickly.
What is the mechanism of action of BTX? The graph here shows the effect of BTX on the membrane potential of a squid giant axon.
Which of the following is the most likely explanation for the effect of BTX on the squid giant axon?
a. Inactivation of Na+/K+-ATPase
b. Closing of sodium channels
c. Opening of sodium channels
d. Opening of potassium channels

Verified step by step guidance
1
Examine the graph provided, which shows the effect of BTX on the membrane potential of a squid giant axon over time. Initially, the membrane potential is at -50 mV, indicating a resting state.
Observe the change in membrane potential after the addition of BTX. The graph shows a rapid increase in membrane potential, moving towards 0 mV, which suggests depolarization of the axon membrane.
Understand that depolarization typically occurs when sodium channels open, allowing Na+ ions to flow into the cell, reducing the negative charge inside the axon.
Consider the options given: a) inactivation of Na+/K+-ATPase, b) closing of sodium channels, c) opening of sodium channels, d) opening of potassium channels. The rapid depolarization observed is most consistent with the opening of sodium channels.
Conclude that the most likely explanation for the effect of BTX on the squid giant axon is the opening of sodium channels, as this would lead to the observed increase in membrane potential.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Batrachotoxin (BTX)

Batrachotoxin is a potent neurotoxin found in certain species of frogs, particularly in the genus Phyllobates. It disrupts normal cellular function by affecting ion channels, particularly sodium channels, leading to paralysis or death in prey. Understanding BTX's mechanism is crucial for comprehending its effects on nerve cells, such as those in the squid giant axon.

Membrane Potential

Membrane potential refers to the electrical potential difference across a cell's membrane, primarily determined by the distribution of ions, such as sodium (Na+) and potassium (K+). Changes in membrane potential are critical for the generation and propagation of action potentials in neurons. The graph illustrates how BTX alters the membrane potential, indicating its impact on neuronal excitability.
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Sodium Channels

Sodium channels are integral membrane proteins that allow the selective passage of sodium ions into the cell, playing a key role in the initiation and propagation of action potentials. When these channels open, they cause depolarization of the membrane potential. BTX's action likely involves the opening or inactivation of these channels, which is essential for understanding the observed changes in the squid giant axon's membrane potential.
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Why is memory thought to involve changes in particular synapses?

a. At some synapses, more neurotransmitters are released after learning takes place.

b. At some synapses, a different type of neurotransmitter is released after learning takes place.

c. When researchers stimulated certain neurons electrically, individuals replayed memories.

d. When researchers changed synapses in the brains of patients during surgery, the patients' memories changed.

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Explain why drugs that prevent neurotransmitters from being taken back up by a presynaptic neuron have dramatic effects on the activity of postsynaptic neurons.

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Alzheimer's disease is a common form of dementia affecting millions of people, especially the elderly. Two regions of the brain are particularly affected, often shrinking dramatically and accumulating large deposits of extracellular material. Based on your knowledge of memory, what two brain regions do you think these are? Explain.

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Textbook Question

Certain species of frogs in the genus Phyllobates have a powerful defensive adaptation—their skin can secrete a milky fluid that contains an extremely toxic compound called batrachotoxin (BTX). These frogs, which are found in Colombia, are known as poison dart frogs because some indigenous Colombian hunters coat the tips of their blowgun darts with the frogs' skin secretions. An animal hit by one of these darts dies quickly.

What is the mechanism of action of BTX?

Identify a research technique that could be used to discover how BTX affects specific membrane proteins.

Based on the graph in Question 11, what would you expect this technique to show?

615
views
Textbook Question

Certain species of frogs in the genus Phyllobates have a powerful defensive adaptation—their skin can secrete a milky fluid that contains an extremely toxic compound called batrachotoxin (BTX). These frogs, which are found in Colombia, are known as poison dart frogs because some indigenous Colombian hunters coat the tips of their blowgun darts with the frogs' skin secretions. An animal hit by one of these darts dies quickly.

What is the mechanism of action of BTX? As the graph in Question 11 shows, BTX depolarizes the membrane and prevents repolarization.

What effect would this have on electrical signaling by the nervous system?

876
views
Textbook Question

Certain species of frogs in the genus Phyllobates have a powerful defensive adaptation—their skin can secrete a milky fluid that contains an extremely toxic compound called batrachotoxin (BTX). These frogs, which are found in Colombia, are known as poison dart frogs because some indigenous Colombian hunters coat the tips of their blowgun darts with the frogs' skin secretions. An animal hit by one of these darts dies quickly.

What is the mechanism of action of BTX?

Like neurons, cells in skeletal and cardiac muscle also produce action potentials. Create a concept map showing how BTX could kill a mammal through its effects on nervous and muscle tissues.

696
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