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Ch. 43 - Animal Nervous Systems
All textbooksFreeman 8th EditionCh. 43 - Animal Nervous SystemsProblem 15
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Chapter 42, Problem 15

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? Predict the effects of each of the following on the membrane potential of a neuron simultaneously poisoned with BTX: (a) removing extracellular sodium ions; (b) increasing the intracellular potassium ion concentration; and (c) adding tetrodotoxin from puffer fish.

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Key Concepts

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

Batrachotoxin Mechanism of Action

Batrachotoxin (BTX) is a potent neurotoxin that primarily affects sodium channels in neurons. It binds to these channels, preventing them from closing, which leads to prolonged depolarization of the neuronal membrane. This results in continuous action potentials, causing excessive neuronal firing and ultimately leading to paralysis or death in affected organisms.
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Membrane Potential

Membrane potential refers to the voltage difference across a cell's plasma membrane, primarily determined by the distribution of ions, such as sodium (Na+) and potassium (K+). Changes in ion concentrations can significantly affect the membrane potential, influencing neuronal excitability and signaling. Understanding how various ions impact this potential is crucial for predicting neuronal responses to toxins like BTX.
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Effects of Ion Concentration Changes

The effects of altering ion concentrations on membrane potential can be predicted using the Nernst equation and the principles of electrochemical gradients. For instance, removing extracellular sodium ions would hyperpolarize the neuron, while increasing intracellular potassium ions could lead to depolarization. Additionally, tetrodotoxin, another sodium channel blocker, would further inhibit action potentials, compounding the effects of BTX.
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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?

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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? 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?

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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? 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.

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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?Although BTX is a powerful antipredator poison, one snake species in Colombia eats poison dart frogs. Suggest a hypothesis that might explain how the snake is resistant to the toxin.

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