Biology: The Dynamic Science (Mind...

4th Edition
Peter J. Russell + 2 others
ISBN: 9781305389892



Biology: The Dynamic Science (Mind...

4th Edition
Peter J. Russell + 2 others
ISBN: 9781305389892
Textbook Problem

Apply Evolutionary Thinking A biologist hypothesized that the mechanism for the propagation of action potentials down a neuron evolved only once. What evidence would you collect from animals living today to support or refute that hypothesis?

Summary Introduction

To review:

The propagation of action potential through nerve is evolved only once, according to a biologist. Find evidence that either supports or refutes that hypothesis.


The nerve impulse or action potential is generated in the neurons. An action potential is nothing but an electrical impulse. This electrical impulse generates due to the presence of voltage-gated ion channels on the plasma membrane of the neurons and presence of different concentrations of ions (sodium, potassium, calcium) in both sides of the neurons.


There are three types of voltage-gated ion channels that are important in nerve impulse propagation. The genetic study of the genome of unicellular organisms shows that they have the genes that are involved in producing voltage-gated channels in the neurons. Although among these voltage-gated channels, K+ ion channels evolved first, they were not involved in generating an action potential. Although their activities made sure that unicellular cells do not burst out in the hypotonic solution, these voltage-gated channels evolved later and used to communicate between bacterial cells in a biofilm.

Another voltage-gated channel Ca+ ion channel was evolved in Porifera and cnidarians. Both K+ and Ca+ channels were able to generate primitive action potential that is used in the beating of cilia and flagella present on those organisms.

Another voltage-gated ion channel, that is, Na+ ion channel was evolved later in complex animals

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