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Biology: The Dynamic Science (Mind...

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

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BuyFindarrow_forward

Biology: The Dynamic Science (Mind...

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

You learned in this chapter that Na+/K+ active transport pumps in the plasma membrane of the axons are responsible for creating the imbalance between Na+ and K+ inside and outside of the neuron that produces the resting membrane potential. In early research studying the role of ions and the involvement of active transport of ions in neural signaling, investigators used the giant axon of a squid as a model. The diameter of a giant axon is far greater than that of a mammalian axon, which enabled researchers to isolate it easily and use it in in vitro experiments. In one early experiment, researchers investigated the active transport of Na+ out of the axon in response to the presence of cyanide. Experimentally they hooked up a section of axon to a syringe, immersed the axon in artificial seawater, introduced radioactive 22Na (as 22NaCl) into the axon, and then quantified the transport of 22Na out through the axon’s plasma membrane. The rate of 22Na transport out of the axon was determined by measuring the radioactivity released into the fluid sur- rounding the axon over a period of time. The Figure shows the results of the experiment.

Chapter 39, Problem 1ITD, You learned in this chapter that Na+/K+ active transport pumps in the plasma membrane of the axons

What is the effect of cyanide on Na1 transport out of the squid axon? How do the data show the effect?

Source: P. C. Caldwell et al. 1960. The effects of injecting “energy-rich” phosphate compounds on the active transport of ions in the giant axons of Loligo. The Journal of Physiology 152:561–590.

© Cengage Learning 2017

Summary Introduction

To review:

The effects of cyanide on sodium transport out of the squid axon on the basis of given data.

Introduction:

Neurons of the nervous system get excited due to the generation of action potential, which is nothing but electrical impulse. This electrical impulse is generated due to different concentration of sodium and potassium ions present at both sides of the axon of a neuron. The case in which neurons are in resting condition, sodium concentration is higher in the outside region than in the inside of the neuron. This makes inside of the neuron negatively charged (–70mv).

Explanation

The graph showing the results of the experiment done on the giant squid.

Voltage-gated sodium ion channels are present in the plasma membrane of neurons. They function as pumps and they pump sodium from the outside to the inside. These pumps have two gates—the activation gate and the inactivation gate. The normal condition (when cyanide is absent), during generation of the action potential, sodium enters the cell from the outside through sodium transporters. This occurs because the outside of the neuron has a higher concentration of sodium than the inside. The equilibrium has to be maintained, so that sodium enters the neuron and it makes inside of the neuron more positive (+30 mv), and the action potential is generated. The function of the sodium transporters is important in order to maintain different concentration gradients of sodium ion on both sides of the membrane...

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