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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

In the propagation of a nerve impulse:

a. the refractory period begins as the K+ channel opens, allowing K+ ions to flow outward along their concentrationgradient.

b. Na+ ions flow out of the axon with their concentration gradient.

c. positive charges lower the membrane potential to its lowestaction potential.

d. gated K+ channels open at the same time as the activationgate of Na+ channels closes.

e. the depolarizing stimulus lowers the membrane potential toopen the Na+ gates.

Summary Introduction

Introduction:

The neurons carry nerve impulses to the brain. The neurons get excited by stimuli and action potential, generated in the neuron. An action potential is nothing but an electrical impulse that is generated due to the movement of ions like potassium and sodium, throughout the neuron membrane.

Explanation

Justification/explanation for the correct answer:

Option (a) states that in the propagation of a nerve impulse, the refractory period begins as the K+ channels open, allowing K+ ions to flow outward along with their concentration gradient. The refractory period begins when the action potential is at peak. The K+ ion pumps present in the neuron membrane open and K+ ions flow out of the neuron at the beginning of this period. The K+ ions flow out of the neuron because the concentration of K+ ions outside (5 nM) the cell is less than that of the inside (150 nM). This decreases the membrane potential and helps neuron achieve the resting membrane potential in which, inside of the neuron is negative relative to the outside of the membrane. Hence, option (a) is the correct option.

Explanation for the incorrect answers:

Option (b) states that in the propagation of a nerve impulse, Na+ ions flow out of the axon with their concentration gradient. The Na+ ions flow into the cell through Na+/K+ ion pumps to generate action potential or nerve impulse. So, it is an incorrect option.

Option (c) states that the positive charges lower the membrane potential to its lowest action potential in the propagation of a nerve impulse. The condition when a neuron is not excited, it is said to be in resting membrane potential in which, inside of the neuron is negatively charged (–70 mV)

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