Action Potential: A Tutorial Study Guide

Nicoladie Tam

• Publisher: Nicoladie Tam, Ph.D.
• ISBN:
  9781301115372
• Topic: Biowissenschaften
• Subtopic: Neurowissenschaft

"Action Potential" is a part of the college-level Principles of Biology course series and the Neuropsychopharmacology course series textbooks. It is a tutorial written in questions and answers format to describe the physiology of action potentials, nerve impulses and graded potentials in neurons.

It is a study guide with in-depth explanations. Each section is a modular unit that is self-contained for easy reading. The principles and concepts are introduced systematically so students can learn and retain the materials intuitively.

1.Action Potential

Objectives

• Understand the electrical potentials
• Understand the function of membrane potentials
• Understand the function of action potentials
• Understand the mechanisms in generating membrane potentials
• Understand the mechanisms in generating action potentials
• Understand the factors affecting conduction velocity
• Understand the role of myelination

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1.1.Membrane Potentials

Objectives

• Understand how electrical potentials are generated across the membrane

Concepts to Learn

• Understand how electrical charge difference can create electrical potentials
• Generation of resting potential
• Role of influx of Na⁺ ions
• Role of efflux of K⁺ ions
• Role of Na-K pump

Q&A

What is membrane potential?

It is the electrical potential difference generated between the inside and outside of a cell. That is, a cell is electrically charged, resulting in a voltage difference across the membrane.

Many cells in the body are electrically charged for communication or for direction motility. The electrical charge provides attraction and repulsion depending on whether electrical charges are opposite or the same. Opposite charges (positive and negative charges) attract whereas same charge (either both positive or both negative) repels.

If we put a voltmeter across the membrane and measure the electrical potential between the inside and outside of a cell, and if the cell is electrically charged, it will show a voltage difference.

What is an electrical potential?

It is the difference in electrical charge between two locations, which produces potential energy if the charges are released.

This electrical difference generates an attraction force if the charge separations are between positive and negative charge. This attraction force creates a potential for energy dissipation, i.e., when you release the charges, they will attract each other, and move with energy to come closer together. This capacity to produce energy as a result of the movement of attraction is called the electrical potential, or potential energy.

An analogy is gravitational potential, which is also another form of potential energy. When you separate two objects apart, such as moving a rock above the earth, it creates gravitational potential energy. It means that when you release the rock, the rock will fall toward the earth (come closer together), releasing the potential energy. That is, the farther apart they are, the more potential energy they will gain.

Similarly, if you have two charges (positive and negative charges), the farther apart they are, the more potential they will have. When you release them and they will come together, releasing the potential energy.

The phenomenon is the same for magnetic potential energy. When you separate the magnet (north and south) apart, it releases its potential energy and attracts each other when you release them.

How can a cell use membrane potential to perform its function?

A cell can use this membrane potential to move charges around because of the attraction/repulsion, sending an electrical signal as a result. Some cells can use membrane potential to guide the growth of other cells by providing the attractive force to them.

Therefore, cells use electrical charge and electricity to do many of its function. In the nervous system, neurons use electrical charge to send signals to communication with each other. Glial cells also use electrical membrane potentials to do its work too to help the other neurons.

Since electrical charges can move much faster than diffusion of molecules, this electrical signal is much faster than chemical signal of moving molecules around over long distances.

Is a neuron positively or negatively charged inside?

Most neurons are negatively charged inside the membrane with respect to the outside.

Since electrical charge (and electrical potential) is relative, as a convention, we define the outside of a cell as zero voltage. That is because it is easier to measure the outside of a cell, and we just call that zero volt. Then we measure the inside of a cell, and it happens that the voltage inside a neuron is negative.

What is a typical voltage inside a neuron?

The typical voltage is -70 mV for a neuron.

That is, the inside of a neuron is -0.07 Volt relative to the outside (which is 0 Volt). One mV = 0.001 V. A typical battery is 1.5 V, so a neuron can generate a significant voltage, about 5% of the voltage in a battery.

What does this voltage use for in neurons?

This voltage is used to generate action potentials (nerve impulses) to communicate between neurons over long distances.

Since the neuron is electrically charge with a voltage ...

Table of contents

• Preface
• 1.Action Potential
• About the Author
• Other Books Published by the Author