Neuronal Action Potential
Neurons rely on a number of mechanisms to perform their important jobs of (i) receiving information, (ii) information processing, (iii) signal propagation, and (iv) signal transmission. One such mechanism that is at the core of neuronal function is based on rapid and reversible reversal of the electrical potential difference across the plasma membrane. By reversal, it is meant that the membrane potential rapidly changes from its resting level of approximately −70 mV to around +50 mV and, subsequently, rapidly returns to the resting level again. The rapid reversal of membrane potential forms an important basis for information processing, propagation, and transmission and is referred to as the action potential, electrical impulse, or nervous impulse. In this fashion, neurons are said to be excitable cells. The focus of this lecture is to learn about the details of the neuronal action potential. Neurons are not the only excitable cells in the human body. Muscle cells (skeletal, cardiac, and smooth muscle), and some endocrine cells (i.e., hormone producing cells) are also excitable (i.e., exhibit action potentials). These cells will be discussed in later lectures.
After studying this lecture, you will be able to:
- Predict the nature of the response of excitable and non-excitable cells to artificial electrical stimulation.
- Describe the details of the neuronal action potential.
- Explain the Na+ and K+ permeability changes during the action potential, and how they are related to different phases of the action potential.
- Understand the molecular mechanism for inactivation of voltage-gated Na+ channels.
- Describe the ball-and-chain model of Na+ channel inactivation.
- Describe the details of neuronal refractory periods, including both the absolute refractory period and relative refractory period.
- Calculate the maximum frequency at which action potentials can be generated in a neuron, given the absolute and relative refractory periods.
- Name a few toxin and non-toxin blockers of voltage-gated Na+ and K+ channels.
- Compare and contrast graded potentials and action potentials.
Required Mastery of Previous Materials
In order to fully understand this lecture, you need to have already mastered the following topics:
- Physiological values for the extracellular and cytoplasmic concentration of ions, particularly those of Na+ and K+.
- The mechanisms responsible for establishing the membrane potential, and the factors that influence the value of the membrane potential.
- The electrochemical driving force that acts on an ion at any given membrane potential.
- The basic structure and function of voltage-gated ion channels, particularly voltage-gated Na+ and K+ channels.
- Artificial stimulation of cells by using electrophysiological methods. The use of electrophysiological methods to apply square-wave pulses to cells. In particular, the notion that injection of positive charge into the cell leads to depolarization and, conversely, injection of negative charge into the cell leads to hyperpolarization.
After studying this lecture, you should be able to define all of the following terms:
Posted: Thursday, July 5, 2012
Last updated: Sunday, February 16, 2014