Neurons Generating and Conducting Nerve Impulses

► Neurons have an electric charge difference across their plasma membranes. This resting potential is created by ion pumps and ion channels. Review Figure 44.4

► The sodium-potassium pump concentrates K+ on the inside of a neuron and Na+ on the outside. Potassium channels allow K+ to diffuse out of the neuron, leaving behind unbalanced negative charges. Review Figures 44.5, 44.6. See Web/CD Tutorial 44.1

► A potassium equilibrium potential exists when the tendency of K+ ions to diffuse out of the neuron is balanced by the nega tive charges pulling them back in. This potential can be calculated using the Nernst equation. Review Figure 44.7

► The resting potential is perturbed when ion channels open or close, changing the permeability of the plasma membrane to charged ions. Through this mechanism, the plasma membrane can become depolarized or hyperpolarized. Review Figure 44.8

► An action potential is a rapid reversal in charge across a portion of the plasma membrane resulting from the sequential opening and closing of voltage-gated sodium and potassium channels. These changes in voltage-gated channels occur when the plasma membrane depolarizes to a threshold level. Review Figure 44.9. See Web/CD Tutorial 44.2

► Action potentials are all-or-nothing, self-regenerating events. They are conducted down axons because local current flow depolarizes adjacent regions of membrane and brings them to threshold. Review Figure 44.10

► Patch clamping allows the study of single ion channels. Review Figure 44.11

► In myelinated axons, action potentials appear to jump between nodes of Ranvier, patches of axonal plasma membrane that are not covered by myelin. Review Figure 44.12

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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