Principles of Physiology and Biochemistry Neurotransmission

Pumping and Diffusion of Ions Creates an Electric Potential Difference across the Plasma Membrane An Action Potential Is a Wave of Local Depolarization and Repolarization of the Plasma Membrane Action Potentials Are Mediated by Voltage-Gated Ion Channels 

Synaptic Transmission Is Mediated by Ligand-Gated Ion Channels 

The cell body of a mammalian motor neuron has an extended process termed an axon that branches at its tip to make multiple contacts (synapses) with a muscle cell (fig. S1.1). Some axons actually reach lengths of several meters. Much of the axon may be encased in myelin sheaths, which are multilayered membranes formed by other cells that wrap themselves around the neuron. Shorter processes (dendrites) extend from the cell body to make contacts with other neurons. If a motor neuron is stimulated electrically or is triggered by its connecting neurons, an electric signal called an action potential sweeps down the axon and is transmitted to the muscle cell, which then proceeds to contract. Other 

Schematic diagram of a typical motor neuron (a nerve cell conducting impulses to muscle cells). 

Pumping and Diffusion of Ions Creates an Electric Potential Difference across the Plasma Membrane 

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Part 6 concludes with two brief, informative supplements that integrate physiological and biochemical principles as they apply to the nonmetabolic functions of amino acids and lipids Supplement 1 —Principles of Physiology and Biochemistry Neurotransmission and Supplement 2—Principles of Physiology and Biochemistry Vision. 

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