The Physiology of Control: Neurons and Endocrine Cells Compared

• Neurons transmit electrical signals to target cells
• Endocrine cells broadcast hormones
• Nervous systems and endocrine systems tend to control different processes

Neurons Are Organized into Functional Circuits in Nervous Systems

The Cellular Organization of Neural Tissue

• Neurons are structurally adapted to transmit action potentials
• Glial cells support neurons physically and metabolically

The Ionic Basis of Membrane Potentials

• Cell membranes have passive electrical properties: Resistance and capacitance
• Resting membrane potentials depend on selective permeability to ions: The Nernst equation
• Ion concentration differences result from active ion transport and from passive diffusion
• Membrane potentials depend on the permeabilities to and concentration gradients of several ion species: The Goldman equation
• Electrogenic pumps also have a small direct effect on V_m

The Action Potential

• Action potentials are voltage-dependent, all-or-none electrical signals
• Action potentials result from changes in membrane permeabilities to ions
• The molecular structure of the voltage-dependent ion channels reveals their functional properties
• BOX 12.1 Evolution and Molecular Function of Voltage-Gated Channels
• There are variations in the ionic mechanisms of excitable cells
• BOX 12.2 Optogenetics: Controlling Cells with Light, Matthew S. Kayser

The Propagation of Action Potentials

• Local circuits of current propagate an action potential
• Membrane refractory periods prevent bidirectional propagation
• The conduction velocity of an action potential depends on axon diameter, myelination, and temperature
• BOX 12.3 Giant Axons