Chapter 12 Outline
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 Vm
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