CNS Flashcards
2 major types of ion channels in neuronal membranes
- Voltage gated
* Ligand gated (ionotropic receptors)
Transmembrane ion channels regulated by changes in membrane potential
Voltage-gated ion channels
Transmembrane ion channels that are regulated by interactions between
neurotransmitters and their receptors (also called ionotropic receptors)
Ligand-gated ion channels
Channels responsible for membrane depolarization in action potential generation
Voltage Gated Sodium Channels
Plays an important role in both linking muscvle excitation with contraction as well as neuronal excitation with transmitter release.
Voltage Gated Calcium Channels
Role in repolarization of cell membrane after action potential.
Voltage Gated Potassium Channels
G protein-coupled receptors that respond to neurotransmitters either by a direct action of G proteins on ion channels or by G protein-enzyme activation that leads to formation of diffusible second messengers
Metabotropic receptors
Work by activating other proteins called G porteins. They stimulate or inhibit the opening of ion channels in the cell membrane. But they work more slowly than ionotrophic receptors
Metabotropic receptors
Binding site + channel combined. Second messenger-independent Short latency action Rapid responses Postsynaptic
Ionotropic receptors
Excitatory postsynaptic potential. A depolarizing potential change
EPSP
Inhibitory postsynaptic potential. A hyperpolarizing potential change
IPSP
Ability of an administered chemical to mimic the actions of the natural neurotransmitter
Synaptic mimicry
Respond to changes in membrane potential. They are concentrated on the axons of nerve cells and include the sodium channels responsible for action potential propagation. Cell bodies and dendrites also have voltage-sensitive ion channels for
potassium and calcium.
Voltage-gated Ion Channels
Also called ionotropic receptors. Respond to chemical neurotransmitters that bind to receptor subunits present in their macromolecular structure. Neurotransmitters also bind to G protein-coupled receptors (metabotropic receptors) that can modulate voltage-gated ion channels. Neurotransmitter-coupled ion channels are found on cell bodies and on both the presynaptic and postsynaptic sides of synapses.
Ligand-gated Ion Channels
In the case of ligand-gated ion channels, activation (or inactivation) is initiated by the interaction between chemical neurotransmitters and their receptors.
Coupling may be:
(1) through a receptor that acts directly on the channel protein
(2) through a receptor that is coupled to the ion channel through a G protein, or
(3) through a receptor coupled to a G protein that modulates the formation of diffusible second messengers, including:
a) cyclic adenosine monophosphate (cAMP)
b) inositol trisphosphate (IP3)
c) diacylglycerol (DAG),
Excitatory postsynaptic potentials (EPSPs) are usually generated by the
opening of
sodium or calcium channels
Inhibitory postsynaptic potentials (IPSPs) are usually generated by the opening of
potassium or chloride channels
The effects of most therapeutically important CNS drugs are exerted mainly at
synapses