Pharmacology Chapter 21 Flashcards

1. Types of Ion Channels
2. Types of Receptor-Channel coupling
3. Role of the Ion current carried by the channel

1. Voltage gated Channels

2. Ligand Gated Channels

Voltage-gated ion channels respond to changes in membrane potential.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.

Ligand-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 : 1. cell bodies and on presynaptic synapses 2. cell bodies on the postsynaptic side of synapse.

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 (B) (2) through a receptor that is coupled to the ion channel through a G protein (C) (3) through a receptor coupled to a G protein that modulates the formation of diffusible second messengers--including cAMP, inositol trisphosphate (IP3) , and diacyl- glycerol (DAG)--which secondarily modulate ion channels (D).

1. EPSPs

2. IPSPs

Excitatory postsynaptic potentials (EPSPs) are usually generated by the opening of sodium or calcium channels. In some synapses, similar depolarizing potentials result from the closing of potassium channels.

Inhibitory postsynaptic potentials (IPSPs) are generated by the opening of potassium or chloride channels. For example, activation of postsynaptic metabotropic receptors increases the efflux of potassium. Presynaptic inhibition can occur via a decrease in calcium influx elicited by activation of metabotropic receptors.

1. through direct interactions with molecular components of ion channels on axons
ex.
carbamazepine
phenytoin
2. at synapses

1. Hierarchial System


2. Diffuse System

clearly delimited in their anatomic distribution generally contain large myelinated, rapidly Conducting fibers. control major sensory and motor functions. excitatory transmitters = aspartate and glutamate. numerous small inhibitory interneurons, which utilize 3,-aminobutyric acid (GABA) or glycine as transmitters. Drugs that affect hierarchical systems often have profund effects on the overall excitability of the CNS.

broadly distributed, with single cells frequently sending processes to many different areas. The axons are fine and branch repeatedly to form synapses with many cells. Axons commonly have periodic enlargements (varicosities) that contain transmitter vesicles. The transmitters = amines (norepinephrine, dopamine, serotonin) or peptides = exert actions on metabotropic receptors. Drugs that affect these systems have marked effects on attention, appetite, and emotional states.

1. Acetylcholine
2. Dopamine
3. Norepinephrine
4. Serotonin
5. Glutamic Acid
7. Gaba and Glycine
8. Peptide Transmitters
9. Endocannabinoids

chemical must be present in higher concentration in the synaptic area than in other areas (ie, must be localized in appropriate areas) must be released by electrical or chemical stimulation via a calcium-dependent mechanism must produce the same sort of postsynaptic response that is seen with physiologic activation of the synapse (ie, must exhibit synaptic mimicry).

mediated by a large family of G protein-coupled muscarinic M receptors that lead to slow excitation when activated = involves a decrease in membrane permeability to potassium. nicotinic receptors = those on the Renshaw cells activated by motor axon collaterals in the spinal cord Drugs affecting the activity of cholinergic systems in the brain include the acetylcholinesterase inhibitors used in Alzheimer's disease (eg, tacrine) muscarinic blocking agents used in parkinsonism (eg, benztropine).