Synaptic Conduction What happens when an action potential

Synaptic Conduction • What happens when an action potential reaches the axon terminals? • Depends on the nature of “synapse” • Synapse = special communication region between two adjacent neurons or neuron and effector cell (i. e. , muscle)

Electrical Synapse

Chemical Synapse

Action potential Synaptic vesicle active uptake Ca 2+ voltagegated Ca channel Ca 2+ docking protein Postsynaptic cell K+ Na+ 1. action potential arrives at terminal 2. voltage-gated Ca channels open 3. Ca triggers exocytosis of vesicles 4. neurotransmitter is released, binds to receptor 5. ligand-gated Na or K channels open 6. neurotransmitter broken down, taken up 7. synaptic vesicles reconstituted 8. neurotransmitter stored, awaits next impulse

Neurotransmitters • Acetylcholine • Monoamines – Norepinephrine – Dopamine – Serotonin • • Amino Acids Polypeptides Purines Gases

Cholinergic Synapse

Muscarinic cholinergic synapse acetylcholine X muscarine (agonist) atropine (antagonist)

Neuromuscular Junction acetylcholine botulinum toxin X X acetylcholinesterase nicotine (agonist) curare (antagonist) Nicotinic cholinergic synapse

Transmission at an Adrenergic Synapse

Antidepressants • Monoamine Oxidase Inhibitors (MAOIs) • Tricyclic Antidepressants (TCAs) • Selective Serotonin Reuptake Inhibitors (SSRIs) • Atypical Antidepressants

Monoamine Oxidase Inhibitors • Inhibit the production of the enzyme monoamine oxidase • Increases amount of neurotransmitter at the synapses and alleviates depression • Examples: Nardil, Parnate

Tricyclic Antidepressants • Inhibit the reuptake of neurotransmitters at the synapses and alleviates depression • Improve moods • Stimulate appetite • Increase activity levels • Help people sleep • Have fewer problems than MAOIs • Examples: Pamelor, Elavil

Selective Serotonin Reuptake Inhibitors • More specific than other antidepressants— block the reuptake of Serotonin • Examples: Prozac, Zoloft, Paxil, Celexa

Atypical Antidepressants • Work in a variety of different ways to inhibit breakdown or reuptake of selective neurotransmitters • Most similar to TCAs and SSRIs • Examples: Wellbutrin, Effexor • Side effects: dizziness, weight gain or loss, increased or decreased appetite, and dry mouth