1/29/15 – Lecture 6 – Synaptic Transmission- Goal: to discover how an action potential from one neuron effects another - Action Potential Propagation: domino effect of action potential down the axon of the neurono 1. Influx on Na+ from AP flows into adjacent membrane areao 2. New patch of membrane depolarizes, forms action potential, which depolarizes the next patch of membrane Opens the next section’s Na+ channel and keeps goingo 3. Pervious patch cant reform action potential because it is in the refractory period due to closing and inactivation of Na+ channels during hyper polarization Only moves in one direction, down the axon to synapse -> closed -> open -> inactivated (refractory period/ hyper polarization) -> de-inactivated -> closed -> ect- Saltatory Conductiono Myelin sheath surrounds axon except bare patches on the axon called “Nodes of Ranvier” Action potentials “jump” from node to node because myelin insulates the axon, allowing less ions to flow out the membrane Saltatory: jumping, speeds the rate of conduction and propagation down the axon- Allows for fast and complex messages being sent- Synaptic Gapo The axon of one neuron comes close to the dendrite of the new neuron but doesn’t actually touch The action potential allows for the release of special chemicals called neurotransmitters across the synaptic gap- Neurotransmitters: chemicals produced by the presynaptic neuron and released due to the action potential, finally effects the post synaptic neurono 3 Main classes of Neurotransmitters Small Molecule: amino acids (glycine, glutamate) or synthesized from them or other metabolites (dopamine, serotonin, norepinephrine)- Synthesized – in the axon- Stored – in vesicles in the axon terminal Peptide: long chains of amino acids linked together to form a peptide or protein chains- Synthesized – in the cell body- Stored – in secretory vesicles  Transmitter Gases: gases synthesized from atoms (NO and CO)- Synthesized – in the axon terminal- NOT stored, immediately diffused out of the cello Neurotransmitters Released and Synaptic Transmission 1. Action potential travels down axon into axon terminal 2. Opens voltage gated Ca2+ channels- Allows Ca2+ to flow into the cell down its concentration gradient 3. Causes fusion of neurotransmitter vesicles with the membranes or the synthesis of gas neurotransmitters 4. Fusion causes vesicles to dump neurotransmitters into the synaptic cleft/ gap- Most neurons release one main type of neurotransmitterso Neurotransmitter Systems: groups of neurons using the same neurotransmitter through out the brain and the nervous system 4 Major Neurotransmitter Systems- Dopaminergic: uses dopamine within brain to regulate reward and movement- Noradrenergic: uses norepinephrine within brain to regulate arousal and attention- Serotonergic: uses serotonin within brain to regulate mood and compulsions- Cholinergic: uses acetylcholine within brain to regulate arousal and attentiono When Neurotransmitters are released…? Neurotransmitters bind to post synaptic proteins called receptors (found on dendrites of post synaptic neurons that bind to neurotransmitters)- After binding they make changes to post synaptic cells 2 Main Types of Receptors- Ionotropic: binding of Neurotransmitters directly opens the ion channel in the receptor and allows ions to flow into the cello Ligand – gated ion channels- Metabotropic: binding of neurotransmitters doesn’t directly open an ion channel but rather indirectly opens an ion channel by activating other intracellular proteinso Opens and closes the channels near