LECTURE 17 3-4-15-Steps of Neurotransmission1. Neurotransmitters must be synthesized and stored in the axon terminalDerived in 2 waysSynthesized in the cell body (via DNA), packed in Golgi bodies and transported on microtubules to the terminal button.Or, synthesized in the terminal button itself, built from building blocks derived from food via transportersTransporter- protein molecule that pumps substances across a membraneStorage Granule- holds several vesicles2. The neurotransmitter must be transported to the presynaptic membrane and released in response to an action potentialAction PotentialCa2+Presynaptic membrane has voltage-sensitive calcium channelsExtracellular fluid is rich in Ca2+Calcium channels activate (opening) and Ca2+ rushes in and it binds to the protein calmodulnPresynaptic membrane- exocytosisTerminal buttons (microfilaments)- move in3. The neurotransmitter must be able to activate the receptors on the target-cell membrane located on the postsynaptic membraneTransmitter-activated receptors- proteins with binding sites for specific neurotransmitters and is embedded in the membrane of a cellDepending on type of neurotransmitter and the specific receptor1. Depolarize the postsynaptic membrane (excitation)2. Hyperpolarize the postsynaptic membrane (inhibition)3. Initiate other chemical reactions in the cell that influence other cell functionsAlso, neurotransmitters can also travel back to the presynaptic membrane and activate receptors thereAutoreceptors- “self-receptor” in a neural membrane that responds to the neurotransmitter of the neuron it belongs to.The smallest postsynaptic potential is produced by the release of just one synaptic vesicleQuantum- amount of neurotransmitter, equivalent to the contents of a single synaptic vesicle, that produces a just observable change in postsynaptic electric potentialIt takes several quanta to produce an action potentialThe number of quanta that are released from the presynaptic membrane in response to an action potential depends on two factors:1. The amount of Ca2+ that enters the terminal button (axon terminal) in response to the action potential2. The number of vesicles docked at the membrane, waiting to be released4. The neurotransmitter must be inactivated, or its effects will last foreverDeactivation1. Diffusion- neurotransmitter diffuses away2. Degradation- enzymes in the synaptic cleft break them down (similar to the game red rover)3. Reuptake- presynaptic membrane transporter proteins bring the transmitter back into he presynaptic axon terminal for subsequent reuse4. Glial uptake- neighboring glial cells take up the transmitter and store it for reintroduction to axon terminalPSYC 260 1st EditionLecture 17Outline of Last LectureI. Steps of Neurotransmission Outline of Current LectureI. Steps of Neurotransmission Current Lecture LECTURE 17 3-4-15-Steps of Neurotransmission- 1. Neurotransmitters must be synthesized and stored in the axon terminal o Derived in 2 ways Synthesized in the cell body (via DNA), packed in Golgi bodies and transported on microtubules to the terminal button.  Or, synthesized in the terminal button itself, built from building blocks derived from food via transporters Transporter- protein molecule that pumps substances acrossa membrane Storage Granule- holds several vesicles - 2. The neurotransmitter must be transported to the presynaptic membrane and released in response to an action potentialo Action Potential Ca2+ Presynaptic membrane has voltage-sensitive calcium channels Extracellular fluid is rich in Ca2+ Calcium channels activate (opening) and Ca2+ rushes in and it binds to the protein calmoduln Presynaptic membrane- exocytosis Terminal buttons (microfilaments)- move in- 3. The neurotransmitter must be able to activate the receptors on the target-cell membrane located on the postsynaptic membraneo Transmitter-activated receptors- proteins with binding sites for specific neurotransmitters and is embedded in the membrane of a cell Depending on type of neurotransmitter and the specific receptor 1. Depolarize the postsynaptic membrane (excitation) 2. Hyperpolarize the postsynaptic membrane (inhibition) 3. Initiate other chemical reactions in the cell that influence other cell functions o Also, neurotransmitters can also travel back to the presynaptic membrane and activate receptors there Autoreceptors- “self-receptor” in a neural membrane that responds to the neurotransmitter of the neuron it belongs to.o The smallest postsynaptic potential is produced by the release of just one synaptic vesicle  Quantum- amount of neurotransmitter, equivalent to the contents of a single synaptic vesicle, that produces a just observable change in postsynaptic electric potential It takes several quanta to produce an action potentialo The number of quanta that are released from the presynaptic membrane in response to an action potential depends on two factors: 1. The amount of Ca2+ that enters the terminal button (axon terminal) in response to the action potential 2. The number of vesicles docked at the membrane, waiting to be released- 4. The neurotransmitter must be inactivated, or its effects will last forevero Deactivation 1. Diffusion- neurotransmitter diffuses away 2. Degradation- enzymes in the synaptic cleft break them down (similar to the game red rover) 3. Reuptake- presynaptic membrane transporter proteins bring the transmitter back into he presynaptic axon terminal for subsequent reuse 4. Glial uptake- neighboring glial cells take up the transmitter and store it for reintroduction to axon