Lecture 5.docx - RECAP Neuronal Action Potential 1 Neuron...

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RECAP: Neuronal Action Potential 1. Neuron is at rest. There aren’t enough opened receptors to start the action potential. The receptors open when the neurotransmitters bind on the dendrites and then ion channels open either directly ionotropic or indirectly. Ions then move passively down concentration and electrochemical gradient. Ion flow changes the voltages inside the neuron. At rest and on average (there is still some flow), the inside is 70 mV more negative than the outside. 2. DEPOLARIZATION: With enough opening of receptors from positive influx, then depolarization threshold is reached at -55 mV. Ligand gated sodium ion channels are no longer the primary source of positive charge influx, and the voltage gated sodium ion channels take over and open automatically at -55 mV threshold. MUCH larger influx of sodium at this point. a. Potassium hasn’t done anything bc it responds to greater voltage. 3. Sodium channels close after a certain amount of time and no positive inflow, but no positive ions have left yet 4. At the same time, Voltage gated potassium channels open at around 30 mV and potassium streams out a. Fall in voltage b. Potassium has both electrical and chemical gradients pushing it out of the neuron (too much potassium inside, and its too positive inside) 5. REPOLARIZATION: Cellular machinery: sodium/potassium pump which maintains ionic concentrations across membrane to maintain them in the state that they were at rest a. Pump is always working but can only handle small changes b. During multiple firing of neurons, it is overwhelming of this pump and starts the action potential c. Voltage falls, and pump still helps by pulling 3 sodium ions out and 2 potassium ions in (- 1 net result charge) 6. HYPERPOLARIZATION: a. Inside of neuron is more negative than the inside because potassium channels are slow to close and more potassium leaves the neuron than needed to get back to resting potential of -70 mV. b. Actions of sodium potassium pump moving those respective ions across the membrane to restore resting membrane potential with all channels finally being closed - Different neurons have different shaped action potentials but same neuron will always produce same looking action potential WHERE WE LEFT OFF: How do drugs affect brain cells? (table 3.1) - Might increase or decrease neurotransmitter synthesis by: increasing the amounts of amino acids necessary to create transmitter or slowing down synthesis - Increase or decrease neurotransmitter transport to the axon terminals - Interfere with storage of neurotransmitter in vesicles: can make them leaky and neurotransmitters flood out
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- Directly cause neurotransmitter release from the axon terminals - Interfere with degradation of neurotransmitter in the synapse: affect neurotransmitter being degraded or being uptake, the result is that the neurotransmitter stays in the synapse longer, the molecules can either be sucked up by vacuum of presynaptic transporter (GOOD) or degrade
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  • Fall '19
  • Neurotransmitter

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