Class 04 SYNAPSE

Class 04 SYNAPSE - Bio 208 Class #4 How Neurons...

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Bio 208 Class #4 How Neurons Communicate. II Chemical Transmission Sept 11, 2008
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Notes to me Does Botox prevent blinking or eye movements when used for Hemifacial spasm or blepharospasm?
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Outline for Today’s Lecture 1. How neurons release chemical transmitters 2. How neurons respond to these chemical transmitters 3. Animal and plant toxins that disrupt this process 4. Potential therapeutic use of some of these toxins.
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Synaptic transmission 1. How are chemical transmitters released from neurons? 2. What effects do these transmitters have on the target neuron? A. chemically gated ion channels B. G-protein-linked receptors C. affect DNA
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Chemical Synapse
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Events at the synapse involving release
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Summary of Transmitter Inactivation
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Termination of chemical signals Degraded enzymatically: as acetylcholine (Ach) is by ACh esterase; AChE inhibitors are antidotes for insecticides and mustard gas Cellular uptake: as in the cases of dopamine and serotonin. SSRIs (Selective Serotonin Reuptake Inhibitors) like Prozac maintain extracellular levels of serotonin. Cocaine causes a massive release of dopamine and prevents its reuptake. Diffusion
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General Statement on Synaptic Potentials and Excitability Excitatory postsynaptic potentials (EPSP) are DEPOLARIZING (Na+ enters) Inhibitory postsynaptic potentials (IPSP) are HYPERPOLARIZING (K+ leaves or Cl- enters) The response depends on the RECEPTOR not the transmitter
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Major Types of Transmitter Action 1. Direct action on membrane channel 2. Amplification with second messenger cascades. 3. Modifies gene activity; results in protein synthesis. (will discuss this in another lecture).
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1. Direct action on membrane channel
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Na + influx produces an EPSP (Excitatory Post Synaptic Potential)
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Cl - influx produces an IPSP (Inhibitory Post Synaptic Potential)
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The amplitude of EPSPs gets smaller with distance.
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Summation of EPSPs
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Temporal Summation – below threshold
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Temporal Summation – above threshold
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Summation of Synaptic Potentials Synaptic potentials are graded. Thus, they can summate in space or
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Class 04 SYNAPSE - Bio 208 Class #4 How Neurons...

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