Ch 4: Synaptic Transmission

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Slide 1: 

How Neurons Send and Receive Signals Chapter 4 Neural Conduction and Synaptic Transmission

Synaptic Transmission of Chemi-cal Signals: Structure of Synapses : 

Synaptic Transmission of Chemi-cal Signals: Structure of Synapses Most common Axodendritic – axons on dendrites Axosomatic – axons on cell bodies Dendrodendritic – capable of transmission in either direction Axoaxonic – may be involved in presynaptic inhibition

Synthesis, Packaging, and Transport of Neurotransmitter Molecules : 

Synthesis, Packaging, and Transport of Neurotransmitter Molecules Neurotransmitter molecules Small Synthesized in the terminal button and packaged in synaptic vesicles Large Assembled in the cell body, packaged in vesicles, and then transported to the axon terminal

Release of Neurotransmitter (NT) Molecules : 

Release of Neurotransmitter (NT) Molecules Exocytosis – the process of NT release The arrival of an AP at the terminal opens voltage-activated Ca2+ channels The entry of Ca2+ causes vesicles to fuse with the terminal membrane and release their contents

Activation of Receptors by NT Molecules : 

Activation of Receptors by NT Molecules Released NT molecules produce signals in postsynaptic neurons by binding to receptors Receptors are specific for a given NT Ligand – a molecule that binds to another A NT is a ligand of its receptor

Receptors : 

Receptors There are multiple receptor types for a given NT Ionotropic receptors – associated with ligand-activated ion channels Metabotropic receptors – associated with signal proteins and G proteins

Ionotropic Receptors : 

Ionotropic Receptors NT binds and an associated ion channel opens or closes, causing a PSP If Na+ channels are opened, for example, an EPSP occurs If K+ channels are opened, for example, an IPSP occurs

Metabotropic Receptors : 

Metabotropic Receptors Effects are slower, longer-lasting, more diffuse, and more varied (1) NT 1st messenger binds. (2) G protein subunit breaks away. (3) Ion channel opened/closed OR a 2nd messenger is synthesized. (3) 2nd messengers may have a wide variety of effects.

Slide 9: 

Ionotropic and Metabotropic Receptors

Reuptake, Enzymatic Degradation, and Recycling : 

Reuptake, Enzymatic Degradation, and Recycling As long as NT is in the synapse, it is active – activity must somehow be turned off Reuptake – scoop up and recycle NT Enzymatic degradation – a NT is broken down by enzymes