Presentation Transcript
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