PSYC 251 Lecture Notes - Lecture 7: Reuptake, Endocytosis, Axon Terminal
22 Jun 2018
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A4: Impulse Conduction in Axons
Action Potential Conduction
Requires both ACTIVE and PASSIVE current flows
o Potential falls to a small fraction of its value
o Injected current leaks out of the axonal membrane
o Therefore there is less current to produce a reaction
Axon Potential Propagation
o Passive Flow (explained)
Depolarizing stimulus/ Synaptic Potential
Locally depolarized axon
Opens voltage gated Na channels in that area
Na(+) moves inside
Current generated by action potential flows down axon
Depolarizes membrane potential in neighboring membrane
Spreads down until end of axon
Repolarization
After potential has passed, voltage gated K channels open
Leaves a wake of refractoriness
Prohibits the backwards flow of the potential
o ...Improving Passive Current Flow
Increase Diameter of Axon
Decreases internal resistance
Myelination (Vertebrates)
Insulates axonal membrane (electrical insulator)
Decreases leakage
Increases distance that a current can flow
Glial cells wrap axons in myelin
Speeds up action potential conduction
Action potential generation occurs ONLY at Nodes of Ranvier
A5: Synaptic Transmission
Synapses
o junctions where muscles and neurons communicate
Chemical Synapse
o Most common type
o Synaptic Transmission
Begins when nerve impulse reaches presynaptic axon terminal
Depolarization of presynaptic membrane leads to...
Transmitter Release
Activation of receptor on Postsynaptic Membrane
Synaptic Vesicles
exist in either
attached to exoskeleton in a reserve pool
or free in cytoplasm
Document Summary
Requires both active and passive current flows: potential falls to a small fraction of its value. Injected current leaks out of the axonal membrane: therefore there is less current to produce a reaction. Axon potential propagation: passive flow (explained) Opens voltage gated na channels in that area. Current generated by action potential flows down axon. After potential has passed, voltage gated k channels open. Prohibits the backwards flow of the potential. Action potential generation occurs only at nodes of ranvier. Synapses junctions where muscles and neurons communicate. Chemical synapse: most common type, synaptic transmission. Begins when nerve impulse reaches presynaptic axon terminal. Attached to exoskeleton in a reserve pool. Some free vesicles make their way to plasma membrane and dock. Prepare vesicular and plasma membranes for fusion. Cause membranes of synaptic vesicles are drawn together via protein complexes. Vesicles fuse with the axon membrane and release cargo into synaptic cleft.
