Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download presentation source
Document related concepts
Development of the nervous system wikipedia , lookup
Long-term depression wikipedia , lookup
SNARE (protein) wikipedia , lookup
Axon guidance wikipedia , lookup
Neuroregeneration wikipedia , lookup
Activity-dependent plasticity wikipedia , lookup
Biological neuron model wikipedia , lookup
Signal transduction wikipedia , lookup
Nervous system network models wikipedia , lookup
Patch clamp wikipedia , lookup
Synaptic gating wikipedia , lookup
Single-unit recording wikipedia , lookup
Neuromuscular junction wikipedia , lookup
Membrane potential wikipedia , lookup
Resting potential wikipedia , lookup
Nonsynaptic plasticity wikipedia , lookup
Action potential wikipedia , lookup
Stimulus (physiology) wikipedia , lookup
Electrophysiology wikipedia , lookup
Neurotransmitter wikipedia , lookup
Molecular neuroscience wikipedia , lookup
Neuropsychopharmacology wikipedia , lookup
Synaptogenesis wikipedia , lookup
End-plate potential wikipedia , lookup
Transcript
Lecture 4- Action Potential propagation and synaptic transmission ©Dr Bill Phillips 2002, Dept of Physiology • • • • Continuous Propagation of action potentials Saltatory Propagation Electrical and chemical synapses Reasons for chemical synapses Continuous propagation • The action potential normally starts at the axon hillock where the density of voltagegated Na+ channels is high • In un-myelinated nerves the action potential propagates continously along the axons by sequentially activating populations of Na+ channels in adjoining segments of axon Continuous Propagation of the AP in un-myelinated nerve fibres Axon Nucleus hillock The membrane has electrical properties that affect the spread of changes in membrane potential Membrane has electrical capacitance stored charge must be discharged ++++ -------- Ion channels in the membrane have resistance but allow leakage of local circuit currents out of the membrane The axoplasm is narrow and has resistance impedes the depolarising current down the membrane Electrical components of the resting membrane Axon Equivalent circuit + Vm Dist ance along dendrit e or axon Saltatory Propagation • Adaptation to permit faster propagation • Myelin internodes formed by glial (Schwann) cells wrapped around internode regions of axons (~0.2mm long) • Inward current during the rising phase of the action potential creates “local circuits” • Local circuits depolarise neigbouring “Node of Ranvier” stimulating regeneration of the action potential Myelinat ed Int ernode Axon hillock Nucleus Node of Ranvier In saltatory propagation: • Voltage-gated Na+ channels are concentrated at the axon hillock and Nodes of Ranvier • The Hodgkin Cycle is triggered at one Node after another. This amplifies the signal. • The signal travels passively as an electrical current between Nodes. • The thick myelin insulation of the Internode allows the local circuit current to spread much further and faster than in un-myelinated fibres Synaptic transmission Muscle fibre Mot or neurone Nucleus Synaptic connections between cells • Electrical synapses: local circuit currents flow through gap-junctions between adjacent cells • Chemical Synapses: chemical neurotransmitter substance is released by the presynaptic terminal onto the postsynaptic cell to activate its receptor proteins What is a chemical synapse • Nerve terminal releases chemical neurotransmitter when action potential depolarises the terminal membrane • Chemical transmitter diffuses across synaptic cleft and binds to a receptor protein • Receptor protein on postsynaptic membrane initiates changes in the postsynaptic cell Reasons for having chemical synapses • Amplification • Inhibition • Modification • Plasticity Amplification Muscle fibre Mot or neurone Nucleus Depolarising current Small < Large Inhibition Mot or neurone Nucleus Presynaptic Depolarisation Postsynaptic Hyperpolarisation Modification Plasticity
