Lecture 4 Membrane Potential in Excitable Cells II

Lecture 4 Membrane Potential in Excitable Cells II: Action Potential Propagation Neuromuscular Transmission

The propagation of an AP along an axon

Propagation as a moving local circuit

Passive spread of depolarization = distance over which Vm falls to 1/e of initial depolarized value From Lodish et al. , Molecular Cell Biology, 4 th edition – Fig. 21 -11

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The conduction velocity of action potentials = time it takes for Vm to reach 63% of steady state

Action Potential Propagation: Saltatory Conduction Myelin: a fatty sheath made by wrapping membranes around axons Myelination carried out by Schwann cells (PNS) or oligodendrocytes (CNS) Node of Ranvier Internode regions

Nodes of Ranvier

AP propagation: the circuit and the effect of myelin

Extracellular Recordings

Summation of presynaptic output leading to an AP

Nicotinic ACh Receptor

Single ACh-gated channel i-V

The Motor End Plate

The neuromuscular junction

Signaling in the neuromuscular junction

End Plate Potential (EPP)

Effect of ACh. E on EPP

Ionic basis of the EPP

ACh release from the presynaptic nerve terminal

The Ca 2+ influx hypothesis for transmitter release

Miniature EPPs (or MEPPs)

Relation of MEPPs and EPPs