APK 2105C Lecture Notes - Lecture 29: Choline, Muscarinic Acetylcholine Receptor, Skeletal Muscle
5 Jun 2018
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Chapter 8, Lecture 2
Synaptic Transmission
• Excitatory synapses
o Excitatory post-synaptic potentials (EPSP) bring Vm closer to threshold—
depolarization
▪ May allow Na and K to flow through
• K flows out
o K has chemical driving force out of cell
o K has electrical driving force to stay in the cell
▪ Why it moves slows than Na
• Na flows in
o Higher force of this happening than K flowing out
▪ Na has higher driving force into the cell
▪ Na has electrical driving force into the cell
• Causes depolarization
o Closure of K channels acts to depolarize a cell by preventing cations from leaving
the cells
▪ Adenylate cyclase uses ATP to make a 2nd messenger
▪ Accumulate K inside the cell
• Inhibitory synapses
o Hyperpolarization or Vm stabilization
o K or Cl movement
▪ Open K channels
• K leaves
• Cell gets more negative
▪ Open Cl channels
• Higher conc outside the cell
• Brings Cl into cell
• Makes cell more negative
o Inhibitory post-synaptic potentials (IPSP) move the Vm further from the
threshold—hyperpolarization
▪ Harder to generate AP
• Neural integration
o One synapse alone doesn’t determine whether an
AP will result
▪ Very unlikely that one synapse will
generate enough for AP
o An AP is triggered if the Vm is depolarized to
threshold at the axon hillock
▪ Summation is necessary
o Typically have more of these systems
o May go to multiple axons throughout the body =
divergence
o May converge onto one neuron = convergence
• Temporal and spatial summation
o Have to sum up all the synapses to get to threshold for AP
o Separately they will not give enough to get to threshold
o EPSP and IPSP will be lower by the time it gets to the axon hillock
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