13.7 Synaptic Communicaton

• A synapse between neurons involves an axon terminal and dendrite (axodendritic), cell body (axosomatic), axon (axoaxonic). At axon terminal, nerve impulse triggers events at synapse that transfers the information to another neuron or cell.
• A synapse is a site of intercellular communication between a neuron and another cell
• A synapse is a site of intercellular communication between a neuron and another cell. May be chemical (vesicular) or electrical (nonvesicular)
• Chemical Synapses. Chemical synapse also called vesicular synapse
• Chemical Synapses. Neurotransmitter released at presynaptic membrane of axon terminal
• Chemical Synapses. Binds to receptor proteins on postsynaptic membrane
• Chemical Synapses. Triggers temporary change in postsynaptic cell’s membrane potential
• Chemical Synapses. Communication is unidirectional, from presynaptic neuron to postsynaptic neuron
• Chemical Synapses. Neuromuscular junctions are chemical synapses releasing neurotransmitter ACh, most common
• Chemical Synapses. ACh released at many synapses in CNS and PNS
• Chemical Synapses. Sequence of events similar across synapses or neurotransmitters:
• Chemical Synapses. Sequence Step One. Arrival of action potential at axon terminal causes release of neurotransmitter from secretory vesicles by exocytosis at presynaptic membrane
• Chemical Synapses. Sequence Step Two. Neurotransmitter diffuses across synaptic cleft and binds to receptors on postsynaptic membrane
• Chemical Synapses. Sequence Step Three. Receptor binding changes permeability of postsynaptic membrane, resulting effect may be excitatory or inhibitory
• Chemical Synapses. Sequence Step Three. Receptor binding changes permeability of postsynaptic membrane, resulting effect may be excitatory or inhibitory
• Chemical Synapses. Sequence Step Three. More.

  • Excitatory effects promote generation of action potentials 
  • Inhibitory effects reduce ability to generate action potentials
• Chemical Synapses. Sequence Step Four. Excitation if sufficient, receptor binding leads to generation of action potential in… 

  • Axon (if postsynaptic cell is a neuron) 
  • Sarcolemma (if postsynaptic cell is a skeletal muscle fiber)
• Chemical Synapses. Sequence Step Five. Effects of one action potential of postsynaptic membrane are short lived bc neurotransmitter molecules are either enzymatically broken down or reabsorbed
• Electrical Synapses. Electrical synapse also known as non vesicular synapse
• Electrical Synapses. Here the presynaptic and postsynaptic membranes bound together
• Electrical Synapses. Here communicating junctions permit passage of ions between cells
• Electrical Synapses. Unlike chemical synapses, electrical synapses convey nerve impulse in either direction
• Myasthenia gravis is a disease that decreases the amount of acetylcholine released from the axon terminal. What effect, if any, would this have on the generation of an action potential?

  If the axon terminal cannot release the appropriate amount of acetylcholine at a chemical synapse, an action potential will not be generated at the postsynaptic membrane.