Lecture: Synapses

Overview of Synaptic Transmission

• Transmission of information along neurons is electrical.
• Synaptic transmission is primarily chemical, not electrical.
• Discovery of chemical reactions at synapses occurred in the early 20th century.

Historical Background

• Sherrington: Identified synapses, believed in electrical transmission at synapses.
• T.R. Eliot (1905): Proposed sympathetic nervous system works via adrenaline, ignored due to Sherrington's influence.

Otto Loewy's Contribution

• 1920s: Experiment inspired by a dream.
• Dissected two frog hearts, stimulated nerves.
• Transferred fluid between containers, observing heart rate changes.
• Concluded that chemical molecules (not electrical ions) mediate synaptic transmission.

Neurotransmitters

• Chemicals affecting postsynaptic neurons.
• Around 100 known neurotransmitters, mostly amino acids.
• Examples:
  • Amino Acids: Glutamate, GABA, Glycine.
  • Amino Acid Derivatives: Acetylcholine, Serotonin, Dopamine, Norepinephrine, Epinephrine.
  • Peptides: Endorphins, Substance P.
  • Gases: Nitric Oxide (NO).

Formation and Storage of Neurotransmitters

• Derived from food-based amino acids.
• Examples of raw materials:
  • Acetate (from acidic foods) and Choline (from milk, eggs) form Acetylcholine.
  • Tryptophan (from soybeans) forms Serotonin.
  • Phenylalanine and Tyrosine (from high-protein foods) form Dopamine, Epinephrine, Norepinephrine.
• Stored in synaptic vesicles at presynaptic terminals.

Visualizing Synapses

• Electron Micrograph (Image A):
  • Visualization of synapse, highlights presynaptic and postsynaptic areas.
• Figure B:
  • Blue structures: Presynaptic terminals.
  • Orange area: Cell body of postsynaptic neuron.

Conclusion

• This lecture covered historical perspectives, experiments, and the nature of neurotransmitters.
• Next lecture will focus on synaptic events and neuronal information exchange.