Lecture on Synapses

Introduction to Synapses

• Synapses: Meeting points between neurons; derived from the Greek word meaning "to clasp or join."
• Essential for nervous system function, converting neural structure into a working system.
• Synapse functions as a bio-electrical engineering feat.

Synapses in Numbers

• Human brain: ~100 billion neurons.
• Each neuron has 1,000 to 10,000 synapses.
• Total synapses: 100 to 1,000 trillion.

Function of Synapses

• Synapses are tiny computers capable of running multiple programs and adapting.
• Key to learning, memory, psychiatric disorders, and substance addiction.

Types of Synapses

Electrical Synapses

• Immediate ion current flow through gap junctions.
• Fast communication as signals remain electrical.
• Example: Muscle cells in the heart for synchronized actions.

Chemical Synapses

• Use neurotransmitters to send signals; slower but more precise.
• Convert electrical signals to chemical and back to electrical.
• Allows for signal modification, amplification, inhibition, and splitting.

Chemical Synapse Transmission Process

• Presynaptic Neuron: Sends signal via axon terminal using synaptic vesicles with neurotransmitters.
• Postsynaptic Neuron: Receives neurotransmitters in receptor regions.
• Synaptic Cleft: The gap between neurons (~5 millionths of a cm).
• Sequence: Action potential → Ca2+ channels open → release of neurotransmitters → diffusion → receptor binding → ion channel opening.

Role of Neurotransmitters

• Over 100 types, affecting movement, organ function, mood, and alertness.
• Brief receptor binding; degraded or reabsorbed post-message.
• Drugs exploit neurotransmitter processes for effects (e.g., cocaine affects serotonin, dopamine, norepinephrine).

Impact of Drugs on Synapses

• Drugs can excite/inhibit neurotransmitter processes or mimic them.
• Cocaine blocks reuptake, especially of dopamine, causing euphoria then depletion.

Health and Dysfunction

• Synapses need balance; artificial imbalances cause dysfunction.
• Healthy synapses manage electrical and chemical messaging effectively.

Conclusion

• Summary of synapse functioning and drug-induced imbalances.
• Acknowledgments: Contributors to the Crash Course episode.
• Written by Kathleen Yale, edited by Blake de Pastino, consulted by Dr. Brandon Jackson, directed by Nicholas Jenkins and Michael Aranda, graphics by Thought Café.