Lecture on Synapses and Neural Communication

Introduction

• Synapse: Junction between two neurons
• Vital for forming the nervous system
• Connect neurons enabling communication

Definitions and Overview

• Synapse: From Greek "to clasp or join"
• Converts electrical messages to different signals and transmits them
• Human brain: ~100 billion neurons, each with 1,000 - 10,000 synapses
• Total synapses: 100 - 1,000 trillion
• Synapses adapt, strengthen, or weaken over time

Importance of Synapses

• Enable learning and memory
• Influence psychiatric disorders
• Basis for effects and addiction of drugs

Types of Synapses

Electrical Synapses

• Like sending a group text
• Ion current flows directly through gap junctions
• Faster, no signal conversion
• Essential for synchronized actions, e.g., heart muscle cells
• Less control, can overstimulate if widespread

Chemical Synapses

• More common, slower, more precise
• Use neurotransmitters to send signals
• Convert signals in steps (electrical -> chemical -> electrical)
• Can be modified, amplified, inhibited, or split

Structure of Chemical Synapses

• Presynaptic Neuron: Sends signal
  • Uses presynaptic terminal (axon terminal)
  • Contains synaptic vesicles with neurotransmitters
• Postsynaptic Neuron: Receives signal
  • Receptor region on dendrite or cell body
  • Synaptic cleft: Gap between neurons

Signal Transmission Process

• Action potential activates voltage-gated calcium channels
• Calcium influx leads to neurotransmitter release
• Neurotransmitters cross synaptic gap, bind to receptors
• Signal conversion back to electrical occurs

Neurotransmitter Types

• Excitatory: Depolarize postsynaptic neuron, closer to action potential
• Inhibitory: Hyperpolarize postsynaptic neuron, harder to excite
• Neurons balance excitatory and inhibitory signals to determine action potential

Neurotransmitter Lifecycle

• Brief receptor binding, then degradation or recycling
• Reuptake: Re-absorption by presynaptic neuron
• Enzymatic breakdown or diffusion away

Drug Effects on Synapses

• Drugs alter neurotransmitter production, release, reuptake
• Example: Cocaine
  • Targets serotonin, dopamine, norepinephrine
  • Blocks reuptake, causing neurotransmitter accumulation
  • Results: Euphoria, paranoia, jitteriness
  • Long-term use depletes neurotransmitters, reduces receptors

Conclusion

• Healthy synapses balance excitation, inhibition, and neurotransmitter dynamics
• Dysfunction illustrates the importance of synaptic health

Credits

• Written by Kathleen Yale
• Script edited by Blake de Pastino
• Consultant: Dr. Brandon Jackson
• Directed by Nicholas Jenkins and Michael Aranda
• Graphics: Thought Café