Lecture Notes: Synapses and Neurotransmission

Introduction

• Synapses: Tiny, powerful connections between neurons.
  • Thinner than paper, more numerous than grains of sand in the body.
  • Origin of the term: Greek for clasp or join.

Function of Synapses

• Essential for converting nervous system structure into a functional system.
• Neurons without connections (synapses) are ineffective.
• Enable learning, memory, and can influence psychiatric disorders and drug addiction experiences.

Types of Synapses

Electrical Synapses

• Fast communication, similar to sending an immediate group text.
• Involves ion currents flowing through gap junctions.
• Advantages: Speed and synchronized activity (e.g., heart muscle cells).
• Limitation: Lack of control, leading to potential overload.

Chemical Synapses

• More common, slower, and precise.
• Use neurotransmitters to send signals, which allows for more control.
• Convert signals: electrical → chemical → electrical.

Chemical Synapse Mechanics

• Components:
  • Presynaptic neuron: Sends signals via axon terminals.
  • Postsynaptic neuron: Receives signals at receptors.
  • Synaptic cleft: Gap where neurotransmitters cross (5 millionths of a cm apart).
• Process:
  • Electrical signal triggers calcium release, prompting synaptic vesicles to release neurotransmitters.
  • Neurotransmitters bind to receptors, inducing ion channel opening.
  • Depending on the neurotransmitter, it can excite (depolarize) or inhibit (hyperpolarize) the postsynaptic neuron.

Neurotransmitters

• Over 100 types influence various bodily and mental functions.
• Examples:
  • Dopamine: Regulates mood, appetite, and pleasure.
  • Serotonin: Influences mood and circadian rhythm.
  • Norepinephrine: Triggers fight-or-flight response.
• Neurotransmitters don't stay bonded for long; they are recycled, degraded, or diffused.

Impact of Drugs

• Mechanism: Drugs can alter neurotransmitter behavior by enhancing or inhibiting their release or reuptake (e.g., cocaine).
• Effects:
  • Cocaine blocks dopamine reuptake, enhancing mood temporarily but leading to depletion and dysfunction.
  • Prolonged drug use can cause the brain to adapt, requiring more substance for normal function.

Conclusion

• Synapses are crucial for proper neurological function and understanding their role helps in comprehending system dysfunctions.
• Example of dysfunction: Drug-induced imbalances.

Acknowledgments

• Thanks to contributors and supporters of Crash Course.