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Synaptic Transmission Essentials

Nov 10, 2025

Overview

  • Summary of synaptic transmission: how neurons communicate via chemical signals across synapses.
  • Focus on components, sequence of events, and signal outcomes in postsynaptic cells.

Synapse Basics

  • Synapse: specialized area where two neurons exchange chemical signals.
  • Neurons are separated by the synaptic cleft, not physically connected.
  • Synaptic cleft width is less than 40 nm, extremely small space.

Key Structures and Roles

  • Presynaptic neuron: initiates the signal and releases neurotransmitters.
  • Postsynaptic neuron: receives the signal and responds via receptors.
  • Vesicles: small sacs in the presynaptic neuron holding neurotransmitters.
  • Neurotransmitters: chemical messengers released into the synaptic cleft.
  • Receptors: postsynaptic membrane proteins that bind neurotransmitters.

Process of Synaptic Transmission

  • Action potential reaches presynaptic terminal, exciting the neuron.
  • Vesicles fuse with the presynaptic membrane and release contents.
  • Neurotransmitters enter the synaptic cleft and diffuse to receptors.
  • Binding to receptors triggers actions in the postsynaptic neuron.
  • Effects can increase or decrease likelihood of postsynaptic firing.

Neurotransmitter Clearance Mechanisms

  • Diffusion: neurotransmitters drift away from the synaptic cleft.
  • Reuptake: presynaptic neuron retrieves neurotransmitters for reuse.
  • Enzymatic breakdown: enzymes degrade transmitters in the cleft.
  • Components from breakdown can be returned to synthesize more transmitter.

Structured Summary

Component/StepDescriptionOutcome
SynapseJunction for neuron communication via chemicalsEnables signal transfer without physical connection
Synaptic cleftGap less than 40 nm between neuronsSpace for neurotransmitter diffusion
Presynaptic neuronOrigin of signal; contains vesiclesReleases neurotransmitters upon activation
VesiclesSacs with thousands of transmitter moleculesFuse and release contents during transmission
Action potentialElectrical signal arriving presynapticallyTriggers vesicle fusion and release
NeurotransmittersChemical messengers in cleftBind receptors to influence postsynaptic cell
ReceptorsPostsynaptic binding sitesModulate likelihood of action potential
DiffusionPassive spread of transmitters awayReduces transmitter concentration in cleft
ReuptakeRetrieval into presynaptic neuronRecycling and reuse of transmitters
Enzymatic breakdownDegradation within cleftParts returned to make more transmitter

Key Terms & Definitions

  • Synapse: junction enabling chemical communication between neurons.
  • Synaptic cleft: tiny gap separating presynaptic and postsynaptic neurons.
  • Presynaptic neuron: neuron sending the chemical signal.
  • Postsynaptic neuron: neuron receiving the chemical signal.
  • Vesicle: sac storing thousands of neurotransmitter molecules.
  • Action potential: electrical signal triggering neurotransmitter release.
  • Neurotransmitter: chemical messenger released into the synaptic cleft.
  • Reuptake: transport of neurotransmitters back into the presynaptic neuron.
  • Diffusion: passive movement of molecules away from the synaptic cleft.
  • Enzymatic breakdown: cleavage of neurotransmitters by enzymes in the cleft.

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