Synaptic Transmission Steps to Know for Drugs, Brain, and Mind

Synaptic transmission is the process by which neurons communicate, crucial for brain function and behavior. Understanding these steps reveals how drugs can influence neurotransmitter release and receptor activity, impacting our thoughts, emotions, and overall mental health.

1. Action potential reaches presynaptic terminal

   • An electrical signal travels down the axon to the presynaptic terminal.
   • This signal is crucial for initiating the release of neurotransmitters.
   • The arrival of the action potential triggers a series of events leading to synaptic transmission.

2. Voltage-gated calcium channels open

   • The depolarization of the presynaptic membrane causes these channels to open.
   • Calcium ions (Ca²⁺) are essential for neurotransmitter release.
   • The opening of these channels is a key step in converting the electrical signal into a chemical signal.

3. Calcium influx into presynaptic terminal

   • Calcium ions flow into the presynaptic terminal from the extracellular space.
   • The increase in intracellular calcium concentration is a trigger for synaptic vesicle fusion.
   • Calcium acts as a signaling molecule that facilitates neurotransmitter release.

4. Synaptic vesicles fuse with presynaptic membrane

   • Synaptic vesicles containing neurotransmitters move toward the presynaptic membrane.
   • Fusion is mediated by proteins called SNAREs, which help the vesicles merge with the membrane.
   • This process is essential for the release of neurotransmitters into the synaptic cleft.

5. Neurotransmitters released into synaptic cleft

   • Once fused, the vesicles release neurotransmitters into the space between the presynaptic and postsynaptic neurons.
   • This release is often referred to as exocytosis.
   • The neurotransmitters diffuse across the synaptic cleft to reach the postsynaptic receptors.

6. Neurotransmitters bind to postsynaptic receptors

   • Neurotransmitters specifically bind to receptors on the postsynaptic membrane.
   • This binding is highly selective and can lead to various effects depending on the type of neurotransmitter and receptor.
   • The interaction initiates a response in the postsynaptic neuron.

7. Ion channels open or close on postsynaptic membrane

   • Binding of neurotransmitters can cause ion channels to open or close.
   • This alters the membrane potential of the postsynaptic neuron.
   • The change in ion flow can lead to excitatory or inhibitory postsynaptic potentials.

8. Postsynaptic potential generated (EPSP or IPSP)

   • Excitatory postsynaptic potentials (EPSPs) increase the likelihood of an action potential in the postsynaptic neuron.
   • Inhibitory postsynaptic potentials (IPSPs) decrease this likelihood.
   • The balance of EPSPs and IPSPs determines the overall response of the neuron.

9. Neurotransmitter reuptake or degradation

   • After their action, neurotransmitters are either taken back into the presynaptic neuron (reuptake) or broken down by enzymes (degradation).
   • Reuptake helps recycle neurotransmitters for future use.
   • Degradation ensures that neurotransmitters do not continuously activate receptors.

10. Synaptic vesicle recycling

    • After neurotransmitter release, synaptic vesicles are retrieved and refilled with neurotransmitters.
    • This recycling process is crucial for maintaining synaptic function.
    • Efficient recycling allows for rapid and repeated neurotransmitter release during ongoing neuronal activity.