Video Summary - Psychology - Synaptic Transmission & Neurotransmitters

Main ideas & concepts (Synaptic transmission & neurotransmitters)

An action potential travels along a neuron and must pass the signal to the next neuron at a specialized connection called a synapse.

Synapse: the connection between two neurons
Presynaptic neuron: the neuron that comes before the synapse
Postsynaptic neuron: the neuron that comes after the synapse
Synaptic cleft: the gap between the presynaptic and postsynaptic neurons
Presynaptic terminal: the end of the presynaptic neuron containing neurotransmitters
Vesicles: sacs that store neurotransmitters in the presynaptic terminal

Action potential arrives at the presynaptic terminal.
This triggers neurotransmitter release:
- Neurotransmitters are released from the presynaptic terminal into the synaptic cleft.
Diffusion and receptor binding:
- Neurotransmitters diffuse across the cleft to the postsynaptic neuron.
- They bind to specific receptors on the postsynaptic membrane.
- This binding passes the signal to the postsynaptic neuron.
Termination of signaling:
- Neurotransmitters are either:
  - reuptaken by the presynaptic neuron for recycling, or
  - broken down by enzymes in the synaptic cleft.

Increase the likelihood that the postsynaptic neuron generates a new action potential.
Examples:
- Glutamate
  - Most common excitatory neurotransmitter in the brain.
  - Involved in learning and memory.
- Acetylcholine
  - Key role in muscle movement.
  - Also involved in attention and arousal.

Decrease the likelihood that the postsynaptic neuron generates an action potential.
Example: GABA (gamma-aminobutyric acid)
- Helps calm neural activity.
- Important for reducing anxiety and promoting relaxation.

Do not directly excite or inhibit neurons.
Instead fine-tune or regulate other neurotransmitter systems.
Examples:
- Dopamine
  - Involved in rewards and motivation.
- Serotonin
  - Helps regulate mood, sleep, and appetite.

SSRIs (Selective Serotonin Reuptake Inhibitors)
- Block serotonin reuptake, allowing serotonin to remain in the synaptic cleft longer.
- This enhances serotonin’s mood-regulating effects.
Parkinson’s disease
- Associated with loss of dopamine-producing neurons.
- Treatments often aim to increase dopamine levels in the brain.

Chemical transmission wasn’t confirmed until the early 1900s, when there was debate over electrical vs chemical communication.
Loewi (1921) provided key evidence:
- Used two frogs.
- Electrically stimulated the vagus nerve in the first frog.
  - The vagus nerve can slow the heart when electrically stimulated.
- Collected fluid around the heart from the first frog and transferred it to the second frog’s heart.
- The second frog’s heart slowed down, even though its vagus nerve wasn’t stimulated.
- Conclusion: stimulation caused release of a chemical substance into the fluid.
- Loewi named it vagusstoff, later identified as acetylcholine.
- Argument: if communication were purely electrical, transferring fluid would not affect the second heart.

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