Lecture on Perceptual Motor, Motivation, and Emotion

Overview

• Introduction to synapse and history of its discovery.
• Explanation of neurotransmitters and chemical events at the synapse.
• Material from Collat textbook, Chapter 2, Module 2.2.

Chemical Events at the Synapse

Synthesis and Release of Neurotransmitters

• Synthesis:
  • Small neurotransmitters synthesized at the axon terminal.
  • Large neurotransmitters (peptides) synthesized in the cell body.
• Action Potential:
  • Triggers release of neurotransmitters.
  • Calcium ions enter the presynaptic cell, leading to neurotransmitter release into the synapse.
• Crossing the Synapse:
  • Neurotransmitters cross synaptic cleft and bind to postsynaptic receptors.

Effects on Postsynaptic Neuron

• Receptor Binding:
  • Binding alters postsynaptic neuron activity.
• Inactivation of Neurotransmitters:
  • Inactivated via reuptake or degradation by enzymes.
• Feedback Mechanism:
  • Postsynaptic neuron signals presynaptic neuron to stop neurotransmitter release.

Types of Receptors

Ionotropic vs Metabotropic Receptors

• Ionotropic Receptors:

  • Allow charged ions (e.g., sodium) to enter the cell.
  • Fast, short-lived effects.
  • EPSP: Excitatory; neurotransmitters like glutamate and acetylcholine.
  • IPSP: Inhibitory; neurotransmitters like GABA and glycine.

• Metabotropic Receptors:

  • Do not function as ion channels.
  • Slower, longer-lasting effects.
  • Involves G-proteins and second messengers.
  • Affects ion channels, enzymes, protein production, chromosomes.

Neurotransmission Process

• Steps at the Synapse:
  1. Arrival of action potential.
  2. Opening of calcium channels.
  3. Vesicle fusion and neurotransmitter release (exocytosis).
  4. Binding to postsynaptic receptors.
  5. Postsynaptic response (excitatory/inhibitory).
  6. Inactivation via reuptake or enzymatic breakdown.

Key Concepts in Synaptic Transmission

Neurotransmitter Inactivation

• Reuptake:

  • Complete reabsorption by presynaptic neuron.
  • Allows recycling of neurotransmitters.

• Degradation by Enzymes:

  • Break down neurotransmitters into inactive fragments.

Autoreceptors and Feedback

• Autoreceptors:

  • Track neurotransmitter levels and regulate synthesis.

• Chemical Feedback:

  • Postsynaptic neuron releases chemicals to inhibit presynaptic neurotransmitter release.

Exceptions: Electrical Synapses

• Gap Junctions:
  • Direct ion channel connection between neurons.
  • No synaptic gap; allows for synchronized neuron activity.
  • Example: Neurons controlling breathing or heart rate.

This lecture provided an in-depth look into the chemical synapses and how they function, highlighting the differences between ionotropic and metabotropic receptors, and the unique nature of chemical versus electrical synapses.