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Neuronal Communication and Synapse Insights

Sep 16, 2024

Perceptual Motivation and Emotion Lecture Notes

Introduction

  • Focus: Understanding communication between neurons.
  • Previous Topics:
    • Neuronal structures and their functions.
    • Information transmission within a neuron via membrane potential changes.

Key Concepts

  • Neuron Communication: Understanding how information is sent from one neuron to another.
  • Synapse: The gap between neurons where communication occurs.

Historical Context

  • Santiago Ramon y Cajal: Demonstrated that neurons are separate with gaps between them using the Golgi staining technique.
  • Charles Sherrington (1906): Coined the term "synapse" and studied physiological processes at the synapse.

Terms and Definitions

  • Presynaptic Neuron: Neuron that sends information, located before the synapse.
  • Postsynaptic Neuron: Neuron that receives information, located after the synapse.
  • Postsynaptic Potential: Changes in the electrical potential of a neuron (depolarization or hyperpolarization).

Sherrington's Research

  • Study: Used a dog to measure response times to skin pinches, leading to insights into synaptic transmission.
    • Flexion Reflex: Automatic bending of the leg in response to stimuli.
    • Reflex Arc: Pathway of sensory information from skin to spinal cord to muscles.
  • Conclusions:
    1. Transmission Speed: Slower along the reflex arc (15 m/s) compared to down an axon (40 m/s).
    2. Temporal Summation: Weak stimuli given successively at the same location can trigger a response.
    3. Spatial Summation: Multiple weak stimuli at different locations can trigger a response.

Mechanisms of Neuronal Communication

  • EPSP (Excitatory Postsynaptic Potential): Graded depolarization that increases the likelihood of an action potential.
  • IPSP (Inhibitory Postsynaptic Potential): Graded hyperpolarization that decreases the likelihood of an action potential.
  • Graded Potentials:
    • Occur briefly and decay over time and distance.
    • Can be combined temporally or spatially to reach the excitation threshold.

Summation Effects

  • Temporal Summation: Cumulative effect of successive inputs over time.
  • Spatial Summation: Cumulative effect of inputs from different locations.
  • Analogy: Repeated weak pokes or simultaneous pokes at different locations build up to a detectable sensation.

Integration of Inputs

  • Neuronal Integration: Each neuron integrates EPSPs and IPSPs from multiple presynaptic neurons.
  • Threshold for Action Potential: Achieved when the combined effect depolarizes the membrane at the axon hillock.

Synaptic Transmission

  • EPSPs and IPSPs:
    • Spread passively and decay with distance.
    • Subthreshold potentials are summed for potential action.
  • Information Transmission:
    • Requires a sum of EPSPs and IPSPs to reach the threshold.
    • The net effect is calculated by subtracting IPSPs from EPSPs.

Summary

  • Understanding the mechanisms of neuronal communication is crucial for comprehending how the brain processes information through complex networks of synapses.

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