Neuron Function and Signal Transmission

Jul 17, 2024

Lecture on Neuron Function and Signal Transmission

Main Parts of a Neuron

  • Dendrites:
    • Receive information
  • Cell body:
    • Processes and integrates information
  • Axon:
    • Carries information over long distances
  • Axon Terminal:
    • Transmits information to the next cell

Nerves

  • Defined as a bundle of axons traveling together
  • Can be very long for long-distance transmission

Signal Reception and Transmission

  • Dendrites receive incoming signals
  • Decision to pass signal depends on strength
  • If strong enough, an action potential occurs (neuron fires)

Ions and Electrical Gradients

  • Signal transmission depends on ion movement
  • Sodium (Na+), potassium (K+), and chloride (Cl-) ions are important
  • Chemical gradient: Na+ higher outside, K+ higher inside
  • Electrical gradient: More positively charged ions outside
  • Electrochemical gradient combines both gradients
  • Membrane potential:
    • Difference in charge across membrane
    • Resting potential: ~ -70 millivolts

Ion Channels and Transport

  • Ions move through ion channels
    • Passive diffusion
    • Voltage-gated channels open at specific membrane potentials
    • Ligand-gated channels open when bound by specific molecules
    • Mechanically-gated channels open with physical force
  • Sodium-potassium pump restores resting potential and gradients (3 Na+ out, 2 K+ in)
    • Important for neuron energy use

Action Potential

  • Triggered when depolarization reaches -55 millivolts
  • Stages:
    1. Depolarization: Na+ channels open, Na+ enters cell, membrane potential becomes positive
    2. Overshoot: Membrane potential reaches +30 millivolts
    3. Repolarization: K+ channels open, K+ exits cell, membrane potential becomes negative
    4. Hyperpolarization: Membrane potential more negative than resting
    5. Restoration: Sodium-potassium pump restores resting potential
  • Refractory periods:
    • Absolute refractory period: Neuron cannot fire
    • Relative refractory period: Larger stimulus needed to fire

Signal Frequency and Myelination

  • All-or-nothing principle: Action potential amplitude constant
  • Frequency can change based on stimulus intensity
  • Myelin sheaths speed up transmission via saltatory conduction
    • In PNS, made by Schwann cells, includes nodes of Ranvier
    • In CNS, made by oligodendrocytes