The Biological Bases of Behaviour

Neurons

  • Definition: Specialized cells that constitute the nervous system.
  • Four Main Parts:
    • Cell body (soma): Contains structures essential for keeping the cell alive, including the nucleus.
    • Dendrites: Branch-like extensions from the cell body that receive signals from other neurons.
    • Axon: A long, slender projection that conducts electrical impulses away from the cell body.
    • Axon Terminals: Specialized endings of the axon that send signals to other cells.
  • Neuron Support - Glial Cells:
    • Hold neurons in place.
    • Produce and transport nutrients.
    • Form the Myelin Sheath.
    • Remove toxins.
    • Contribute to the Blood-brain barrier.
  • Two Basic Functions of Neurons:
    1. Generate electricity: Create nerve impulses.
    2. Release chemicals: Communicate with other cells.

Neural Impulses

  • Activation Process (Three Steps):
    1. Resting Potential: The cell is at an electrical resting potential (e.g., -70 ext{mV}).
      • This state is maintained by a 10:1 concentration of sodium ( ext{Na}^+) ions outside the neuron and negative protein ( ext{A}^-) ions inside.
      • Potassium ( ext{K}^+) ions are primarily inside the cell.
    2. Action Potential (Firing): The cell is stimulated, causing electrical charges (ions) to flow across the cell membrane.
      • Sodium channels open, and sodium ( ext{Na}^+) ions flood into the axon.
      • This reverses the charge of the resting potential, producing an action potential or neural impulse, which can reach approximately +40 ext{mV}.
      • Potassium channels remain closed during this phase.
    3. Restoration of Resting Potential: The distribution of ions is restored, returning the cell to its resting state.
      • Sodium channels that were open during the action potential close.
      • Potassium channels open, allowing potassium ( ext{K}^+) ions to exit the neuron.
      • This outflow of positive charge restores the negative resting potential.
      • This process propagates along the axon.
  • Absolute Refractory Period:
    • During this period, a neuron cannot fire again, regardless of stimulus strength.
    • Purpose:
      • Limits how often nerve impulses can occur.
      • Ensures that impulses travel in a single direction along the axon.
  • The All-or-None Law:
    • Action potentials occur at a uniform and maximal intensity, or they do not occur at all.
    • Stronger signals do not cause stronger action potentials.
    • Instead, stronger signals create more action potentials, meaning the rate of cell firing is increased.
  • The Myelin Sheath:
    • A fatty, whitish insulating layer that surrounds axons.
    • Derived from glial cells during development.
    • Function: Insulates neurons, increasing the speed and efficiency of neural impulse conduction.
  • Nodes of Ranvier:
    • Gaps in the myelin sheath where the axon membrane is exposed.
    • Function: Allow conduction to