6.2.5 Speed of Conduction of Impulses

1. Myelination

• Myelin sheath: Axons surrounded by a myelin sheath conduct impulses much faster than non-myelinated axons.
• Saltatory conduction: In myelinated axons, action potentials "jump" between nodes of Ranvier (gaps in the myelin sheath), rather than travelling continuously along the entire length of the axon.
  • This process increases the speed of conduction significantly.

2. Axon Diameter

• Larger axon diameter allows for faster conduction of impulses.
  • A wider axon reduces resistance to the flow of ions, enabling depolarisation to occur more rapidly.
  • Example: The giant squid axon (1 mm diameter) transmits impulses faster than a human axon (approximately 22 μm diameter).

3. Temperature

• Higher temperatures increase the kinetic energy of ions, which accelerates their diffusion across the axon membrane during action potentials.
• Temperature also influences the rate of respiration, which produces the ATP required for the sodium-potassium pump to restore resting potential.
  • At extremely high temperatures, proteins and enzymes involved in the nerve impulse process (e.g., ion channels) may denature, slowing or stopping conduction.