12.5

• refractory period

  • from beginning of action potential to resting state
  • when membrane will not respond normally to additional stimuli
• absolute refractory period

  • all voltage-gated Na+ channels are already open or inactivated
  • cannot respond to further stimulation
• relative refractory period

  • Na+ channels regain resting condition
  • continues until membrane potential stabilizes
  • only strong stimulus can initiate another action potential
• type A fiber - type of axon

  • myelinated
  • largest diameter
  • transmit information to and from CNS rapidly
  • sensory info that threatens survival
  • motor commands that prevent injury
• type B fiber - type of axon

  • myelinated
  • medium diameter
  • transmit info at intermediate speeds
• type C fiber - type of axon

  • unmyelinated
  • small diameter
  • transfer info slowly