Nonadaptive Fibres

• Nonadaptive Fibres:

  • 2 types:
  • static bag fibres
  • chain fibres
  • do not alter their shape, and so do not have a mechanism to take tension off their membrane when the intrafusal fibres are being lengthened, tensioning up the central portion, tensioning up the annulospiral endings and then generating action potentials
• Nonadaptive Fibres:

  • what would happen to the frequency of action potentials over time if we lengthened the intrafusal fibres creating tension, generating action potentials
  • action potentials would continue being generated as theres no mechanism to reduce the tension
  • so for nonadaptive fibres, the frequency of action potentials being generated will be directly proportionate to the length of the muscle and the frequency will continue for as long as a muscle is held at a given length

  
• Nonadaptive Fibres:

  • the diagram on the bottom right shows the frequency of action potentials generated by nonadaptive fibres during the time a muscle is being lengthened
  • when the muscle is at small length, theres a small amount of tension on the nonadaptive fibres and the annulospiral ending membrane, causing slight increase in permeability, so a little bit of sodium can flow in, causing little depolarisation, so small amount of action potentials generated - decreased frequency of action potentials generated

  
• Nonadaptive Fibres:

  • the diagram shows frequency of action potentials generated by nonadaptive fibres while a muscle is being lengthened
  • when muscle is lengthened, theres a large amount of tension on the nonadaptive fibres and the annulospiral ending membrane, causing large increase in permeability, so a lot of sodium can flow in, cause large amounts of depolarisation, so a large amount of action potentials generated - increased frequency of action potentials generated
  • as theres no mechanism to release the tension, the high frequency continues for as long as the muscle is held at that length