VPB 121: Veterinary Physiology - II (2+1)

CLASSIFICATION OF NERVE FIBRE

• Classified as Type A, Type B and Type C fibers based on the diameter, myelination and propagation speed. According to the diameter of the fiber, a physiological property of nerve fiber varies. As diameter increases, the conduction velocity increases which requires lower threshold of excitation with greater magnitude of response. Time of conduction is shorter with shorter refractory period.
• Based on the characteristics, nerve fibers are classified into 3 groups viz A, B and C fibres. Large fibers conduct impulses rapidly whereas small fibers are slow in conduction. The speed of conduction can be achieved by 2 nodes
  • By employing myelinated fibers
  • By increasing the diameter of the fibers.
• Group A consists of largest fibres (up to 30 microunit in dia) with conduction rates of 50-100m/sec. The fibres of this group are myelinated. This group is further typed into alpha, beta, gamma and delta.
  • Alpha is subtype is concerned with proprioception, to carry impulses from muscle spindle and golgi tendon organs.
  • Beta fibres are concerned with touch, pressure and other somatomotor impulses carrying from muscle spindle.
  • Gamma fibres are concerned with motor functions to muscle intrafusal fibers.
  • Delta fibres are similar to beta in function.Group B fibres are which are rich in preganglionic autonomic fibers and group C functions in post ganglionic sympathetic fibers.