5 Nerve Fibers


Sensitivity to Pressure : A > B > C

Sensitivity to Hypoxia : B > A > C

Sensitivity to Local Anaesthetic : A gamma & A delta > A alpha & A beta > B > C 
(Ref: Read text below)

Miller's Anaesthesia (7th ed , pg 921 , 922 ) 
"Different fiber types are differentially sensitive to local anesthetic blockade.
In vivo experiments in which continuous superperfusion of peripheral nerve allows equilibration with drug and experiments in which a drug bolus is delivered by percutaneous injection, analogous to clinical peripheral nerve block, show unequivocally that small myelinated axons (Aγ motor and Aδ sensory fibers) are the most susceptible to impulse annihilation. Next in order of block are the large myelinated (Aα and Aβ) fibers, and the least susceptible are the small, nonmyelinated C fibers.
In fact, in this last group, impulses in the slowest conducting population (conduction velocity of 0.5 to 0.8 msec) are the most resistant to local anesthetic.
The generalized notion that local anesthetics block the smallest fibers first or most is clearly wrong. "


  1. Thanks a lot sir. I used to think senstivity to LA as BCA. Thanks for clarifying with reference.

    1. BCA is answer for susceptibility not sensitivity

  2. thats the problem with this question. the sensitivity to local anesthesia is given different in Ganong and Millers. I think for entrance exams, its better to follow Ganong.

    1. We prefer to follow anaesthesia book when it comes to anaesthetic drug.

  3. Which nerve fiber is most sensitive to pressure? A alpha, A beta, A gamma?


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