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What is Chronaxie varies for different nerve fibers. Which of the following types of nerves has minimum chronaxie? and explain in detail?
Chronaxie is the minimum time for which a direct current equivalent to twice the intensity of the rheobase must be applied to trigger an action potential. Rheobase of an axon is the threshold current for an infinitely long-duration stimulus. The chronaxie is inversely propoional to the degree of fiber myelination, therefore chronaxie is minimum in myelinated nerves. Sensory fibers are less myelinated than motor fibers. Consequently, a sho duration electrical stimulus should trigger action potentials in motor fibers (A alpha) without triggering the sensory fibers (A delta, C). Chronaxie of C fiber (unmyelinated): 400 microsecond Chronaxie of A delta fiber (myelinated): 150 microsecond Chronaxie of A alpha fiber (myelinated): 40-100 microsecond Ref: Pediatric Anesthesia By Bruno Bissonnette, 2011, Page 758.