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Impulse conduction in the shrimp medullated giant fiber with special reference to the structure of functionally excitable areas
Author(s) -
Kusano Kiyoshi,
Lavail Matthew M.
Publication year - 1971
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.901420406
Subject(s) - axolemma , impulse (physics) , nerve conduction velocity , thermal conduction , myelin , biophysics , biology , anatomy , fiber tract , neuroscience , materials science , physics , white matter , composite material , classical mechanics , central nervous system , magnetic resonance imaging , medicine , radiology
The external potential field along the functionally isolated medullated giant fiber of the shrimp ( Penaeus setiferus ) was recorded during impulse conduction using 1 M NaCl‐filled glass capillary electrodes. The giant fiber displays no nodes of Ranvier, yet shows a conduction velocity greater than 90m/second at 20°C. Recordings from most parts of the myelin‐covered giant fiber surface showed only small monophasic positive potentials. However, at the areas of giant fiber‐motor giant fiber synapses and where giant fiber axons branch into abdominal ganglia, a small positivity was followed by a negativity (sink of the action current). The local application of action potential depressants to these areas abolished the negativity and converted it into positivity, and consequently impulse conduction was blocked. Application of the action potential depressants to other areas of the giant fiber did not block impulse conduction. The sink of the action current was not found from the axolemma in the myelin cylinder; this part of the axolemma together with the low resistance gap fluid simply serves as a passive current conductor. Light and electron microscopic studies of the two functionally excitable areas revealed the absence of a myelin sheath in some small areas of both regions. Thus, impulse conduction appears to be saltatory, and these excitable areas function as nodes of Ranvier.