Histological and electrophysiological Studies On The Giant Axons Of The Cockroach Periplaneta Americana

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Abstract
Nerve cords of the American cockroach were cut between the 5th and 6th abdominal ganglia. All giant axons degenerated in the abdominal regions and were present but collapsed in the thoracic connectives. Unilateral lesions permitted identification of ventral giant axons all along the nerve cord. 4. The diameter of abdominal giant axons descreases progressively from 60µ at the metathoracic ganglion to 7 µ at the suboesophageal ganglion. 5. It is concluded that abdominal giant fibres do not synapse at the thoracic ganglia but form narrow isthmuses. 6. The tapering of the giant fibres in the thoracic nerve cord may be responsible for the sequence of nicotine blockade from rostral to caudal regions.