UNMYELINATED AXONS IN TRIGEMINAL MOTOR ROOT OF HUMAN AND CAT

The fiber composition of the human and cat trigeminal motor roots were studied utilizing the EM. Twelve to 20% of fibers in the human trigeminal motor root are unmyelinated whereas 9-15% are unmyelinated in the cat. The only previous examination of the fiber composition of the peripheral trigeminal motor nerve utilized the light microscope and indicated that less than 5% of fibers were unmyelinated in cat. No study of the fiber composition of the motor nerve root is available. The present results are similar to those recently obtained by others for spinal ventral roots. The function of unmyelinated fibers in the trigeminal motor root is unknown; indirect evidence, both laboratory and clinical, suggests a potential sensory function. The findings question seriously the concept that the functional separation of the nervous system into motor and sensory systems has anatomical correlates in the spinal and cranial nerve roots. The results relate directly to this conceptualization of the nervous system and also to the design of methods for the treatment of intractable pain.