ABSTRACT
As marked differences in the Acetylcholinesterase (ACHE)-activity of myelinated nerve fibres of ventral and dorsal spinal roots can be found also in human post mortem material (ZENKER et al. 1978), the Karnovsky-method for histochemical demonstration of ACHE-activity has been used for differentiation of motor and sensory fibres in the human phrenic nerve. In cross sections of the phrenic nerve 1--2 cm above its entrance into the diaphragm, after an incubation period of 24 hours, 86% of the medullated nerve fibres displayed a high enzyme activity and therefore were classified as motoric. The histogram of these stained fibres revealed a large group of fibres with a peak at 9--10 micron in diameter which were interpreted as A-alpha fibres and a small group of fibres with a peak at 2--3 micron which were classified as A-gamma fibres. The mean diameter of the A-alpha group fibres is smaller than the mean diameter in a "typical" muscle nerve. Furthermore, the number of A-gamma fibres in the phrenic nerve, as compared with a "typical" muscle nerve is strikingly small. This seems to be in accordance with the small number of unstained fibres (14% only) which were interpreted as sensoric. In this group no fibre was found larger than 9 micrometers in diameter. This could mean a complete lack of primary afferents within the human phrenic nerve.
