Human motor end plate: some ultrastructural aspects of its development

Abstract

Material from human foetuses of nine weeks to nine months development was examined by electron microscopy to obtain some information about the various stages in the development of skeletal muscle and structures intimately related to it such as blood vessels, nerves, neuromuscular spindles, motor end plates and fibroblasts.Regarding the motor end plates, the earliest evidence of the formation of such structures was observed in the muscle of foetuses of nine and ten weeks development. At this stage the developing motor end plate consits of several small axons covered on their outer aspect by Schwann cell cytoplasm, while on the inner aspect they are separated by a layer of basement membrane of the myotube with which they make contact. At this stage there is no evidence of secondary synaptic clefts but by the twenty eight weeks the motor end plate is similar to that seen in the adult. MATERIAL AND METHODSThe material used in this investigation is derived from twenty seven human foetuses ranging from nine weeks to nine months development. They have been studied in detail in longitudinal and transverse sections by electron microscopy.The age of the foetuses was. established by the obstetricians who suplied the specimend and was calculated according to the crown-rump lenght. The ages of the foetuses of 5,7,8 and 9 months development were based on the menstrual age. The muscle was usually taken from the thigh, even that from the minute foetuses and laid immediately on a piece of card and kept slightly streched by means of pins applied to either end of the specimen.The specimens were then immersed in cold 3% glutaraldehyJe in Sorensen's phosphate buffer at pH 7.4.After tw,o hours of fixation the muscle held by the pins was released and cut in small pieces of about 1-2 mm thick.These were washed in two changes of Sorensen's buffer at pH 7.4

Ultrastructure of Developing Human Muscle

“…With respect to the structures related to the muscle cells, it was possible to note that the developing blood vessels [Minguetti and Mair, 1979a], nerves [Minguetti and Mair, 1979b] and even motor end plates [Minguetti and Mair. 1978] are structurally similar to those seen in normal fetuses of the same developmental age.…”