title: Ultrastructural differentiation of peripheral nerves and neuromuscular junctions in the hindlimb of the bovine fetus.
abstract: The differentiation of sciatic nerve, intramuscular nerves, and neuromuscular junctions was studied by light and electron microscopy in bovine fetuses from 47 days' gestation to neonatal calves 3 days of age. Rudimentary neuromuscular junctions were observed in 2-month-old fetuses, at which time spontaneous movements were observed in the limbs and trunk. By 5 months, the terminal axons occupied a well-developed synaptic gutter with early secondary infoldings and, subsequently, extensive infoldings developed so that at birth the subneural apparatus was well developed. In the peripheral nerve of 47-day-old fetuses, the unmyelinated axons were in bundles, and by 3 months, single axons were separated from the bundles that were surrounded by the Schwann cell on a 1:1 basis in cross sections; myelination of axons had begun. At 5 months, individual axons in the nerves had a thick myelin sheath.
mesh_terms: D000818:Animals; D001369:Axons / Q000648:ultrastructure; D002417:Cattle / Q000196:embryology*; D005260:Female; D005865:Gestational Age; D006614:Hindlimb / Q000196:embryology / Q000294:innervation*; D009469:Neuromuscular Junction / Q000196:embryology* / Q000648:ultrastructure; D010525:Peripheral Nerves / Q000196:embryology*; D012583:Schwann Cells / Q000648:ultrastructure; D012584:Sciatic Nerve / Q000196:embryology / Q000648:ultrastructure