![]() ![]() The splanchnic nerve terminals contain multiple clear vesicles measuring 300–500 Å and occasional larger vesicles (1000 Å) with an electron-dense core ( Coupland, 1963). ![]() ![]() The nerve terminals form true synapses with the adrenal chromaffin cells the pre- and postsynaptic membranes both show increased electron density and are separated by a gap of 150–200 Å ( Fig. The three splanchnic nerves innervating the cat adrenal have recently been found to terminate within nonoverlapping portions of the medulla ( Marley and Prout, 1965) this may provide a basis for the preferential secretion of epinephrine or norepinephrine. After traversing the cortex, the nerve fibers split into smaller groups within the medulla and then run adjacent to the large blood vessels. They are cholinergic in nature and analogous to the presynaptic neurons that terminate in sympathetic ganglia. These axons pass with the motor fibers through the ventral roots. The splanchnic nerves to the adrenal medulla contain axons from neurons in the lower thoracic and lumbar regions of the spinal cord most are unmyelinated ( Coupland, 1965a, pp. ![]()
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